Electrocardiographic signal monitoring system

It is well known to continuously monitor one or more physiological conditions of certain subjects of clinical studies, athlete s or medical patients. The monitored conditions may include, but are not limited to, ECG activity, pulse rate, 25 respiration rate, body temperature and blood pressure.

Today's medical patient monitoring systems, for example, are highly sophisticated telemetry systems particularly at the central receiving or monitoring stations. Indeed, medical technology has progressed to the point where central moni- 30 toring stations now consist of mainframes with interchangeable receiver modules that can be updated to avoid obsolescence. These modules receive and record such individual physiological parameters as ECG signals, arterial and pulmonary arterial characteristics, central venous pressure 35 dynamics and peripheral pulse oximetric data.

While recent research and development has focused on state-of-the-art mainframe and module improvements, relatively little research has been directed toward improving input systems (transmitters) located at the patient-system 40 interface. These transmitters are used to detect physiological parameters (most commonly ECG signals) and send these signals via radio frequency to the central receiving stations. It is not uncommon to have thirty (30) or more receiving monitors in operation simultaneously in an average sized 45 hospital.

Conventional single channel ECG telemetry transmitter units normally consist of three major components:

1. Three (3) independent electrodes or sensors 50

2. Three (3) lead cables

3. Transmitter and battery pack

Hospitalized patients that require ECG telemetry monitoring thus must endure the encumbrances of elongated cables (usually three to five feet in length) that indepen- 55 dently connect generally three ECG sensor electrodes to a transmitter and battery pack housing. Typical electrode patches are approximately two inches in diameter, usually circular, and adhere to the skin firmly with biologically compatible adhesive. They are conventionally placed just 60 below the left and right shoulder and the left side of the upper abdomen at an approximate distance of between about 15 to 20 inches for a typical adult patient. The cables are commonly run through the patient's shirt sleeve or beneath the bed clothing. The transmitter and battery pack housings 65 are formed as a plastic case measuring approximately 4x7x 1.5 inches and are placed in paper pouches that are attached

to the patient's clothing with a safety pin or the like. With a transmitter unit so constructed and arranged, the patient is burdened by the bulky transmitter housing and the lead cables that are apt to be caught on bed rails, lavatory equipment, food trays, IV poles and other objects regularly encountered by the patient. Additionally, the cables are prone to entangle and dislodge from the patient, thereby interrupting signal transmission.

Further, when a patient is undergoing an operation, a mainframe monitor is permanently stationed in the operating room for enabling the anesthesiologist to monitor vital signs such as heart rate and ECG signals. Upon completion of the operation, the patient is placed upon a transportable bed and moved to a recovery area. It is during this transportation that the sensor lead cable connections of conventional systems often become dislodged or entangle with other wires or intravenous (IV) tubing. Additionally, a rather large and heavy monitor must accompany the patient, thereby compounding the difficulties attendant to this delicate postoperative patient transport period.

Examples of ECG monitoring systems which describe sophisticated developments in mainframe technology can be found in U.S. Pat. Nos. 3,832,994,4,981,141,5,025,808 and 5,036,869. These patents, however, provide little disclosure as to the construction or operation of their patient-carried ECG sensors. Additionally, each recite conventional practice as to sensor placement on the patient's body, i.e., widely separated across the patient's torso or, in the case of U.S. Pat. No. 5,025,808, on the patient's arms and legs.

U.S. Pat. Nos. 3,972,320, 4,494,553, 4,889,131 and 4,819,860 represent various endeavors in physiological monitoring system apparatus particularly directed to the remote sensors carried by the patient. Of these, U.S. Pat. No. 3,972,330 and 4,819,860 teach of wrist-carried sensors which transmit to a central receiving station data signals corresponding to detected physiological conditions; whereas, U.S. Pat. No. 4,494,553 and 4,889,131 each describe belt-like sensor equipment that is worn about a user's torso.

U.S. Pat. No. 3,253,588 describes user-carried physiological sensors of complex construction and operation. The sensors include not only means for detecting a particular physiological condition, but also means for receiving an interrogation signal from a remote station and means responsive to the interrogation signal for transmitting to the remote station a signal corresponding to the detected physiological condition.

U.S. Pat. No. 3,943,918 discloses a disposable physiological telemetric sensor including microcircuitry, wiring and multiple electrodes and batteries, all at which are discarded after a single use of the sensor. As will be appreciated, the waste attendant to disposal of the sensors and the many internal electrical components thereof after a single application renders usage of Such sensors somewhat impractical and economically unattractive from the perspective of large-scale users of such equipment, e.g., health care providers such as hospitals, clinics and nursing homes.

An advantage exists, therefore, for a telemetric physiological condition (particularly an ECG signal) sensing and transmitting unit that is compact, unobtrusive to the wearer, uncomplicated in design, and offers comparatively inexpensive and reliable long-term service. A further advantage exists for a system incorporating such a sensing and transmitting unit and a lightweight and completely portable receiver unit capable of displaying in real-time visual information corresponding to the patient's physiological signals, SUMMARY OF THE INVENTION

According to the present invention, there is provided a miniature ECG signal detecting and transmitting module that is typically worn by a patient during hospital stays. The 5 module comprises a rugged, non-conductive plastic housing containing the essential ECG signal detection and radio frequency transmission circuitry, as well as a DC power source. Additionally, the module includes an electrode patch externally and detachably connectable to the housing. The 1Q patch receives the patient's ECG signals and, when attached to the housing, is electronically connected to the ECG signal detection circuitry.

