U.S. patent number 3,716,059 [Application Number 05/066,189] was granted by the patent office on 1973-02-13 for cardiac resuscitator.
This patent grant is currently assigned to Cardiac Resuscitator Corporation. Invention is credited to Melvin A. Holznagel, Warren S. Welborn.
United States Patent |
3,716,059 |
Welborn , et al. |
February 13, 1973 |
CARDIAC RESUSCITATOR
Abstract
A resuscitator apparatus includes means for detecting and
counting the electrical and mechanical output of the heart of a
suspected heart attack victim, and means for substantially
immediately applying a pacing pulse or a defibrilating pulse, as
required. Thus, if both electrical and mechanical outputs have low
rates, or are nonexistent, a pacing pulse is automatically applied
for stimulating a heart beat in time with such pulse. However, if
electrical activity is present while mechanical output is absent,
indicative of ventricular fibrillation, a defibrillating pulse is
applied to the patient. If both electrical and mechanical activity
are present, indicative of substantially normal operation,
appropriate indication is given, and no corrective action is taken.
The apparatus attaches to the patient for administering the correct
electrical stimulation to the patient as soon as possible after the
occurrence of the suspected attack.
Inventors: |
Welborn; Warren S. (Portland,
OR), Holznagel; Melvin A. (Sherwood, OR) |
Assignee: |
Cardiac Resuscitator
Corporation (Portland, OR)
|
Family
ID: |
22067844 |
Appl.
No.: |
05/066,189 |
Filed: |
August 24, 1970 |
Current U.S.
Class: |
607/4 |
Current CPC
Class: |
A61N
1/3904 (20170801); A61N 1/365 (20130101); A61N
1/39046 (20170801); A61N 1/36585 (20130101); A61N
1/3987 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 1/365 (20060101); A61n
001/36 () |
Field of
Search: |
;128/2.6A,2.6E,2.6F,2.6R,2.1E,2.1R,2.1Z,419D,419P,2.5P,2.5R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Stratboeler et al., "Rocky Mountain Engineering Society," 1965, pp.
57-61..
|
Primary Examiner: Kamm; William E.
Claims
What is claimed is:
1. A cardiac resuscitator comprising:
means for detecting electrical activity of a patient's heart,
means for detecting mechanical activity of a patient's heart,
and means for applying a defibrillating pulse to said patient in
the presence of electrical activity accompanied by the absence of
mechanical activity as compared with predetermined activity
levels.
2. The apparatus according to claim 1 including means for rendering
said means for detecting mechanical activity effective only
immediately following detected electrical activity.
3. The apparatus according to claim 1 wherein said means for
detecting mechanical activity comprises means for detecting
impedance changes in a patient's body.
4. Cardiac resuscitator apparatus comprising:
first means for detecting an electrocardiac signal generated by a
patient's heart including the QRS wave of the electrocardiac
complex,
second means responsive to mechanical movement in the patient's
body indicative of a patient's heart beat,
means for applying a pacing pulse at a predetermined rate to the
patient in response to the absence of both electrical and
mechanical activity of the patient's heart as indicated by failure
of both said first and second means to produce outputs above
predetermined limits,
and means for applying a defibrillating pulse to the patient in
response to the presence of an electrical activity indicating
output above a predetermined limit from said first means and the
absence of a mechanical activity indicating output above a
predetermined limit from said second means.
5. The apparatus according to claim 4 wherein said means for
detecting mechanical activity comprises means for applying a signal
to the patient, and means for detecting a change in voltage drop
produced by said signal for detecting changes in body impedance
caused by mechanical heart activity.
6. The apparatus according to claim 5 wherein said means for
applying a signal to a patient includes a first electrode connected
to the means for applying a signal, a second electrode for
application to the patient, and means connecting the second
electrode to the means for detecting a change in voltage drop.
7. The apparatus according to claim 6 wherein at least one of said
electrodes is also coupled to said first means for detecting the
electrocardiac signal.
8. A cardiac resuscitator comprising:
electrode means for application to a patient suffering from
possible heart attack,
first means coupled to said electrode means for detecting the
electrocardiac signal generated by the patient's heart including
the QRS wave of the electrocardiac complex, if present,
second means coupled to said electrode means for detecting
impedance changes in the patient's body,
logical means coupled to receive outputs from said first and second
means and for determining when said first and second means produce
output rates respectively indicative of acceptable electrical and
mechanical activity of the patient's heart, as the pulse rate
detected by each of said first and second means exceeds
predetermined levels,
pacer means coupled to said logical means and responsive to the
absence of both electrical and mechanical activity, as indicated by
failure of the outputs of either said first and second means to
exceed predetermined levels, for providing an output comprising
periodic pacing pulses at a predetermined rate, means coupling the
last mentioned output to said electrode means,
and defibrillator means coupled to said electrode means and
responsive to said logical means, as the output of said first means
above a predetermined level indicates electrical activity of the
patient's heart, while the output of the second means fails to
exceed a predetermined level indicating absence of acceptable
mechanical activity of the patient's heart, for applying a
defibrillating pulse to said electrode means.
9. The apparatus according to claim 8 including indicating means
responsive to said logical means when both said first and second
means produce outputs above predetermined limits for indicating
normal heart activity.
10. The apparatus according to claim 8 including a coincidence
detector for receiving the outputs of both said first and second
means and providing the output of said second means to said logical
means only in the event that the output of said second means occurs
within predetermined time limits of the output of said first means
such that mechanical activity will only be detected in each
instance substantially immediately following a detection of
electrical activity of a patient's heart.
11. The apparatus according to claim 8 wherein said logical means
comprises means for counting the outputs of said first means and
said second means within predetermined time periods and producing
logical outputs in accordance with the count of said outputs as
they exceed predetermined lower activity levels.
12. The apparatus according to claim 8 wherein said means for
detecting impedance changes of the patient's body comprises means
for generating a high frequency alternating current for application
to said patient's body via said electrode means, and means
responsive to the signal received at other electrode means for
detecting changes in said signal.
13. The apparatus according to claim 8 including means for
decoupling said detecting means from said electrode means during an
output from said pacemaker means or said defibrillator means.
14. The apparatus according to claim 8 including means for
determining the continuity of connection of said electrode means
with the patient's body, and means for inhibiting the pacing pulse
and defibrillating pulse application of said resuscitator
apparatus, in response to a lack of such continuity.
15. The apparatus according to claim 8 wherein said first detecting
means includes a variable sensitivity signal channel, having means
for receiving and coupling the electrocardiac signal and means for
storing previous peak values detected, the signal channel being
coupled to the means for storing for changing the sensitivity of
said signal channel in response to the previous level of peak
values stored for causing said first detecting means to be
responsive to signals exceeding at least a predetermined proportion
of said peak values.
16. The apparatus according to claim 15 further including means for
limiting the level stored by said storing means to a predetermined
multiple of said peak values stored theretofore.
17. The apparatus according to claim 8 including a U-shaped
applicator wherein said electrode means are carried by said
U-shaped applicator positionable for yieldably urging said
electrode means into firm contact with the patient's body, at least
one of said electrode means being mounted from an upper leg of said
applicator for location against the patient's chest over the heart
area, and a second electrode means being mounted upon a lower leg
of said applicator for positioning against the patient's back
opposite the first mentioned electrode means.
Description
BACKGROUND OF THE INVENTION
An unusually large number of heart attack victims die each year as
a result of delays in providing the intensive care required. A
suspected heart attack victim typically must be hospitalized before
receiving adequate medical attention. However, a great many
patients suffering from a coronary attack never reach the hospital.
