WO2009155300A1

WO2009155300A1 - Fluid monitor

Info

Publication number: WO2009155300A1
Application number: PCT/US2009/047562
Authority: WO
Inventors: David Brown
Original assignee: Lifeflow Technologies, Inc.
Priority date: 2008-06-17
Filing date: 2009-06-16
Publication date: 2009-12-23

Abstract

Devices and methods for detecting at least one flow characteristic of a fluid, for example, found at a single location in a subject and/or found between two locations in a subject. Devices include an elongate member and/or an external member for detecting the flow of fluid using electromagnetic wave emission, reflection, detection and/or signal processing to determine a flow characteristic of the fluid. Provided are devices that include a nasogastric tube for determining nearby flow in the thoracic aorta in order to determine placement of the nasogastric tube in the esophagus and methods for determination thereof.

Description

FLUID MONITOR

CROSS-REFERENCE

[0001] This application claims the benefit of U.S. Provisional Application No. 61/129,292, filed June 17, 2008, which application is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] Devices for monitoring and treating patients can be used in a multitude of situations. For example, monitoring Cardiac Output (CO) is useful when treating acutely unwell patients in the Intensive Care Unit or Cardiac Care Unit (CCU) setting. One method is by using a Swan-Ganz catheter which is a device that is placed invasively into a large vein and directed into the heart. Another situation in which a device is used in monitoring or treating a patient is a nasogastric (NG) tube. Typically, a NG tube that is placed in a patient must be verified to be lying in the esophagus as opposed to the bronchi of the lungs which can occur by mistake when inserting the tube. When the tube is placed in the lungs accidentally then any food, fluid, or medicine placed in the tube would end up in the lungs instead of the stomach leading to an acutely unwell patient and often death. NG tube placement is typically verified by chest X-ray.

SUMMARY OF THE INVENTION

[0003] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal emitter adapted to emit a signal; and an external member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

[0004] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal detector adapted to detect a signal; and an external member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject.

[0005] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal emitter adapted to emit a signal; and an elongate member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

[0006] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal detector adapted to detect a signal; and an elongate member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject.

[0007] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising a subassembly comprising a signal generator and a signal processor, an external member coupled to the subassembly; and an elongate member coupled to the subassembly, wherein at least one of the external member and the elongate member comprises a signal emitter that emits a signal generated by the signal generator, and a signal detector that detects the signal after the signal is reflected from at least one of flowing fluid and a reference member and that sends a detected signal to the signal processor.

[0008] In some embodiments, the signal comprises an electromagnetic wave signal. In some embodiments, the electromagnetic wave signal is at least one of a radio wave signal, a micro wave signal, an infrared wave signal, and a near infrared wave signal. In some embodiments, the signal emitter emits electromagnetic waves to nearby fluid.

[0009] In some embodiments, the emitter emits the electromagnetic waves wirelessly. In some embodiments, the emitter is hard- wired to the signal processor.

[0010] In some embodiments, the emitter is coupled to a signal generator that generates the electromagnetic wave. In some embodiments, the signal generator is programmable to generate the electromagnetic wave within at least one of the radio, micro, infrared, and near infrared wave ranges. In some embodiments, the emitter is coupled to a signal processor.

[0011] In some embodiments, the signal detector comprises a sensor that detects the signal from at least one of the external member and flowing fluid, and wherein the signal is an electromagnetic wave signal. In some embodiments, the sensor is sealed from contact with bodily fluids. In some embodiments, the device further comprises a signal processor adapted to generate a flow characteristic output of a flowing fluid in a vessel located between the elongate member and the external member.

[0012] In some embodiments, the device comprises memory that stores a flow characteristic output that is generated by the signal processor. In some embodiments, the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, time integral of the maximum velocity of the fluid, volume, flow time, and volume of fluid flowing over time. In some embodiments, the fluid is blood. In some embodiments, the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, stroke distance, stroke volume, flow time, and cardiac output. [0013] In some embodiments, the signal detector comprises a transmitter that is capable of transmitting the signal to a signal processor, wherein the signal comprises an electromagnetic wave signal. In some embodiments, the transmitter transmits the electromagnetic wave wirelessly. In some embodiments, the transmitter is hard- wired to the signal processor.

[0014] In some embodiments, the device comprises an output monitor. In some embodiments, the device comprises an input module. In some embodiments, at least a portion of the elongate member is adapted to remain substantially stationary relative to the external member when the elongate member is inserted into the subject. In some embodiments, the tip of the elongate member is the portion of the elongate member that remains substantially stationary relative to the external member. In some embodiments, the portion of the elongate member that remains substantially stationary relative to the external member is a portion of the elongate member that lies in close proximity to the descending aorta.

[0015] In some embodiments, the external member is coupled to the subject's back. In some embodiments, the external member comprises an adhesive pad. In some embodiments, the external member is adapted to remain substantially stationary relative to at least a portion of the elongate member when the elongate member is inserted into the subject.

[0016] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to be placed adjacent the descending aorta.

[0017] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to lie in close proximity to the descending aorta.

[0018] Provided herein is a device for detecting at least one flow characteristic in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to be placed adjacent the descending aorta.

[0019] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to lie in close proximity to the descending aorta.

[0020] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location in a subject, providing a reference member to be positioned at the second location on the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0021] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location on a subject, providing a reference member to be positioned at the second location in the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0022] A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location on the subject, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0023] A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location in the subject, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0024] In some embodiments, the first location in the subject is the esophagus of the subject, wherein the second location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta. In some embodiments, the second location in the subject is the esophagus of the subject, wherein the first location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta. In some embodiments, the first location is the back of the subject, and wherein the method comprises providing a coupling element for coupling the reference member to the back of the subject.

[0025] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the portion of the elongate member at the first location toward the external member at the second location, detecting a first signal reflected from the external member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid, and generating a flow characteristic output.

[0026] In some embodiments, the reference member is substantially stationary relative to the first location.

[0027] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the external member at the second location toward the portion of the elongate member at the first location, detecting a first signal reflected from the elongate member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid. In some embodiments, the fluid is blood.

[0028] In some embodiments, a portion of the elongate member at the first location is substantially stationary relative to the external member at the second location.

[0029] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject comprising: an elongate member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from the fluid, and an interface for coupling the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector.

[0030] Provided herein is a device for detecting at least one flow characteristic in a subject comprising: an external member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from a fluid, and an interface for connecting the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector, and wherein the external member is adapted to be coupled to the subject's skin.

[0031] Provided herein is a device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

[0032] Provided herein is a device for reflecting at least one electromagnetic wave signal, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

[0033] Provided herein is a device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

[0034] Provided herein is a device for reflecting at least one electromagnetic wave signal, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

[0035] Provided herein is a device for monitoring blood flow comprising: a nasogastric tube; a first sensor coupled to the nasogastric tube, wherein the sensor is capable of sensing blood flow in a blood vessel and is capable of generating a sensor output; and a processor for processing the sensor output to monitor blood flow in the blood vessel.

[0036] In some embodiments of the device, the processor is adapted to generate an output indicating location of the tube. In some embodiments of the device, the processor is adapted to generate a flow characteristic output from the sensor output.

[0037] In some embodiments of the device, the first sensor is adapted to sense energy from the descending aorta. In some embodiments of the device, the first sensor comprises a signal detector. In some embodiments of the device, the first sensor is adapted to sense at least one of acoustic energy, vibratory energy, thermal energy, mechanical energy, electrical energy, magnetic energy, and electromagnetic energy.

[0038] In some embodiments of the device, the device comprises a second sensor, and wherein the processor determines aortic blood flow pulsation peak velocity as distance between the first sensor and the second sensor divided by the time it takes for a blood pulsation to travel from the first sensor to the second sensor. In some embodiments of the device, at least one of the first sensor, the second sensor, and a third sensor comprises a signal detector for detecting a blood vessel dimension.

