Life Detecting Medical Instrument

Abstract

An electronic medical instrument to detect the presence or absence of life includes an electroencephalograph (EEG) and an electrocardiogram (EKG), connected to one or more data scanners, a stimulator, an analog or digital data analysis device such as an average response computer, a graphic recorder, and a time stamp. A portable version of this instrument is hand-carried and gives a visual display indicating the presence or absence of life.

Parent Case Text

The present invention relates to electronic medical instruments and more particularly to such an instrument for testing if a patient is alive. This application is a continuation-in-part of U.S. application Ser. No. 782,863, filed Dec. 11, 1968, now abandoned, and having the same title.

Description

Medical science has for several years been able to remove organs, such as the kidney, from the body of a donor and implant them into the body of a recipient. Recently, medical science has progressed to the point where such transplants may even be of the heart.

Unlike some other organ transplants in which the donor may be alive or dead at the time of the operation, heart transplants the donor must be dead when the organ is removed. A definite test of life is needed to guide the doctor, who may be subject to criminal sanctions and civil liability if he removes the heart from a donor who is still medically and legally alive.

In addition, a definition and test of life is needed in some medical procedures, such as operations, in order to accurately determine the extent to which the operation or other medical procedure should be continued. There is no justification for terminating attempts to save a patient as long as he is still alive. Not only is this crucial for the patient, but the doctor may subject himself to censure or liability if he stops the operations or other medical procedures while the patient is alive since it might later be established that, had he continued, the patient might have recovered. Similar considerations are relevant at the scene of accidents, on a battlefield, or in hospital emergency rooms, particularly where skilled medical personnel may not be present. It is therefore necessary to have a portable instrument to provide a rapid, accurate and definite test of life so that the medical or resuscitative procedure may be continued until the time of death, and not wasted by continuing beyond that point, and so that emergency transportation may be given only to live patients.

At the present time there have been various medical indications used to test and define death. The historical indications are the stopping of the patient's heartbeat and the stopping of his breath. These indications are reflected in the definition of death in Black's Law Dictionary 488 (4th Edition, 1951) as: "The cessation of life; the ceasing to exist; defined by physicians as a total stoppage of the circulation of the blood; and a cessation of the animal and vital functions consequent thereon, such as respiration, pulsation, etc.". These indications, however, are unsatisfactory for the sophisticated medical techniques involved in organ transplants or in determining if a medical procedure should be continued. A heart which has stopped may be revived and may beat again. Similarly, breath, although it has ceased, may also be revived. A variety of medical groups have expressed dissatisfaction with existing criteria of death, emphasizing that the critical question is whether or not death of the brain, i.e., cerebral death, has occurred.

It is the objective of the present invention to provide an instrument which accurately, definitely, reliably, continuously and quickly determines the presence or absence of life. In one embodiment the instrument is portable and so may be utilized by a medical aide in the field or used in an ambulance, and is relatively low in cost.

It is a further objective of the present invention that the instrument give an objective and recorded output which would be legally and medically acceptable evidence of the presence or absence of life over a period of time.

In accordance with the present invention, electronic medical instruments are provided. One instrument is hand-carried, to be used in the field, and the other is fixed, to be used in hospitals. These instruments each include two input devices, an electrocardiographic amplifier (EKG) and an electroencephalographic amplifier (EEG), a multi-sensory stimulator and a special purpose computer. Belts strapped around the chest of the patient, or on his wrist and ankles, carry electrodes which monitor the electrical signals generated by the heart. These electrodes are connected to the EKG amplifier. A plurality of electrodes attached to different places on the patient's scalp monitor the activity of visual (V), auditory (A) and somatic (S) receiving areas of the brain, and are sequentially connected to the EEG amplifier. The output of the amplifier is connected to the special purpose computer and/or to a recording device. In the embodiment used in hospitals, by means of a clock and cycle control device, and a data scanning device, an output is provided, in timed sequence, of the EKG, the EEG, and the results of computer analysis of the sensory evoked response in the EEG, each of the different brain areas being monitored. Each of these outputs is provided for a determined adjustable time, and this sequence of outputs is constantly repeated and may be changed.

The clock and cycle control and the data scanning devices are connected to the stimulators, the special purpose computer and to a power amplifier which drives a recording device. Thus, as the data scanning device sequentially scans the available inputs and the cycle control switches the stimulator outputs, a record will be provided which will provide a sample of the EKG for a brief period ("raw" EKG), followed by a sample of the EEG from the visual area ("raw" visual EEG), then the average visual evoked potential from the visual area (visual AEP), then the EEG from the auditory area ("raw" auditory EEG), then the auditory AEP, then the EEG from the somatic area ("raw" somatic EEG), then the somatosensory AEP, and then the cycle would resume with the EKG again. As each sample period began, the clock time would be printed on the permanent record.