Cardiac arrests and arrhythmias such as ventricular fibrillation
frequently develop within a short time after the onset of the
attack, e.g. within the first hour, with fatal results unless
remedial steps are taken within minutes. Unless a normal rhythm can
be restored to a heart in ventricular fibrillation within minutes,
serious brain damage or death will result.
SUMMARY OF THE INVENTION
In accordance with the present invention, a cardiac resuscitator is
provided which is compact enough for attachment to a suspected
heart attack victim at nearly any location, and which may be
operated by comparatively unskilled personnel. The resuscitator may
be carried in an ambulance, for example, or may be conveniently
stored in an industrial plant, office building, hotel, or the like,
for immediate application to the suspected victim of a heart
attack. The resuscitator electrode current applicator is applied to
the patient, and the apparatus measures the electrical and
mechanical output of the patient's heart. If a normal heart beat is
detected, an appropriate indication is given. However, if the heart
beat is excessively slow or nonexistent indicating substantial
cardiac arrest, a pacing pulse is applied to the patient for
restoring a normal heart beat. If electrical output is present
while mechanical output is absent, indicative of ventricular
fibrillation or ventricular tachycardia, an appropriate
defibrillating impulse is applied to the patient. The apparatus may
remain applied to the patient for detecting possible arrhythmias
occuring after the onset of a possible heart attack until adequate
hospitalization can be provided.
It is an object of the present invention to provide an improved
cardiac resuscitator apparatus which may be applied to a suspected
heart attack victim in nearly any location prior to
hospitalization.
It is a further object of the present invention to provide an
improved cardiac resuscitator apparatus for detecting arrhythmias
and providing appropriate corrective action in the absence of a
physician.
It is a further object of the present invention to provide an
improved cardiac resuscitator apparatus which is substantially
portable in nature.
It is a further object of the present invention to provide an
improved cardiac resuscitator apparatus which accurately interprets
the electrical and mechanical signals from a suspected heart attack
victim and applies a corrective impulse in cases of then determined
arrhythmias.
It is a further object of the present invention to provide an
improved cardiac resuscitator apparatus which is substantially
foolproof in operation.
The subject matter which we regard as our invention is particularly
pointed out and distinctly claimed in the concluding portion of
this specification. The invention, however, both as to organization
and method of operation, together with further advantages and
objects thereof, may best be understood by reference to the
following description taken in connection with the accompanying
drawings wherein like reference characters refer to like
elements.
DRAWINGS
FIG. 1 is a perspective view of cardiac resuscitator apparatus
according to the present invention, shown applied to a patient;
FIG. 1A is a side view of an electrode current applicator portion
of the present resuscitator apparatus;
FIG. 2 illustrates typical electrical signals corresponding to
normal cardiac conditions;
FIG. 2A illustrates typical signals corresponding to fibrillation
of the patient's heart;
FIG. 3 is a simplified block diagram of cardiac resuscitator
apparatus according to the present invention;
FIG. 3A is a more specific block diagram of cardiac resuscitator
apparatus according to the present invention;
FIG. 4 is a schematic diagram of interface 1 portion of the
apparatus as referenced in the FIG. 3A block diagram;
FIG. 5 is a schematic diagram of the ECG detector 2 portion in the
block diagram;
FIG. 6 is a schematic diagram of the ICG detector 3 in the block
diagram;
FIG. 7 is a schematic diagram of coincidence detector 4;
FIG. 8 is a schematic diagram of counter 5;
FIG. 9 is a schematic diagram of clock 6;
FIG. 10 is a schematic diagram of pacer 7; and
FIG. 11 is a schematic diagram of the defibrillator 8 portion of
the FIG. 3A block diagram.
DETAILED DESCRIPTION
Referring to FIGS. 1 and 1A, illustrating resuscitator apparatus
according to the present invention, the apparatus includes a
U-shaped electrode current applicator 110 provided with a handle
116 and electrodes 1 , 2 , 3 and 41 which are individually
connected to the control cabinet 112 via cable 114. The applicator
is desirably formed of spring plastic or plastic-covered metal
electrically insulated from the electrodes. As illustrated in the
FIG. 1A, the applicator tends to urge contacts 1 and 2 toward one
another so that when placed on the patient as illustrated in FIG.
1, contacts 1 , 2 , 3 and 4 make firm contact with the patient's
body.
The electrode current applicator is placed over the left shoulder
of the patient so that electrodes 1 and 2 are positioned
appropriately above and below the heart, with the patient
ordinarily being in a prone position. The patient is desirably
stripped to the waist so that such contact may be made with the
body or, alternatively, the applicator can be inserted beneath
clothing to some extent. Electrode is designated the chest
electrode, with electrode 2 comprising the back electrode. The
third electrode 3 , termed an indifferent or neutral electrode,
makes contact with the patient in the shoulder region. A fourth
electrode, 41 , located near 1 , is called the current source
electrode.
The control cabinet 112 suitably contains electronic circuitry for
sensing the electrocardiac signal generated by the heart,
electronic circuitry for sensing changes in the electrical
impedance of the patient's body, and electronic circuitry for
making logical decisions based upon the analysis of the
electrocardiac (ECG) and impedance (ICG) signals. As hereinafter
disclosed, other means may be employed for measuring mechanical
activity of the heart in place of circuitry for sensing impedance
changes, but the latter is preferred. The control cabinet also
contains electronic circuitry for generating defibrillating or
pacing pulses in response to the logical decisions and for applying
these pulses to the patient electrodes.
FIG. 2 shows typical waveforms which may be present in the cardiac
resuscitator when attached to a patient having normal heart
operation. Waveform A is the ECG signal as obtained from the
patient. The QRS portion of the waveform is associated with
contraction of the ventricles and is of great importance in the
cardiac resuscitator, while the P and T portions are of no
importance in this application. Filtering of waveform A results in
waveform B in which the P and T portions are essentially
eliminated. Waveform C shows a typical ICG signal which may be
obtained by processing a high frequency signal provided at the
patient electrodes, and waveform D is a filtered version of
waveform C. The voltage peaks of waveform D, which are
representative of electrical impedance changes in the patient's
chest, occur somewhat later than, but in a definite time
relationship with, the peaks of waveform B. The impedance changes
are brought about by mechanical movement of the patient's heart,
blood flow, or the like. Not shown in FIG. 2 are waveform artifacts
which may be present on the ICG waveforms due to patient
respiration or externally induced motion. The cardiac resuscitator
makes use of the time relationship of the ECG and ICG waveforms to
reduce the effects of artifacts by requiring that an ICG pulse, to
be valid, must be immediately preceded by an ECG pulse.
FIG. 2A shows waveforms typical of those to be found in the cardiac
resuscitator when the patient is in ventricular fibrillation.
Waveform A is the ECG waveform as obtained from the patient.
Although random in nature, the waveform typically contains
fast-rising portions which may be more clearly defined by
filtering, to produce waveform B. The same circuitry which converts
waveform A to waveform B in FIG. 2 will convert waveform A to
waveform B in FIG. 2A. Thus the circuitry is capable of recognizing
the presence of electrical activity in a fibrillating heart while
rejecting the P and T portions of a normal ECG.
While in fibrillation, the heart muscle fibers contract in a
random, uncoordinated manner so that no effective pumping of blood
occurs. Thus no significant mechanical changes are present which
would bring about body impedance changes, and the ICG pulses are
absent. This fact is used to distinguish fibrillation from normal
heart operation in the present invention.