[0039] In some embodiments of the device, the processor is adapted to generate an indication of cardiac output from the aortic blood flow pulsation peak velocity multiplied by a blood vessel cross sectional area determined using the blood vessel dimension. In some embodiments of the device, the processor is adapted to generate an alert if the first sensor does not detect blood flow in the blood vessel.

[0040] Provided herein is a method of monitoring a subject's blood flow using a device of any preceding claim, the method comprising the steps of (a) inserting the nasogastric tube into the esophagus of the subject so that the first sensor coupled to the nasogastric tube is in close proximity to the subject's descending aorta, and (b) the processor generating data concerning blood flow in said descending aorta. In some embodiments of the method, the data is generated in real-time for a sufficient period to indicate subject response to a procedure.

[0041] Provided herein is a device substantially as described with reference to the accompanying drawings.

INCORPORATION BY REFERENCE

[0042] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments and drawings of which:

[0044] FIG. 1 is a diagram showing insertion of an embodiment of a device described herein in a subject.

[0045] FIG. 2 is a diagram showing the esophagus and descending aorta viewed from the back of the subject.

[0046] FIG. 3 depicts a subject having an external member of an embodiment of the device on the subject's back and coupled to a signal generator for generating an electromagnetic wave. [0047] FIG. 4 depicts a subject having an elongate member of an embodiment of the device in the esophagus of the subject and extending to a position adjacent to the thoracic aorta, wherein the elongate member comprises a reference member.

[0048] FIG. 5 depicts a subject having an external member of an embodiment of the device on the subject's back, wherein the external member comprises a reference member.

[0049] FIG. 6 depicts a subject having an elongate member of an embodiment of the device in the esophagus of the subject extending to a position adjacent to the thoracic aorta, wherein the elongate member comprises a an electromagnetic wave signal emitter and an electromagnetic wave signal detector, and wherein the elongate member is a esophogeal probe and is coupled to an electromagnetic wave signal generator and an electromagnetic wave signal processor.

DETAILED DESCRIPTION OF THE INVENTION

[0050] Provided herein are devices, and methods for determining fluid flow characteristics in a subject.

[0051] For non-limiting example, in certain embodiments, a device is provided for monitoring cardiac output in a patient. In other embodiments, a device is provided for determining if a nasogastric (NG) tube is placed in the esophagus of a subject, and not in the bronchial passages of the subject, by detecting a blood flow characteristic in the nearby the descending aorta of the subject. As used herein, the terms "subject" and "patient" are interchangeable. The use of either term does is not meant to imply that the person is under a physician's care (previously or currently), although he/she may be, or that the person has a particular condition that makes him or her a "patient," although he/she may have such condition.

[0052] A nasogastric (NG) tube is a narrow diameter, thin walled tube that may be inserted into the nose of a subject and further directed through the nasal passage, down the back of the throat and through the esophagus finally coming to rest in the stomach. Its main functions are to either transport food and medications to the stomach for subjects that are unable to swallow appropriately or to remove material from the stomach of subjects experiencing an obstruction of the gastrointestinal tract.

[0053] When properly positioned in a subject in order to either transport food and medications to the subject's stomach or to remove material from the subject's stomach, at least a portion of the NG tube while inside the lumen of the esophagus sits (or lies) in close proximity to the descending thoracic aorta. As used herein, the anatomical position of the esophagus may also and/or alternatively be considered to be adjacent the descending aorta. [0054] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal emitter adapted to emit a signal; and an external member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

[0055] In some embodiments, a device is provided comprising an elongate member, and does not require a separate device member (external member or other member) for reflecting the EM waves emitted by the elongate member. In some embodiments, the EM waves emitted by the elongate member is reflected by another stationary element, which may be a part of the subject's anatomy, and not a particular element of the device. Likewise, in some embodiments, a device is provided comprising an external member, and not requiring a separate device member (elongate member, reference member, or other member) for reflecting the EM waves emitted by the external member. In some embodiments, the EM waves emitted by the external member is reflected by another stationary element, which may be a part of the subject's anatomy, or another stationary element which is not a particular element of the device.

[0056] In some embodiments, the EM waves that are emitted are then reflected back to a detector element may be referred to as a reflected EM wave. The reflected EM wave may be altered by such reflection, or may be an identical reflection of the emitted EM wave. The signal detector may detect the reflected EM wave (as altered by reflection) or as the identical reflection. In some embodiments, alteration of the EM wave when reflected by the fluid and/or by the reference element, may comprise, for non-limiting example, a phase shift, a wavelength change, an energy change, a peak change, or any other alteration.

[0057] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal detector adapted to detect a signal; and an external member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject.

[0058] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal emitter adapted to emit a signal; and an elongate member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

[0059] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal detector adapted to detect a signal; and an elongate member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject. [0060] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising a subassembly comprising a signal generator and a signal processor, an external member coupled to the subassembly; and an elongate member coupled to the subassembly, wherein at least one of the external member and the elongate member comprises a signal emitter that emits a signal generated by the signal generator, and a signal detector that detects the signal after the signal is reflected from at least one of flowing fluid and a reference member and that sends a detected signal to the signal processor.

[0061] In some embodiments, the signal comprises an electromagnetic wave signal. In some embodiments, the electromagnetic wave signal is at least one of a radio wave signal, a micro wave signal, an infrared wave signal, and a near infrared wave signal. In some embodiments, the signal comprises an electromagnetic wave signal is at least one of a visible wave signal, an ultraviolet wave signal, X-ray wave signal, and a gamma wave signal. In some embodiments, the signal emitter emits electromagnetic waves to nearby fluid.

[0062] In some embodiments, the emitter emits the electromagnetic waves wirelessly. In some embodiments, the emitter is hard- wired to the signal processor.

[0063] In some embodiments, the emitter is coupled to a signal generator that generates the electromagnetic wave. In some embodiments, the signal generator is programmable to generate the electromagnetic wave within at least one of the radio, micro, infrared, and near infrared wave ranges. In some embodiments, the signal generator is programmable to generate the electromagnetic wave within at least one of the visible, an ultraviolet, X-ray, and a gamma wave ranges. In some embodiments, the emitter is coupled to a signal processor.

[0064] In some embodiments, the signal detector comprises a sensor that detects the signal from at least one of the external member and flowing fluid, and wherein the signal is an electromagnetic wave signal. In some embodiments, the sensor is sealed from contact with bodily fluids. In some embodiments, the device further comprises a signal processor adapted to generate a flow characteristic output of a flowing fluid in a vessel located between the elongate member and the external member.

[0065] In some embodiments, the device comprises memory that stores a flow characteristic output that is generated by the signal processor. In some embodiments, the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, time integral of the maximum velocity of the fluid, volume, flow time, and volume of fluid flowing over time. In some embodiments, the fluid is blood. In some embodiments, the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, stroke distance, stroke volume, flow time, and cardiac output. [0066] In some embodiments, the signal detector comprises a transmitter that is capable of transmitting the signal to a signal processor, wherein the signal comprises an electromagnetic wave signal. In some embodiments, the transmitter transmits the electromagnetic wave wirelessly. In some embodiments, the transmitter is hard- wired to the signal processor.

[0067] In some embodiments, the device comprises an output monitor. In some embodiments, the device comprises an input module. In some embodiments, at least a portion of the elongate member is adapted to remain substantially stationary relative to the external member when the elongate member is inserted into the subject. In some embodiments, the tip of the elongate member is the portion of the elongate member that remains substantially stationary relative to the external member. In some embodiments, the portion of the elongate member that remains substantially stationary relative to the external member is a portion of the elongate member that lies in close proximity to the descending aorta.

[0068] In some embodiments, the external member is coupled to the subject's back. In some embodiments, the external member comprises an adhesive pad. In some embodiments, the external member is adapted to remain substantially stationary relative to at least a portion of the elongate member when the elongate member is inserted into the subject.

[0069] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to be placed adjacent the descending aorta.

[0070] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to lie in close proximity to the descending aorta.

[0071] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to be placed adjacent the descending aorta.

[0072] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to lie in close proximity to the descending aorta.

