U.S. patent number 3,554,198 [Application Number 04/658,478] was granted by the patent office on 1971-01-12 for patient-isolating circuitry for cardiac facing device.
This patent grant is currently assigned to Cardiac Electronics, Inc.. Invention is credited to Richard R. Ceier, George Tatoian.
United States Patent |
3,554,198 |
Tatoian , et al. |
January 12, 1971 |
PATIENT-ISOLATING CIRCUITRY FOR CARDIAC FACING DEVICE
Abstract
A circuit for isolating a cardiac pulsing device from a periodic
timing source to prevent stray voltages from being transmitted to a
cardiac patient including a high speed relay having a solenoid in
series with a resistor to form a primary circuit and the relay
contacts in series with a battery to form a secondary circuit which
provides the voltage for stimulating the heart of a cardiac
patient, with the secondary circuit including variable resistor
means for varying the voltage supplied to the patient and a
built-in test circuit associated for periodically testing the
battery to insure that it possesses sufficient voltage for
providing adequate stimulation.
Inventors: |
Tatoian; George (Williamsville,
NY), Ceier; Richard R. (East Aurora, NY) |
Assignee: |
Cardiac Electronics, Inc.
(Clarence, NY)
|
Family
ID: |
24641401 |
Appl.
No.: |
04/658,478 |
Filed: |
August 4, 1967 |
Current U.S.
Class: |
607/9; 128/908;
307/328 |
Current CPC
Class: |
A61N
1/362 (20130101); A61N 1/3625 (20130101); Y10S
128/908 (20130101) |
Current International
Class: |
A61N
1/362 (20060101); A61n 001/36 () |
Field of
Search: |
;128/419,421--423,419P(Digests),419D(Digests) ;335/151,152
;307/93,94,96,100,104 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Claims
We claim:
1. An isolating unit for utilizing a periodic timing source to
drive a cardiac pulsing device while electrically isolating said
pulsing device from said timing source to thereby prevent stray
voltages from said timing source from being transmitted to a
cardiac patient comprising a primary circuit including a solenoid,
first lead means for coupling said solenoid to said timing source,
a secondary circuit including a switch operable by said solenoid in
response to the energization of said primary circuit by said
periodic timing source, said switch being electrically isolated
from said first circuit, a battery in said second circuit coupled
to said switch, second lead means in said second circuit for
effectively coupling said battery to a cardiac patient for applying
an electric voltage to said patient on the closing of said switch
whereby stray voltages in said timing source are not transmitted to
said cardiac patient, said solenoid and switch means comprising a
reed relay, and resistance means in series with said solenoid for
speeding up the action of said relay.
2. A circuit as set forth in claim 1 including second resistance
means coupled across said solenoid for discharging the voltage
across said solenoid coil upon the termination of flow of current
into said primary circuit.
3. An isolating unit for utilizing a periodic timing source to
drive a cardiac pulsing device while electrically isolating said
pulsing device from said timing source to thereby prevent stray
voltages from said timing source from being transmitted to a
cardiac patient comprising a primary circuit including a solenoid,
first lead means for coupling said solenoid to said timing source,
a secondary circuit including a switch operable by said solenoid in
response to the energization of said primary circuit by said
periodic timing source, said switch being electrically isolated
from said first circuit, a battery in said second circuit coupled
to said switch, second lead means in said second circuit for
effectively coupling said battery to a cardiac patient for applying
an electric voltage to said patient on the closing of said switch
whereby stray voltages in said timing source are not transmitted to
said cardiac patient, said solenoid and switch means comprising a
reed relay, means for varying the amount of current flowing in said
secondary circuit, a test circuit coupled across said battery for
determining whether said battery voltage is in excess of a
predetermined value to thereby assure the providing of sufficient
voltage in said secondary circuit upon the closing of said switch
means, and resistance means in series with said solenoid for
speeding up the action of said relay.
4. A circuit as set forth in claim 3 including second resistance
means coupled across said solenoid for discharging the voltage
across said solenoid coil upon the termination of flow of current
into said primary circuit.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an improved device for pacing the
heart of a cardiac patient while eliminating the possibility of
applying stray voltages which might cause the heart to
fibrillate.