The clock and cycle control device controls a number of stimulators whose outputs are directed to the patient. These stimulators are preferably a visual stimulator, an audio stimulator, and a shock stimulator. Because sensory-sensory interaction facilitates the electrical response of the brain to sensory stimuli, these stimulators will usually be operated so as to deliver a flash of light, a loud clock and a mild electrical shock to the arm and leg of the patient. If desired, the stimulators can be operated sequentially and synchronized with the scanning device so that a flash of light will occur while the visual EEG is recorded, a click will occur while the auditory EEG is recorded, electric shock to arm and leg will occur while the somatic EEG is recorded. A variety of repetition rates might be used, but present knowledge suggests 8 cycles per second as the optimal stimulus repetition rate. In certain situations it will be desirable to examine the later components of the evoked response, for example, so-called component P.sub.3, and a slower repetition rate will be desirable, e.g., 3-4 per second. Each stimulator output will be accompanied by a trigger pulse.

The trigger pulse will be recorded by a marker pen on the permanent record. The output of the data scanning device will go to a pen recorder and it will also go to a special purpose average response computer (ARC), which may include either a digital or analog memory device. The analysis epoch of the average response computer is preferably 125 or 250 milliseconds, and will be triggered by the trigger pulse from the stimulator. If the ARC is digital, the analog output of the data scanning device will be converted to digital form and then stored in a digital memory so that the voltage values of the EEG response to the signal in successive intervals of time are stored in successive digital registers. With each repetition of the signal to the patient, the digital values of corresponding segments of the EEG response will be accumulated in the appropriate registers of the memory. Alternatively, the data scanning device may be connected to a current source and to a capacitance memory-integrator which will constitute an analog average response computer. In this fashion, the average evoked response of the brain to the sensory stimulus will be computed. The average EEG will also be computed. Once in each cycle, the resistance of each of the testing electrodes is tested by an appropriate circuit. If the resistance exceeds permissible limits, an alarm signal will be activated and a mark will be made on the permanent record to invalidate it.

The portable, i.e., hand-carried, version is an instrument about the size of a one-quarter inch electric drill. It has a rechargeable internal battery power source and a body portion containing the EEG amplifier, the EKG amplifier, an electrode impedance checking circuit, a stimulator, a "one-word" average response computer and a visual display. Cables lead from the body portion and terminate in various needle electrodes and various transducers (microphone, loudspeaker, light source). The electrodes and transducers are arranged in clamping devices which rapidly fit on the patient. The visual display gives simple "go - no go" indications of the life functions of heartbeat and brain activity, preferably in the form of red and green lamps.

Other objectives of the present invention will be apparent from the detailed description which follows, presenting the inventors' best mode of carrying out the invention. The detailed description which follows should be taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block schematic diagram of the first embodiment of the hospital instrument of the present invention;

FIG. 2 is a block schematic diagram of the second embodiment of the hospital instrument of the present invention;

FIG. 3 is an illustration of the graph produced by the single-pen graphic recorder of the instrument of FIG. 1;

FIG. 4 is an illustration of the graph produced by the three-pen graphic recorder of the instrument of FIG. 2;

FIG. 5 is a perspective view of the portable hand-carried instrument of the present invention;

FIG. 6 is a top plan view of the visual display of the instrument of FIG. 5;

FIG. 7 is a block diagram of one portion of the circuit of the instrument of FIG. 5;

FIG. 8 is a block diagram of the other portion of the circuit of the instrument of FIG. 5;

FIG. 9 is a block diagram of the one-word average response computer of the instrument of FIG. 5; and

FIGS. 10A and 10B are diagrams of the electrical wave shapes within the average response computer of FIG. 8.

I. THE DEFINITION OF DEATH

The definition of death may be critical in certain organ transplants, such as heart transplants.

Successful transplantation may depend on removal of the organ as soon as possible after death. If the doctor delays removal of the heart, there is a risk that it will be so damaged and may be unusable for the transplant. The removal of the heart precludes any revival of the donor's life. The doctor runs the risk of civil liability and criminal sanctions if it is later held that a patient was not legally dead at the time the organ was removed.

