U.S. patent number 3,759,265 [Application Number 05/251,412] was granted by the patent office on 1973-09-18 for pulse-width controlled heartbeat stimulating apparatus monitoring system.
This patent grant is currently assigned to American Optical Corporation. Invention is credited to Barough V. Berkovits, Sherwood S. Thaler.
United States Patent |
3,759,265 |
Thaler , et al. |
September 18, 1973 |
PULSE-WIDTH CONTROLLED HEARTBEAT STIMULATING APPARATUS MONITORING
SYSTEM
Abstract
Pulse-width controlled heartbeat stimulating apparatus. The
apparatus includes an electrical power supply and a pulser for
generating stimulation pulses on terminals connected to a patient's
heart. An integral control is provided for automatically varying
the width of the stimulation pulses as a function of the power
supply (energy source) value to maintain the energy output above a
predetermined level. The present invention can be used with many
types of heart stimulating devices including extra-corporeal
pacers, but is particularly useful when utilized with
non-accessible or implanted pacers. In an illustrative embodiment,
a circuit is provided for indicating the approximate amount of
remaining power supply life and for controlling energy supplied to
the heart with each stimulation pulse to greater than a minimum
required value regardless of energy source variation.
Inventors: |
Thaler; Sherwood S. (Lexington,
MA), Berkovits; Barough V. (Newton Highlands, MA) |
Assignee: |
American Optical Corporation
(Southbridge, MA)
|
Family
ID: |
27360571 |
Appl.
No.: |
05/251,412 |
Filed: |
May 8, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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163619 |
Jul 19, 1971 |
|
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16478 |
Mar 4, 1970 |
3674015 |
|
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727129 |
Apr 11, 1968 |
3528428 |
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Current U.S.
Class: |
607/11 |
Current CPC
Class: |
A61N
1/3931 (20130101); A61N 1/365 (20130101); G01R
29/0273 (20130101); A61N 1/3906 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 1/08 (20060101); A61N
1/365 (20060101); G01R 29/02 (20060101); G01R
29/027 (20060101); A61n 001/36 () |
Field of
Search: |
;128/2.5P,2.5R,2.5T,2.6F,2.6R,419P,421,422 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a division of co-pending U.S. Pat.
application Ser. No. 163,619 filed July 19, 1971 which in turn is a
continuation-in-part of U.S. Pat. application Ser. No. 16,478
entitled "Electrocardiographic Monitor System" filed Mar. 4, 1970
which has matured into U.S. Pat. No. 3,674,015 and which is a
division of patent application Ser. No. 727,129 entitled "Demand
Pacer" which was filed on Apr. 11, 1968 and which issued as U.S.
Pat. No. 3,528,428. Background information disclosed in U.S. Pat.
No. 3,528,428 is incorporated herein by reference. The present
application is related to the following co-pending applications:
U.S. Pat. application Ser. No. 10,225 entitled "Pacemaker" filed
Feb. 10, 1970 and which issued as U.S. Pat. No. 3,635,224; U.S.
Pat. Application Ser. No. 810,519 entitled "Atrial and Ventricular
Demand Pacer" filed Mar. 26, 1969; and which issued as U.S. Pat.
No. 3,595,242 and U.S. Pat. application Ser. No. 884,825 entitled
"Bifocal Demand Pacemaker" filed Dec. 15, 1969 and which issued as
U.S. Pat. No. 3,661,158. All of the above copending patent
applications are filed in the name of Barouh V. Berkovits, who is a
joint inventor in the present patent application, and are assigned
to the same assignee as that of the present patent application.
Subject matter of these related applications is incorporated herein
by reference.
Claims
We claim:
1. A monitoring system comprising heartbeat stimulating apparatus
for providing electrical pulses for stimulating the heartbeat of a
patient, a power supply for supplying voltage to said apparatus,
means for sensing decrease of said voltage, and pulse-width control
means responsive to the operation of said sensing means for
controllably varying the width of each of said electrical pulses as
a function of said voltage decrease and thus providing an
indication of said voltage remaining in said supply.
2. A monitoring system as recited in claim 1 and wherein said
pulse-width control means includes means for increasing the width
of said each of said electrical pulses to compensate for said
voltage decrease of said power supply, and wherein said monitoring
system is capable of being implanted within the body of said
patient.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electronic
heartbeat-stimulating apparatus. More particularly, the present
invention relates to a system for automatically controlling the
energy in each heartbeat-stimulating pulse and to a system for
indicating the remaining useful life of the battery power
supply.
