U.S. patent number 3,805,796 [Application Number 05/325,334] was granted by the patent office on 1974-04-23 for implantable cardiac pacer having adjustable operating parameters.
This patent grant is currently assigned to Cordis Corporation. Invention is credited to Gomer L. Davies, Reese S. Terry, Jr..
United States Patent |
3,805,796 |
Terry, Jr. , et al. |
April 23, 1974 |
IMPLANTABLE CARDIAC PACER HAVING ADJUSTABLE OPERATING
PARAMETERS
Abstract
In the implantable cardiac pacer disclosed herein, various
operating parameters are determined or controlled by the
information held in a digital storage register such as a binary
counter. The information so held may be varied by means of pulse
signals transmitted through the body of a patient within whom the
pacer is implanted. Rate-sensing and count threshold control
circuits are provided to prevent unintended changes in operating
parameters.
Inventors: |
Terry, Jr.; Reese S. (Miami,
FL), Davies; Gomer L. (Fort Lauderdale, FL) |
Assignee: |
Cordis Corporation (Miami,
FL)
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Family
ID: |
26839372 |
Appl.
No.: |
05/325,334 |
Filed: |
January 22, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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141694 |
May 10, 1971 |
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Current U.S.
Class: |
607/30 |
Current CPC
Class: |
A61N
1/37211 (20130101) |
Current International
Class: |
A61N
1/362 (20060101); A61N 1/372 (20060101); A61n
001/36 () |
Field of
Search: |
;128/419C,419B,419E,419P,419R,422,423 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Kenway, Jenney & Hildreth
Parent Case Text
This is a continuation of application Ser. No. 141,694 filed May
10, 1971, now abondoned.
Claims
What is claimed is:
1. An implantable cardiac pacer comprising:
means for detecting pulse signals having predetermined
characteristics, which pulse signals can be applied externally of a
patient within whom said pacer is adapted to be implanted;
a first counter interconnected with said detecting means for
selectively counting detected pulse signals;
a second counter, controlled by said first counter and also
responsive to said pulse signal detecting means for counting
detected pulse signals occurring after the count held by said first
counter reaches a preselected threshold value;
a cardiac stimulation pulse generator having at least one
changeable output parameter; and
decoding means interconnected with said second counter for
controlling said output parameter in predetermined correspondence
with the value of the count held by said second counter.
2. In a fully implantable therapeutic device providing an
electrically controlled physiological function, apparatus for
adjusting the operating parameters of the device while implanted,
said apparatus comprising:
means for detecting pulse signals having predetermined
characteristics, which pulse signals can be applied externally of a
patient within whom said device is adapted to be implanted;
a first counter interconnected with said detecting means for
selectively counting detected pulse signals;
a second counter, controlled by said first counter and also
responsive to said pulse signal detecting means for counting
detected pulse signals occurring after the count held by said first
counter reaches a preselected threshold value;
decoding means interconnecting with said second counter for
controlling operating parameters of said device in accordance with
the count held by said second counter; and
means for resetting said first counter if no pulse signals are
received for a predetermined period.
3. In a fully implantable device for automatically providing an
electrically controlled physiological function, apparatus for
adjusting the operating parameters of the device while the device
is implanted, said apparatus comprising:
a magnetically operable switch for detecting magnetic pulse
signals, which pulse signals can be applied externally of a patient
within whom said device is adapted to be implanted;
a first counter interconnected with said switch for selectively
counting operations of said switch;
means for resetting said first counter if no pulse signals are
received for a preselected period;
a second counter, controlled by said first counter and selectively
responsive to the operation of said switch;
means controlled by said first counter for resetting said second
counter when the count held by said first counter reaches a
preselected threshold level and for subsequently enabling said
second counter to count switch operations; and
decoding means interconnected with said second counter for
controlling the operating parameters of said device in accordance
with the count held by said second counter.
4. A device as set forth in claim 3 including a one-shot
multivibrator which is triggered by the operation of said switch
and which generates square-wave output pulses of predetermined
duration, said counters being responsive to the multivibrator
output pulse to count operations of said switch.
5. A device as set forth in claim 3 wherein said first and second
counters comprise complementary MOSFET integrated logic
circuits.