By way of background, various cardiac pulsing devices are currently
in use for pacing the heart of a cardiac patient from an external
source by causing this source to provide periodically-timed voltage
pulses which are transmitted to the patient. In the past, the
pulsing device was susceptible of picking up 60-cycle stray
voltages from stray electromagnetic and electrostatic fields, and
these stray voltages could initiate fibrillation. These stray
voltages originated from the equipment itself and from common
ground loops inasmuch as the patient had to be connected to machine
ground when he was being paced from an external pacing device. It
is with an improved external pacing device which overcomes the
foregoing shortcomings that the present invention is concerned.
SUMMARY OF THE INVENTION
It is accordingly one object of the present invention to provide an
external pacing device for stimulating the heart of a cardiac
patient, the external pacing device being completely electrically
isolated from a timing device which triggers it thereby completely
eliminating any possibility of fibrillation producing stray
voltages in the timing device from being transmitted to the heart
of the cardiac patient.
Another object of the present invention is to provide an improved
external cardiac pacing device in which the pulses are transmitted
through an isolating circuit substantially instantaneously without
delay, thereby permitting the isolation of the two circuits without
in any way delaying the signals to the patient.
A further object of the present invention is to provide an improved
circuit for isolating a periodic timing source from a cardiac
patient, the improved circuit providing a voltage to catheter leads
from a battery source and including an unique battery testing
circuit for insuring that the battery is of sufficient voltage to
adequately perform its function. Other objects and attendant
advantages of the present invention will readily be perceived
hereafter.
The improved circuit of the present invention utilizes a periodic
timing source, such as an external pacing device, which is subject
to stray electrical and electromagnetic voltages. The external
pacing device drives a cardiac pulsing device while it is
electrically isolated from the patient. Stray electrical or
electromagnetic-induced voltages in the timing source are therefore
isolated from the patient. The improved circuit comprises a primary
circuit including the solenoid of a relay and a secondary circuit
including the switch of the relay. The relay is of the fast-acting
type which instantaneously transmits any pulse sensed in the
primary circuit to the secondary circuit. The secondary circuit
also includes a battery which is coupled to the heart of a patient
by suitable electrical leads and the patient's heart will be
stimulated by the battery as long as the switch is closed. The
secondary circuit also includes a battery test circuit which can be
used periodically to test the voltage of the battery to detect
whether it still possesses sufficient voltage to perform its
function adequately. The present invention will be more fully
understood when the following portions of the specification are
read in conjunction with the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the relationship between the
improved isolating unit of the present invention and the master
cardiac control which is utilized to provide a timing pulse;
and
FIG. 2 is a schematic circuit diagram showing the improved
isolating circuit of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 a master cardiac control 10 is shown which is utilized in
its conventional manner for monitoring the heartbeat of a patient
and performing other functions normally associated therewith
including providing a visual indication of the patient's heartbeat
on an oscilloscope or the like. Devices of this type are
conventional in the field and a further description is not deemed
necessary. Incorporated as a portion of master cardiac control 10
is a pacing unit 11 which is essentially an oscillator for
providing periodic timed pulses which, through suitable leads 13
and 14, are coupled to electrodes implanted in the heart of a
patient and the timing pulses are utilized to periodically
stimulate the heart and thus pace the heartbeat. Pacing unit 11 may
be of any suitable conventional construction, and it is deemed that
a detailed description of this particular unit is unnecessary.
As noted briefly above, if leads 13 and 14 are coupled directly to
the patient, there is the distinct possibility that stray 60-cycle
voltages produced by electrical and electromagnetic circuits within
master cardiac control 10 and associated ground circuit may be
transmitted to the patient. These 60-cycle voltages can induce
fibrillation. Accordingly, in accordance with the present invention
an isolating unit 15 is coupled to leads 13 and 14 extending from
the pacing unit 11. Isolating unit 15 completely electrically
isolates pacing unit 11 from catheter leads 16 and 17 coupled to
the heart of the patient, thereby completely preventing the stray
voltages from being transmitted to the patient.