The circuitry of the present invention counts the rate of the ECG
pulses and the rate of ICG pulses which have been immediately
preceded by ECG pulses to determine whether there is substantial
electrical activity present and whether there is substantial
mechanical activity present.
In order to render the device substantially foolproof, and to
prevent improper application of electrical impulses when a proper
signal cannot be received, the circuitry according to the present
invention is provided with continuity means for determining whether
electrodes 1 , 2 , 3 and 41 are making proper electrical connection
with the patient's body. Only after such a determination is the
heart rate indication able to bring about the aforementioned pacing
or defibrillating impulses. In addition to the inhibition of the
device in the absence of proper contact with the patient's body, a
poor contact indicator 1-D, suitably comprising a pilot lamp, also
warns the operator that proper contact with the patient has not
been established. Cabinet 112 additionally includes power supply
circuitry and batteries for use in case of portable operation. An
off-on switch as well as a pilot lamp indicating the presence of
power are suitably also included.
In operation, the electrode current applicator is applied as
illustrated in FIG. 1, and the power switch is operated for
energizing the apparatus. A normal heart signal may reveal the
patient has merely fainted, rather than having suffered a heart
attack. However, such a signal may only indicate that arrhythmias
have not as yet developed. The device is suitably left applied to
the patient until adequate medical attention is provided, and
meanwhile the device continuously monitors the heart during the
critical period after a possible attack. For example, battery
powered apparatus of the present type may be left attached to the
patient while he is being transported to a hospital in an
ambulance.
The apparatus is relatively compact, and may be transported in an
ambulance and easily carried by hand, or conveniently stored in an
industrial plant, office building, hotel, or the like, for
immediate application to a suspected victim of a heart attack. The
apparatus may be operated by comparatively unskilled personnel,
without the need of an expert diagnosis, while awaiting
conventional medical attention.
FIG. 3 is a simplified block diagram of electronic circuitry
according to the present invention. Patient interface 1
collectively includes the various electrodes or other means for
receiving information from the patient and applying corrective
measures to the patient. Both the ECG detector 2 and mechanical
activity detector 3 receive information from the patient, regarding
the electrical and mechanical activity of the patient's heart,
respectively. The mechanical activity detector suitably comprises
an electrical impedance change detector, but may alternatively
comprise other means for ascertaining mechanical activity of the
heart. For instance, means 3 may alternatively comprise a pressure
transducer or microphone for providing a phono-cardiogram signal of
heart beat activity, or may comprise ultrasonic or other means for
detecting blood flow as understood by those skilled in the art.
The ECG output from detector 2 together with output .DELTA. Z from
detector 3 are applied to time coincidence detector 4. The detector
4 supplies an output to logical analyzer 5 only if the output from
mechanical activity detector 3 occurs within a predetermined time
after an output from ECG detector 2. Logical analyzer 5, which may
comprise means for counting pulse inputs within a predetermined
period of time, directly receives the ECG output from detector 2,
as well as the output from the coincidence detector.
Logical analyzer 5 further comprises means for making a decision on
the basis of input supplied thereto, and in consequence thereof
delivers an output D, an output P or no output. The possible
combinations of ECG activity and .DELTA. Z activity resulting in
the D and P outputs are indicated in the truth table accompanying
FIG. 3. In each of the ECG and .DELTA. Z columns, a zero is
indicative of substantially no activity, or activity below a
predetermined minimum threshold level. Thus, if substantially no
electrical (ECG) nor mechanical (.DELTA. Z) activity occurs,
logical analyzer 5 will provide an output P. If on the other hand,
electrical (ECG) activity is present, but no mechanical (.DELTA. Z)
activity is present which substantially coincides with electrical
activity, logical analyzer 5 will provide an output D. For both,
neither an output D nor an input P is supplied.
Output P is applied to pacer 7, which provides a pacing pulse to
the patient electrodes in the event that neither electrical nor
mechanical activity is detected, i.e. as indicated by the first
combination of the truth table. This situation corresponds
generally to cardiac arrest. An output D is applied to
defibrillator 2 if electrical activity is present, but no
mechanical activity or heart beat ensues within a predetermined
time immediately following each electrical activity. As a
consequence, a defibrillating pulse is applied to the patient. This
situation corresponds to the second line of the truth table. The
fourth line of the truth table corresponds to normal heart
activity, wherein neither a pacing nor defibrillating pulse is
needed, while the third combination of mechanical activity without
electrical activity will generally not occur.
BLOCK DIAGRAM
FIG. 3A is a more detailed electrical block diagram of the
apparatus according to the present invention, principally located
within the aforementioned cabinet 112. Referring to FIG. 3A,
amplifier 1-B in the interface unit 1 receives the composite
electrical signal, comprising a low frequency electrocardiac
signal, a high frequency impedance signal, and unwanted noise
signals, from the patient electrodes, jointly indicated at 1-A, and
applies an amplified version thereof at 8 to an ECG detector 2 and
to an ICG (impedance cardiogram) detector 3. The latter detects
mechanical activity in terms of body impedance. Low pass filter,
2-A, prevents the passage of the high frequency impedance signal to
the ECG amplifier. The ECG amplifier and filter, 2-B, amplifies the
desired components of the remaining signal while attenuating
unwanted signals and noise. In particular, circuit 2-B provides a
high degree of rejection of 60 Hz signals which may be present due
to the proximity of electrical power lines. The output of circuit
2-B is rectified by rectifier 2-C so that the output of rectifier
2-C comprises pulses of only one polarity. As is hereinafter
indicated, disabling claim 2-D operates to inhibit transmission of
the ECG signal at times when electrical stimulation is being
delivered to the patient.
The output of rectifier 2-C is applied to peak detector 2-F and
comparator 2-H. These units comprise detection means of varying
sensitivity for detecting or developing peaks from the ECG signal
relative to previously stored values of such peaks. The detection
means functions over a wide range of input signal amplitude with
little or no degradation in performance. Without such a variable
sensitivity feature, the system would be susceptible to noise
present on large amplitude signals or would be unable to detect the
presence of small amplitude signals, or both. The apparatus also
includes means for essentially ignoring the occasional signal of
unduly high amplitude, e.g. peaks associated with ectopic
beats.
Referring to the drawing, the comparator 2-H provides an output
pulse whenever the input signal 13 exceeds the reference voltage
provided by the peak detector 2-F. The reference voltage represents
a proportion of previous signal peaks. The output of the comparator
is applied to one-shot multivibrator 2-J which serves to widen the
pulse and thus prevent two or more peaks of a QRS complex from
producing multiple output pulses at 18 . One output pulse will be
produced at 18 for each heart beat. The output at 18 is also
coupled to inverter 2-K for supplying a resetting signal 19 to the
pacer as hereinafter more fully described.
The H.F. (high frequency) current generator 3-A supplies an
alternating current of constant amplitude at a frequency of
approximately 100 KHz to the patient electrode 41 . This current
produces a high frequency voltage at the patient electrodes, the
amplitude of which is a function of the electrical impedance of the
patient's body. Thus, the high frequency component of the composite
signal at 8 is representative of the electrical impedance of the
patient's body. The beating of the heart produces a change in the
electrical impedance of the body and thus the beating of the heart
may be detected by detecting changes in the high frequency
component of the signal at 8 .