In accordance with the presently preferred embodiment, the detachable electrode patch supports three ECG elec- 15 trades in close array (generally less than about two and one-quarter inches apart) in either a substantially triangular or substantially linear arrangement. In operation, the electrode patch is attached to the housing via conventional connector structure. The patch, and thus the module housing 20 to which it is attached, are secured to the patient's chest wall with a suitable bio-compatible adhesive provided on the exposed surface of the patch. Once properly placed, the power source in the module housing can be activated whereby monitoring of the patient's ECG activity may 25 proceed.

Due to the compact size of the module in addition to the absence of cumbersome external electrode wiring, patient mobility, comfort and safety, as well as ECG signal reading accuracy, are enhanced, while opportunities for inadvertent 30 dislodgment of the electrodes are minimized. Further, the absence of the electrode wires also eliminates bothersome signal artifacts associated with such wires.

The detecting and transmitting module, hereinafter referred to as the "transmitter module" is thus a self con- 35 tained battery operated and wireless device for transmitting ECG signals to a receiving unit. The transmitter module has the unique ability to detect signals via the triple-electrode patch which has closely spaced electrode pickup pads, Unlike other existing designs, the transmitter module is 40 attached directly to the patient by the adhesive patch placed on the upper chest area. The electrode patch is preferably secured to the module housing by a series of quick-disconnect snaps thus enabling simplified and inexpensive electrode replacement while eliminating unwieldy electrode 45 cables.

The transmitter module is preferably activated by simply installing the battery and remains active until the battery is removed. In accordance with the preferred embodiment, there are no external user controls on the instrument. All 50 controls are internally located and are intended for adjustment by authorized technical personnel only. The module also has the unique feature of switch selectable channel settings. This obviates the need for special circuit components and technical equipment to tune the transmitter to a desired channel.

Along with the basic ECG signal, the module desirably transmits appropriate signals to alert the receiver operator of conditions such as electrode connection problems and low battery voltage.

Further, because no single electrode patch configuration will work suitably for all patients, an optional patch configuration is available to allow connection of a branched electrode. This permits optimum location of the branched 55 electrode to obtain a usable signal.

Additionally, the present invention contemplates an ECG

55

monitoring system incorporating the aforementioned ECG transmitter module and a small, lightweight, portable and wireless receiver module for displaying real-time information corresponding to the patient's ECG signals. According to the presently preferred embodiment, the receiver module resembles a lap-top computer with an LCD screen having dimensions of approximately five by seven inches. Most preferably, the receiver module and the transmitter module are a kit, whereby the transmitter module is stored interiorly of the receiver module when not in use. A particular advantage of this miniaturized, entirely wireless monitoring system is realized when transporting patients from the operating room to a postoperative recovery area.

Other details, objects and advantages of the present invention will become apparent as the following description of the presently preferred embodiments and presently preferred methods of practicing the invention proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more readily apparent from the following description of preferred embodiments thereof shown, by way of example only, in the accompanying drawings, wherein:

FIG. 1 is a schematic diagram broadly representing the general circuitry operation of the transmitter module of the present invention;

FIG. 2 is a perspective view of a preferred embodiment of the transmitter module constructed according to the present invention;

FIG. 3 is a top view of the module illustrated in FIG. 2; FIG. 4 is an end view of the module illustrated in FIG. 2;

FIG. 5 is a bottom view of the module illustrated in FIG. 2 with the electrode patch thereof omitted for clarity;

FIG. 6 is an edge view of an electrode patch which forms a component of the transmitter module of the present invention;

FIG. 7 is a rear surface view of the electrode patch of FIG.

6;

FIG. 8 is a front surface view of the electrode patch of FIGS. 6 and 7 illustrating a first preferred electrode arrangement thereof;

FIG. 9 is a view similar to FIG. 8 depicting a further preferred electrode arrangement of the electrode patch;

FIG. 10 is a perspective view, in a closed condition, of a presently preferred embodiment of a receiver module constructed to operate in conjunction with the transmitter module of the present invention;

FIG. 11 is a perspective view of the receiver module of FIG. 10 in open condition; and

FIG. 12 is a view similar to FIG. 11 with the receiver module shown in operation.

DETAILED DESCRIPTION OF THE
INVENTION

With reference to FIG. 1, there is illustrated the general operational scheme of the ECG signal detecting and transmitting circuitry employed and housed in the transmitter module (described hereinbelow) of the present invention. Although the circuitry may be appropriately modified so as to function with any suitable miniature DC power source, e.g., a 1.5 V to a 9 V alkaline, nickel cadmium or lithium battery, it is presently preferred that the entire circuitry derive power from a conventional 1.5 V "AA" cell alkaline