The isolating circuit 15 includes a fast-acting reed relay 18
consisting of a solenoid coil 19 wound about an highly evacuated
envelope containing a pair of normally open contacts 20. The reed
relay is the type which can close contacts 20 within 0.0002 seconds
after coil 19 is energized, thereby providing a substantially
instantaneous response. In series with coil 19 is a resistor 21
which serves a plurality of functions. Firstly, it acts in
combination with coil 19 to serve as a voltage divider and thus
reduce the voltage on coil 19 so that external leads 13 and 14 can
drive the isolating unit 15. Furthermore, by virtue of the fact
that resistance 21 is in series with coil 19, there will be a
speedup in the action of relay 18 thereby making it an ultraspeed
relay and driving it many times as fast as it would normally be
driven because the number of seconds required for operation of the
relay is equal to L/R and therefore the greater the value of
resistance 21, the smaller will be the number of seconds required
for relay 18 to operate. Coupled across coil 19 is a resistor 22,
across which the voltage of coil 19 is discharged when the voltage
source to leads 13 and 14 opens to thereby provide a slow
collapse.
Upon the closing of contacts 20 when there is a flow of current
through coil 19, a circuit will be completed to patient P from
9-volt battery 23 which is coupled across patient P by lead 24,
resistor 25, lead 26, variable resistor 27 and catheter lead 16, on
one side of the circuit, and on the other side by lead 28, contacts
20, lead 29 and catheter lead 17. Resistors 25 and 27 are for the
purpose of limiting the flow of current in the circuit to the
patient and variable resistor 27 is essentially a potentiometer
which varies the stimulation level to the patient's heart, this
being calibrated for each particular patient, in accordance with
his requirements.
It can readily be seen that there is complete isolation between the
primary circuit in which solenoid coil 19 is located and the
secondary circuit in which contacts 20 are located. Therefore, any
stray voltages in the primary circuit cannot be communicated to the
patient through the secondary circuit.
It will be appreciated that there must be an arrangement for
testing the voltage of battery 23 to insure that adequate voltage
is being supplied to the patient whenever the secondary circuit is
established. To this end, a test circuit is provided for testing
the voltage of the battery. This test circuit is established by
closing of pushbutton 30, and if the battery 23 can provide a
voltage in excess of a predetermined amount, for example, 7.7
volts, there will be a flow of current from battery 23, through
lead 24, lead 31, lead 32, Zener diode 33, resistance 34, lead 35,
transistor 36, lead 37, lead 38, pushbutton 30 and lead 39 to
battery 23. The flow of current from the base to the emitter of
transistor 36 will cause a flow of current from lead 31 through
lamp 40 and lead 41 to provide an indication that the battery 23 is
in excess of the voltage required to trigger Zener diode 33 and
flow through it and the resistance in series with it, namely,
resistance 34 and the resistance provided by transistor 36, thereby
showing that the battery possesses sufficient voltage to provide
adequate cardiac stimulation. Resistor 42 in the circuit is merely
for the purpose of discharging any leakage current which may
collect on the base of transistor 36.
In the event that the battery 23 does not possess the minimum
required voltage to trigger Zener diode 33, there will be no flow
through the above-described circuit including Zener diode 33 and
transistor 36 and thus there can be no flow through lamp 40
inasmuch as transistor 36 will not be energized. In this event,
lamp 40 will not light up and it will be known that battery 23 does
not have the required voltage for adequate cardiac stimulation and
therefore must be replaced.
At this point it is to be noted that there is a resistor 43 coupled
across catheter leads 16 and 17. This resistor is located in the
circuit for external test purposes in testing and checking unit
15.
From the foregoing description it can readily be seen that the
improved isolating unit of the present invention is manifestly
capable of achieving the above enumerated objects and while
preferred embodiments of the present invention have been disclosed,
it will be appreciated that it is not limited thereto but may be
otherwise embodied within the scope of the following claims.
* * * * *