U.S. patent number 3,858,576 [Application Number 05/362,973] was granted by the patent office on 1975-01-07 for portable electrocardioscope.
This patent grant is currently assigned to Hugo Sachs Elektronik Kommanditgesellschaft. Invention is credited to Heinz Dehnert, Hermann Steiert.
United States Patent |
3,858,576 |
Dehnert , et al. |
January 7, 1975 |
PORTABLE ELECTROCARDIOSCOPE
Abstract
A portable electrocardioscope is provided taking the form of a
housing having a plurality of terminals at one end for direct
engagement with the chest of a patient, a cathode ray tube display
at its other end, and a battery-operated circuit within the housing
for converting signals appearing on the terminals into a visual
display on the cathode ray tube.
Inventors: |
Dehnert; Heinz (Freiburg,
DT), Steiert; Hermann (Buchheim, DT) |
Assignee: |
Hugo Sachs Elektronik
Kommanditgesellschaft (Am Bahnhof, Hugstetten,
DT)
|
Family
ID: |
23428271 |
Appl.
No.: |
05/362,973 |
Filed: |
May 23, 1973 |
Current U.S.
Class: |
600/525; 315/410;
327/330 |
Current CPC
Class: |
A61B
5/339 (20210101); A61B 5/336 (20210101); A61B
5/332 (20210101) |
Current International
Class: |
A61B
5/0436 (20060101); A61B 5/044 (20060101); A61B
5/0404 (20060101); A61B 5/0432 (20060101); A61B
5/0402 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2.6B,2.6G,2.6R
;315/29 ;328/171 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
250,557 |
|
Nov 1966 |
|
OE |
|
1,202,427 |
|
Jul 1959 |
|
FR |
|
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Pollock; Elliott I.
Claims
Having thus described our invention we claim:
1. An electrocardioscope comprising a plurality of input terminals
adapted to receive cardiac signals representing the cardiac action
of a patient, display means, and a control circuit disposed between
said terminals and said display means for processing said cardiac
signals to produce output signals which are coupled to said display
means to produce a visual representation of said cardiac action,
said control circuit comprising means connected across a pair of
said terminals and responsive to said received cardiac signals for
producing an input signal, a first pair of diodes connected in
series with one another across said pair of terminals, a second
pair of diodes connected in series with one another and in parallel
with said first pair of diodes, said first pair of diodes being
poled oppositely to said second pair of diodes, means coupling said
input signal across said parallel-connected pairs of diodes, a
differential amplifier comprising first and second interconnected
transistors, capacitor means coupling the opposing ends of said
parallel-connected diode pairs to said first and second transistors
respectively, means connecting the mid-junction of said first pair
of diodes to the mid-junction of said second pair of diodes,
further capacitor means coupling the interconnected mid-junctions
of said pairs of diodes to said first and second transistors
respectively, means defining a point of reference potential, a pair
of oppositely poled zener diodes connected in series with one
another between the interconnected mid-junctions of said diode
pairs and said point of reference potential, and output means
coupling the output of said differential amplifier to said display
means.
2. The combination of claim 1 including a dc battery connected to
said differential amplifier to energize said amplifier.
3. The combination of claim 1 wherein said control circuit is
mounted on a chassis, said point of reference potential comprising
said chassis, said input terminals including a terminal connected
to said chassis.
4. The combination of claim 1 wherein said display means comprises
a cathode ray tube having means for deflecting the beam of said
tube in X and Y directions, said output means including a
Y-amplifier coupled to the output of said differential amplifier,
the output of said Y-amplifier being connected to said Y-deflecting
means for controlling the Y-deflection of said cathode ray tube,
and means for generating a sweep signal for controlling the
X-deflecting means of said cathode ray tube.
5. The combination of claim 4 including means for recording
signals, and terminal means connected to the input of said
Y-amplifier for coupling signals to and from said recording
means.