6. An implantable cardiac pacer comprising:
a magnetically operable switch for detecting magnetic pulse
signals, which pulse signals can be applied externally of a patient
within whom said pacer is adapted to be implanted;
a first counter interconnected with said switch for selectively
counting operations of said switch;
means for resetting said first counter if no pulse signals are
received for a preselected period;
a second counter, controlled by said first counter and selectively
responsive to the operation of said switch;
means controlled by said first counter for resetting said second
counter when the count held by said first counter reaches a
preselected threshold level and for subsequently enabling said
second counter to count switch operations;
a cardiac stimulation pulse generator having at least one
adjustable output parameter; and
means interconnected with said second counter for setting said
output parameter to a value corresponding to the count held by said
second counter.
7. In a fully implantable device for providing an electrically
controlled physiological function, apparatus for adjusting the
operating parameters of the device while the device is implanted,
said apparatus comprising:
means for detecting pulse signals having predetermined
characteristics, which pulse signals can be applied externally of a
patient within whom said device is adapted to be implanted;
means responsive to a first predetermined grouping of detected
pulse signals for providing a control signal;
a parameter control register having a multiplicity of states;
means for controlling the operating parameters of said device in
accordance with the existing state of said control register;
and
means responsive to said control signal for changing the state of
said register in accordance with predetermined groupings of
detected pulse signals following said first grouping of pulse
signals, thereby to vary the operating parameters of said
device.
8. In a fully implantable device for automatically providing
electrical stimulation of tissue, apparatus for adjusting the
operating parameters of the device while the device is implanted,
said apparatus comprising:
means for detecting pulse signals having predetermined
characteristics, which pulse signals can be applied externally of a
patient within whom said device is adapted to be implanted;
means including a counter responsive to a first predetermined
sequence of detected pulse signals for providing a control
signal;
a parameter control counter having a multiplicity of sequential
states;
means for controlling the operating parameters of said device in
accordance with the existing state of said control counter; and
means enabled by said control signal for advancing the state of
said control counter in response to detected pulse signals
following said first sequence of pulse signals, thereby to vary the
operating parameters of said device.
9. Apparatus as set forth in claim 8 wherein said control counter
is responsive to said control signal and is reset thereby to a
preselected state.
Description
BACKGROUND OF THE INVENTION
This invention relates to fully implantable prosthetic or
therapeutic devices and more particularly to cardiac pacers in
which various operating parameters may be adjusted or varied
without surgically obtaining access to the pacer itself.
Various means have been proposed for altering the operating
parameters of an implanted cardiac pacer without requiring surgery
as such. For example, it has been proposed to utilize needle-like
adjusting tools to select resistance values and to use bistable
magnetic reed switches for performing various switching functions.
However, each of these prior art adjustment means has heretofore
typically been rather limited in application. A serious drawback in
most of these prior art systems is that the range of adjustment or
the number of adjustments which can be made is highly limited.
Further, there may be a problem in retaining the desired value
after the adjustment procedure per se is complete. In the case of
bistable magnetic reed switches, transient magnetic fields may
cause the switch to reverse state. The switch will then remain in
that state indefinitely and thereby cause an undesired mode of
operation. In the case of needle-like adjusting tools, the danger
of infection due to penetrating the patient's epidermis remains
even though that danger is reduced by the needle-like character of
the tool.
Among the several objects of the present invention may be noted
that provision of apparatus which permits the adjustment or
variation of several operating parameters of an implanted
prosthetic device such as a cardiac pacer without requiring
surgical access to the device; the provision of such apparatus in
which a parameter may be adjusted over a wide range and to any one
of a wide variety of preselected values within the range; the
provision of such apparatus in which predetermined combinations of
different operating parameters may be selected simultaneously; the
provision of such a system which provides for the reliable storage
of the parameter-determining information; the provision of such
apparatus which is relatively immune to electrical noise and
transient magnetic fields; and the provision of such apparatus
which is highly reliable and which is relatively simple and
inexpensive. Other objects and features will be in part apparent
and in part pointed out hereinafter.
SUMMARY OF THE INVENTION
Briefly, an implantable pacer constructed in accordance with the
present invention employs means for detecting pulse signals having
predetermined characteristics which are applied externally of a
patient within whom the pacer is implanted. A counter is
interconnected with the detecting means and is advanced by the
detected pulse signals. A cardiac stimulation pulse generator is
provided in which at least one output parameter is adjustable.
Decoding means are interconnected between the counter and the pulse
generator for setting the adjustable parameter to a value
corresponding to the particular count accumulated by the counter.