[0073] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location in a subject, providing a reference member to be positioned at the second location on the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal. As used herein, determining a flow characteristic of a fluid between a first location and a second location is not limited to flow that occurs from the first location to the second location, or vice-versa, although it may involve flow in this manner. Rather, flow in any direction that occurs in between the two locations is intended herein. For non-limiting example, flow may occur along the descending aorta, while the first location may be the esophagus, and the second location may be the back of the subj ect.

[0074] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location on a subject, providing a reference member to be positioned at the second location in the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0075] A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location on the subject, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0076] A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location in the subject, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

[0077] In some embodiments, the first location in the subject is the esophagus of the subject, wherein the second location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta. In some embodiments, the second location in the subject is the esophagus of the subject, wherein the first location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta. In some embodiments, the first location is the back of the subject, and wherein the method comprises providing a coupling element for coupling the reference member to the back of the subject.

[0078] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the portion of the elongate member at the first location toward the external member at the second location, detecting a first signal reflected from the external member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid, and generating a flow characteristic output.

[0079] In some embodiments, the reference member is substantially stationary relative to the first location.

[0080] Provided herein is a method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the external member at the second location toward the portion of the elongate member at the first location, detecting a first signal reflected from the elongate member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid. In some embodiments, the fluid is blood.

[0081] In some embodiments, a portion of the elongate member at the first location is substantially stationary relative to the external member at the second location.

[0082] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject comprising: an elongate member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from the fluid, and an interface for coupling the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector.

[0083] Provided herein is a device for detecting at least one flow characteristic of a fluid in a subject comprising: an external member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from a fluid, and an interface for connecting the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector, and wherein the external member is adapted to be coupled to the subject's skin.

[0084] Provided herein is a device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

[0085] Provided herein is a device for reflecting at least one electromagnetic wave signal, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

[0086] Provided herein is a device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

[0087] Provided herein is a device for reflecting at least one electromagnetic wave signal, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

[0088] Provided herein is a device for monitoring blood flow comprising: a nasogastric tube; a first sensor coupled to the nasogastric tube, wherein the sensor is capable of sensing blood flow in a blood vessel and is capable of generating a sensor output; and a processor for processing the sensor output to monitor blood flow in the blood vessel.

[0089] In some embodiments of the device, the processor is adapted to generate an output indicating location of the tube. In some embodiments of the device, the processor is adapted to generate a flow characteristic output from the sensor output.

[0090] In some embodiments of the device, the first sensor is adapted to sense energy from the descending aorta. In some embodiments of the device, the first sensor comprises a signal detector. In some embodiments of the device, the first sensor is adapted to sense at least one of acoustic energy, vibratory energy, thermal energy, mechanical energy, electrical energy, magnetic energy, and electromagnetic energy.

[0091] In some embodiments of the device, the device comprises a second sensor, and wherein the processor determines aortic blood flow pulsation peak velocity as distance between the first sensor and the second sensor divided by the time it takes for a blood pulsation to travel from the first sensor to the second sensor. In some embodiments of the device, at least one of the first sensor, the second sensor, and a third sensor comprises a signal detector for detecting a blood vessel dimension.

[0092] In some embodiments of the device, the processor is adapted to generate an indication of cardiac output from the aortic blood flow pulsation peak velocity multiplied by a blood vessel cross sectional area determined using the blood vessel dimension. In some embodiments of the device, the processor is adapted to generate an alert if the first sensor does not detect blood flow in the blood vessel.

[0093] Provided herein is a method of monitoring a subject's blood flow using a device of any preceding claim, the method comprising the steps of (a) inserting the nasogastric tube into the esophagus of the subject so that the first sensor coupled to the nasogastric tube is in close proximity to the subject's descending aorta, and (b) the processor generating data concerning blood flow in said descending aorta. In some embodiments of the method, the data is generated in real-time for a sufficient period to indicate subject response to a procedure.

[0094] Provided herein is a device substantially as described with reference to the accompanying drawings.

[0095] As described herein, a fluid may comprise any flowable matter, including matter made entirely of solid matter, essentially of solid matter, in part of solid matter, or matter in liquid state. For example, a fluid as provided herein may include the material within a gastrointestinal tract, which may comprise solid matter. Any moving matter may be considered a fluid for the purposes of the devices and methods described herein.

[0096] An embodiment of a device of the invention comprises a nasogastric tube on which are mounted sensors. It also may comprise processing and interfacing components linked with the sensors.

[0097] In some embodiments, a device comprises an NG tube with at least one sensor lying in or along the wall of the tube and a wired or wireless interface to connect to the signal processor. In certain embodiments, the entire NG tube is a disposable item. In some embodiments, the device may also comprise a monitor (an output monitor) consisting of a display panel, a visual, auditory, and hardcopy (paper) output, an interface to the sensors, which may be wired or wireless, an interface to a signal processor, which may be wired or wireless, an interface for a remote monitoring system, a data recording device, software, a CPU for data manipulation, and/or a portable or fixed power source. In some embodiments, the signal processor is physically part of the output monitor.

[0098] An embodiment of the device is shown in Fig. 1 in use. Fig. 1 is a diagram showing insertion of a device described herein in a subject 2. Pictured is the subject's 2 nasal passages (or nasopharynx) 4, tongue 14, trachea 42, and bronchi 44, descending aorta 10, esophagus 6, and stomach 46. Fig. 2 is a diagram showing the esophagus 6 and descending aorta 10 viewed from the back of the subject 2. The device in Fig. 1 is shown as a nasogastric tube 32 passing through the subject's 2 nasal passages 4, down his esophagus 6, and into his stomach 46. The sensors 34a, 34b, 34c of the device of the depicted embodiment are located along the nasogastric tube 32 such that when the nasogastric tube 32 is properly placed down the esophagus 6, and then advanced into the stomach 46, and not misplaced down the trachea 42 and/or the a bronchial passage 44, at least one sensor is adjacent to and/or in close proximity to the descending aorta 10 (specifically the thoracic aorta). So positioned, the at least one sensor (one of sensors 34a. 34b, 34c) that is adjacent to and/or in close proximity to the descending aorta 10 can detect blood flow 48 in the descending aorta 10 to confirm proper nasogastric tube 32 placement, at least. The sensors 34a. 34b, 34c shown are not to scale in Fig. 1. Also shown is output monitor 40 (monitor), which can display at least one characteristic of blood flow, for non- limiting example, aortic blood flow pulsation peak velocity. The monitor 40 can comprise, in certain embodiments, a display panel, a visual, auditory, and hardcopy (paper) output, an interface to the sensors which may be wired or wireless, an interface for a remote monitoring system, a data recording device, software, a CPU for data manipulation, and/or a portable or fixed power source.

[0099] The sensors 34a, 34b, 34c, a single sensor (any one of sensors 34a, 34b, 34c), or a plurality of sensors (2 or more sensors), may detect changes in acoustic, vibratory, thermal, mechanical, electrical, magnetic, and/or electromagnetic energy. Some embodiments of the device, including, but not limited to, the embodiment of the device depicted in Fig. 1, when inserted into the esophagus 6 and overlying the descending aorta 10, will detect energy transmitted from the blood flow 48 turbulence or blood flow 48 pulsations occurring in the aorta 10. As the blood flow pulsation, which is a result of the beating heart or from chest compressions in the case of performing cardiopulmonary resuscitation, for example, travels along the aorta 10 and approximately parallel to an embodiments of the device which has been placed in the esophagus 6, at least one sensor (one of sensors 34a, 34b, 34c) will detect energy transmitted from the pulsation.

[00100] Alternatively, and/or additionally, certain embodiments of the device may comprise at least one sensor (for example, one of sensors 34a. 34b, 34c in Figure 1) that is adjacent to and/or in close proximity to the descending aorta 10 can detect improper placement of the nasogastric tube 32 by detecting a lack of blood flow 48 in the descending aorta 10. The device in some embodiments may detect insufficient energy, or no energy whatsoever, from the nearby vessel (for example, the blood flow 48 in the descending aorta 10) in order to detect improper placement of the nasogastric tube 32.