Law and medical science have traditionally accepted the classical definition of death as being a total stoppage of the circulation of the blood and a cessation of the animal and vital functions consequent thereon, such as respiration and pulsation. But sometimes physicians may revive the heart after it has stopped beating, which should move the time of death to when the cessation of the heartbeat is irreversible. Marshall Houts, in his authoritative work, Death, at sec. 1.03 (4) 1967, has provided the following legal definition of death:

"Death is the final and irreversible cessation of perceptible heartbeat and respiration. Conversely, as long as any heart beat or respiration can be perceived, whether with or without mechanical or electrical aid, and regardless of how the heart beat and respiration were maintained, death has not occurred."

This definition of death takes into consideration the recent medical advances of heart resuscitation. But the underlying standard of determining death is the cessation of heartbeat and respiration.

Many physicians now doubt that the traditional definition of death is adequate. They propose that cessation of brainwave activity is the most reliable index of death, for example, see Hamlin, Life or Death by EEG, 190 J.A.M.A. 1964. Their position is that death occurs when the electrical brain activity, which is measurable on an electroencephalograph (EEG), ceases.

The presence of brain activity, when the only activity is denoted by a flat brain wave, is not, however, a reliable indication of life. Note that the definition of a "flat brain wave" is ambiguous. At sufficient gain, amplifier noise can always be observed. How is amplifier noise to be discriminated from brain activity? In recent years, neurophysiologists have learned to use average response computation to enhance the signal-to-noise ratio of the electrical activity of the brain. A strong stimulus is delivered to the sensory receptors of the organism and the response of the brain is examined for transient activity which is phase-locked to the time of stimulation. Since noise will not be phase-locked, averaging the activity of the brain after a series of stimuli provides a powerful technique for enhancement of signal-related potentials in records derived from the brain. Since particular sensory systems may be damaged in a given patient, preferably one should test three of the major sensory systems. Presence of a non-zero sensory evoked response constitutes definitive proof of life.

II. THE DIGITAL INSTRUMENT

The inventors' digital instrument to determine the presence, or absence, of life is shown in FIG. 1. In the instrument of FIG. 1, an electroencephalograph (EEG) 10 has electrodes (probes) 11, 12 and 13 which are connected to the head of the patient under test. For example, the electrode may be placed on the outside of the patient's head clamped to the skin, or alternatively may be implanted under the skin. A reference electrode R is connected to the ear lobe. All EEG potentials are recorded relative to the reference electrode. The EEG is a device which is able to pick-up the faint electrical activity of the brain and amplify it sufficiently so that it is presented in a useable form as a continuous analog electrical signal. The output of the EEG 10 is connected to a first data scan device 14 through three connecting channels 17, 15 and 16. The number of channels corresponds to the number of electrodes and may be more or less than three. The data scan device 14 samples the analog output of each of the EEG electrodes, for example, in sequence. The output of the data scan device 14, on line 18, is connected to an amplifier 19.

The output of amplifier 19 is divided, with one of its outputs being connected to the second data scan device 21 by means of line 20. The output of amplifier 19 is communicated, on line 22, to a third data scan device 60. The third data scan device 60 is connected to a graphic recorder 23. The graphic recorder 23 has, as shown, three inputs and one recording pen, although the recorder 23 may have two, three or more, pens or other recording means.

The electrocardiograph device (EKG) 24 has an input line 25 which is connected to the patient under test. Line 25, for example, may be a series of belts which are strapped around the chest, wrists and ankles of the patient, the belts having contact electrodes. The EKG device picks up the electrical field accompanying the heart's pumping action and converts it into an analog electrical signal. The output of EKG device 24, on line 26, is communicated to amplifier 27. The output of amplifier 27 is split and one of its outputs 28 is connected to the second data scan device 21. The output of amplifier 27, on line 29, is communicated to the third data scan device 60, providing a second source of input information to the graphic recorder 23. The output of the second data scan device 21, on line 30, is connected to an analog-to-digital converter which converts the analog signals into a useable digital form. The analog-to-digital converter 31 is connected by line 32 to an average response computer 33. The output of the average response computer on line 35 is connected to the third data scan device 60 and provides a third source of information to the graphic recorder 23.

The average response computer 33 provides a powerful and reliable way to extract the response of the brain to sensory stimulation despite a noisy background. Average evoked responses can readily be demonstrated by such computations, even when visual inspection reveals no response to the stimulus in the "raw" ongoing EEG records. Signal averaging is the method of separating a signal from noise performed by the average response computer. When the brain waves of the subject are evoked by some stimulus, for example, a flashing light, the waves may be undistinguishable from the other electrical activity of the brain, which is considered as a form of noise in this context. When viewed on an oscilloscope, a single evoked response may be so buried in the noise as to be undistinguishable.