The composite electrical signal at 8 is applied to H.F. bandpass
filter 3-B which rejects all signals except those which contain the
ICG (impedance cardiogram) information. The output of 3-B is
amplified by H.F. (high frequency) amplifier 3-C which has
provision for AGC (automatic gain control). The output of circuit
3-C is applied to the A.M. detector 3-D (and AGC unit) which
provides a low frequency output to the ICG amplifier and filter
unit 3-E proportional to the changes in electrical impedance
occuring in the patient's body. Circuit 3-D also provides an AGC
signal to H.F. amplifier 3-C which controls the amplifier gain in
such a way as to maintain the average output signal amplitude
relatively constant over a wide range of input signal amplitudes.
This feature allows the system to operate effectively over a wide
range of patient body impedances.
The ICG amplifier and filter 3-E amplifies the desired components
of the ICG signal while attenuating unwanted components. In
particular, low frequency signals due to patient respiration are
attenuated. The output of circuit 3-E is applied to rectifier 3-F
which produces output pulses of a single polarity. Disabling clamp
3-H operates to inhibit the transmission of the ICG signal during
the delivery of electrical stimulation to the patient, as is
hereinafter indicated.
The ICG pulses from circuit 3-H are applied to comparator 3-K which
produces an output pulse at 45 which is applied to one input of
and-gate 4-B. The second input 46 to and-gate 4-B is provided by
one-shot multivibrator 4-A, and is an extended version of the ECG
detector output at 18 . Thus, a pulse is present at 47 if an output
pulse from the ICG detector 45 occurs at the time of, or slightly
later than, an output from the ECG detector 18 .
Counter 5-A counts the output pulses of the ECG detector, and after
receiving a predetermined number of pulses produces an output which
causes flip-flop 5-B to change state. Thus, flip-flop 5-B serves as
a temporary storage element, indicating whether or not a
predetermined number of pulses have been received at the input of
counter 5-A. This information is transferred to J-K flip-flop 5-C
upon receipt of a clock pulse. After completion of the clock pulse,
a reset pulse is applied to counter 5-A and flip-flop 5-B to reset
5-A and 5-B to the zero state and thus initiate a new counting
period. A clear input is provided at J-K flip-flop 5-C to reset
flip-flop 5-C to the zero state when power is first applied to the
resuscitator or when a defibrillating pulse is applied to the
patient, as is hereinafter indicated.
Counter 5-D, flip-flop 5-E and J-K flip-flop 5-F operate in a
manner similar to that described above for counter 5-A, flip-flop
5-B and J-K flip-flop 5-C. The input to counter 5-D, however, is
the output of the coincidence detector unit 4.
Clock pulses, followed immediately by reset pulses, are supplied at
regular intervals. Therefore, the logic levels present at the Q and
Q-not outputs of 5-C and 5-F are representative of the number of
pulses received at 18 and at 47 during the previous interval
between clock pulses.
The interval between clock pulses is desirably 10 seconds, and the
dividing ratio of each counter is desirably five to one. Thus a
high level at the Q output of circuit 5-C indicates an average ECG
rate of at least five pulses per 10 seconds or 30 per minute.
Similarly, a high level at the Q output of circuit 5-F indicates
that an average rate of at least 30 per minute was attained at the
output of the coincidence detector 4 during the previous clock
period. The Q outputs of 5-C and 5-F are connected to and-gate 5-H
which causes the normal heart indicator to be actuated when the two
Q outputs are high and the enable signal 27 is also high. The
enable signal is high after the completion of at least one clock
period as hereinafter indicated.
The Q output of circuit 5-C and the Q-not output of circuit 5-F are
connected to and-gate 5-K. A third input to and-gate 5-K is
provided by the reset pulse. Thus, if during a certain clock period
at least five ECG pulses are detected but fewer than five ICG
pulses which are correlatable to ECG pulses are detected, the reset
pulse which occurs at the end of the clock period causes an output
pulse from 5-K which, in turn, actuates the defibrillator 8 by an
input at 25 .
And-gate 5-L receives the Q-not outputs of flip-flops 5-C and 5-F.
In the event that fewer than five pulses are present at 18 and
fewer than five pulses are present at 47 during a clock period, the
output of and-gate 5-L will be high after the completion of the
clock period. Therefore the pacer 7 will be actuated by an input at
24 .
Clock 6 includes a clock pulse generator 6-B providing pulse
outputs at 10-second intervals at 23 . If a signal is present at
either 26 , indicating defibrillator operation, or at 10 indicating
faulty interface operation or initial start conditions, the clock
pulse generator 6-B is reset from or-gate 6-A. At the same time,
the J-K flip-flops 5-C and 5-F are cleared via lead 20 , and a
reset pulse is provided at 21 , 22 , via or-gate 6-C. Likewise,
flip-flop 6-D is set. After being initially reset from Or-gate 6-A,
clock pulse generator 6-B starts providing clock pulses at 22 , at
10-second intervals. At the end of each such clock pulse, a reset
is provided or-gate 6-C and flip-flop 6-D. The reset via leads 21
and 22 reset the counters 5-A and 5-D as well as flip-flops 5-B and
5-E for another cycle. At the end of such cycle, the clock pulse at
23 causes the J-K flip-flops to register the condition of
flip-flops 5-B and 5-E as hereinbefore described. Flip-flop 6-D
provides an output at 27 effective for enabling the pacer and
normal heart indicator only after a suitable period of time has
elapsed for counter 5 actually to count the heart rate. Otherwise,
pacer 7 could be falsely actuated before proper counter operation.
Operation of flip-flop 6-D will be further described
hereinafter.
In pacer 7, pacemaker timer 7-B generates a series of timing pulses
with a period of approximately 0.85 seconds, whenever the output of
and-gate 7-A is high. The output of and-gate 7-A is high (1) when
the circuitry has operated at least 10 seconds as indicated by a
signal at 27 , (2) when ECG detector 2 does not detect a present
heart beat, and (3) when counter 5 indicates a heart rate of below
30 beats a minute. The output of timer 7-B triggers one-shot
multivibrator 7-C which operates pacer pulse generator 7-D. The
latter delivers a pacing pulse to the patient electrodes via leads
6 , 7 , and switching diodes 1-F. The switching diodes 1-F
essentially disconnect the pacer from the patient electrodes when
the pacer produces no output. During each pacemaker pulse, output
11 of one-shot multivibrator 7-C operates or-gates 2-E and 3-J for
disabling the signal paths. If, between pacer pulses, a heart beat
is detected, reset signal 19 will reset pacer timer 7-B via
and-gate 7-A, restarting the timing of the 0.85 second interval.
Thus, the pacer operates on a demand basis and produces no output
when spontaneous heart beats are present.
When defibrillator 8 receives an input at 25 , one-shot
multivibrator 8-A is set in a second state for approximately 100
milliseconds. Output 12 disables the signal paths, and output 26
resets clock 6 as well as counter 5. The third output of
multivibrator 8-A operates defibrillator generator 8-C through
and-gate 8-B if input 9 is also present. A defibrillating pulse, a
high energy electrical pulse, is applied through leads 4 , 5 , and
switching diodes 1-E, to patient electrodes 1-A. Input 9 is present
if the patient electrodes make proper contact and certain other
conditions are met as hereinafter more fully described. The
switching diodes essentially disconnect the defibrillator when the
same is not in use. It is observed the defibrillator operation
resets clock 6 and counter 5 for successive operations. If, after a
defibrillating pulse is applied to the patient, fibrillation or
tachycardia persists, defibrillator operation will again be
initiated in the same manner as hereinbefore described.