[00101] In an embodiment of a device having at least two sensors, wherein each of the sensors are positioned adjacent to and/or in close proximity to the descending aorta, the energy detection may occur at the sensor nearest to the heart first, and then the energy detection will occur in the next sensor in the path of the blood flow as the pulsation moves down the aorta 10. In embodiments comprising multiple sensors, as the pulsation passes each successive sensor the time it takes to travel from one sensor to the next may be recorded.

[00102] Given the time it takes to travel between sensors and knowing the distance between sensors will enable the calculation of the aortic blood flow pulsation velocity for example: Aortic blood flow pulsation peak velocity (ABFPPV) = distance between sensors / inter-sensor time peak to peak interval. Inter-sensor time peak to peak interval is the amount of time it takes for a pulsation to move from a first sensor to a second sensor as measured from the peak of the waveform detected at the first sensor and the same peak of the waveform detected at the second sensor. A peak may also be a trough, as used herein, such that the inter-sensor time peak to peak interval is measured as the amount of time it takes for a pulsation to move from a first sensor to a second sensor as measured from a trough of the waveform detected at the first sensor and the same trough of the waveform detected at the second sensor. As used herein, the same measurement may be taken at an inflection point of the wave (for example, the integral of the waveform) measured between a peak and a trough, such that the inter-sensor time peak to peak interval is measured as the amount of time it takes for a pulsation to move from a first sensor to a second sensor as measured from an inflection point of the waveform detected at the first sensor and the same inflection point measured at the second sensor. Alternatively, any point on the waveform may be used in this calculation as the peak to peak interval, so long as the same point along the waveform is detected by the first sensor and the second sensor. As the pulsation moves faster, the ABFPPV increases where the distance between sensors is constant since the peak to peak interval is shorter.

[00103] It is possible with further manipulation of this data utilizing the measured aortic blood flow pulsation peak velocity to calculate aortic volumetric flow rate and/or cardiac output. For example, the intraluminal diameter of the aorta along the path of the device and the density of blood, at least, may be used in some embodiments to determine the volumetric flow rate using standard equations known to one of skill in the art. In some embodiments, an ultrasound ECHO device is used to determine the intraluminal diameter of the aorta along the path of the device. For non- limiting example, an ultrasound ECHO device might comprise a Doppler device. The intraluminal diameter may also be determined using standard known values for or estimations based on typical intraluminal diameters, for example, based on the subject's sex, age, and/or height. In another example, the intraluminal diameter of the aorta along the path of the device may be used in some embodiments to determine the cardiac output. The intraluminal diameter allows for the calculation of the cross- sectional area of the inside of the aorta.

[00104] Cardiac output may be approximated as follows: CO = ABFPPV x aorta cross-sectional area. In some embodiments, the CO approximation may be corrected by a correction factor in order to account for the fact that most forward blood flow occurs only when the aortic valve is open (i.e., systole). In some embodiments, the correction factor may be established, for example, by gating the monitor with an ECG and measuring the R-R interval from the ECG output, which is the length of time between heart beats (i.e., systolic + diastolic flow time). Systolic flow time, in some embodiments, may be determined by measuring the base (or time) axis of the produced velocity waveform. For example, in some embodiments, the CO may additionally be multiplied by: systolic flow time/(systolic flow time + diastolic flow time) to give a corrected cardiac output. As used herein, the term cardiac output may refer to either the approximated cardiac output, the corrected cardiac output, and/or a cardiac output presented in different units or calculated in a different manner.

[00105] Embodiments of the device provided herein may be used to monitor cardiac output in a minimally invasive manner. Embodiments of the device may be used to monitor a subject's flow characteristic continuously. Embodiments of the device may be used to monitor a subject's flow characteristic in real-time.

[00106] The device allows patient care to be audited by recording and analyzing the real-time data resulting from the determination of at least one blood flow characteristic as various procedures are performed and medications are given. When using certain embodiments of the devices and methods provided herein, the management of the traditional surgical, ICU or CCU patient may be carried on in a general ward, emergency department, or pre-hospital environment.

[00107] Embodiments of the methods and devices provided here may be used in order to confirm nasogastric (NG) tube placement in the esophagus by confirming that aortic blood flow pulsations are detected. In certain embodiments, a flow characteristic may be used to confirm proper NG tube placement. In certain embodiments, a flow characteristic (or lack thereof) may be used to determine improper NG tube placement. For example, an embodiment of a device provided herein is incorporated into an NG tube, or is used alongside an NG tube. Certain embodiments of the device comprise a nasogastric tube and at least one sensor. The sensor may be, in some embodiments, coupled to the nasogastric tube. The NG tube and the sensor may be positioned in the subject, and aortic blood flow pulsations are detected, NG tube has been placed correctly in the esophagus which overlies the aorta and has not been incorrectly placed into the bronchi of the lungs which do not lie in proximity to the aorta, since when the NG tube is accidentally placed in the right or left lung bronchi no aortic blood flow pulsation will be detected.

[00108] Certain embodiments of the methods and devices provided herein may also be used to monitor subjects in the hospital setting. Improved subject monitoring enables earlier intervention for complications like septic shock where delayed treatment may result in significant risk of death.

Changes in blood flow are known to occur before changes in blood pressure, temperature, and tissue oxygenation. Certain embodiments of the devices and methods provided herein allow for immediate detection of blood flow changes in the aorta, the main conduit for blood leaving the heart.

[00109] Embodiments of devices and methods provided herein use a narrow diameter disposable elongate member that may be placed in any subject, unconscious, conscious, or sedated, by a practitioner (for non- limiting example, a nurse or physician) with ease and minimal subject discomfort. In some embodiments, once in position the device may be secured (for non-limiting example, by taping to the subject a portion of the elongate member that remains external to the subject's body after insertion of the elongate member into the subject) and left in place and, thus, may function independently of subj ect movement.

[00110] The device may be configured to monitor aortic peak and average blood flow velocity and generate a velocity curve, among other characteristics described herein. Together, these variables allow for the calculation of cardiac output as well as changes in intravascular fluid status, as described elsewhere herein. In some embodiments, the device and methods provided herein offer real-time, hands-free monitoring and offer medical staff the ability to optimize subject management.

[00111] In some embodiments, the devices and methods provided herein are used to reduce the likelihood of post-surgical hypotension by detecting early, characteristic changes in aortic blood flow alerting staff to intervene immediately. In some embodiments, the devices and methods provided herein are used to facilitate real-time intervention by the medical staff.

[00112] Provided herein is a device that comprises an elongate member and an external member.

[00113] In some embodiments, a device is provided that comprises an elongate member and an external member, wherein the elongate member is an esophogeal tube. In some embodiments, a device is provided that comprises an elongate member and an external member, wherein the elongate member is an esophogeal probe. In some embodiments, the elongate member is adapted to extend down the esophagus of a subject such that a portion of the elongate member can be placed at a location in the esophagus adjacent to the thoracic aorta (and/or the descending aorta). The elongate member of the device may lie in close proximity to the thoracic aorta (and/or the descending aorta). In some embodiments, the elongate member may be placed to lie (at least in part) within the esophagus. Certain embodiments of the elongate member may be disposable. In some embodiments, at least a portion of the elongate member is configured to lie outside the subject wherein another portion of the elongate member is adapted to extend down the esophagus of a subject.

[00114] In some embodiments, the distal end of the elongate member may have a diameter of at most about 4 millimeters, measured at about the distal end of the elongate member. The distal end of the elongate member is the end first inserted into the subject, whereas the proximal end is the end of the elongate member that is last inserted into the subject or not inserted at all. The proximal end in some embodiments is the location of the elongate member that may be handled by a practitioner when the distal end of the elongate member is in the subject. As used herein, the word "about" when used in the context of the diameter of the elongate member diameter can mean variations of a maximum of 5%, 10%, 20%, 25%, or 50% of the diameter.