In signal averaging, the approach to the signal-noise problem is to take a number of the averages of the signal plus its surrounding noise at a number of intervals in a repeated series. If the repeated series are each of time T, the series is T.sub.1, T.sub.2 . . . T.sub.N. If one takes sub-intervals of each time period T, which need not be uniform but usually are, the sub-intervals (sampling impulses) are t.sub.1, t.sub.2 . . . t.sub.n, etc. One then has for period T.sub.5, for example, five samples T.sub.5.sub.-1, T.sub.5.sub.-2, T.sub.5.sub.-3, T.sub.5.sub.-4 and T.sub.5.sub.-5. At each time period T.sub.1 . . . T.sub.N, the signal is repeated and the noise is random. For each sample t.sub.1 . . . t.sub.n the signal contribution is the same in each interval T.sub.1 . . . T.sub.N, but the noise may add or subtract, or be the same, in a random fashion. Using time periods T.sub.1, T.sub.2, T.sub.3 and T.sub.4, and sample t.sub.1 in each period for example, and arbitarily assigning the value 7 to the signal, the results may look like this:

t.sub.1 = 7 (signal) + 2 (noise) = 9

t.sub.2 = 7 (signal) - 1 (noise) = 6

t.sub.3 = 7 (signal) - 2 (noise) = 5

t.sub.4 = 7 (signal) + 1 (noise) = 8

The sum is 28 and the average is 28/4 = 7, which is the signal value.

It is necessary for the value, in digital form, to be summed and averaged. The averaging may take place at the end of the series samples or after each sample. In either event, the instrument requires a memory system, for example, a magnetic memory system.

Average response computation of sensory evoked responses provides greatly enhanced assurance that brain responsivity to stimuli will be detected. In this usage, the enhancement of the signal-to-noise ratio is approximately proportional to .sqroot.n , where N equals the number of repetitions of the signal. At a repetition rate of 8 cps, 100 signals would be delivered in 121/2 seconds, providing an average evoked response with about a 10-fold improvement of the signal-to-noise ratio. For most purposes, this should be satisfactory.

Although the cycle control will permit cycles of various lengths, it is preferred that each EEG electrode will be monitored for about 15 seconds per cycle. During that time 121/2 seconds of the EEG activity of a given brain area during sensory stimulation will be recorded. The recording device will then switch to the output of the average response computer and the average evoked response from the corresponding brain area will be permanently recorded. The memory of the average response computer will then be erased, so as to permit computation of the next response to be monitored, as the cycle control device advances to the next item to be measured. Clock time will be stamped on the record at the beginning of each cycle by the time stamp 61.

The clock and cycle control 36 performs various functions in the instrument. It is used to calibrate, by means of line 37, the amplifier 19. It is also used to provide a timed sequence control for the first, second and third data scan devices 14 (line 38), 21 and 60, which are at different rates. In addition, it has an output line 39 connected to the analog-to-digital converter 31 and provides the address function on line 40 to the average response computer. The clock and cycle control 36 has output lines 41, 41' and 41", which are connected to the stimulators. Preferably these stimulators are a visual stimulator 42, an audio stimulator 43 and a shock stimulator 44. The visual stimulator may be in the form of light which is flashed before the eyes of the patient. The audio stimulator may be in the form of an audio tone device producing a sharp sound which is communicated to the patient by means of earphones or a speaker. The shock stimulator may be an electrical shock device having output electrodes attached to the arm and leg of the patient. Since the accuracy of this device will literally be a matter of life and death, it is essential that the whole system be tested continuously. Accordingly, a brief calibration pulse will be generated in synchrony with each stimulus pulse by the clock control 36. Via dual leads 50-52, the calibration pulse will be delivered to each electrode at the site of application on the patient. Through the input electrode leads 11, 12, 13 and 25, this pulse will come to the amplifiers 27 and 19, pass through the data scanning device 21, and be stored in the first registers of the average response computer 33. The size and form of the calibration pulse in the recorded averaged responses will serve as evidence that the life detector was functioning properly during the computation.

Appropriate electronic monitoring of the contents of the relevant computer registers will be used to activate an alarm signal. For example, each of the EEG outputs 15, 16 and 17 and EKG output 26 are connected to separate integrating circuits 55, 56, 57 and 58 respectively. The outputs of the integrators 55-58 are connected to the input of an alarm device 59, for example, a bell. The alarm device 59, at each of its inputs, is adjusted to become activated by a fall, at any one of its inputs, below the predetermined level. The integrators 55, 56 and 57, 58 integrate ongoing visual, audio and shock response and heart action. In addition, an integrator 60' is provided, also connected to alarm device 59, to integrate the averaged response.

