|Número de publicación||US20060058690 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||US 11/197,971|
|Fecha de publicación||16 Mar 2006|
|Fecha de presentación||5 Ago 2005|
|Fecha de prioridad||10 Sep 2004|
|También publicado como||WO2006031479A1|
|Número de publicación||11197971, 197971, US 2006/0058690 A1, US 2006/058690 A1, US 20060058690 A1, US 20060058690A1, US 2006058690 A1, US 2006058690A1, US-A1-20060058690, US-A1-2006058690, US2006/0058690A1, US2006/058690A1, US20060058690 A1, US20060058690A1, US2006058690 A1, US2006058690A1|
|Inventores||Daniel Bartnik, Brandon Reynolds|
|Cesionario original||Optical Sensors, Inc.|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citada por (15), Clasificaciones (9), Eventos legales (1)|
|Enlaces externos: USPTO, Cesión de USPTO, Espacenet|
This application claims the benefit under 35 USC 119(e) of U.S. Patent Application No. 60/609,175, filed Sep. 10, 2004, the entirety of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an instrument for the automated measurement of skin perfusion pressure of a local or regional body site. More particularly the invention relates to an instrument for the automated measurement of skin perfusion pressure that detects and rejects motion artifact.
2. Description of the Related Art
Skin perfusion pressure measurements are taken to determine whether local blood flow, i.e. capillary perfusion, of a local or regional body site having an ulcer or wound is sufficient to support wound healing. The accurate measurement of this parameter, therefore, is critical to physicians who treat patients suffering from open surface wounds resulting from complications from diabetes, pressure ulcers, burns, accidents, and the like.
Traditionally, skin or surface perfusion pressure is measured utilizing a surface or skin perfusion pressure-monitoring device coupled to a laser Doppler or other type of optical sensor. For example, U.S. Pat. No. 6,178,342 to Borgos et al. discloses a surface perfusion pressure monitor used in conjunction with a laser Doppler probe that measures the “amount” of moving blood contained within a microvascular observation volume in percent tissue hematocrit. This measurement is taken as a function of applied pressure. The laser Doppler optical probe defines an observation volume in the skin near the surface of the patient and a pressure cuff is used to manually apply pressure to the limb near the optical probe.
The laser Doppler sensor is placed against the skin under a pneumatic cuff that is secured to the affected limb, i.e. toe, ankle, arm, leg, etc. A user using an inflation bulb manually inflates the pneumatic cuff. The inflation pressure must be sufficiently high to stop local blood flow at the site of the optical probe. A display instrument is coupled to the optical probe typically via a fiber optic cable, and to the inflation bulb through a tube. Deflation starts and the optical probe monitors the number of moving red blood cells moving into or out of the observation volume without regard to velocity. The number of moving red blood cells detected within the control volume is expressed as a percent and displayed on the display monitor. This value is shown as both a numeric value and a bar graph on the Y-axis. The instrument also measures the pressure within the cuff and displays the applied cuff pressure in millimeters of mercury on the X-axis of the display. A moving bar chart along the X-axis shows the operator which cuff pressure is currently being measured. As pressure is slowly manually released, an indicator of blood flow return is provided in bar chart form. While a technician conducts the test, a physician interprets the data displayed on the display monitor.
Therefore, a significant problem with the use of skin perfusion pressure instruments described by Borgos et al. is that reliable, reproducible measurements are heavily dependent on operator/technician skill and the skill of the physician who interprets the surface perfusion pressure measurement. Another problem associated with manual deflation is that it is sensitive to motion artifact caused by the operator or patient (e.g. patient movement, pressure tubing movement, or sensor movement). In addition, motion artifact may result from patient movement, involuntary muscular movement, operator intervention, and other causes affecting the reading of skin perfusion pressure. If a patient moves the limb to which the sensor/pneumatic cuff is attached, the physician who makes the determination of the pressure at which flow returns might very easily err by reading “motion artifact” as the surface perfusion pressure measurement. When a skin perfusion pressure test is conducted on a sick patient, the physician is already expecting a low value for the surface perfusion pressure measurement. Consequently, given an occurrence of “motion artifact” the physician may interpret it as a skin perfusion pressure reading that is artificially higher than the actual skin perfusion pressure measurement.