6. The combination of claim 4 wherein said means for generating
said sweep signal includes a storage capacitor, a dc current source
for charging said storage capacitor, a discharge circuit connected
across said capacitor for selectively discharging said storage
capacitor, said discharge circuit including means connecting said
capacitor to a normally nonconductive programmable unijunction
transistor for rendering said transistor conductive when the charge
potential across said storage capacitor reaches a predetermined
level, third and fourth transistors connected in series with one
another to render the conductivity of said third transistor
dependent upon the conductivity of said fourth transistor, means
coupling the output of said Y-deflection amplifier to said third
transistor, means responsive to the X-deflection of the cathode ray
tube beam for controlling the conductivity of said fourth
transistor, and means coupling a signal from said third transistor
to said programmable unijunction transistor for rendering said
programmable unijunction transistor conductive to discharge said
storage capacitor in response to conduction of said third
transistor due to the occurrence of a signal in excess of a
predetermined minimum amplitude at the output of said Y-deflection
amplifier concurrent with conduction of said fourth transistor due
to deflection of the beam in an X-direction beyond a predetermined
position on the screen of said cathode ray tube.
7. The combination of claim 4 wherein said electrocardioscope
includes an elongated, portable housing containing said control
circuit and also containing a battery supply for said control
circuit, said housing having said terminals mounted on one end
thereof for direct engagement with the chest of a patient to
provide said cardiac signals, said cathode ray tube being mounted
in said housing with its screen exposed to view through the other
end of said housing.
8. The combination of claim 7 including pressure sensitive switch
means mounted on said housing for automatically controlling the
energization of said circuit from said battery supply.
9. The combination of claim 8 wherein said switch means is mounted
adjacent said terminals, said switch means being operative to
effect energization of said circuit only when said switch means and
electrodes are in engagement with the chest of a patient.
10. The combination of claim 7 including recording means, a
microphone, and a terminal on said housing connected to said
microphone for coupling audio signals to and from said recording
means.
11. The combination of claim 1 wherein said means for producing
said input signal comprises a frequency filter connected between
said pair of terminals and said parallel-connected pairs of diodes.
Description
BACKGROUND OF THE INVENTION
The present invention relates to electrocardioscopes and, more
particularly, to a light weight, portable, battery-operated
electrocardioscope adapted for use in a variety of circumstances
where conventional electrocardioscopes cannot be conveniently
employed.
In various emergency conditions, if the cardiac action of a patient
is disturbed, the brain may suffer permanent damage within a few
minutes. In such cases, it is essential to establish whether the
patient is suffering from weak heart action, chamber fibrillation,
or asystolia; and in the case of accident victims, or other
emergency cardiac situations, this determination frequently cannot
be deferred until the patient is brought to a hospital for
treatment. In such cases, therefore, it may become necessary to
administer appropriate treatment to the patient before he can be
transported, so as to sufficiently stabilize his circulation for
such transport. The type of emergency treatment which should be
given will normally depend upon analysis of an appropriate
electrocardiogram, but conventional electrocardiographs and
electrocardioscopes suggested heretofore do not lend themselves to
this type of usage since, in general, they constitute comparatively
large, heavy, and delicate pieces of equipment which are energized
from conventional AC power outlets.
In order to obtain an electrocardiogram quickly, and under
conditions where a conventional AC outlet is unavailable, it is
therefore highly desirable that an electrocardioscope be provided
which is portable, light weight, and contains its own power source.
It is the primary object of the present invention to provide such a
portable electrocardioscope, which requires a minimal amount of
operating energy.
Another object of the invention resides in the provision of an
electrocardioscope which is shielded against interference voltages
which may be present in the vicinity of the electrocardioscope,
e.g., caused by other medical treatment devices such as
defibrillators.
A further object of the invention resides in the provision of an
electrocardioscope which may be associated with a recorder device
operative to register changes in the patient's electrocardiogram
during emergency treatment, so as to facilitate subsequent analysis
of the treatment procedure.