2. Description of Prior Art
In the burgeoning field of medical-electronics, electronic pacer
devices for providing stimulation to a patient's heart to induce a
heartbeat have been developed over the past 10 years or so.
Stimulating devices of the demand type, wherein stimulation is
provided only in the absence of natural heartbeats have been
developed and such devices are disclosed in certain of the
copending patent applications herein referenced. And more recently,
devices of the type which will stimulate the atrium and the
ventricle separately have been developed and are disclosed in
certain of the copending patent applications herein referenced. The
present invention is yet another improvement in the growing family
of improvements to heart-stimulating devices.
In the implantable variety of pacers, batteries in a series string
are commonly employed as a power supply. Batteries, of course, run
down and fail individually after periods of time. One of the
problems with most heart stimulating devices to date, and
particularly with the implantable variety, results from battery
deterioration combined with fixed pulse-width of the heartbeat
stimulation pulse. A problem is that energy of the stimulation
pulse (wherein the energy is related to but not equal to battery
voltage decreases. This will eventually cause malfunction of the
pacer.
A certain quantity of energy is required to stimulate a heartbeat.
This energy varies from person to person and is herein termed
"capture energy." Initially after implantation of a particular
pacer, battery voltages are maximum. To provide capture energy
initially after implantation, one requires a relatively narrow
pulse. The pulse area is sufficiently large due to relatively large
pulse height. By comparison, to provide capture energy at a later
point in time, (for example, one year after implantation when
battery voltages have diminished) a sufficiently large pulse width
must have been provided at the time of implantation.
Thus, on the one hand, if the pulse width is preset to be "large" a
great deal of the battery's energy is not used efficiently, since
it is an excess over the required energy. On the other hand,
consider the pulse width set exactly at the minimum width required
to provide capture energy immediately after implantation. After a
period of time when battery voltages diminish or when a battery
fails, pulse height will correspondingly diminish and there will be
insufficient energy associated with the pulse to cause capture.
This "capture energy" and efficiency problem is solved by the
present invention. Applicants provide a device for maintaining the
energy of each stimulation pulse approximately constant (equal to
or greater than the required capture energy) for the duration of
heart stimulator use.
Another problem associated with inaccessible pacers is the lack of
information relating to battery usage and/or to remaining battery
life. The inaccessibility of implanted pacers makes direct
measurement of the batteries impractical. Patients and physicians
were not certain as to when the batteries would deteriorate to the
extent that the pacer would malfunction. This uncertainty created
unnecessary anguish for the patient. The present invention provides
a solution to this problem with an external monitoring/indicating
system for indicating the remaining useful life of the implanted
pacer batteries.
SUMMARY OF THE INVENTION
The present invention relates to a system for controlling the width
of pulses used for heartbeat stimulation. The invention includes a
device for sensing variations in the power supply. It controls the
width of stimulation pulses in response to variations in the power
supply in such a manner as to maintain energy of the stimulation
pulses approximately constant. The pulse width control includes a
device for automatically varying a time constant circuit in
accordance with variations of power supply voltage.
The present invention also relates to a system for monitoring the
power supply or batteries of the heartbeat stimulating apparatus.
This system provides an indication of the remaining life of the
batteries. This information is particularly useful in connection
with an implantable pacer. An ex-vivo (external) indication of
battery life of an implanted heart pacer is obtained on a simple
oscilloscope with the use of ordinary ECG leads. The ECG leads
sense the stimulation pulse and it is displayed on the
oscilloscope. The width of the displayed pulse provides information
from which the remaining useful life (or the amount of life used
up) of the battery or batteries is determined.
There are several advantages of the present invention. One salient
feature or advantage of the present invention is its ability to
allow a physician to determine useful remaining battery life
without resorting to a surgical procedure in order to remove the
batteries and have the batteries checked.
A second distinct advantage of the present invention is that it
permits efficient pre-setting of the stimulation pulse width for
maximum utilization of the supply batteries. This extends battery
life and extends the time between implanted pacer replacement
surgical operations.
