U.S. patent number 3,866,615 [Application Number 05/323,972] was granted by the patent office on 1975-02-18 for portable electronic cardiac stimulator.
This patent grant is currently assigned to Claude W. Daigle. Invention is credited to John R. Hewson.
United States Patent |
3,866,615 |
Hewson |
February 18, 1975 |
Portable electronic cardiac stimulator
Abstract
A light weight portable electronic cardiac emergency stimulator
which includes separate defibrillation and pacemaking electronic
circuits and a self-contained battery pack. The defibrillation and
pacing circuits are selectively connectable, through a switch, to a
pair of electrodes of special design which may be introduced
rapidly into the patient's heart by a needle through his chest
wall. The electrodes are self-spreading within the heart to
establish firm electrical contact with opposite sides of its inner
surface. After the electrodes have been introduced to the heart, as
into the left ventricle, the circuits can be selectively connected
to the electrodes through a switch to controllably apply either
defibrillation or pacemaking electric pulses to the heart without
delay.
Inventors: |
Hewson; John R. (Manset,
ME) |
Assignee: |
Daigle; Claude W. (Ellsworth
Falls, ME)
|
Family
ID: |
23261512 |
Appl.
No.: |
05/323,972 |
Filed: |
January 15, 1973 |
Current U.S.
Class: |
607/4; 607/7;
607/34; 607/10; 607/122 |
Current CPC
Class: |
A61N
1/362 (20130101); A61N 1/0587 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 1/05 (20060101); A61N
1/362 (20060101); A61n 001/36 () |
Field of
Search: |
;128/404,418,419C,419D,419E,419P,421,422,423 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
246,004 |
|
Nov 1969 |
|
SU |
|
1,082,752 |
|
Sep 1967 |
|
GB |
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Wolf, Greenfield & Sacks
Claims
Having thus described the invention what I desire to claim and
secure by
1. A portable emergency cardiac stimulator comprising:
defibrillation circuit means for generating a high voltage
electrical pulse for defibrillating a fibrillating ventricle of a
heart when applied directly to the wall of said ventricle;
pacing circuit means for generating repetitive low voltage
electrical pulses at a predetermined rate;
transthoracically insertable bipolar cardiac electrode means for
directly contacting substantially diametrically opposite portions
the ventricle, said electrode means having leads trailing
therefrom, such that when said electrode means are disposed
interiorly of said ventricle the trailing ends of said leads may
extend transthoracically and be disposed exteriorly of the
patient;
switch means, having an input, said switch means further including
a common output lead, for selectively connecting the output of
either of said defibrillation circuit means or said pacing circuit
means to said common output lead;
means for detachably connecting, in electrically conductive
relation, the trailing leads of said electrode means to said common
output lead to enable said electrode leads to be connected to said
common output lead after transthoracic insertion of said electrode
means into said ventricle; and
battery means connected to the input of said switch means for
powering said
2. A device defined in claim 1 further comprising:
said battery means including pair of identical storage batteries
and second switch means for selectively connecting either of said
storage batteries
3. A bipolar cardiac electrode comprising:
a pair of flexible, electrically conductive wires, each of said
wires having a leading end and a trailing end, said leading ends of
said wires extending generally transversely and away from each
other when relaxed to assume a generally T-shaped configuration
whereby when disposed within said cardiac lumen, the most laterally
disposed regions of the leading ends of said wires may contact
substantially diametrically opposite portions of the inner surface
of said cardiac lumen;
said leading ends of said wires being resilient and flexible to
enable said leading ends to be constrained into a substantially
parallel configuration thereby to enable said leading ends to be
retained within and passed through a cardiac needle and to spread
and return toward said T-shaped configuration when said leading
ends pass through the end of said needle into said cardiac
lumen;
insulation means surrounding said wires fully along the length of
said wires;
the outer extremities of the leading ends of said wires being
curved inwardly toward each other, when relaxed, thereby defining
curved convex configurations at the lateral extremities of said
relaxed leading ends so that the lateral extremities of said wires
are defined by regions between the longitudinal extremities of said
leading ends thereof;
means defining a window in said insulation means surrounding each
of said leading ends, each of said windows being disposed at the
curved convex lateral extremity of its associated wire, each of
said windows exposing its associated conductive wire outwardly and
transversely;
means for exposing each of said wires at their trailing ends to
enable said
4. A bipolar cardiac electrode as defined in claim 3 further
comprising:
said windows are defined by generally laterally outwardly facing
openings in said insulation and circumscribing approximately
180.degree. of the
5. An electrode arrangement as defined in claim 4 wherein said
window is
6. A bipolar cardiac electrode as defined in claim 3 further
comprising:
each of said leading ends being of substantially S-shaped
configuration when relaxed, said S-shaped configuration including
said convex curved outer extremity of said leading end in a reverse
curved segment, the reverse curved segments of said leading ends
merging into a common
7. A bipolar cardiac electrode as defined in claim 4 wherein the
leading ends further comprise:
said wire being biologically nonreactive and being of a diameter of
approximately 0.012 inches; and
said insulative sheath being biologically non-reactive and having
an outer diameter of approximately 0.017 inches.