[00115] In some embodiments, the maximum diameter at or near the distal end of the elongate member may be located at about the sensor location, in embodiments comprising at least one sensor on the distal end of the elongate member. In some embodiments, the maximum diameter on the distal end of the elongate member may be located at about the signal emitter location, in embodiments comprising at least one signal emitter on the distal end of the elongate member. In some embodiments, the maximum diameter on the distal end of the elongate member may be located at about the signal detector location, in embodiments comprising at least one signal detector on the distal end of the elongate member. In some embodiments, the maximum diameter on the distal end of the elongate member may be located at about the reference member, in embodiments wherein the elongate member comprises a reference member on the distal end of the elongate member.

[00116] The maximum diameter on the distal end of the elongate member may be at most 3cm from the tip of the elongate member. For non- limiting example, in an embodiment where the elongate member does not extend into the stomach and is configured to detect blood flow of the thoracic artery, the maximum diameter on the distal end of the elongate member may be at most 3cm from the tip of the elongate member.

[00117] The maximum diameter may be at most 2 cm from the tip of the elongate member. For non- limiting example, in an embodiment where the elongate member does not extend into the stomach and is configured to detect blood flow of the thoracic artery, the maximum diameter may be at most 2 cm from the tip of the elongate member.

[00118] The maximum diameter may be at most 1 cm from the tip of the elongate member. For non- limiting example, in an embodiment where the elongate member does not extend into the stomach and is configured to detect blood flow of the thoracic artery, the maximum diameter may be at most 1 cm from the tip of the elongate member. The maximum diameter may be from 1 cm to 3 cm from the tip of the elongate member in some embodiments. For non- limiting example, in an embodiment where the elongate member does not extend into the stomach and is configured to detect blood flow of the thoracic artery, the maximum diameter may be from 1 cm to 3 cm from the tip of the elongate member.

[00119] The maximum diameter may be from 2 cm to 3 cm from the tip of the elongate member. For non- limiting example, the maximum diameter may be from 2 cm to 3 cm from the tip of the elongate member in an embodiment where the elongate member does not extend into the stomach and is configured to detect blood flow of the thoracic artery.

[00120] The tip of the elongate member is at the very distal end of the elongate member. Where the elongate member is a tube, the tip may be hollow. The tip may have a tapering diameter.

[00121] In some embodiments, the elongate member is a catheter. For non- limiting example, the elongate member may be in some embodiments: an angioplasty catheter, a stent delivery catheter, or a guiding catheter. The elongate member may comprise a polymer. In certain embodiments, the elongate member is a wire. For non- limiting example, the elongate member is a guide wire in some embodiments. The elongate member may comprise a guide wire in some embodiments. The elongate member may comprise metal in some embodiments. The elongate member may comprise carbon fiber in some embodiments. The elongate member may comprise stainless steel in some embodiments. The elongate member may comprise a memory metal, for non-limiting example, a Nickel- Titanium alloy. In another embodiment, the elongate member is a scope, for non-limiting example, an endoscope, a bronchoscope, a choledochoscope, a colonoscope, a duodenoscope, an echoendoscope, an enteroscope, an eseophagoscope, a gastroscope, a laryngoscope, a rhinolaryngoscope, a sigmoidoscope, an ureteroscope, a proctoscope, a neuroscope, an arthroscope, a laprascope, or a thoracoscope.

[00122] In some embodiments, the external member is adapted to couple with a subject, for non- limiting example, to the subject's skin. In some embodiments, the external member is coupled to a subject's body. In some embodiments, the external member comprises a pad adapted to couple to a subject's body. In some embodiments, the external member comprises an adhesive pad that sticks to the subject's back. The external member may be adapted to lie on the back of the subject, such as on the left mid-upper back.

[00123] In some embodiments, the size of the external member is relative to the size of the subject, for non- limiting example, a large size for a large male subject, a small size for a child. In some embodiments, the minimum size for the external member is about 1 cm x 1 cm. For a pediatric subject, in an embodiment wherein the elongate member comprises the signal emitter and/or signal detector, the size of the external member at minimum may be, for example, 3 cm x 6 cm, which. For a large adult subject, in an embodiment wherein the elongate member comprises the signal emitter and/or signal detector, the size of the external member may be about 10 cm x 20 cm. Any size for an external member is appropriate so long as it is sufficient for the reflection of EM signals where the elongate member comprises the signal emitter and/or detector, and/or for the signal emission and/or detection where the external member comprises the signal emitter and/or detector. For non-limiting example, the external member could be the table upon which the subject lies during a procedure, so long as the table is coupled to the subject (by the subject lying on the table, for example). For non- limiting example, the external member may be a very small size, sufficient only to comprise a signal emitter and/or a signal detector, which may be even smaller than lcm x lcm where such signal emitter and/or detector is smaller.

[00124] In some embodiments, the external member comprises a coupling element. In certain embodiments, the coupling element comprises at least one of a gel, a tape adhesive, a glue, gauze, a wrap. In some embodiments, the external member comprises a coupling element which does not break the skin of the subject in order to couple the external member to the subject. Some embodiments, the external member comprises a coupling element which may break the skin in order to couple to the subject, or the skin may be broken (not necessarily by the coupling element itself) in order to couple the external member to the skin (such as by a suture). Any coupling element that ensures that the external member couples to the skin of the subject is contemplated herein.

Additionally, while the external member may, in some embodiments, make direct contact to the skin of the subject, it is contemplated that in some embodiments, the external member is coupled to the subject's skin with an intervening element (for non-limiting example, conductive gel, clothing, or another intervening element that does not interfere with the function of the external member as either a emitter and/or detector, or as a reference member). While the external member may, in some embodiments, be referred to as stationary, the external member need not be fixed in place in order to be stationary, and may instead simply lie on the subject in order to remain stationary. The external member may be disposable.

[00125] In some embodiments, the device comprises a signal emitter. In some embodiments, the device comprises a signal detector. In some embodiments, at least one of the signal emitter (i.e., emitter) and the signal detector (i.e., detector) is incorporated into (and/or is part of) at least one of the elongate member and the external member. In some embodiments, at least one of the emitter and the detector is coupled to at least one of the elongate member and the external member.

[00126] In some embodiments the signal emitter is configured to emit an electromagnetic (EM) wave. In some embodiments, the EM wave comprises at least one of a radio wave, a micro wave, an infrared wave, a near infrared wave. In some embodiments, the EM wave comprises at least one of a visible wave, an ultraviolet wave, an X-ray wave, and a gamma wave. In some embodiments, the EM wave comprises a radio wave. In some embodiments, the EM wave comprises a micro wave. In some embodiments, the EM wave comprises an infrared wave. In some embodiments, the EM wave comprises a near infrared wave. In some embodiments, the EM wave comprises a visible wave. In some embodiments, the EM wave comprises a an ultraviolet wave. In some embodiments, the EM wave comprises an X-ray wave. In some embodiments, the EM wave comprises a gamma wave. In some embodiments, the EM wave comprises a combination of at least two of a radio wave, a micro wave, an infrared wave, and a near infrared wave. In some embodiments, the EM wave comprises a combination of at least two of a radio wave, a micro wave, an infrared wave, a near infrared wave, a visible wave, an ultraviolet wave, an X-ray wave, and a gamma wave. In some embodiments, the EM wave comprises a combination of at least three of a radio wave, a micro wave, an infrared wave, a near infrared wave, a visible wave, an ultraviolet wave, an X-ray wave, and a gamma wave. In some embodiments, the EM wave comprises a combination of a radio wave, a micro wave, an infrared wave, and a near infrared wave. While the EM wave is described as a function of wavelength, the EM wave may alternatively be described by its correlating energy and/or frequency and still be contemplated as part of the invention described herein.