SUMMARY OF THE INVENTION
In accordance with the present invention, a light weight, portable,
battery-operated electrocardioscope is provided which can be
employed at the site of an accident, or in an ambulance, or in the
emergency room, operating room, or intensive care unit of a
hospital, or in other more conventional circumstances, e.g., where
it is desired to examine a patient in his hospital room, or at home
or in a doctor's office.
The electrocardioscope is comparatively light weight, e.g.,
approximately 4.5 pounds, and is comparatively small in dimension,
e.g., substantially 5 inches wide, 3 inches high, and 11 inches
long, and comprises a housing containing a unitary terminal tripod
at one end thereof for engagement with the chest of the patient, a
display taking the form of an 8 cm. cathode ray tube and associated
scale at its other end, and a battery operated circuit within the
housing which is responsive to signals on said terminals for
producing an electrocardioscope display on the screen of the
cathode ray tube. The circuit within the housing is comparatively
simple and rugged in configuration, operates with a minimum
consumption of time and energy, and includes a synchronizing
circuit which operates to produce a standing electrocardioscope
image on the screen.
The apparatus is also preferably so arranged that it is rendered
operative only when an electrocardioscope is actually being taken,
thereby to keep the energy consumption in the device at a minimum.
The device may, for example, include a switch mounted on the
housing adjacent the terminal tripod, operative to energize the
circuit only when the switch and terminals engage the chest of a
patient. Alternatively, the device may be associated with a bracket
in which the electrocardioscope is mounted when not in use, and the
side of the electrocardioscope housing may include a switch which
cooperates with the bracket to de-energize the circuit when the
device is within the bracket, and which automatically energizes the
circuit when the device is removed from its bracket.
In operation, the electrocardioscope, which may be easily held in
one hand of an operator, is placed with its terminal end directly
in engagement with the patient's chest; and an electrocardiogram
thereupon appears on the screen of the cathode ray tube at the
other end of the device for visual examination. Additional
terminals are provided for supplying signals from the
electrocardioscope to a separate piece of equipment, e.g., a
cassette-type magnetic recorder and/or for supplying signals from a
microphone to such a recorder, to provide a permanent record of the
patient's cardiac condition and the treatment being administered,
for later review.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing objects, advantages, construction and operation of
the present invention will become more readily apparent from the
subsequent description and accompanying drawings wherein:
FIG. 1 is a schematic block diagram of the logic circuit employed
in the electrocardioscope of the present invention;
FIG. 2 is a schematic of the input circuit of FIG. 1;
FIG. 3 is a schematic of the sweep and synchronization circuit of
FIG. 1; and
FIG. 4 is a perspective view of an electrocardioscope constructed
in accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The general nature and construction of the electrocardioscope, in
respect to the housing and terminal configuration which is
employed, has been described above; and this earlier description is
incorporated herein by reference. More particularly, the housing H
employed (see FIG. 4) includes a set of fixed electrodes R, S, T at
one end thereof adapted to engage the chest (thorax) of a patient
or accident victim, a cathode ray tube display 4 at its other end,
and an intervening circuit for processing the electrode signals to
provide a meaningful electrocardioscope display. These aspects of
the invention are diagrammatically illustrated in FIG. 1.
The terminals (or electrodes) which are intended for engagement
with the chest of the patient are designated R, S, and T, and these
three terminals are disposed in a tripod or triangular
configuration relative to one another. Terminal S is connected to
the chassis 10 of the equipment, and terminals R and T are
connected as inputs to an input circuit 1, the specific
configuration of which will be more fully described hereinafter in
reference to FIG. 2. Input circuit 1 operates to impose amplitude
limitations on signals passing therethrough, along with phase
suppression of certain such signals, and also provides for
preamplification of proper signals, as will be discussed
hereinafter.
The signal appearing at the output of circuit 1 is coupled via a
switch 6 and a potentiometer 2 to the input of an amplifier 3.