Description
BACKGROUND OF THE INVENTION
Cardiac disorders are believed to be among the major causes of
death. Usually, acute disorders appear with no warning and where
the patient is remote from medical assistance. While in some less
severe cardiac disorders there is sufficient time to transport the
patient to a hospital for treatment, in other more severe types of
cardiac disorders, such as an acute myocardial infarction,
immediate aid is often required. For example, in the United States,
it is estimated that approximately 1,200,000 persons suffer an
acute myocardial infarction each year. Of these, 200,000 people die
within 15 minutes of the onset of their myocardial infarction, and
another 50,000 die in the time interval between 15 minutes and 2
hours of the onset of their myocardial infarction. The death of a
great proportion of the people in the latter group of 50,000 could
largely be prevented by administering suitable medical aid quickly
and without a delay. As to those persons who die of acute
myocardial infarction within fifteen minutes of its onset, a great
proportion could likewise be saved if proper medical attention
could be employed immediately. Treatment of such acute cardiac
disorders typically requires apparatus which is bulky and does not
lend itself to portability. Thus, it has been necessary to
transport the patient to a hopsital or other facility where such
apparatus is available. The time interval ordinarily is too great
and the patient dies.
In the great proportion (95 percent) of acute cardiac deaths, the
patient is suffering from ventricular fibrillation. The remaining
patients are in asystole, in which all heart activity has stopped.
In each of these instances, there is no detectable arterial
pulsation. As a result, the patient can deteriorate rapidly. For
example, permanent brain damage can begin to occur approximately
three minutes after pulsation stops.
Where the patient is suffering from ventricular fibrillation, it is
essential first that the fibrillation be stopped before the heart
can resume more regular activity. The usual emergency procedure for
treating a pulseless patient is to check his air passages and
perhaps attempt mouth-to-mouth resuscitation. If that fails to
restart the heart, a sharp blow is applied to the chest generally
in the region of the heart. That failing, closed chest cardiac
message is initiated primarily in order to maintain a semblance of
blood circulation in an attempt to avoid or minimize brain damage.
These techniques are rarely effective to defibrillate a
fibrillating heart and do not generally restart the heart. They are
employed primarily as supportive therapy until the patient can be
brought to a hospital or facility where fibrillation or asystole
can be more effectively treated. When the patient has reached the
hospital the vigorous closed chest massage is continued until the
electric defibrillation apparatus has been readied. Such apparatus
generates a substantial electrical pulse which is applied to the
patient by means of a pair of paddle-like electrodes which are
applied to the patient's chest. In general, it has been found that
the most effective way to defibrillate is by applying such an
electric pulse to the patient. The urgency of immediate
defibrillation cannot be overstated. When the patient has no
apparent pulse, closed chest massage is at best a poor substitute
for a normally beating heart. Thus, even with vigorous closed chest
massage the patient's brain and heart deteriorate quickly. Lactic
acid builds up due to poor oxygenation of tissue which is the
direct result of poor cardiac output. Thus, even when the patient
reaches the hospital where he can be defibrillated electrically,
the degree of deterioration which he may have suffered often is
such that the defibrillation apparatus is ineffective and the
patient dies. Because of the relatively nonportable bulky nature of
defibrillation apparatus, many people have died within the time
interval necessary to transport the patient to the hospital.