[00127] In some embodiments, the signal detector comprises at least one sensor. In some embodiments, the signal detector comprises at least one sensor that detects reflected EM wave signals from the fluid nearby. For example, in an embodiment wherein the device is adapted for detecting thoracic aorta blood flow, the signal emitter emits EM wave(s) to the blood in the thoracic aorta, which is/are reflected back to and detected by the signal detector. The signal detector may, in some embodiments, comprise a transmitter that can be either hard- wired or wirelessly coupled to the signal processor. The signal detector may, in some embodiments, be hard-wired or wirelessly coupled to the signal generator.

[00128] In some embodiments, the sensor is sealed from contact with bodily fluids (for example, blood, bile), other bodily tissue (organs, or any non- fluid biological material), or any fluids or materials used during, before, or following use of the device. In some embodiments, the sensor comprises a seal that keeps the sensor from contacting bodily fluids, other bodily tissue, or any fluids or materials used during, before, or following use of the device. In some embodiments, the sensor is comprised of a material that reduces or avoids protein adherence to the sensor. In some embodiments, the sensor is coated with a coating that reduces or avoids protein adherence to the sensor. In some embodiments, the coating is porous. In some embodiments the coating is not porous to bodily fluids.

[00129] In some embodiments, the signal emitter is hard- wired or wirelessly coupled to a signal generator. In some embodiments, the emitter is hard-wired or wirelessly coupled to the processor. In some embodiments, the detector is hard-wired or wirelessly coupled to the signal generator. The signal generator may be hard-wired or wirelessly coupled to the signal processor, in some embodiments.

[00130] In some embodiments the signal generator is capable of generating the EM wave that is emitted by the signal emitter. The signal generator may be programmed to generate an EM wave that is then emitted by the signal emitter, in some embodiments. The EM wave frequency, wavelength, or energy may be set by a practitioner, may be determined based on certain subject factors, may be one of a pre- determined set of options (within at least one of the radio, micro, infrared, near infrared, visible, ultraviolet, X-ray, and gamma wave ranges), may be fixed at a particular setting (and/or a combination of settings) within any of the radio, micro, infrared, near infrared, visible, ultraviolet, X-ray, and gamma wave ranges.

[00131] In some embodiments, the signal generator and/or the signal processor may be part of a subassembly of the device, wherein the subassembly is adapted to perform at least one function (for non-limiting example, signal generation and/or signal processing). The signal generator may be part of the signal processor or vice versa.

[00132] In some embodiments, the subassembly adapted to perform at least one function related to signal generation, signal emission, signal capture, signal processing, signal conversion, signal display and presentation. The signal generator of the subassembly is the element of the subassembly that is adapted to perform the function of signal generation, at least, in some embodiments. The signal processor of the subsassembly is the element of the subassembly that is adapted to perform the function of signal processing, at least, in some embodiments.

[00133] In some embodiments, the signal processor is configured to receive transmitted and/or detected EM wave signals from the signal detector and output flow velocity and acceleration data to an output monitor. The device in some embodiments may comprise a signal processor adapted to generate a flow characteristic output from the output of a sensor. The device in some embodiments may comprise a signal processor adapted to generate a flow characteristic output from the EM wave signal transmitted from the signal detector. The signal processor may be capable of translating and/or converting EM wave signals received in order to generate a flow characteristic output using the EM wave signal, a converted EM wave signal, or a translated EM wave signal. For example the signal processor in some embodiments may be capable of using the EM wave signal to generate an output showing: average velocity, peak velocity, acceleration, stroke distance (i.e., time integral of the maximum velocity of the fluid), volume, flow time, pressure, and volume of fluid flowing over time. In embodiments of the device wherein blood flow characteristics are determined, the blood flow characteristics may include, for non-limiting example, average velocity, peak velocity, acceleration, stroke distance (i.e., time integral of the maximum velocity of the blood flowing), stroke volume, flow time, central aortic pressure, and cardiac output. The output from the signal processor may be displayed in a number of manners, for example, on a monitor, in a chart, in a graph, in a summary table, in a table, as text in a readable format.

[00134] The signal processor in some embodiments may be capable of generating a flow characteristic output from the EM wave signals in real-time, or near-real time (with minimal delay, for example, no more than 10 milliseconds, no more than 100 milliseconds, no more than 0.5 seconds, no more than 1 second, no more than 2 seconds, no more than 5 seconds, no more than 10 seconds, or no more than 15 seconds). Some embodiments of the device may be capable of detecting the reflected EM wave signals from at least one of the fluid flowing and the external member and determining a blood flow characteristic in real-time, or near-real time (with minimal delay, for example, no more than 10 milliseconds, no more than 100 milliseconds, no more than 0.5 seconds, no more than 1 second, no more than 2 seconds, no more than 5 seconds, no more than 10 seconds, or no more than 15 seconds).

[00135] In some embodiments, the device may comprise memory that stores the blood flow characteristics and/or other characteristics for storage, later display, later presentation or later review. The memory may, alternatively or additionally, save the raw data EM wave signals transmitted to the processor. The signal processor of the subassembly may comprises such memory. In some embodiments, the device may comprise computer readable media that can summarize a flow characteristic in a report, present a plurality of flow characteristics in a report in summary form, present all raw data for a flow characteristic, present a subset of all raw data for a flow characteristic, present at least one flow characteristic in a chart or in a graph.

[00136] In some embodiments, the device may include an input module that allows an operator, such as a practitioner to input subject information or to mark the time of an event, a detail regarding an event, or other information within the device's memory. A practitioner as used herein may include a technician, a nurse, a physician, or another individual. The signal processor, in some embodiments, may be programmed to mark certain events and to alert, or to save the data and information relevant to the event for later practitioner review. Events may include changes to a characteristic (sudden or gradual), or a characteristics that are outside predetermined limits, for non- limiting example. The signal processor may comprise, in some embodiments, the ability to correlate information both temporally (according to the time of its occurrence) and generally to the characteristics recorded and/or displayed for the subject. In some embodiments, the signal processor comprises the ability to record the characteristics and the correlating display information (which can be used to re-generate the display) on a continuous basis, or upon prompting by a practitioner. The signal processor may comprise a computer program or computer readable media that provides the above functionality to the signal processor, in some embodiments. [00137] The device may further comprise an output monitor in certain embodiments. The output monitor may comprise a display. The output monitor may be part of the subassembly. The output monitor may display a blood flow characteristic, for non-limiting example: average velocity, peak velocity, acceleration, stroke distance, stroke volume, flow time, and cardiac output. The blood flow characteristic may be an aortic blood flow characteristic, where the device is used to measure a thoracic aortic blood flow characteristic, for non- limiting example. The output monitor may display any of said characteristics in real-time, or near-real time (with a minimal delay). The output monitor may display quantitative (i.e., numeric) and/or qualitative (i.e., continuous plot) of a flow characteristic, at least. The output monitor may be hard-wired or wirelessly coupled to the signal processor.

[00138] In some embodiments, the output monitor may be remote from signal processor, or remote from the subject. The output monitor may be provided at a monitoring station, which may be at a central location, at a practitioner's location remote from the subject, at a nurse's station, or at another location remote from the subject, in some embodiments. There may be multiple output monitors that can provide at least one characteristic for review by and display to multiple practitioners simultaneously, in some embodiments. The multiple practitioners could review the same characteristic or characteristics at the same time in the same manner (for example blood flow velocity as a real-time continuous plot), review a different characteristic or different characteristics at the same time, or review the same characteristic or the same characteristics in a different manner (for example, a first output monitor displays blood flow velocity as a real-time continuous plot, while a second output monitor displays blood flow velocity as a quantitative number in real time). Any of the output monitors provided herein could also display a blood flow image or picture.

[00139] In an embodiment where the elongate member comprises at least one of a signal emitter and a signal detector, the external member comprises a reference member. In an embodiment where the external member comprises at least one of a signal emitter and a signal detector, the elongate member comprises a reference member. The reference member need not be coupled to other components of the device, although it may be.