Amplifier 3 controls the Y-deflection of cathode ray tube (CRT) 4;
and potentiometer 2 may be adjusted to vary the height of the
resultant image on the screen of CRT4. The signal at the output of
Y-amplifier 3 is also coupled to a sweep and synchronization
circuit 5 (to be described in further detail hereinafter in
reference to FIG. 3) the output of which is coupled via X-amplifier
8 to the X-deflection plates of tube 4. By reason of this
arrangement, therefore, when signals appear at the output of
amplifier 3, the X-deflection of the CRT-4 will be synchronized
with the signals applied to the Y-plates of said tube 4, to create
a stationary image representing the cardiac activity of the patient
being monitored.
In order to assure that the circuit is properly operative, and to
permit appropriate set-up and calibration of the equipment if
necessary, a reference signal may be provided at the output of a
square wave generator 11, and this reference signal may be applied
to potentiometer 2 and amplifier 3 in place of the signal appearing
at the output of input circuit 1, by manipulating the
aforementioned switch.
A major problem which is often encountered in connection with the
operation of electrocardioscopes involves possible distortion of
the heart-generated signals being monitored as a result of the
presence of interference signals generated by other sources. Such
interference signals may even be generated by other electronic
devices which are simultaneously being employed to treat the
patient. For example it is common to use defibrillators, if the
patient's condition requires such use, to supply rhythmic
high-power electric pulses operative to stabilize the patient's
heart action; and such pulses could, in the absence of other
considerations, create voltage surges in the input circuit 1 of
sufficient magnitude to actually destroy the preamplifier 13 (FIG.
2) in that circuit. This could be avoided, of course, by
interrupting the diagnostic monitoring of the patient's cardiac
activity when the patient is being treated with a defibrillator or
similar device; but in order to avoid the need for such
interruption, the input circuit 1 is provided with means for
achieving amplitude limitation and phase suppression.
More particularly, referring to FIG. 2, it will be seen that the
signal arriving at terminals R and T first pass through a frequency
filter consisting of resistors R.sub.1, R.sub.2, and R.sub.3, and a
capacitor C.sub.1. The signal at the output of the aforementioned
filter then passes through an amplitude limiter and phase
suppression circuit consisting of diodes D.sub.1, D.sub.2, D.sub.3
and D.sub.4 associated with Zener diodes Z.sub.1 and Z.sub.2. The
signals appearing at the points P and Q in FIG. 2 are then supplied
to the inputs of a differential amplifier consisting of two field
effect transistors T.sub.1 and T.sub.2, resistors R.sub.4, R.sub.5
and R.sub.6, R.sub.7, and a DC power source 7 (i.e., a 15 volt
battery disposed within the electrocardioscope housing). The output
from the said differential amplifier is connected to a preamplifier
13 the output of which is coupled, as described in reference to
FIG. 1, via switch 6 and potentiometer 2 to the input of
Y-amplifier 3.
Diodes D.sub.1 and D.sub.3 are disposed in series with one another
across the input signal, i.e., across the output from the
aforementioned filter. Similarly, diodes D.sub.2 and D.sub.4 are
connected in series with one another, but in opposite polarity to
the D.sub.1 -D.sub.3 circuit, across the same signal source. The
mid-points of these two series-connected diode arrangements are
interconnected to one another at the points designated M, M', and
this interconnected mid-point is coupled via capacitor C.sub.2 to
the source electrodes of the two transistors T.sub.1, T.sub.2.
By reason of this arrangement, it becomes impossible for the
voltage between the points P and Q to exceed the sum of the
threshold voltages of diodes D.sub.1 and D.sub.3, or of diodes
D.sub.2 and D.sub.4, respectively. Accordingly, it is impossible
for the voltage between the points P and M, or between the points Q
and M, respectively (in other words, the voltage between the source
and gate electrodes of the transistors T.sub.1 and T.sub.2) to
exceed the threshold voltage of one of the diodes D.sub.1, D.sub.2,
D.sub.3 and D.sub.4. The differential amplifier is thus effectively
protected against excessive input voltage signals.