Interface 1 further includes continuity checker 1-C, which
determines if the patent electrodes are in proper electrical
contact with the patient's body. If not, a poor contact indicator
1-D, suitably comprising a pilot lamp, is energized, and
defibrillator and-gate 8-B is disabled via and-gate 1-K and lead 9
, thus preventing defibrillator operation and possible patient
burns in case of poor electrical contact. Also in such case, clock
6 is reset via lead 10 and inverting gate 1-L, and flip-flop 6-D is
set to prevent operation of the pacer via output 27 . When the
resuscitator is first started, start circuit 1-H disables and-gate
1-K, thereby disabling defibrillator 8, resetting clock 6 and
disabling pacer 7. Pacer 7 is operable when flip-flop 6-D is reset
from clock pulse 6-B. The output from the start circuit 1-H is of
short duration, and the main purpose thereof is the disabling of
the pacer until the counter has time to count.
The individual units of the resuscitator will now be considered in
greater detail.
INTERFACE
Referring to FIG. 4, illustrating interface unit 1 in greater
detail, transistors Q101 and Q102 provide DC current sources for
patient electrodes 1 and 2 to ground via indifferent or neutral
patient electrode 3 . The DC voltage at electrodes 1 and 2 depends
upon the resistance between each electrode and ground, and
therefore, if either electrode 1 or 2 is in poor contact with the
patient, a comparatively high DC voltage will occur at that
electrode. Patient electrode 1 is coupled to the input and an
operational amplifier U101, while the patient electrode 2 is
coupled to the input of an operational amplifier U102, with diodes
D105, D106, D107 and D108 protecting the amplifiers during the
application of a pacing or defibrillating pulse. If the voltage at
patient electrode 1 is less than about +0.15 volts, then the output
of U101 will be about +15 volts, and the voltage at the junction of
D109 and D110 will be clamped to about +5.6 volts. However, if the
voltage at patient electrode 1 exceeds +0.15 volts, the voltage at
the output of U101 will be about -15 volts, and the voltage at the
junction of diodes D109 and D110 will be clamped at about -0.6
volts. The output of amplifier U102 is similarly controlled by the
voltage at patient electrode 2 .
The output of amplifier U107 is controlled by the amplitude of the
high frequency AC voltage which exists at electrode 41 due to
current supplied at 40 . The AC voltage is rectified by diode D142
so that the voltage at the minus input of amplifier U107 is a DC
voltage representing the peak value of the AC voltage at 41 . Thus
if electrode 41 is in poor contact with the patient, the voltage at
the minus input of amplifier U107 is relatively high, causing the
voltage at the junction of diodes D143 and D144 to be about -0.6
volts.
Nand-gate 30 receives the outputs of the three amplifiers U101,
U102 and U107 and drives nand-gate 32, here used as an inverter,
which is coupled to transistor Q103 having a poor contact indicator
lamp in its collector circuit. Thus, if the output of any of the
three amplifiers U101, U102 or U107 drops, indicating poor patient
electrode contact, lamp 1-D will light.
Likewise, nand-gate 32 drives nand-gate 34 in conjunction with
start circuit 1-H comprising transistor Q104. When power is first
turned on, transistor Q104 is momentarily turned on. Capacitor C101
charges so that transistor Q104 cuts off, thereby providing a high
input to nand-gate 34. Assuming good contact is made by the patient
electrodes, and the power has been applied for a short period of
time, both inputs to nand-gate 34 will be up, and the output of
nand-gate 36, driven by nand-gate 34, will also be up. The output
of nand-gate 36 is applied to leads 9 and 10 . Since nand-gates are
employed throughout, no inverting gate is employed in lead 10 , nor
is an inverting gate required in the output of the start circuit.
Both outputs 9 and 10 will be energized so long as continuity is
present to the patient's body from the patient electrodes, and so
long as power has been applied to the apparatus for at least a
short time. Then, the clock and defibrillator are operable.
Switching diodes 1-E and 1-F, from the defibrillator and pacer,
respectively, couple these units to the patient electrodes, and
essentially decouple these units when neither provides an output
pulse. Also, the respective diodes prevent application of a
defibrillator pulse to the pacer or a pacer pulse to the
defibrillator.
Operational amplifiers U104 and U105 receive signal outputs from
patient electrodes 1 and 2 , and diodes D116 and D117, D118 and
D119 limit the voltage excursion of the inputs of these amplifiers
during the occurrence of defibrillator or pacer pulses. Each of the
amplifiers U104 and U105 is connected as a voltage follower, so the
outputs thereof are the same as those from patient electrodes 1 and
2 , respectively, except the DC component has been removed, and the
impedance level is greatly reduced. The outputs of amplifiers U104
and U105 are applied as inputs to differential amplifier U106 which
has a voltage gain of approximately 10 as determined in part by
feed back resistor R135. The output of amplifier U106 at lead 8 is
therefore an amplified version of the signal existing between
patient electrodes 1 and 2 except that any DC component has been
removed.
ECG DETECTOR
Referring to FIG. 5 further illustrating the aforementioned ECG
detector 2, a low pass filter 2-A comprises inductors L201 and L202
and capacitors C201 and C202. The cutoff frequency of filter 2-A is
such that the 100KHz component of the signal at 8 is severely
attenuated, while the low frequency ECG signal is allowed to pass.
Capacitor C203 and resistor R201 operate as a differentiating
network so the signal at the positive input of amplifier U201 is
representative of the rate of change of the ECG signal. Thus the
very low frequency components of the signal, including baseline
shift and the P and T portions of the normal electrocardiogram, are
effectively reduced.
Amplifiers U201 and U202, together with twin-tee filter 50 and
other associated components, operate as an active filter which
rejects any 60 hertz component which may appear upon the ECG signal
due to proximity of electrical power lines or apparatus, while
providing amplification of other frequency components. Thus the
signal at the base of transistor Q201 is a highly refined version
of the signal at 8 , with all undesirable components reduced to
small amplitude. Rectifier 2-C comprises transistor Q201 operating
as a phase inverter so that the signals at the emitter and
collector terminals of Q201 are of equal magnitude, but of opposite
polarity, the magnitude being nearly equal to the magnitude at the
base terminal. The collector of Q201 is coupled through capacitor
C208 to the base of transistor Q202 and to one end of resistor
R211, which has its opposite end connected to ground. Similarly,
the emitter of transistor Q201 is coupled through capacitor C209 to
the base of transistor Q203 and to one end of resistor R214 which
has its opposite end connected to ground. The emitter terminals of
transistors Q202 and Q203 are connected together and to one end of
resistor R215, the other end of which is grounded.
A positive signal at the base of transistor Q201 produces a
positive signal at the base of transistor Q203 and a positive
signal at the common emitter terminals of transistors Q202 and
Q203. A negative signal at the base of transistor Q201 causes a
positive signal at the base of transistor Q202 and a positive
signal at the common emitter terminals of transistors Q202 and
Q203. However, positive signals at the base terminals of
transistors Q202 and Q203, which are smaller in amplitude than 0.6
volts, will be severely attenuated because of the nonlinear
characteristics of the base-emitter junctions of transistors Q202
and Q203. Therefore, the signal at the common emitter terminal of
transistors Q202 and Q203 is a series of positive pulses which
occur whenever the signal at the base of transistor Q201 exceeds
0.6 volts in either the positive or negative direction, and which
correspond to the fast-rising portions of the ECG component of the
signal at 8 .
The common emitter terminal of transistors Q202 and Q203 is coupled
through resistor R216 to the positive input of amplifier U204 and
to the collector of transistor Q204, forming a part of disabling
clamp circuit 2-D. The base of transistor Q204 is coupled to the
output of gate 2-E employed for causing transistor Q204 to conduct
and clamp the signal at its collector terminal to ground whenever
either of the inputs, 11 and 12 , are low. Clamping occurs during
the delivery of defibrillating or pacing pulses to the patient.