[00140] In some embodiments, the reference member is configured to be substantially stationary relative to the signal emitter during use. In some embodiments, the reference member is configured to be substantially stationary relative to the signal elongate member tip during use. In some embodiments, the reference member is configured to be substantially stationary relative to the signal detector during use. In some embodiments where the reference member is a part of the external member, the reference member is substantially stationary due to the coupling of the external member to the subject. [00141] A substantially stationary reference member of certain embodiments facilitates the detection of doppler shifts, for example, in the reflected signals of the moving target (i.e., red blood cells) in comparison to the substantially stationary reference member. In an embodiment wherein at least one of the emitter and detector are located on the elongate member, the less that the reference member of the external member moves relative to the emitter or the detector, the smaller the shifts that can be detected. Likewise, in an embodiment wherein at least one of the emitter and detector are located on the external member, the less that the external member moves relative to reference member of the elongate member, the smaller the shifts that can be detected.

[00142] The device of some embodiments may be used to compare reflected electromagnetic (EM) signals from fluid (or other liquid) flow to EM signals reflected from the reference member. The device emits an EM wave toward the fluid of interest (blood flowing), which then is either reflected back from the blood, or from the reference member which is situated on the opposite side of the fluid of interest relative to the emitter. The flow may be blood flow, and in certain examples provided herein the flow is aortic blood flow. In such an example, the EM wave may be reflected off red blood cells flowing in an aorta. For example, where the elongate member (or a portion thereof) is placed in the esophagus such that it lies in close proximity to the thoracic aorta, the external member having a reference member is configured to lie on the approximate opposite side of the aorta (i.e., the left mid- upper back of the subject). In this embodiment of the device, the device measures thoracic aortic blood flow. The device so configured may also measure and/or calculate average velocity, peak velocity, acceleration, stroke distance, stroke volume, flow time, and cardiac output in real time, near real time (with minimal delay), or it may store such characteristics. Devices so configured are depicted in FIG. 3-6.

[00143] FIG. 3 depicts a subject 2 having an external member 24 of an embodiment of the device 36 on the subject's 2 back and coupled to a signal generator 16 for generating an electromagnetic wave. Related to FIG. 3 is FIG. 4, depicting a subject 2 having an elongate member 26 of an embodiment of the device 36 in the esophagus 6 of the subject 2 and extending to a position adjacent to the thoracic aorta 8, wherein the elongate member 26 comprises a reference member 28.

[00144] FIG. 5 depicts a subject 2 having an external member 24 of an embodiment of the device 36 on the subject's 2 back, wherein the external member 24 comprises a reference member 28. Related to FIG. 5 is FIG. 6, depicting a subject 2 having an elongate member 26 of an embodiment of the device 36 in the esophagus 6 of the subject extending to a position adjacent to the thoracic aorta 8, wherein the elongate member 26 comprises a an electromagnetic wave signal emitter 18 and an electromagnetic wave signal detector 20, and wherein the elongate member 24 is a esophogeal probe 30 and is coupled to an electromagnetic wave signal generator 16 and an electromagnetic wave signal processor 22 and an output monitor . [00145] Certain embodiments of the device may be configured to detect frequency shifts caused by the EM waves reflected from fluid flow. Certain embodiments of the device (for example, the signal processor of the device of some embodiments), may be configured to subtract, reduce, or eliminate noise from the reflected EM wave transmitted by the detector. The elimination, reduction, or subtraction of noise may be sufficient to detect frequency shifts that are, for example, at least 0.0001% of the frequency detected, at least 0.001% of the frequency detected, at least 0.01% of the frequency detected, at least 0.1% of the frequency detected, at least 0.5% of the frequency detected, at least 1% of the frequency detected, at least 5% of the frequency detected, at least 10% of the frequency detected, at least 25% of the frequency detected, at least 30% of the frequency detected, at least 40% of the frequency detected, at least 50% of the frequency detected, at least 75% of the frequency detected, and/or at least 100% the frequency detected.

[00146] Certain embodiments of the device as described herein may be used in subjects undergoing surgical procedures requiring cardiac output monitoring and guided fluid management (i.e., continuous intravenous fluid input and urinary output monitoring). Subjects may include those undergoing any abdominal, lung, or heart surgery and many orthopedic, obstetric, gynecologic, and neurologic procedures requiring general anesthesia. Certain embodiments of the device as described herein may be used in critically ill subjects in medical and intensive care units requiring cardiac output monitoring and fluid guided management.

[00147] Certain embodiments of the device as described herein may be used in subjects with abdominal aortic aneurysms for monitoring pathologic changes or those who need to undergo a repair procedure. As well the device may benefit subjects with peripheral vascular disease who have developed obstruction of arteries in the limbs and require procedures to remove or bypass the obstruction. By monitoring changes in arterial flow in these subjects, early intervention may be facilitated without the need for potentially harmful invasive studies using dyes or contrast.

[00148] Additional populations of subjects in some embodiments may include all acute medical and surgical ward patients (i.e., most subjects being non-critically ill) and outpatient congestive heart failure subjects requiring regular monitoring for gradual changes in cardiac output and fluid volume status.

[00149] Embodiments of the device as described herein may be applied as a diagnostic tool to confirm malignancies of tumors, and additionally and/or alternatively play a part in localized delivery and customization of chemotherapies. [00150] Certain embodiments of the device as provided herein may be used to determine intra- operatively if a by-pass graft (i.e., placement of a conduit for blood flow around an occluded region of an artery) has been placed effectively and blood flow through the new graft is sufficient.

[00151] Certain embodiments of the device as provided herein may comprise a stent as the reference member and fluid flow velocity monitored as it flows through the stent (for example blood flow through a coronary stent or a peripheral vascular stent, or bile flow through a biliary stent). The device may be used to determine the flow properties during the placement of the stent as well as on follow-up review for restenosis.

[00152] The invention is not limited to the embodiments described but may be varied in construction and detail. The sensors may be of any of a variety of types, including those described in the art for use in cardiac output monitoring.

[00153] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.

Claims

CLAIMS WHAT IS CLAIMED IS:

1. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal emitter adapted to emit a signal; and an external member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

2. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an elongate member comprising a signal detector adapted to detect a signal; and an external member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject.

3. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal emitter adapted to emit a signal; and an elongate member adapted to reflect the signal emitted by the signal emitter, wherein the external member is adapted to be coupled to the subject.

4. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: an external member comprising a signal detector adapted to detect a signal; and an elongate member adapted to reflect the signal to the signal detector, wherein the external member is adapted to be coupled to the subject.

5. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising a subassembly comprising a signal generator and a signal processor, an external member coupled to the subassembly; and an elongate member coupled to the subassembly, wherein at least one of the external member and the elongate member comprises a signal emitter that emits a signal generated by the signal generator, and a signal detector that detects the signal after the signal is reflected from at least one of flowing fluid and a reference member and that sends a detected signal to the signal processor.

6. The device of one of claims 1, 2, 3, 4, and 5, wherein the signal comprises an electromagnetic wave signal.

7. The device of claim 6, wherein the electromagnetic wave signal is at least one of a radio wave signal, a micro wave signal, an infrared wave signal, and a near infrared wave signal.

8. The device of one of claims 1, 3, and 5, wherein the signal emitter emits electromagnetic waves to nearby fluid.

9. The device of claim 8, wherein the emitter emits the electromagnetic waves wirelessly.

10. The device of claim 8, wherein the emitter is hard- wired to the signal processor.

11. The device of claim 8, wherein the emitter is coupled to a signal generator that generates the electromagnetic wave.

12. The device of claim 11, wherein the signal generator is programmable to generate the electromagnetic wave within at least one of the radio, micro, infrared, and near infrared wave ranges.

13. The device of claim 8, wherein the emitter is coupled to a signal processor.

14. The device of one of claims 2 and 4, wherein the signal detector comprises a sensor that detects the signal from at least one of the external member and flowing fluid, and wherein the signal is an electromagnetic wave signal.

15. The device of claim 14, wherein the sensor is sealed from contact with bodily fluids.

16. The device of one of claims 1, 2, 3, and 4 further comprising a signal processor adapted to generate a flow characteristic output of a flowing fluid in a vessel located between the elongate member and the external member.