The third data scan device 60 is provided with a switch 62 so that any one or two of the channels may be switched out. For example, to record only the average response the switch 62 may be set so that data on line 29 (ongoing EKG) and line 22 (ongoing EEG) will not be scanned or recorded.

A typical graph produced by the graphic recorder 23 is shown in FIG. 3. The graphic recorder 23 has a single marking means, such as a single pen, and three inputs which are switched in predetermined order and sequence by the third data scan device 60. The "raw" EEG data from electrodes 11, 12 and 13 are shown by lines 11 1, 12 1 and 13 1, respectively. The raw EKG data is shown by line 23 1. The data from the average response computer 33 is on line 33 1 and its origin designated by, for example, 33 1-11 if the data derives from electrode 11. The time periods, for example, 121/2 seconds and 21/2 seconds, are designated by t.sub.1 . . . t.sub.n.

The timing and switching among the inputs is preferably selectable. As shown in FIG. 3 the timing is selected so that the sequence is the raw visual EEG data 11 1 for 121/2 seconds, a calibration mark, the averaged visual evoked response 33 1-11 for 21/2 seconds, raw auditory EEG 12 1 for 121/2 seconds, calibration mark, averaged auditory evoked response 33 1-12 for 21/2 seconds, raw somatic EEG 13 1 for 121/2 seconds, calibration mark, averaged somatic evoked response 33 1-13 for 21/2 seconds, raw EKG 23 1 for 121/2 seconds, calibration mark, and averaged EKG 33 1-23 for 21/2 seconds. The labeling on the FIG. 3 is only for the purpose of clarification as the actual record, i.e., the paper tape, would consist only of the time stamp, the record of stimuli delivered, heart beats detected, calibration pulses, and the raw and averaged data, without labels.

The instrument of FIG. 1 uses a graphic recorder having a single marking means, such as a single pen. A data scan device distributes the inputs 22, 29 and 35 so that they are recorded in sequence. Alternatively, as shown in the instrument of FIG. 2, the instrument of the graphic recorded may record the various inputs (EEG, EKG and computer) on separate channels by using three or more marking pens. Similarly, the single pen graphic recorder of FIG. 1 may be utilized in the analog instrument of FIG. 2 by using a data scan device.

The instrument of FIG. 1 also has indicating devices which do not make use of the average response computer. An amplitude detector 150, connected to EEG amplifier 19, measures the amplitude of the peak-to-peak voltage of the brain wave and displays the results on a meter or employs a warning alarm. For example, the instrument may be used in an intensive care unit and monitored by a nurse so that if the peak-to-peak brain wave voltage level drops from the normal 10 microvolts toward the level of 2 microvolts, indicating death, an alarm will flash, at the 5 microvolt level. A cardiotachometer 151, the circuitry of which is explained subsequently, is connected to the EKG amplifier 27, as is an audio device 152, such as a loudspeaker. The cardiotachometer gives the heartbeat rate and the audio device gives the heartbeat sound.

III. THE ANALOG INSTRUMENT

The inventors' analog instrument is shown in FIG. 2. In FIG. 2 an electroencephalograph 110 has probes or electrodes 111, 112 and 113 which are attached to the head of the patient under test. The output of the EEG 110 is connected to a first data scan device 114 through three connecting channels 115, 116 and 117, the number of channels corresponding to the number of electrodes, which may be more or less than three. The first data scan device 114 samples the analog output of each of the EEG electrodes in sequence. The output of the data scan device 114, on line 118, is connected to an amplifier 119. One of the outputs of amplifier 119 is connected to the second data scan device 121 by means of line 120. Amplifier 119 is also connected, by line 122, to the graphic recorder 123. The graphic recorder 123 has at least three simultaneous input channels, see FIG. 2.