In addition to the foregoing difficulties, even if a patient has
been defibrillated, he may still remain pulseless, in asystole.
Among the most effective treatments for this condition is the
application of electrical pulses of a smaller magnitude to the
heart at a rate approximating that of a normal heart beat.
Application of such pacing pulses is of considerable assistance in
restarting an asystolic heart and maintaining regular operation of
that heart. However, even in a hospital environment this takes some
time which may add further to the interval so critical to the
patient. This is true even though the electrodes for the heart
pacing arrangement are applied through a transthoracic catheter of
the type shown in the Ackerman patent or through a major vein into
the heart. These procedures take time in addition to the time
already elapsed. Although closed chest massage is maintained
throughout these intervals the patient deteriorates further.
Moreover, it may be noted that ventricular fibrillation is
recurrent and can begin again even after the heart has been
defibrillated but before the pacing electrodes have properly placed
in operation. In such instance, the procedure may have to be
restarted with the attendant loss in time. It is among the primary
objects of my invention to provide a device and technique which
minimizes greatly any interval between the time at which medical or
paramedical personnel reach the patient and the time in which
proper electrical stimulation of his heart is provided.
SUMMARY OF THE INVENTION
My invention includes independent defibrillation and pacing
circuits which are assembled in a compact portable housing. The
housing also contains a battery power pack and a switching
arrangement to enable either of the circuits to be connected to the
power pack. The output from the device is connectable to an
arrangement of electrodes which are adapted to be introduced
directly into the heart by a transthoracic needle. The electrodes
are arranged to make good electrical contact with the inner surface
of the heart, such as within the left ventricle. After the
electrodes are disposed properly within the heart, the
defibrillation or pacing pulse can be applied immediately. Further
aspect of the invention relates to the bipolar configuration of the
electrodes. The electrodes are highly flexible and normally tend to
assume a spread apart configuration. When introduced into the heart
they spread apart and against opposite sides of the inner surface
of the left ventricle. The portions of the electrodes which contact
the wall of the ventricle are of a broad and curved configuration.
The electrodes are arranged so that there is little tendency for
the electrical pulse to short circuit through the blood in the
heart. This ensures that the electrical pulse will be applied
directly to the myocardium. Because of the direct contact of the
electrodes with the heart, there is significantly less impedance to
the electrical pulse than that which is presented by the usual
bulky defibrillation apparatus in which the pulse is applied to the
exterior of the chest. As a result, there is a substantially
smaller power requirement necessary which facilitates the
portability of the device so that it may be carried easily to the
patient thus saving time. Additionally, the electrode configuration
is highly flexible and presents substantially no resistance to
contraction of the heart.
It is among the objects of my invention to provide a portable
cardiac stimulator capable of immediately applying defibrillation
pulses to a cardiac victim.
Another object of the invention is to provide a portable
defibrillation device which can selectively be employed to apply
pacing pulses to the patient.
A further object of the invention is to provide a portable
apparatus which avoids the critical lag in time incurred in the
usual emergency treatment of such heart disorders.
Another object of the invention is to provide a portable cardiac
stimulator which is capable of immediately and selectively applying
either of a defibrillation pulse or a repetitive series of pacing
pulses.
Further object of the invention is to provide an improved electrode
arrangement employing a pair of poles which are self-spreading into
contact with the opposite sides of the patient's ventricle.
Still another object of the invention is to provide an improved
electrode arrangement in which each of the poles of the electrode
contact the inner surface of the ventricle along a substantial area
and not just point contact.