It is thus an object of the present invention to provide a
heartbeat-stimulating device which has an approximately constant
stimulation-pulse energy.
It is yet another object of the present invention to provide a
monitoring system for indicating remaining useful life of the pacer
power source.
Other objects and advantages of the present invention will become
apparent to one having reasonable skill in the art after referring
to the detailed descriptions of the appended drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit diagram of a type of demand pacer that is
disclosed in U.S. Pat. No. 3,528,428 incorporating the improvement
of the present invention;
FIG. 2 is a circuit diagram of part of a heartbeat stimulating
device of the type disclosed in patent application Ser. No. 10,225
including the improvement of the present invention; and,
FIG. 3 is a graph of two superimposed stimulation pulses plotting
amplitude vs. time.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is a circuit schematic diagram of a demand pacer of the type
disclosed in U.S. Pat. No. 3,528,428. Subject matter disclosed in
that patent is incorporated herein by reference. Thus, only partial
operation of this circuitry will be described below. The reader is
referred to U.S. Pat. No. 3,528,428 for complete description of the
circuitry. For purposes of simplifying the discussion, consider
switch S to be closed thereby rendering transistor T6
non-conductive. (The present invention is operative with switch S
open as well.)
In U.S. Pat. No. 3,528,428, capacitor 57 is a timing capacitor. It
charges from the series arrangement of batteries 3, 5, and 7,
(hereafter referred to sometimes as the energy source or as the
battery) through potentiometers 35 and 37 and resistors 61 and 63.
The voltage on capacitor 57 charges to a threshold voltage
determined by the voltage on the base of transistor T7 established
in this embodiment by batteries 3 and 5. When the voltage on
capacitor 57 exceeds the voltage on the base of transistor T7 by
the base-emitter voltage drop, transistor T7 is rendered
conductive, which renders transistor T8 conductive. Transistor T7
and T8 conduct and capacitor 57 discharges through both transistors
and only potentiometer 37 (in U.S. Pat. No. 3,528,428).
The improvement depicted in a particular illustrative embodiment
comprises resistors 100, 101, 102, and 103, and transistor T100.
These components are arranged in an integral control circuit to
sense fluctuations in battery voltage and to automatically vary its
effective circuit resistance value in accordance therewith. (In
U.S. Pat. No. 3,528,428, junctions 104, 105, and 106 are a common,
unnumbered junction.)
In the control circuit, resistor 100 is in parallel connection with
the emitter-collector of transistor T100. The collector of
transistor T100 is connected to junction 104. The emitter of
transistor T100 is connected to one end of resistor 101, the other
end being connected to junction 105. The base of transistor T100 is
connected to resistor 102, the other end being connected to
junction 106. Resistor 103 is connected between junctions 105 and
106.
In the present invention the charge path of capacitor 57 still
includes resitors 61 and 63 since capacitor 57 is charged from
batteries through that circuitry, and the discharge path of
capacitor 57 still does not involve resistors 61 and 63. But now,
capacitor 57 discharges not only through potentiometer 37, but also
through resistor 101 and the parallel combination of resistor 100
and transistor T100. (Potentiometer 37 is still used to preset the
pulse width but otherwise can be considered as series resistance in
the discharge path of capacitor 57. Functionally, it can be
considered to be lumped in with the resistance value of resistor
101.) A resistor can replace potentiometer 37.
Resistor 103 can be considered to be one resistor of a resistive
voltage divider across batteries 3, 5, and 7. The resistive voltage
divider comprises resistors 61 and 63, potentiometer 35 and
resistor 103.
In operation, the voltage developed across resistor 103 acts as the
biasing source of transistor T100. The higher the voltage developed
across resistor 103, the greater the voltage applied to the
circuitry to its left. The voltage developed across resistor 103 is
due to current flow therethrough only from the series of batteries,
and not from capacitor 57. Thus, resistor 103 is a battery voltage
sensing resistor. It can also be considered as an energy-source
sensing or battery-current sensing resistor.
The voltage developed across resistor 103 causes a base current to
flow from emitter to base in transistor T100 (in the direction of
the emitter arrow). The greater the base current, the more
transistor T100 turns on and the more readily it conducts capacitor
57 discharge current from its emitter to its collector. Thus,
transistor T100 acts like a variable resistor automatically
controlled by its base current which is proportional to voltage
developed across sampling or sensing resistor 103.