There is, of course, the possibility that both of the terminals R
and T may be at a high potential relative to the potential of the
chassis, i.e., the potential on terminal S. This condition could
similarly lead to destruction of transistor T.sub.1 and/or T.sub.2.
In order to prevent this from occurring, the common mid-point M, M'
described previously is connected to the chassis via the two Zener
diodes Z.sub.1 and Z.sub.2. This arrangement accordingly limits the
maximum voltage on terminals R and T, when said voltages are in
phase relative to the chassis, to the equivalent of the sum of the
Zener voltage of diode Z.sub.1 or Z.sub.2, and the threshold
voltage of one of the diodes D.sub.1 -D.sub.4. The overall circuit
thus provides amplitude limitation and phase suppression which
protects transistors T.sub.1 and T.sub.2 against damage due to
signal surges at the input leads R, S and T. These protective
features of the input circuit 1 similarly protect the operation of
the Y-amplifier 3.
In order to assure proper operation of the electrocardioscope, it
is necessary to assure that the X-deflection of CRT 4 is achieved
reliably and in proper relation to the Y-deflection. More
particularly, in order to obtain a stationary image on the screen
of CRT 4, it is necessary to synchronize the X-deflection with the
input signal from the patient's heart, appearing at the output of
amplifier 3. When such synchronization is achieved, a meaningful
electrocardiogram will appear on the screen of CRT 4 which can be
interpreted and analyzed in conjunction with appropriate
calibration scales extending in the X direction of said screen, to
permit a direct reading of the patient's pulse rate.
Synchronization circuits capable of achieving this type of
operation are already known in conjunction with conventional
oscilloscopes. However in order to provide the portable apparatus
of the present invention, it was found necessary to use a
particularly simple and robust type of synchronization circuit
which would operate in the desired fashion, without any noticeable
time delay, and with a minimum of energy consumption. This sweep
and synchronization circuit (designated 5 in FIG. 1) will now be
described in detail by reference to FIG. 3.
The X-deflection signal is generated, in conventional fashion, by
charging and discharging a capacitor C.sub.3. Capacitor C.sub.3 is
charged from a constant current source 12 (e.g., of the transistor
type) which is in turn energized by the battery supply within the
electrocardioscope housing. Capacitor C.sub.3 is selectively
discharged by a programmable unijunction transistor (PUT) via a
diode D.sub.5, electrodes a, b of PUT, and resistor R.sub.9 when
the voltage across capacitor C.sub.3 reaches a predetermined level,
e.g., 9.5 volts (provided that no synchronization signal is applied
to PUT, as will be described hereinafter). After the capacitor
C.sub.3 has discharged, PUT is blocked, and the sequence of
operation described repeats itself to produce a saw-tooth voltage
having a regular repetition rate. The saw-tooth voltage thus
produced is coupled via a field effect transistor T.sub.3, acting
as an impedance converter, to terminal A which constitutes the
input of X-deflection amplifier 8 (see FIG. 1).
The circuit of FIG. 3 includes provision for rendering PUT
conductive at selected times, even though the voltage across
C.sub.3 has not reached the predetermined potential described
earlier. This mode of operation is accomplished by applying a
synchronization signal to electrode c of PUT when it is desired to
render PUT conductive. Such a synchronization signal is generated
when the following two conditions occur simultaneously:
a. The X-deflection has caused the beam in CRT 4 to be deflected
completely across the screen and beyond its right-hand edge (the
potential then present on capacitor C.sub.3 nevertheless being less
than the potential required to effect its discharge); and
b. The sweep circuit 5 receives a signal of predetermined minimal
amplitude, via connection B, from the output of the Y-deflection
amplifier 3 (i.e., a meaningful signal is present which would not
be observable since the CRT beam has been deflected beyond the
visible area of the screen).