A further object of the invention is to provide an electrode
configuration which presents substantially no resistance or damage
to the heart in the event of contraction of the heart.
DESCRIPTION OF THE DRAWINGS
The foregoing and other objects and advantages of the invention
will be understood more fully from the following detailed
description thereof, with reference to the accompanying drawings
wherein:
FIG. 1 is a diagrammatic cross section through a patient's thorax
at the level of the fifth intercostal space, showing the invention
with the self-spreading bipolar electrode inserted into the left
ventricle of the heart;
FIG. 2 is an illustration of the electrode arrangement when in its
spread configuration and having portions thereof broken away to
illustrate its internal configuration;
FIG. 3A-3F are cross sections of the lead to the bipolar electrode
and the bipolar electrodes themselves showing the internal
arrangement of the electrode leads along successive portions of the
electrode and as seen along the lines 3A--3A, 3B--3B, 3C--3C,
3D--3D, 3E--3E and 3F--3F of FIG. 2;
FIG. 4 is a longitudinal sectional illustration of the
transthoracic needle by which the bipolar electrode may be inserted
into the patient's left ventricle and showing the configuration of
it in the manner in which the bipolar electrode is disposed within
the needle in readiness to be inserted into the patient;
FIG. 5 is an enlarged illustration of the arrangement by which the
electrode may be connected to the circuitry of the device;
FIG. 6 is a diagrammatic illustration of the circuitry of the
invention; and
FIG. 7 is an illustration of the face of the control panel and
housing for the circuitry.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the invention in readiness to apply electric
stimulating pulses to the patient. It includes the bipolar
electrode 10 which has been inserted, in the manner described
herein, through the patient's chest wall 12 at the level of the
fifth intercostal space, to the left of the sternum 14. When
properly located, the bipolar electrode 10 is disposed within the
left ventricular lumen 16 of the heart. The electrode leads are
connected by a connector 18 to the output leads 20 from a compact
integral and controllable pulse generator 22. As described more
fully below, the pulse generator includes independent circuits
adapted to generate a defibrillating pulse and pacemaking pulses
which can be selectively applied to the bipolar electrodes 10.
The bipolar electrode 10 is formed from a pair of thin flexible
electrically conductive wires 24 made from a metal which is
biologically non-reactive such as No. 316 extra low carbon
stainless steel wire. In the illustrative embodiment, the wires
approximate 0.012 inches in diameter. A pair of such wires is
embedded in a flexible insulative sheath which, in the preferred
embodiment, has an external diameter of approximately 0.034 inches.
The sheath should be made from an appropriate material which is
similarly biologically non-reactive such as silastic.
The parallel insulated wires 24 and surrounding sheath 26 are
bifurcated at the end of thee electrode to define a generally
T-shaped configuration in which the ends of the wires 24 extend
generally in opposite directions. The sheath 26 continues
integrally along the separated electrode portions of the wires 24
to define electrode sheaths 28 which insulate the bifurcated
electrodes 30. The insulative sheaths 28 extend fully to and about
the tips of the electrodes 30 except for cutout segments 32 through
which the inner electrodes 30 are exposed.
The bifurcated electrodes 30 are fabricated so that they tend to
assume the spread configuration shown in FIG. 2 which is somewhat
S-shaped. The outer ends of the sheathed electrodes 30 are curved
with their tips tending to extend inwardly. The arrangement is such
that the lateral regions of the electrodes define a substantial
convex configuration. It may be noted that the outer diameter of
the electrode sheaths 28 is approximately 0.017 inches. At the
outwardly facing side of each of the outer arcuate segments 36, the
electrode sheaths 28 are cut away at 32 to define outwardly exposed
semicircular sections of the electrodes 30. The cutout segments 32
preferably are approximately 3/16 of an inch long and begin
approximately 3/16 of an inch from the tip 34 of each electrode 30.