If the pacer were recently implanted, the battery voltage is high
or at a peak; transistor T100 is strongly turned on, and its
effective resistance to flow of emitter-collector current is
relatively low. Thus, capacitor 57 will discharge with ease in a
relatively short time through this low resistance path. This is
what we expect and desire when the battery potential is high or at
a maximum.
By comparison, consider a period of time after implantation (i.e.
perhaps a year or so) during which the batteries have individually
failed or diminished by virtue of their use. For this situation,
after capacitor 57 charges sufficiently to overcome the threshold
established on the base of transistor T7, transistors T7 and T8
conduct current as usual. However, when the transistors conduct
(and provide a discharge path for capacitor 57 through them and
through resistors 101 and 100, and transistor T100), a lower
battery voltage is impressed across the resistive voltage divider
than described in the previous paragraph.
Resistor 103 now develops smaller voltage than before and voltage
applied to base-emitter terminals of transistor T100 and base
current of transistor T100 are proportionately reduced. The usual
effect on a transistor of reducing its base current is to decrease
the ability with which it can conduct current between its emitter
and collector. Transistor T100 thus conducts less current and acts
like an increased resistance in the discharge path of capacitor 57.
Accordingly, for lower battery voltages, capacitor 57 requires a
greater time to discharge completely than it required in the
previous example. Thus, discharge time of capacitor 57 is
automatically controlled by battery voltage in this integral pulse
control.
FIG. 2 is a partial schematic of a demand pacer of the type
disclosed in patent application Ser. No. 10,225. It may
functionally be the same as U.S. Pat. No. 3,528,428 but has at
least one important difference. The battery arrangement and the
biasing arrangement for transistors T7 and T8 are different. Any
decrease in any battery value is proportionately sensed at the base
of transistor T7. Thus, the threshold at the base of T7 moves in
direct proportion to the variation of supply voltage. The
improvement which comprises the present invention operates with the
circuitry of FIG. 2 as it operated with the circuitry of FIG.
1.
The effect of the discharge time control circuit may best be
illustrated by reference to FIG. 3. FIG. 3 represents two pulses
that are used for stimulation of a heartbeat. Pulse A is generated
when the battery voltage is high or at its maximum. The pulse
amplitude is correspondingly high or maximum, and the pulse width
is low or minimum. Conversely, pulse B represents the heart
stimulation pulse generated after a period of use. The pulse
amplitude is substantially reduced and the pulse width is
substantially increased. Shaded area "a" is approximately equal to
shaded area "b." Thus, area of pulse A is approximately equal to
area of pulse B. This is the situation in which the energy supplied
to the heart remains approximately constant over a period of time
even though the supply voltage varies. Pulse area is preset with
potentiometer 37 to the capture energy required by the particular
patient being stimulated.
But, if area of pulse A is initially preset to the minimum energy
necessary to provide capture, and if the present invention is not
used, the pulse width does not increase as amplitude decreases.
There would be insufficient energy associated with future pulses to
cause capture (to stimulate a heartbeat). Therefore, to ensure
capture at a future time, an excessive amount of energy would
initially have to be used, and thus some would be wasted. For
example, the width of pulse A would have to be made at least as
large as the width of pulse B to ensure capture at the amplitude of
pulse B when not using the present invention.
According to the present invention, the width of the heart
stimulation pulse is inversely related to the amplitude of the
battery supply. This relationship could be of the form where the
product of battery voltage and pulse width is a constant. But,
other relationships can work also. Thus, one can monitor the
failure of an individual battery or deterioration of the entire
battery supply voltage by monitoring the heart stimulation pulse.
By using electrocardiogram leads operatively connected to an
oscilloscope to externally sense and display the stimulation pulse
width, one can monitor the batteries and provide an indication of
remaining battery life. The pulse width indicates battery usage.
Quantitative measurements can be made. Thus, the present invention
includes an implantable pacer-battery external
monitoring-system.
The invention may be embodied in other specific forms without
departing from the spirit or essential characteristics thereof. For
example, any point in the circuitry which varies as a function of
the energy supply can be used to control at least one transistor
switch which in turn can control stimulation pulse width in a
discrete fashion. Thus, the present embodiments are to be
considered in all respects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description, and all changes which
come within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
* * * * *