The electrocardiograph device (EKG) has an input line 125 which is connected to the patient under test. The output of EKG device 124, on line 126, is communicated to amplifier 127. One of the outputs 128 of amplifier 127 is connected to the second data scan device 121 and the second output of amplifier 127, on line 129, is communicated to the graphic recorder 123. The second data scan device 121, by line 130, is connected to a current source which provides a current I.sub.o directly proportional to its input voltage Vi on line 132. The current source 131 is connected, by line 132, to an analog average response computer 133 having a capacitor memory. The computer 133, by line 135, is connected to the graphic recorder 123. A clock and cycle control device 136 calibrates, by line 137, the amplifier 119 and it provides the sequence control for the first data scan device 114 and the second data scan device 121. An output line 139 of clock control 136 is connected to the current source 131 and its output line 140 is connected to provide the address function to the analog computer 133. The clock and cycle control also has an output line 141 which is connected to the visual stimulator 142, audio stimulator 143 and shock stimulator 144, which may be similar to the stimulators of the digital device.

The analog instrument basically operates in the same general manner as the digital instrument, the only difference being in the type of average response computer. In the analog instrument of FIG. 2 the data storage for producing an average response is by means of a bank of capacitors and an integrative circuit, which may also use a capacitor. Other types of analog average response computers or analog data storage devices may alternatively be utilized.

The operation of the instrument of FIG. 2 is illustrated by FIG. 4. The three recorded channels produced by graphic recorder 123 are C1 (EKG), C2 (the analog average response computer 133) and C3 (EEG). The time units, determined by the clock control 136 are t1 through t6. As shown on channel C3, the data scan 114 shows the output of the EEG output lines 115, 116 and 117 in sequence, corresponding to electrodes 111, 112 and 113 respectively. The chart line 111 1-1 indicates that it is the line 1 from electrode 111 in time unit 1. This comparison provides an indication of trend and will answer such questions as: Is the brain wave activity decreasing?, Is the EKG activity increasing?, etc.

Preferably, the analog instrument of FIG. 2 also includes the time stamp mechanism 61; the calibration pulse checking lines 50-52; and the integrative circuits and alarm 59 and its connecting lines; all of which would function and be located as in the device shown in FIG. 1. These have been omitted from FIG. 2 for the purpose of simplifying that figure.

As shown in FIG. 5, the portable hand-carried life detecting medical instrument 200 is about the size of a 1/4-inch electric drill. It includes a cylindrical body portion 201 and a handle 202 having a switch 203. A first tubular noise shield 204 and a second tubular noise shield 205 protrude from the body portion 201. The noise shields 204 and 205 have within them response EEG needle electrodes 206 and 207 which are spring-loaded and are leads to the EEG amplifier 230. The unloading mechanism, i.e., the release mechanism, is operated by the switch 203. When the switch 203 is depressed, the springs are released and the needle electrodes 206 and 207 spring out and pierce the skin of the head of the patient. The needle tubes 204 and 205 are separated, so that one of the needles 206 may be located at the vertex, i.e., center, of the head and the other needle 207 located at the side of the head.

A first cable 208 protrudes from the body portion 201 and has on its end a clamping mechanism which fits over the head of the patient. The clamping mechanism has a loudspeaker 209 which preferably fits over the ear of the patient, and a flash tube 210 which is positioned over the patient's eyes. Cable 208 also is connected to a first needle clamp 211 which is adapted to be strapped to the patient's leg with its needle piercing his skin. A second needle clamp 212, connected to cable 208, fits over the patient's wrist, for example, by strapping the clamp to the wrist, and has its needle piercing his skin. The needle clamps 211 and 212 are adapted to provide mild electrical shocks to the patient, the flash tube 210 is adapted to provide a light flash to the patient, and the loudspeaker 209 is adapted to provide click or other noise to the patient. These various stimulations, namely, the loudspeaker's click, the flash tube's light, and the electric shock from the needle clamps, are generated by a stimulator 213 within the body portion 201.

A second cable 220 and a third cable 221 are also connected to the body portion 201. The cable 221 leads to an EKG needle electrode 222. The cable 220 leads to a microphone 223 which fits over the heart of the patient and also to a second EKG needle electrode 224. Electrodes 222 and 224 are leads of the electrocardiograph amplifier 225. A spring 226 loads the clamp 227 which slips over the shoulder of the patient.

As shown in FIG. 7, the stimulator 213 is triggered by the switch 203 to provide stimulations at the predetermined rate of 2 per second, although other rates may be utilized. The stimulator receives its timing pulse from alternate outputs of the timer 214, which is connected by line 215 to provide the timing trigger pulse and polarity switching pulses to the one-word average response computer 216, the details of which are described subsequently.