Assuming that the disabling clamp circuit 2-D is inactive, the
series of positive pulses present at the common emitter terminals
of transistors Q202 and Q203 is applied to the positive input of
amplifier U204, to the anode of diode D201 and to the emitter of
transistor Q207. A positive pulse causes diode D201 to conduct and
to charge capacitor C210 to the peak value of the pulse (less the
diode voltage). Resistor R230 allows capacitor C210 to discharge at
a rate which is slow in comparison with the time between normal
heart beats. Therefore capacitor C210 acts as a peak storage
capacitor and discharges only slightly between input pulses.
Amplifier U205 is connected as a typical voltage follower except
that diode D202 is connected between the output and the inverting
input. This diode compensates for the voltage drop which occurs
across diode D201 while capacitor C210 is charging, in order to
make the output voltage of amplifier U205 more nearly equal to the
peak value of the input pulse.
The output of amplifier U205 is applied to amplifier U206 through a
delay network comprising resistor R234 and capacitor C213. Thus the
input to amplifier U206 does not immediately respond to a change in
the output of amplifier U205. Amplifier U206 is connected in a
noninverting configuration with a gain of two, so that the output
of amplifier U206 is a voltage approximately equal to twice the
stored value on capacitor C210. The output of amplifier U206 is
coupled to the base of transistor Q207 which operates as a limiter
inasmuch as its emitter is coupled to the input line of the peak
detector 2-F, i.e. at the anode of diode D201. Thus, if the input
becomes more positive than twice the previously stored value,
transistor Q207 conducts, preventing an input pulse of large
amplitude but short duration from charging C210 to a voltage more
positive than twice the previously stored peak value. This limiting
feature prevents a single large pulse, whether originating in the
patient as in the case of an ectopic beat, or induced into the
patient from an external source, from raising the stored peak value
to some value which is entirely unrepresentative of the average
signal amplitude. The limiting feature particularly prevents the
large voltage peaks associated with ectopic beats from decreasing
the sensitivity of the circuit to the point where the next normal
QRS heart signal complex would be undetected.
The output of amplifier U205 is also coupled to a divider
comprising resistors R232 and R233 which allows approximately
one-third of the stored peak value to be coupled to the negative
input of comparator amplifier U204 as a reference voltage.
Capacitor C211 is connected in shunt with resistor R233 to cause a
delay in any change in the reference voltage, so the reference
cannot follow the input signal.
Since the reference voltage for the comparator varies with the peak
amplitude of the signal, the system is of variable sensitivity,
rendering it operable with respect to cardiac signals of different
average amplitude values. It is noted that the one-third reference
value allows detection of a normal signal after an ectopic beat,
the storage of which is restricted to double amplitude.
When an input pulse at the positive input of amplifier U204 exceeds
the reference voltage at its negative input, the output of
amplifier U204 goes positive, causing a positive voltage spike to
be coupled to one-shot multivibrator 2-J, triggering 2-J, and
causing a positive pulse of about 5 volts in amplitude and 100
milliseconds in width to occur at 18 . During the width of the
output pulse at 18 , the one-shot multivibrator 2-J cannot respond
to further inputs. This prevents the QRS complex of the normal
electrocardiac signal, which may comprise several peaks closely
adjacent in time, from being registered as multiple pulses.
Nand-gate 2-K, here connected as an inverter, provides an output 19
for resetting the pacer.
ICG DETECTOR
Referring to FIG. 6, further illustrating the ICG detector, high
frequency current generator 3-A includes 100 KHz crystal oscillator
U301 which is coupled through transformer T301 to high frequency
amplifier U302 which also has an automatic gain control (AGC)
input, numbered 5. The output of amplifier U302 is coupled through
tuned transformer T302 to capacitors C303 and C304 and to the anode
of diode D301, the signal at this junction being a sinusoidal
voltage symmetrical with respect to ground. The cathode of D301 is
coupled to the base of transistor Q301, the emitter of which is
connected to the positive input of amplifier U303 and to the
parallel combination of resistor R306 and capacitor C305. The time
constant of circuit R306, C305 is long with respect to the period
of the sinusoidal signal at the anode of diode D301, so that
capacitor C305 is maintained at a voltage which is representative
of the peak value of the sine wave applied to capacitors C303 and
C304.
Amplifier U303 is connected in a noninverting configuration having
a feedback resistor R307 connected between output and inverting
input, and resistor R308 connected between the inverting input and
a +5 volt supply. The output of amplifier U303 is connected to the
AGC input of high frequency amplifier U302. Thus a closed-loop
feedback system is established which maintains the peak amplitude
of the 100 KHz signal, applied to capacitors C303 and C304, at
approximately 5 volts.
Capacitor C303 couples the 100 KHz signal to the base of transistor
Q302 which is biased so that the base is approximately 14.4 volts
DC. The emitter of transistor Q302 is coupled through resistor R302
to the +15 volt supply. Thus, when the sinusoidal signal swings
positive, transistor Q302 is cut off, and when the signal swings
negative, a half sine wave of current flows to output terminal 40 .
Similarly capacitor C304 couples the 100 KHz signal to transistor
Q303, which conducts a half sine wave of current to the output
terminal when the signal at the base swings positive. Thus, a full
sine wave of current is supplied at the output terminal 40 , the
magnitude of the current being approximately 5 milliamperes peak,
and independent of load impedance for impedances less than about
1,000 ohms. The output current is coupled to the patient electrodes
in order to detect changes in the electrical impedance of the body.
A constant current output is required in order to avoid artifacts
in the impedance cardiogram (ICG) waveform due to changes in
impedance at the electrode-patient interface.
Also, in order to avoid sensing changes in the electrode-patient
interface impedance, separate electrode means are used for
supplying the constant current and for sensing the voltage which is
representative of the body impedance, as hereinbefore
described.
The composite signal obtained from the patient, including the 100
KHz ICG signal, the low frequency ECG signal, and superimposed
noise, is applied at 8 in FIG. 5. Bandpass filter 3-B, comprising
tuned transformer T303, rejects all components of the signal except
the 100 KHz component, which is an amplitude modulated signal
containing the ICG information. The 100 KHz signal is amplified by
high frequency amplifier U304 which has provision for AGC at its
terminal 5. The output of amplifier U304 is coupled through tuned
transformer T304 to the base of transistor Q305 which has its
emitter terminal connected to capacitor C317. The base-emitter
junction of transistor Q305 serves as a rectifier, and in
conjunction with capacitor C317, as an amplitude modulation
detector. Capacitor C317 filters out the 100 KHz component of the
signal and the resultant voltage applied to capacitor C320 is
therefore a low frequency signal which is proportional to the
impedance of the patient's body between electrode 41 and electrodes
1 , 2 .
The collector terminal of Q305 is connected to ground through
resistor R314 in parallel with capacitor C315. The voltage at the
collector is an inverted version of the ICG signal at the emitter.
This signal is coupled through a filter network comprising resistor
R313 and capacitor C316 to the base of transistor Q304. The time
constant of the R313, C316 combination is long with respect to the
period of a normal heart beat, so that the voltage at the base of
transistor Q304 is essentially a DC voltage representative of the
average amplitude of the 100 KHz signal at the output of amplifier
U304. Transistor Q304 serves as an emitter follower to couple this
DC voltage to the AGC input of amplifier U304, thus providing a
closed-loop system to maintain the output of amplifier U304
relatively constant. Thus the system is operable over a wide range
of body impedance levels with a relatively constant amplitude of
ICG signal being obtained.