The cutout segments 32 expose the electrode only laterally
outwardly and over approximately 180.degree. of the cross sectional
circumference of the electrode. The portions of the electrodes 30
which are so exposed serve as the conductive terminal ends of the
electrode and are intended to bear against and establish electrical
communication with the opposite inner surfaces of the ventricle
wall. The electrode configuration shown in FIG. 2 is that in its
completely relaxed condition. The bifurcated end of the electrode
is dimensioned so as to be somewhat greater than the inner diameter
of the ventricle. When the electrode arrangement is disposed within
the ventricle and expands against diametrically opposite sides of
the inner surface of the ventricle, the lateral arcuate segments 36
and, particularly the exposed surfaces of the electrodes 30 will
bear against the ventricle wall snugly to establish firm electrical
connection. When properly disposed within the ventricle, the
electrodes assume a more T-shaped configuration than that shown in
FIG. 2 with the reversely curved segments 38 of the electrodes
being somewhat less curved than shown in FIG. 2. This is suggested
somewhat in FIG. 1. While the dimensions of the electrode wire are
such to enable it to be biased with sufficient firmness against the
ventricle wall, it is sufficiently light as to present
substantially no resistance to contraction or flexure of the
myocardium. The foregoing arrangement ensures that electrical
contact will be maintained with the ventricle during contraction or
other movement of the heart.
The foregoing electrode arrangement provides a number of
advantages. The exposed portions of the electrodes define a
relatively substantial area of electrical contact thus tending to
reduce the magnitude of impedance presented. It also reduces
significantly the possibility of short circuiting through the
relatively conductive blood within the left ventricle. The
electrodes 30 are exposed only laterally and are biased firmly
against the slightly into the ventricle wall which tends to
cooperate with the insulative sheathing to isolate the electrode
from the blood within the ventricle. This enhances the likelihood
of the electrical pulse being applied to the ventricle wall and not
being short circuited through the blood. In addition, the
engagement of the electrodes with diametrically opposite portions
of the ventricle further reduces the possibility of
short-circuiting by maximizing the distance between the exposed
portions of the electrodes. Still another significant advantage of
the electrode configuration is that by applying the electrodes at
opposite internal surfaces of the ventricle it is more effectively
ensured that a substantial portion, if not all of the ventricle
wall will be subjected to the electrical pulse. The arrangement of
the insulated tips 34 by which they extend inwardly toward each
other and away from the ventricle wall affords a further safety
feature by eliminating the possiblity of accidental puncture of the
ventricle wall. In this regard it may be noted that when the
electrodes are properly disposed within the ventricle, the tips 34
extend inwardly toward each other even to a greater extent than
that shown in FIG. 2.
FIGS. 3A-3F show the cross section of the electrode leads at
various locations along their length and the manner in which the
leads may be connected to the pulse generator 22. The wires 24
extend within the sheath and are connected to a pair of conductive
sleeves 40 which are spaced along the distal end of the leads and
are exposed about the circumference of the sheath 26. The wires 24
are connected by appropriate means to the sleeves 40 as shown in
FIGS. 3B and 3D.
The sleeved end of the sheath 26 is connected to the pulse
generator 22 by a connector 18 in the manner described below.
The electrode is introduced transthoracically into the left
ventricle of the heart before its trailing end is electrically
connected to the pulse generator and by means of an arrangement
shown in FIG. 4. This arrangement includes a plastic tube 42 having
an internal diameter of approximately 0.040 inches which encloses
the bipolar electrodes as shown. The electrodes are sufficiently
resilient as to be able to be slipped into the tube 42 with its
normally S-shaped bifurcations being constrained in the
substantially straight configuration shown. The outer diameter of
the tube 42 is dimensioned to fit within the hub 44 of a 17 gage
cardiac needle indicated generally at 46. The electrodes are
introduced by inserting the cardiac needle 46 into the ventricle
then removing the obturator (not shown) normally within the needle
and thereafter inserting the plastic tube 42 into the hub 44 of the
cardiac needle 46. The needle 46 and tube 42 are approximately each
five inches long. The electrode then is advanced along the tube
into and through the needle until the trailing end of the electrode
sheath is flush with the end of the plastic sleeve. The length of
the electrodes and sheath are related to the combined length of the
cardiac needle 46 and tube 42 so that when the trailing end of the
sheath is flush with the end of the tube 42 the electrode end of
the sheath will have extended approximately 1 3/4 inches past the
inner end of the cardiac needle 46 and will have spread into its
generally T-shaped configuration. The needle and tube then may be
withdrawn with the electrode properly disposed within the left
ventricle and with its leads extending outwardly from the
patient.