The needles 206 and 207 are the leads to the electroencephalograph amplifier 230 (EEG). The EEG 230 is connected to a microvolt (MCV) amplitude detector 231 which measures the average peak-to-peak voltage over a short time period, for example, one-tenth of a second. If the average peak-to-peak voltage over that time period is above 2 mc.v. the green light 232 will light. Conversely, if it is below 2 mc.v., the red light will become lit. The 2 mc.v. level has been selected because it is in accordance with the definition of death as proposed by the International EEG Society. If the red light is lit and stays lit, and if the other signs of life as determined by the instrument are also negative, then the patient is dead. However, even if the other signs of life are negative and the green light 232 is on, then it cannot be assumed that the patient is dead.

The EEG amplifier 230 is also connected to the one-word average response computer 216 and the one-word average response computer 216 is connected to the up-down counter 217. If the output of the up-down counter 217 is negative, then the red light 218 will be lit. Conversely, if the output is positive, the green light 219 will be lit.

As shown in FIG. 8, the EKG amplifier 225 is connected to a switch 240, which, if closed, will cause the light 241 to directly flash at each heartbeat, providing a direct visual indication of the heartbeat rate. The EKG amplifier 225 is also connected to a peak detecting circuit 242. The peak detecting circuit is connected to a switch 243B which is connected to audio amplifier and speaker 244. The peak detecting circuit 242 is also connected to another switch 243A which is connected to the light 241. Consequently, the light 241 will flash either on the raw heartbeat or, alternatively, at the heartbeat as shown by the peak detector. The peak detector is a circuit similar to an automatic volume control circuit which searches for level given by the peaks of the output (the high amplitude R pulses). It will produce a standard wave form output pulse at each high amplitude R peak heartbeat pulse by means of a standardizing circuit such as a Schmitt trigger. The peak detector 242 is connected to a cardiotachometer 246. The cardiotachometer, for example, of the type described in U.S. Pat. No. 3,474,778, is a rate meter (an integrative circuit) which measures the intervals between heartbeat pulses, i.e., the number of heartbeat pulses in a time period, for example, 30 seconds. The cardiotachometer 246 is connected to a visual display meter 247. The meter 247 has an acceptable zone 248 which is marked in green, a lower and unacceptable zone 249 and a higher and unacceptable zone 250, both zones 249 and 250 being marked in red. If the heartbeat rate is too low, the meter will point within the zone 249; and if the heartbeat is too high, it will point within the zone 250. The cardiotachometer is also connected to the lights 251 and 252. If the heartbeat is acceptable (within the zone 248) then the green light 251 will be lit; but if the rate is too high or too low (the meter needle is within the zones 249 or 250) then the red light 252 will be lit.

The one-word average response computer 216 is shown in FIG. 9 as being connected to the EEG amplifier 230. The absolute value circuit 261, for example, a bridge rectifier having four diodes, first produces an absolute value, that is, it produces a voltage output which is independent of the incoming polarity. The outgoing polarity, positive or negative, is then controlled by a polarity reversing circuit 262. The polarity reversing circuit 262 is connected to an integrator 263. The integrator 263 is connected to a comparator 266 and the comparator is connected to the up-down counter 217.

The polarity reversing switch 262 and the integrator 263, as well as stimulator 213, are connected to timer 214 by lines 215A and 215B. Every pulse from timer 214 reverses the polarity switch 262. In addition, every other pulse 269 erases and resets the integrator 263, while the next pulse 271 activates the stimulator 213, as described below and in FIG. 10A.

The computing cycle is initiated by pulse 269 from the timer 214. Pulse 269 resets the polarity switch 262, erases the integrator 263 and begins the baseline sampling interval 270 lasting 250 milliseconds. Pulse 271 from timer 214 reverses the polarity switch, delivers a stimulus to the patient via stimulator 213, and briefly interrupts the computing cycle to protect against artefact, after which the evoked response sampling interval 272 begins and lasts for 250 seconds. Thus, the integrated activity accumulated during the period of evoked response to the stimulus is subtracted from the integrated baseline activity preceding delivery of the stimulus.

For example, if the integrator output during interval 270 is a rising positive waveform, the polarity shift occasioned by pulse 271 will cause a descending negative waveform of equal duration 272. The signals shown in FIG. 10A are taken at the output of the integrator 263. If there is only noise and no signal, as seen in baseline interval 280 of FIG. 10B, then the rising level during baseline interval 270 will go to a certain height 273. On the other hand, if there is both noise and signal present (as shown by response interval 280 of FIG. 10B), then the descending voltage during interval 272 will cross the zero value of the integrator and go to the level 274.