The low frequency signal at the emitter of Q305 is coupled through
the differentiating circuit comprising capacitor C320 and resistor
R320 to the inverting input of amplifier U305 which is connected
for conventional operation as an inverting amplifier. Capacitor
C321 connected in shunt with feedback resistor R321 serves to
eliminate any residual high frequency component present on the
signal. The signal at the output of amplifier U305 is proportional
to the rate of change of the patient's body impedance due to the
differentiating action of components C320 and R320.
The output of amplifier U305 is applied to rectifier circuit 3-F
which operates in a manner similar to that hereinbefore described
in reference to rectifier 2-C. Thus the signal applied at the
noninverting input of amplifier U306 is a series of positive
pulses, each pulse corresponding to a rapid change in the
electrical impedance of the patient's body.
Disabling clamp 3-H, comprising transistor Q309 clamps the signal
to ground during times when defibrillating or pacing pulses are
being generated. Amplifier U306 here operates as a comparator (3-K)
causing a positive rectangular pulse to be applied at output
terminal 45 whenever the signal at the noninverting input exceeds
the reference voltage supplied by the voltage reference 3-L
comprising resistors R333 and R334 and capacitor C324.
Thus a positive rectangular pulse occurs at 45 whenever a rapid
change in the patient's body impedance occurs.
COINCIDENCE DETECTOR
Referring to FIG. 7, coincidence detector 4 comprises one-shot
multivibrator 4-A and an and-gate 4-B. Rectangular pulses from the
ECG detector are applied at input 18 and are differentiated by
capacitor C401 and resistor R401. The positive spikes generated at
the leading edge of the input pulses trigger the multivibrator,
comprising transistors Q401 and Q402, into its quasi-stable state,
causing a positive rectangular pulse, approximately 200
milliseconds in width, to be generated at the collector of
transistor Q402. The collector of transistor Q402 is connected to
one input of nand-gate U401A, the second input of U401A being
connected to the output of the ICG detector at 45 . The output of
gate U401A is connected to the inputs of nand-gate U401B, here
employed as an inverter. Thus the output 47 is low except when a
high level signal is received at 45 during the first 200
milliseconds after the receipt of a high level input at 18 . In
essence, this means that in order for an output of the ICG detector
to be considered valid, it must be immediately preceded by an
output from the ECG detector. This feature reduces the probability
that artifacts in the ICG signal can cause a false diagnosis of the
patient's condition.
COUNTER
Referring to FIG. 8, counter 5-A receives input pulse at 18 from
the ECG detector and after receiving five pulses produces a
negative-going voltage step which is differentiated and applied to
flip-flop 5-B. Thus, after five pulses are applied at 18 , the J
input of J-K flip-flop 5-C is high, while the K input is low.
Clock pulses are supplied at 23 at intervals of approximately 10
seconds, the width of the clock pulse being small with respect to
the 10-second interval. The clock pulse causes the information
present at the J and K inputs of flip-flop 5-C to be stored in such
flip-flop and to be registered at the Q and Q-not outputs thereof.
Thus, if J is low and K is high at the time of the clock pulse,
then Q will be low and Q-not high after the end of the clock pulse.
J-K flip-flops are well known to those skilled in the art and need
not be described in detail.
Immediately succeeding each clock pulse, high level and low level
reset pulses are provided at 21 and 22 , respectively, resetting
counter 5-A and flip-flop 5-B to their zero states in preparation
for a new period of counting.
Clear pulses are supplied at 20 to set the J-K flip-flop 5-C to its
zero state under certain conditions hereinafter indicated.
Counter 5-D, flip-flop 5-E and J-K flip-flop 5-F operate in a
similar manner to count input pulses presented at 47 during the
clock interval and to register the result at the Q and Q-not
outputs of flip-flop 5-F. Thus, at any given time, the states of
the outputs of flip-flops 5-C and 5-F are representative of the
number of pulses received at 18 and 47 , respectively during the
previous interval between clock pulses. A high level at the Q
outputs of both flip-flops 5-C and 5-F indicates that the patient's
heart has both significant electrical activity and significant
mechanical activity. The two Q outputs are connected to two inputs
of nand-gate 5-H. A third input to gate 5-H is supplied at 27 to
enable 5-H only after a full clock period has elapsed for counting.
Thus the output of gate 5-H is low when significant electrical and
mechanical activity is present in the patient and after sufficient
time has elapsed for counting, causing the normal heart indicator
5-J including transistor Q501 to be energized. If the Q output of
flip-flop 5-C is high while the Q-not output of flip-flop 5-F is
high, indicating significant electrical activity but no significant
mechanical activity by the patient's heart, i.e. a fibrillation
condition, the reset pulse 21 immediately following the clock
period in which such determination was made causes the output of
nand-gate U206B to be low and the signal at 25 to be high,
triggering the defibrillator. If predetermined electrical or
mechanical activity of the heart is not present, the two Q-not
outputs applied to nand-gate U207A will be high, causing the signal
at 24 to be high, activating the pacemaker.
CLOCK
Referring to FIG. 9, gate portions 6-A' and 6-C' perform the
functions of or-gates 6-A and 6-C on the block diagram. This
structure is conveniently provided as a four-nand-gate integrated
circuit including nand-gates 60, 62, 64, and 66, which are
consecutively connected. Nand-gate 60 receives inputs 10 from the
interface circuit, and 26 from the defibrillator circuit. Providing
both these inputs are up, the output of nand-gate 60 is low, and
the clock pulse generator 6-B can operate in a normal fashion.
In clock pulse generator 6-B, transistor Q601 receives the output
of nand-gate 60 at its base, and its collector-emitter terminals
are coupled across capacitor C601 coupled between the emitter and
lower base terminals of unijunction transistor Q602. The circuit
normally operates as a relaxation oscillator whereby the
unijunction transistor periodically discharges capacitor C601 to
supply a pulse output at its lower base. If either input 10 or 26
should drop, transistor Q601 would be rendered conducting and short
capacitor C601 causing immediate discharge thereof. At the
conclusion of such input at 10 or 26 , the operation of the
oscillator including unijunction transistor Q602 would be
restarted.
The normal period of the oscillator is here adjusted to be 10
seconds by means of potentiometer R606, and at the end of
conduction of transistor Q601, a new 10-second interval is started.
Thus, at the conclusion of a defibrillator pulse, or the conclusion
of a period of time during starting, or a period of time when the
electrodes are improperly connected to the patient, a new 10-second
interval will start.
The output of unijunction transistor Q602 is connected via a
Schmitt trigger circuit, comprising transistors Q603, Q604, and
Q605, to an input of nand-gate 68, the output of which provides the
clock pulse on lead 23 . The output of the Schmitt trigger circuit
comprising transistors Q603, Q604, and Q605 is also coupled to a
second Schmitt trigger circuit comprising transistor Q606 and Q607.
The output of the latter trigger circuit is applied to nand-gate 70
and the output of nand-gate 70 is connected to an input of
nand-gate 74 which forms flip-flop 6-D together with nand-gate 72.
The output of nand-gate 74 is connected to one input of nand-gate
72, and vice versa. Another input of nand-gate 72 is derived from
the output of nand-gate 62. As thus appears, flip-flop 6-D will be
set upon the operation of nand-gates 60 and 62, and will then be
reset upon the occurrence of a clock pulse. The signal at 27 from
nand-gate 74 enables the pacemaker at the first clock pulse after
power has been applied for a short period, or after any difficulty
with respect to continuity has been rectified, or after the
occurrence of a defibrillator pulse. Thus, the pacer is disabled
until a proper count can be made.