For example, illustrated in
Given the situation described above, there is a need for a system that compensates for, or eliminates, motion-induced artifacts in patient-attached critical care monitoring instruments. In addition, there is a need for a system that increases reliability and reproducibility by eliminating user-created error for example, variable inflation and deflation and/or variable interpretation of the results. A new and improved skin perfusion system that automatically inflates and deflates the pressure cuff, controls inflation and deflation, and detects and rejects motion artifact, and automatically determines an SPP value is needed.
Accordingly it is an object of the present invention to overcome the problems and disadvantages of the surface perfusion pressure instruments of the prior art. It is, therefore, an object of the present invention to automate the measurement of skin perfusion pressure and generate an SPP value.
It is a further object of the present invention to provide a skin perfusion pressure system that automatically inflates and deflates and controls the inflation pressure and deflation rate of cuff pressure.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that automatically detects and rejects motion artifact.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that uses a perfusion sensitive tolerance that progressively adjusts sensitivity thresholds as perfusion returns.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that actively controls the rate of cuff deflation.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that determines when motion is severe enough to affect either the rate of cuff deflation or an accurate determination of an SPP value.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that does not report an SPP value if motion is determined to be too severe or if the resulting SPP waveform does not have a recognizable perfusion signature.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that evaluates duration of perfusion change.
It is a further object of the invention to provide a skin perfusion pressure monitoring system that evaluates the profile of perfusion change.
In a first embodiment of the present invention a skin perfusion pressure monitoring system that automatically calculates the SPP value from perfusion measurements is disclosed. The monitoring system controls and measures cuff pressure and closely controls the rate of cuff deflation during the critical deflation portion of the skin perfusion pressure test cycle.
In another embodiment of the present invention, the monitoring system uses a perfusion sensitive tolerance that progressively adjusts sensitivity thresholds as perfusion returns. This allows for measurements of perfusion over a wide dynamic range while being less sensitive to motion transients.
In another embodiment of the present invention, the monitoring system actively controls the rate of cuff deflation and determines when motion is severe enough to affect this rate. The test is ended if motion is determined to be too severe.
In another embodiment of the present invention, the monitoring system monitors duration of perfusion change. As microcirculation returns it produces a perfusion signal that changes from baseline flow. Motion aritfact, on the other hand, produces a perfusion signal that has greater oscillatory content.
In another embodiment of the present invention, the monitoring system monitors the profile of perfusion change. As both macrocirculation and microcirculation normal flow resumes, it produces a change in perfusion signals that have recognizable and differentiable patterns. Motion artifact, on the other hand, produces a perfusion signal that is generally random, short-lived, and has more oscillatory content. Therefore, changes that do not follow a perfusion return signature are ignored by the monitoring system of the present invention. In addition, there are known perfusion return signatures that do not have a signature amenable to the automated qualification of an SPP value and the data can be displayed for the physician to interpret. For example, non-reactive hyperemia is a circulatory condition that results in such a known perfusion pattern.
These and other objects and advantages of the present invention will become apparent during the course of the following detailed description and appended claims. The invention may best be understood with reference to the accompanying drawings, wherein an illustrative embodiment is shown.
Before the inventive devices and methods are disclosed and described, it is to be understood that certain terminology is used to describe the invention but different aspects of it may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.
The term “adequate perfusion” means the perfusion criteria used to continue the cuff inflation sequence. This criterion ensures that there is proper contact between the probe and the patient's skin. It is typically perfusion that is greater than 0.1%.
The term “no flow” means the perfusion criteria at which cuff deflation is initiated and is approximately less than 0.1%.
The term “baseline flow” means the flow between the determination of “no flow” and qualified SPP value.
The term “motion artifact” means the absence of the characteristic patterns of perfusion return including caregiver, operator or environmental influences such as patient movement, voluntary and involuntary muscle contraction, unwanted noise, and caregiver and operator interference.
The term “perfusion measurement” is the calculation proportional to the AC/DC ratio of the signals acquired by a perfusion sensor measured at an applied cuff pressure.
The term “pressure cuff” or “cuff” and similar references means a pneumatic cuff or any device that applies pressure to the site, e.g. from above, adjacent the site, circumferentially, etc.