If the signal plus the noise is greater than the noise, the lower level 274 of the descending voltage slope will be below a predetermined voltage level and there will be a plus one count registered in the up-down counter 217. Conversely, if the signal plus the noise is less than the noise, then the lower end 274 will be above the predetermined voltage level and a minus one will be registered in the up-down counter 217. If only noise is present, then the run-up and the run-down should average to zero or about zero. If there is a signal, in addition to the noise, then there will be a positive average or a negative average, the negative average corresponding to systematic inhibition of the noise, as in EEG "arousal." The one-word average response computer, consequently, only determines the presence, or absence, of a signal; but does not give any information regarding its wave shape or amplitude. In this instrument the presence of a signal implies brain activity in response to stimulation and the presence of brain activity is an indication of life.

The tester simply depresses the switch and the various tests will have a duration which is automatically determined. The level of plus or minus counts over the time period registered in the up-down counter are compared to a number which is statistically determined. For example, the critical count level and the test duration may be adjusted so that there is a 0.001 or 0.0001 chance that the test would yield a negative result even though the person, by a more sophisticated technique, might be shown to have brain activity.

The visual display, at the rear of the body portion, is shown in FIG. 6. It includes lights 275, 276 and 277 which are lit when the impedance levels at the stimulator needle, EKG electrodes and EEG electrodes, respectively, are above a predetermined level. If one, or more, of these lights are lit the leads must be resecured to the patient. The power switch 278 is used as a safety device so that accidental operation of the trigger will not start the test and the pilot light 279 indicates that the power is on. The heart (EKG) test results are shown by the heartbeat light 241 and the cardiotachometer lights 251,252 and the meter 250. The brain activity (EEG) test results are shown by the level (2 microvolts) lights 232 and 233 and the response (up-down counter) lights 218 and 219.

In summary, the electronic medical instrument of the present invention will do the following:

Using self-contained circuitry, it will generate visual, auditory, and somatic stimuli which will be delivered to a patient in a predetermined scheduled way. It will obtain an electrocardiogram (EKG) and a series of electroencephalograms (EEG) from the visual, auditory, and somatic areas of the brain. Resistance measurements and calibration pulses will automatically validate the accuracy of these data. A built-in average response computer analyzes these data and provides an estimate of the average EKG wave shape and of the average evoked response obtained from each of the monitored areas of the brain. In the hospital version of the instrument, a permanent record of these data will be provided. For example, the record may include, on a cycle repeated once a minute, (1) a 121/2second record of ongoing EKG; (2) the average EKG wave shape; (3) a 121/2 second record of EEG from the visual area; (4) the average visual evoked response; (5) a 121/2 second record of EEG from the auditory area; (6) the average auditory evoked response; (7) a 121/2 second record of EEG from the somatic area; (8) the average somatic evoked response; and (9) the clock time of each of the foregoing items.

In the use of the portable instrument, the person who wishes to conduct the test, for example, an army medical corpsman on a battlefield or ambulance personnel at the scene of an accident, or a fireman at a fire, places the portable instrument near the person to be tested. He places (1) the leg and arm clamps on the leg and arm, (2) the headband on the person's head, with its lamp and microphone, (3) the EEG needle electrodes next to the person's scalp. He then pulls the trigger switch so that the EEG needles are released and pierce the skin and the instrument starts to operate. He then watches the cardiotachometer meter and the various green and red lights. If all the lights are red and the meter is in an "unacceptable" zone, the person is dead. If any of the lights are green or the meter in the "acceptable" zone, he may still be alive.

Claims

We claim:

1. A portable instrument for the detection of the presence of life in a person, the instrument comprising a body portion, a handle portion, a visual display means, and protruding connecting means;

said protruding connecting means including a plurality of electrodes adapted to be rapidly fastened to the patient;

said body portion including an electric shock stimulator means and a timer means, said stimulator means being connected to said timer means and to one of said electrodes to provide timed electric shocks to the patient, an electroencephalograph amplifier means connected to at least one of said electrodes, a data averaging means connected to said electroencephalograph amplifier means and said stimulator means, an electrocardiograph amplifier means connected to at least one of said electrodes,

said visual display means being connected to said data averaging means and said electrocardiograph amplifier means.

2. An instrument as in claim 1 and also including a cardiotachometer in said body portion and a meter in said visual display means connected to said cardiotachometer.

3. An instrument as in claim 1 wherein the data averaging means is an average response computer including, connected in series, a polarity reversing circuit, a timing circuit, an integrating circuit and an up-down counter circuit.

4. An instrument as in claim 1 wherein at least one of said electrodes comprises a needle connected to said electroencephalograph amplifier means, said needle being spring-loaded and releasable by a trigger within said handle portion.