The output of nand-gate 70 drops at the end of a clock pulse, and
the output of nand-gate 70 is also applied to nand-gate 64 in
conjunction with the output of nand-gate 62. Thus, assuming both
signals 10 and 26 are up, a reset is provided by nand-gate 64 on
lead 21 at the conclusion of a clock pulse. This signal is inverted
by nand-gate 66 to provide the reset signal on lead 22 .
It is noted a clear signal is provided on lead 20 at the same time
that either input 10 or 26 lowers, and the J-K flip-flops in the
counter circuit will be cleared at such time.
PACER
In FIG. 10, nand-gate 70 receives input 24 from the counter,
enabling signal 27 from the clock circuit, and reset signal 19 from
the ECG detector. Input 24 from the counter is the one indicating a
slow heart beat and the desirability of applying pacing pulses.
Enabling signal 27 indicates that the interface is operating
properly and that sufficient time has elapsed for the counter to
make a proper count after application of power or application of a
defibrillator pulse. The output of gate 7-A, which here comprises a
nand-gate, is applied to transistor Q702, and assuming all three of
the aforementioned inputs, 19 , 24 , and 27 are present, the input
to transistor Q702 will be low. Therefore, the pacemaker 7-B is
operable.
Pacer timer 7-B comprises a unijunction transistor Q703 having a
capacitor C703 coupled between its emitter terminal and lower base.
This circuit is a relaxation oscillator similar to that described
in connection with the clock circuit, except in the present
instance the relaxation oscillator suitably has a period of
approximately 0.85 seconds. The output of timer 7-B is applied to
one-shot multivibrator 7-C including transistors Q704 and Q705. The
output at the collector of transistor Q705 is a series of positive
pulses, each pulse having a duration of about 100 milliseconds, and
this output is connected to the input of nand-gate 76. Nand-gate 76
provides signal 11 applied to the ECG detector and ICG detector for
disabling the signal channels when a pacer pulse is being
generated. It should be noted that the duration of the output pulse
at 11 is considerably longer than the duration of the pacing pulse
applied to the patient. This allows time for the amplifier 1-B and
other signal circuits to recover from the overdriven condition
imposed by the pacing pulse.
The output of one-shot multivibrator circuit 7-C is also applied
via transistor Q706 as the input of pulse transformer T701, the
secondary of which is coupled to provide the input of thyristor
Q701. AC voltage from a power supply is normally applied across a
bridge circuit comprising diodes D701, D702, D703 and D704
connected in DC charging relationship to capacitors C701 and C702,
with thyristor Q701 being interposed between the positive end of
capacitor C702 and connection 6 coupled to the patient electrodes.
Thus when transistor Q706 turns on, current flow rapidly increases
through the primary winding of pulse transformer T701, and a
resultant secondary pulse triggers thyristor Q701 into a conducting
state. When thyristor Q701 is turned on, capacitor C702 discharges
through diodes 1-F and through the patient's body. As capacitor
C702 discharges, the current through thyristor Q701 decreases until
the minimum holding current is reached. At this point, thyristor
Q701 turns off, and capacitor C702 begins recharging.
If, during the operation of the pacer, spontaneous hear beats occur
in the patient, the spontaneous beats are detected by the ECG
detector, and a low level pulse 19 is applied to one input of gate
7-A resetting the pacer timer. Another pacing pulse will occur
after 0.85 seconds unless another spontaneous beat takes place.
Thus, the pacer is of the demand type and produces pacing pulses
only in the absence of spontaneous heart beats in the patient.
DEFIBRILLATOR
Referring to FIG. 11, illustrating the defibrillator 8, an input is
received at 25 from counter 5 when significant electrical activity
in the absence of significant mechanical activity has been
detected, indicative of ventricular fibrillation or ventricular
tachycardia. The input pulse operates one-shot multivibrator 8-A
comprising transistors Q802 and Q803, which in turn applies a
lengthened output to gate 8-B, here comprising nand-gates 78, 79
and 80 consecutively connected. The output of nand-gate 78 is
connected to leads 26 and 12 which, respectively, disable and
recycle the clock, and clamp the input signal channels during the
defibrillator pulse. The output of the one-shot multivibrator 8-A
is longer than the duration of the defibrillating pulse applied to
the patient to allow time for amplifier and other circuits to
recover. Signal 9 , comprising a disabling input from the interface
circuit, is also connected to nand-gate 80, and when this signal
drops, indicating improper connection of the patient electrodes or
the start of operation, the defibrillator is disabled.
The output of nand-gate 80 is connected to the base of transistor
Q801 which has the operating coil of relay K801 serially connected
in its collector circuit. The contacts of relay K801 normally
connect capacitor C801 to the output of a bridge circuit comprising
diodes D801, D802, D803 and D804, receiving a high voltage
alternating current input. However, when transistor Q801 conducts,
relay K801 connects capacitor C801, theretofore charged through the
aforementioned bridge circuit, to leads 4 and 5 via inductance
L801. Leads 4 and 5 are coupled through diodes 1-E to the patient
electrodes, as hereinbefore mentioned. Capacitor C801, initially
charged to a high voltage from the power supply, applies this high
voltage across a circuit comprising inductance L801, the switching
diodes 1-E, and the body resistance of the patient. Inductance L801
controls the resulting current. At the conclusion of the
defibrillation pulse, clock 6 is recycled as the output at 26
rises. Thus, the clock circuit begins a new 10-second period, and
signals are allowed to pass through the disabling clamp 2-B so that
monitoring of the electrocardiac signal is resumed.
OPERATION
In general operation, the device is applied to the suspected heart
attack patient as illustrated in FIG. 1, with the patient
electrodes in direct contact with his body. Thus, patient
electrodes 1 and 41 are positioned in good contact with the
patient's chest, and patient electrodes 2 and 3 are positioned in
direct contact with the patient's back. The device is turned on to
operate the apparatus power supplies, and if proper contact is not
made with the patient, indicator 1-D will light, and moreover,
operation of the instrument is prevented. Normally, counter 5 will
cycle under the control of clock 6 for the first 10-second period,
and if a normal condition exists, normal heart indicator 5-J will
light. However, if a cardiac arrest has taken place, or the heart
rate is extremely low, pacer 7 will operate through switching
diodes 1-F, and the patient electrodes, to provide a pacing pulse
to the patient as long as required. Should a normal heart beat
resume without the aid of the pacer, the pacer will be disabled via
input 19 of and-gate 7-A. If, on the other hand, electrical
activity is present, while mechanical activity is absent,
indicating ventricular fibrillation, defibrillator 8 will be
energized to provide a defibrillating pulse to the patient via
switching diodes 1-E. The apparatus will then be recycled to take
another measurement of the heart rate, and appropriate corrective
action will again be taken.
Since the corrective action taken by the resuscitator may be
accomplished as soon as or even before an ambulance team or fist
aid personnel have reached the patient, the chances for survival
are materially increased as compared with the chances for survival
when treatment must await telemetry or transport of a heart patient
to a hospital.
While we have shown and described a preferred embodiment of our
invention, it will be apparent to those skilled in the art that
many changes and modifications may be made without departing from
our invention in its broader aspects. We therefore intend the
appended claims to cover all such changes and modifications as fall
within the true spirit and scope of our invention.
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