The term “P0” is the perfusion measurement that is being evaluated or qualified for an SPP value.
The term “return flow” means the resumption of normal microcirculatory flow.
The term “skin perfusion pressure value” or “SPP value” represents the cuff pressure at which microcirculatory flow returns to the observation volume of tissue during the cuff deflation portion of the test.
The optical probe 12 monitors microcirculatory flow within the observation volume of tissue 20. Microcirculation detected within the observation volume of tissue 20 is expressed as a percent and displayed on the Y-axis of the perfusion pressure display instrument. As best seen in
Optical probe 12 depicted in
Notwithstanding, those skilled in the art will recognize that there are many ways to determine the point at which microcirculatory flow returns to a given observation volume. For example, visual observation such as the change in color of the observation site; ultra-sound; optical plethysmography, measurements of increases in temperature; sound, e.g. a microphone for pulsatile flow in the macrocirculation; metabolic indicators such as pCO2 or lactate; and bioimpedance or pulse oximetry or both, each with a pulsatile measurement and a blood volume measurement.
Some back-scattered photons are frequency shifted by moving cells present in the microcirculation. The collected photons are collected by the skin perfusion pressure instrument 22 via cable 24 where they impinge on a photodiode. Thus, photons are impinging on the photodiode as a result of scattering off moving and stationary cells. The photodiode voltage contains both frequency and power information. The Doppler shifted frequency is related to cell velocity while the spectral power information is related to the volume of moving cells at that given frequency. The DC signal component results from the total number of photons received by the receive fiber 34. The AC signal component results from the mixing of frequency shifted photons with photons from stationary structures. If the number of moving cells present within the observation volume increases then the magnitude of the AC component will increase while the DC offset will remain nearly constant. The AC component increases because more returned photons undergo a Doppler shift. The DC component remains nearly constant because the total number of photons scattered by collisions with stationary cells within the measurement volumn is reduced only slightly by moving cells. Therefore, the perfusion measurement is proportional to the ratio of the AC signal to the DC signal, which is an indication of the volume of moving cells in the observation volume of tissue. This type of measurement is commonly computed with both analog and digital signal processing. For example, it is common to convert the AC signal to an RMS equivalent through analog processing. It is these values that are presented to the A/D converter. The microprocessor then may square these digitized values prior to forming the ratio. The ratio value may be scaled by an empirically derived scaling factor that depends on the gain distribution throughout the signal processing paths.
Referring now to
FIGS. 5A-D illustrate different stages of output data as depicted on the display monitor. Referring to
As a preliminary screening step, if motion artifact is severe enough to affect the rate of deflation, i.e. severe patient movement, the instrument will halt the test and inform the operator that the sensor/probe is unable to make accurate measurements.
Initially as a first criterion, P0 must be within a valid range for the system to qualify an SPP value. If P0 is not within a valid range, for example from approximately 1 mmHg to approximately 150 mmHg, the system will not indicate that a particular P0 is an SPP value.
TABLE 1 APPLIED CUFF APPLIED CUFF PRESSURE > PERFUSION PRESSURE <100 OR = 100 MEASUREMENT mm Hg mm hg <0.15% (Low) 100% 100% 0.15 to 0.20% 50% 50% (Medium) >0.20% (High) 25% 40%
Another criterion is whether the perfusion increase is large enough relative to the measurement. If the perfusion increase is not large enough an SPP value will not be qualified. In interpreting “step size” (i.e. perfusion increase large enough from the prior measurement) the instrument uses a perfusion sensitive tolerance that progressively adjusts sensitivity thresholds as perfusion returns. This allows the system to qualify SPP values over a wide dynamic range while being less sensitive to motion transients. For example, if perfusion is very low then the instrument allows for the detection and rejection of motion artifact due to its perfusion sensitive tolerance. Referring to Table 1, preferred perfusion increases are noted. If the perfusion measurement is greater than 0.20% (i.e. high perfusion measurement) and the applied cuff pressure is less than 100 mmHg a perfusion increase of from 10% to 50% and preferably 25% relative to the prior measurement, is necessary. If the perfusion measurement is greater than 0.20% (i.e. high perfusion measurement) and the applied cuff pressure is greater than or equal to 100 mmHg a perfusion increase of from 20% to about 80%, and preferably 40%, relative to prior measurement is necessary. If the perfusion measurement is between 0.15 to 0.20% (i.e. medium perfusion measurement) and the applied cuff pressure is any valid pressure a perfusion increase of from 25% to 100%, and preferably 50%, relative to the prior perfusion measurement is necessary. If the perfusion measurement is less than 0.15% (i.e. low perfusion measurement) and the applied cuff pressure is any valid pressure a perfusion increase of from 50% to 200%, and preferably 100%, relative to the prior perfusion measurement is necessary.