The outwardly disposed lead of the electrode is connected to the
output leads 20 from the pulse generator 22 by means of an
appropriate connector such as that shown in FIG. 5. The illustrated
connector is formed integrally with the end of the output leads 20
and has an enlarged cylindrical portion 48 formed from insulative
material integral with the insulative material surrounding the
output leads 20. The cylindrical portion 48 has a center bore
formed therethrough approximately 0.040 inches in diameter. The
bore 50 is defined in part, at spaced locations along its length,
by conductive sleeves 52. Sleeves 52 are electrically connected to
the conductive leads 20 and are spaced identically to the sleeves
40 disposed at the trailing end of the electrode leads. The
trailing end of the electrode leads may be inserted into the bore
50 to align the sleeves 52 with the sleeves 40 and can be secured
therein by a number of arrangements such as the screws 54. The set
screws 54 are of non-conductive material. Transthoracic insertion
of the electrode arrangement into the ventricle and subsequent
connection of the trailing end of the electrode arrangement to the
pulse generator can be accomplished quickly and simply and requires
no moving of the patient to a hospital or the like. After the
electrodes have been connected, the pulse generator may be operated
immediately either to apply a defibrillating pulse or a pacing
pulse to the patient.
The circuitry shown in FIG. 6 generally includes switch 60,
defibrillator circuit 62, pacemaker circuit 64, and energy supply
means. The source of electrical energy comprises battery banks 66
and 68 which are mutually exclusively connectable by switch 60 to
mode switch 70. Each of the battery banks includes a pair of
commercially available 8.4 volt mercury batteries connected in
series. When the unit is to be operated the switch 60 is thrown to
select either bank 66 or 68. The unused battery bank remains
readily available as a spare power source.
A battery failure indicator 72 couples to the common contact of
switch 60 and indicates when the battery output falls to 85 percent
of the full battery power, thus indicating the need to switch to
the spare set of batteries by throwing switch 60 to its alternate
position.
The mode switch 70 is a four position/double throw switch having a
set of common contacts 70C and two sets of fixed contacts 70A and
70B. With switch 60 connected to either of the battery banks 66,
68, switch 70 can either be in its neutral position with its
movable contacts 70C open, or it can be moved to either the "defib"
position where the movable contacts 70C couple to the fixed
contacts 70A, or the "pace" position where the movable contacts 70C
connect to the fixed contacts 70B. When switch 70 is in the defib
position energy is coupled to the defibrillator circuit 62 and an
output signal is developed across output lines 74 and 76. In FIG. 6
the switch 70 is shown in the defib position. Alternatively, the
switch can be moved to the pace position wherein energy is coupled
to the pacemaker circuit 64 which develops its output across lines
74, 76.