When the above two conditions occur simultaneously, it is
necessary, in order to obtain a stationary image which makes use of
the entire width of the CRT screen, to start a new sweep
immediately, i.e., to discharge capacitor C.sub.3 even though the
potential across the capacitor has not yet reached the
aforementioned discharge potential, e.g., 9.5 volts. This mode of
operation is accomplished by the arrangement shown in FIG. 3
comprising transistors T.sub.4, T.sub.5, T.sub.6 and resistor
R.sub.8.
Transistors T.sub.4 and T.sub.5 are in series with one another. The
Y-deflection signal appearing at terminal B can only be amplified
by field effect transistor T.sub.5, and transferred via transistor
T.sub.6 to electrode c of PUT, when transistor T.sub.4 is
conductive. The base of transistor T.sub.4, however, is biased by
the sweep voltage through an intermediate trimming potentiometer
R.sub.8. Potentiometer R.sub.8 is set to provide a potential which
causes transistor T.sub.4 to be rendered conductive when the CRT
beam passes beyond the right-hand edge of the CRT screen.
When transistor T.sub.4 is triggered for conduction, transistor
T.sub.5 is able to amplify any signal which appears at terminal B.
If such a signal should appear at terminal B, the resultant output
signal from transistor T.sub.5 is coupled via transistor T.sub.6 to
electrode c to render the unijunction transistor PUT conductive;
and the capacitor C.sub.3 is accordingly immediately discharged to
initiate a new X-deflection of the electron beam. Appropriate
synchronization operative to produce the stationary image is
therefore assured.
It is sometimes of considerable importance to have a permanent
record of the patient's cardiac condition during treatment, and the
nature of the treatment and procedures which were employed, since
such a record makes it possible to conduct a later review of the
treatment, and a more deliberate analysis of the patient's
condition. In order to provide such a record, the
electrocardioscope of the present invention includes a terminal 14
connected via lead C (see FIG. 1) to the input of amplifier 3, to
permit signals to be supplied to a separate magnetic recording
device, e.g., a cassette-tape recorder, for storage and later
retrieval. The electrocardioscope may also include a further
terminal 15 associated with a microphone 9, which can, for example,
be permanently installed in the face of the equipment adjacent the
CRT display, and which is associated with a selectively operable
switch 10, to permit contemporaneous oral comments to be recorded
as well. These terminals 14, 15 act as both input and output
terminals, i.e., if a permanent record has been made, it is
entirely possible to replay the cardiac signals via connection C to
produce a viewable image on the CRT screen, and to simultaneously
replay the oral information through the microphone which then acts
as a speaker.
As discussed earlier, the terminals or electrodes R, S, T are
mounted in unitary fashion on the end of the housing opposite to
the face of cathode ray tube 4, so that by placing that end of the
housing and said electrodes directly on the patient's chest, a
viewable electrocardioscope will be produced. In order to assure
that the battery supply is not unnecessarily drained, it can be
associated with a pressure-sensitive switch 16 mounted on the
housing directly adjacent the three electrodes (see FIG. 1), with
said switch 16 being arranged to close only when the electrodes are
in engagement with the patient's body thereby to energize the
circuit of the present invention. In this way, when the
electrocardioscope is not in actual use, it is automatically
de-energized. A similar result can be achieved, if the
electrocardioscope is intended to be stored in a bracket when not
in use, by providing such a pressure-sensitive switch on a portion
of the housing which would engage the bracket when the
electrocardioscope is not being used. In this form of the
invention, depression of the switch, due to storage of the device,
should be arranged to de-energize the circuit, so that removal of
the device from its storage location automatically energizes the
circuit to place the device in condition for monitoring the cardiac
action of a patient.
The various terminals R, S, and T can be arranged to receive
elongated flexible leads terminating in electrodes adapted for
attachment to a patient's chest, to permit the unit to be placed on
a table or the like beside the patient when the device is being
used under non-emergency conditions.
* * * * *