Those skilled in the art will recognize that the foregoing criterion does not need to be limited to high, medium and low perfusion measurements or a few isolated points for applied cuff pressure, i.e. above and below 100 mmHg. These may be expressed as a continuous function of perfusion measurements or applied cuff pressure, or both.
Another criterion is whether the perfusion measurement under evaluation, i.e. PO, is large enough, i.e. whether flow is above baseline. The perfusion should be preferably from between 0.05 to 0.2% and more preferably at least 0.10% at point PO or no skin perfusion pressure will be recorded.
Another criterion determines whether the “next steps,” i.e. those following point PO, are increasing or decreasing. Next steps must not be decreasing as this is not characteristic of a typical signature for returning microcirculatory flow to an observation volume with decreasing pressure. This fourth criterion focuses on the duration of increasing perfusion change. As microcirculation flow returns it produces a perfusion signal that increases and holds in a signature pattern. Motion artifact produces a perfusion signal that has more oscillatory content, thereby having greater tendencies to decrease.
TABLE 2 Applied Cuff Pressure Range Number of Following Steps LOW 1 MEDIUM 2 HIGH 3 VERY HIGH 5
When applied cuff pressure is low, i.e. preferably from about 0 to 20 mmHg and more preferably less than 15 mmHg, the number of next steps analyzed in determining whether next steps are increasing or decreasing is one. When the applied cuff pressure is in a medium range, for example from about 10 to 50 mmHg and more preferably from about 15 to about 20 mmHG, the number of next steps analyzed in determining whether next steps are increasing or decreasing is two. When applied cuff pressure is high, for example from about 40 to 120 mmHg and preferably greater than 50 mmHg but less than 100 mmHg, the number of next steps analyzed in determining whether next steps are increasing or decreasing is three. When pressure is very high, preferably from 80 to 150 mmHg, and most preferably greater than 100 mmHg, the number of next steps analyzed in determining whether next steps are increasing or decreasing is five. The higher the number of next steps being analyzed, i.e. N, the more confidence that the system has qualified an SPP value.
Another criterion for detecting and rejecting motion artifact is the profile of perfusion change. Microcirculation produces a perfusion signal that increases step-wise while motion produces a perfusion signal that has more oscillatory content. Changes that do not follow a perfusion return signature are ignored. Referring again to Table II, the perfusion change profile criterion for detecting and rejecting motion artifact is whether the specified number of steps following P1 are at least at or above the perfusion value for P1. These steps must not be decreasing. In other words, P2 to PN must all be greater than P1. This criterion is especially effective in rejecting motion, as those signals are not long-lived.
If all criteria are met the skin perfusion pressure system will qualify P0 as the SPP value 38.
Although the description of the preferred embodiment has been presented, it is contemplated that various changes, including those mentioned above, could be made without deviating from the spirit of the present invention. It is therefore desired that the present embodiment be considered in all respects as illustrative, not restrictive, and that reference be made to the appended claims rather than to the foregoing description to indicate the scope of the invention.
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|Clasificación de EE.UU.||600/504, 600/507|
|Clasificación cooperativa||A61B5/0261, A61B5/0048, A61B5/7207|
|Clasificación europea||A61B5/00M, A61B5/72B2, A61B5/026B|
|29 Ago 2006||AS||Assignment|
Owner name: OPTICAL SENSORS INCORPORATED, MINNESOTA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BARTNIK, DANIEL J.;REYNOLDS, BRANDON W.;REEL/FRAME:018186/0221
Effective date: 20060829