When switch 70 is in the defib position power is coupled to trigger
button 78 which is a typical normally open momentary contact
switch. When trigger button is depressed the high voltage
defibrillatory shock pulse is generated and applied to the bipolar
electrode thru lines 74, 76. The defibrillation circuit 62
illustrated may be considered as being of conventional design and
generally comprises a DC to DC converter 80, transistor 82, neon
tube 84, capacitor 86, SCR 88, and a series of resistors
appropriately interconnected. The circuit 62 is substantially
identical to the pulse circuit shown in U.S. Pat. No. 3,614,955 and
operates as follows: When button 78 is depressed a relatively high
voltage signal, approximately 2,500 volts, is established at the
output of DC to DC converter 80. This voltage is developed across
capacitor 86. The resistor chain and the tube 84 are interconnected
in such a manner that when the voltage across capacitor 86 reaches
a full 2,500 volts, the tube 84 conducts. When the capacitor 86 is
fully charged, the transistor 82 becomes conductive, due to the
now-conducting neon tube 84. When the tube conducts there is a
sufficient conduction path by way of resistors 90, 92 and 94 to
cause conduction of transistor 82. Concurrently therewith, a drive
current is provided to the gate of SCR 88 and the SCR also
conducts, applying the voltage from the capacitor 86 across the
output lines 74, 76. The output of circuit 62 has a preferable
pulse width of approximately 100 milliseconds as determined by the
time constant of the network. The energy output is of the order of
15 joules at a current of approximately 25ma. This is significantly
less than the energy requirements for previous defibrillation
devices. The neon tube 84 serves the double function of being an
integral part of the trigger circuit and, because it also lights up
for an instant during voltage buildup in the converter 80 it also
indicates that the circuit is in operation.
The device may be controlled to immediately apply lower voltage
"pacing" pulses by operation of the switch 70 to the position in
which the movable contacts 70C are connected to the fixed contacts
70B. The power from one of the battery banks 66 or 68 is coupled to
the circuit 64 and the cyclic output of that circuit is coupled to
the output lines 74, 76. A typical output from circuit 64 is a
signal 0 to 30 milliamp, of 2.8 millisecond duration at a
repetition rate of 70 pulses per minute.
The pacing circuit 64 comprises a conventional astable
multivibrator including transistors 96 and 98, a pulse width
regulator including transistors 100, 102, a voltage regulator
including transistor 104 and a current source including transistor
106. The astable multivibrator is of conventional design and
includes cross-coupling capacitors 108, 110 and collector resistors
112, 114. A potentiometer 116 is coupled to the base of transistor
96 for varying the frequency of operation of the astable
multivibrator.
The output of the multivibrator couples by way of resistor 118 to
transistor 100. The collector of transistor 100 couples through
resistor 120 to the power source and also by way of capacitor 122
to resistor 124 and to the base of transistor 102. When transistor
100 is not conducting capacitor 122 is discharging and transistor
102 is non-conductive. When transistor 100 conducts because of a
change of state of the astable multivibrator, capacitor 122 is
charged by way of resistor 124 and after a predetermined time
period transistor 102 conducts. Transistor 102 conducts in one
embodiment for approximately 2.8 milliseconds before transistor 100
can change its state causing transistor 102 to stop conducting.
During the brief time that transistor 100 conducts Zener diode 126
is shorted out and transistor 104 becomes conductive via Zener
diode 128 to transistor 106. When this occurs, transistor 106 also
conducts and a constant current is fed by way of switch 70 to
output leads 74, 76. The potentiometer 130 is used to control the
output current which may be varied from 0 to 30 milliamps. A pulse
indicator 132 may be coupled from the collector of transistor 106
to the emitter of transistor 104 for verifying that the pacemaker
circuit is functioning properly. The indicator 132 may also be
coupled, in an alternate embodiment, directly to the astable
multivibrator.
FIG. 7 shows the control panel with mode switch 70 which may be in
any of its off, defib or pace positions. When the switch 70 is in
its defib position, depression of the trigger button 78 causes
almost instantaneous charging and discharging of the defibrillator
circuit 62 and an attendant flashing of neon bulb 84 associated
therewith. This indicates that the high voltage pulse has been
coupled to the output leads 74 and 76. When the switch 70 is in the
pace position, indicator 132 reveals a pulse rate of 70 beats per
minute, for example. The milliamperage rating from the output of
the pace circuit is adjusted by dial 134 shown in FIG. 7 which is
coupled to the potentiometer 130.
Thus, I have described my invention which enables controlled
electrical pulses to be selectively applied to a cardiac patient
both as an emergency first aid measure as well as in a hospital
environment. It should be understood, however, that the foregoing
description of the invention is intended merely to be illustrative
thereof, and that other modifications and embodiments may be
apparent to those skilled in the art without departing from the
spirit.
* * * * *