17. The device of claim 5 wherein the device comprises memory that stores a flow characteristic output that is generated by the signal processor.

18. The device of one of claims 16 and 17 wherein the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, time integral of the maximum velocity of the fluid, volume, flow time, and volume of fluid flowing over time.

19. The device of claim 16 wherein the fluid is blood.

20. The device of claim 19 wherein the flow characteristic output comprises at least one of average velocity, peak velocity, acceleration, stroke distance, stroke volume, flow time, and cardiac output.

21. The device of one of claims 2, 4, and 5, wherein the signal detector comprises a transmitter that is capable of transmitting the signal to a signal processor, wherein the signal comprises an electromagnetic wave signal.

22. The device of claim 21, wherein the transmitter transmits the electromagnetic wave wirelessly.

23. The device of claim 21, wherein the transmitter is hard- wired to the signal processor.

24. The device of one of claims 1, 2, 3, 4, and 5, further comprising an output monitor.

25. The device of one of claims 1, 2, 3, 4, and 5, further comprising an input module.

26. The device of one of claims 1, 2, 3, 4, and 5, wherein at least a portion of the elongate member is adapted to remain substantially stationary relative to the external member after the elongate member is inserted into the subject.

27. The device of claim 26, wherein the tip of the elongate member is the portion of the elongate member that remains substantially stationary relative to the external member.

28. The device of claim 26, wherein the portion of the elongate member that remains substantially stationary relative to the external member is a portion of the elongate member that lies in close proximity to the descending aorta.

29. The device of claim 26, wherein the external member is coupled to the subject's back.

30. The device of one of claims 1, 2, 3, 4, and 5, wherein the external member comprises an adhesive pad.

31. The device of one of claims 1 , 2, 3, 4, and 5, wherein the external member is adapted to remain substantially stationary relative to at least a portion of the elongate member when the elongate member is inserted into the subject.

32. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to be placed adjacent the descending aorta.

33. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal generator, a signal emitter adapted to emit a signal generated by the signal generator, a reference member adapted to reflect the signal emitted by the signal emitter wherein at least one of the reference member and the signal emitter is adapted to lie in close proximity to the descending aorta.

34. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to be placed adjacent the descending aorta.

35. A device for detecting at least one flow characteristic of a fluid in a subject, the device comprising: a signal processor, a signal detector adapted to detect a signal, a reference member adapted to reflect the signal to the signal detector, wherein at least one of the reference member and the signal detector is adapted to lie in close proximity to the descending aorta.

36. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location in a subject, providing a reference member to be positioned at the second location on the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

37. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing a signal emitter to be positioned at the first location on a subject, providing a reference member to be positioned at the second location in the subject, emitting an electromagnetic wave from the signal emitter toward the reference member, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

38. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location on the subject, detecting, at the first location in the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location in the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

39. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: emitting an electromagnetic wave toward a reference member positioned at the second location in the subject, detecting, at the first location on the subject, a first signal of the electromagnetic wave reflected off the reference member, detecting, at the first location on the subject, a second signal of the electromagnetic wave reflected off the fluid, determining a flow characteristic of the fluid using at least one of the first signal and the second signal.

40. The method of one of claims 36 and 38, wherein the first location in the subject is the esophagus of the subject, wherein the second location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta.

41. The method of one of claims 37 and 39, wherein the second location in the subject is the esophagus of the subject, wherein the first location on the subject is the back of a subject, and wherein fluid is blood flowing in the descending aorta.

42. The method of one of claims 37 and 39, wherein the first location is the back of the subject, and wherein the method comprises providing a coupling element for coupling the reference member to the back of the subj ect.

43. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the portion of the elongate member at the first location toward the external member at the second location, detecting a first signal reflected from the external member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid, and generating a flow characteristic output.

44. The method of one of claims 36, 37, 38, and 39, wherein the reference member is substantially stationary relative to the first location.

45. A method for determining a flow characteristic of a fluid between a first location and a second location, the method comprising: providing an elongate member configured for insertion into the subject such that a portion of the elongate member can be placed at first location in the subject, providing an external member configured for coupling to the subject at the second location on the body of the subject, emitting an electromagnetic wave from the external member at the second location toward the portion of the elongate member at the first location, detecting a first signal reflected from the elongate member, and a second signal reflected from the fluid between the first location and the second location, processing the first signal and the second signal to determine the flow characteristic of the fluid.

46. The method of one of claims 43 and 45 wherein the fluid is blood.

47. The method of claim 45 wherein a portion of the elongate member at the first location is substantially stationary relative to the external member at the second location.

48. A device for detecting at least one flow characteristic of a fluid in a subject comprising: an elongate member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from the fluid, and an interface for coupling the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector.

49. A device for detecting at least one flow characteristic of a fluid in a subject comprising: an external member comprising a signal emitter capable of emitting a signal, a signal detector capable of detecting the signal reflected from a fluid, and an interface for connecting the signal detector to a signal processor, wherein the signal processor is adapted to generate a flow characteristic output from the signal reflected from the fluid and detected by the signal detector, and wherein the external member is adapted to be coupled to the subject's skin.

50. A device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

51. A device for reflecting at least one electromagnetic wave signal, the device comprising an elongate member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

52. A device for reflecting at least one electromagnetic wave signal emitted from a signal emitter, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to the signal emitter during use of the signal emitter.

53. A device for reflecting at least one electromagnetic wave signal, the device comprising an external member comprising a reference member, wherein the reference member is configured to be substantially stationary relative to a signal detector during use of the signal detector.

54. A device for monitoring blood flow comprising: a nasogastric tube; a first sensor coupled to the nasogastric tube, wherein the sensor is capable of sensing blood flow in a blood vessel and is capable of generating a sensor output; and a processor for processing the sensor output to monitor blood flow in the blood vessel.

55. The device of claim 54, wherein the processor is adapted to generate an output indicating location of the tube.

56. The device of claim 54, wherein the processor is adapted to generate a flow characteristic output from the sensor output.

57. The device of one of claims 54, 55, and 56 wherein the first sensor is adapted to sense energy from the descending aorta.

58. The device of claim 57, wherein the first sensor comprises a signal detector.

59. The device of claim 57, wherein the first sensor is adapted to sense at least one of acoustic energy, vibratory energy, thermal energy, mechanical energy, electrical energy, magnetic energy, and electromagnetic energy.

60. The device of claim 54, wherein the device further comprises a second sensor, and wherein the processor determines aortic blood flow pulsation peak velocity as distance between the first sensor and the second sensor divided by the time it takes for a blood pulsation to travel from the first sensor to the second sensor.

61. The device of claim 60, wherein at least one of the first sensor, the second sensor, and a third sensor comprises a signal detector for detecting a blood vessel dimension.

62. The device of claim 61, wherein the processor is adapted to generate an indication of cardiac output from the aortic blood flow pulsation peak velocity multiplied by a blood vessel cross sectional area determined using the blood vessel dimension.

63. The device of claim 54, wherein the processor is adapted to generate an alert if the first sensor does not detect blood flow in the blood vessel.

64. A method of monitoring a subject's blood flow using a device of any preceding claim, the method comprising the steps of (a) providing the nasogastric tube adapted for insertion into the esophagus of the subject so that the first sensor coupled to the nasogastric tube is in close proximity to the subject's descending aorta, and (b) the processor generating data concerning blood flow in said descending aorta.

65. A method of monitoring a subject's blood flow using a device of any preceding claim, the method comprising the steps of (a) inserting the nasogastric tube into the esophagus of the subject so that the first sensor coupled to the nasogastric tube is in close proximity to the subject's descending aorta, and (b) viewing data concerning blood flow in said descending aorta.

66. The method of one of claims 64 and 66, wherein the data is viewable in real-time for a sufficient period to indicate subject response to a procedure.

67. The method of one of claims 64 and 66, wherein the data is a flow characteristic of blood in the subject's descending aorta.

68. A device substantially as described with reference to the accompanying drawings.