Accordingly, the output parameter may be adjusted by means of pulse
signals applied externally of the patient.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing is a schematic block diagram of an implantable
cardiac pacer having operating parameters which are adjustable in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing, an essentially conventional cardiac
stimulation pulse-generating circuit is indicated generally at 11.
Appropriate supply potentials are provided as indicated. An NPN
transistor Q1 and a PNP transistor Q2 are interconnected in a
so-called complementary-symmetry type of relaxation oscillator. The
voltage at the base terminal of PNP transistor Q2 is controlled by
a voltage divider comprising resistors R12 and R14, this voltage
being filtered by a capacitor C4 with the filter source impedance
being determined by a resistor R11.
The collector of transistor Q2 is connected to the base of
transistor Q1 through a capacitor C5 and a resistor R17 connected
in series therewith. As will be understood by those skilled in the
art, this connection provides regenerative feedback during the
pulse output portion of the oscillator's cycle of operation. The
oscillator output signal, taken from the collector of transistor
Q2, is applied, through a pair of resistors R15 and R16, to the
base terminal of an NPN output transistor Q3. This transistor is
normally biased off by means of a resistor R13. The collector
terminal of output transistor Q3 is provided with a load resistor
R10 and is coupled, through a capacitor C3, to the pacer output
terminal 13. As is understood, the output terminal 13 will be
coupled to a patient's cardiac tissue through an appropriate lead
system, as is conventional. The lead system also establishes a
common ground potential. The output circuit is protected by a zener
diode Z1 in conventional manner.
As is understood, the repetition rate of the complementary symmetry
oscillator depends upon the bias current provided to the base
terminal of transistor Q1. This current serves to re-charge the
capacitor 5 between output pulses. This bias current is provided
from the positive supply voltage through a series of timing
resistors R4-R8 which are graded in value according to a
predetermined sequence. Selected ones of the resistors R4-R8 may be
shunted by the operation of a quadbilateral switch 15. As will be
understood by those skilled in the use of integrated circuits in
digital applications, the quadbilateral switch 15 will typically
comprise a plurality of active semiconductor elements formed in a
single semiconducting wafer or chip. However, for the purpose of
facilitating the description of the present invention, the
switching function performed by this circuitry is conveniently
represented in the drawing by four conventional switch symbols.
Each such switch is under the control of a respective input signal,
as indicated. As will be understood, 16 values of total series
resistance may be obtained by closing the individual switches in
various combinations. Correspondingly, 16 different pulse
repetition rates will be available from the oscillator comprising
transistors Q1 and Q2.
The junction between resistors R15 and R16 can selectively be
shunted to ground through a resistor R9 and a semiconductor switch
or gate 17. Again, this function is indicated by a conventional
switch symbol although semiconductor switching elements are
preferred in actual practice. The operation of the switch is under
the control of a respective input signal, as indicated. When the
gate or switch 17 is closed, a portion of the drive or output
current from the oscillator transistors Q1 and Q2 is shunted away
from the base circuit of the output transistor Q3 through resistor
R9. The stimulation pulse output current is correspondingly
reduced. Thus, the gate 17 provides a means for selecting between
two output current levels. In other words, means are provided for
adjusting the value of a second operating parameter of the
stimulation pulse generating circuitry. Since the number of
available states double with each further stage added to the binary
counter, it can be seen that the number of combinations of several
different parameters may easily be expanded. For example, selected
count bits may be used to control whether the pacer operates in a
synchronous or non-synchronous mode or in a standby or continuous
mode.
In accordance with the present invention, the pulse repetition rate
and the output current of this stimulation pulse generator 11 may
be adjusted or controlled while the pacer is implanted, without
surgically entering the patient's body. In the embodiment
illustrated, pulse signals for transmitting the information used in
determining these output parameters is transmitted into the
patient's body by means of a magnetic field which is sensed by a
magnetic reed switch 21. Reed switch 21 is interconnected with the
positive supply so as to provide a source of input pulses to one of
the input terminals of a NOR gate 23. This input terminal is
normally biased negatively through a resistor R1. The output signal
from NOR gate 23 is coupled, through a capacitor C1, to both input
terminals of a second NOR gate 25, which thus functions as an
inverter. These input terminals are normally biased in the positive
sense through a resistor R2. The output signal from NOR gate 25 is,
in turn, applied back to the other input terminal of the first NOR
gate 23.
As will be understood by those skilled in the art, this
interconnection of the NOR gates 23 and 25 provides the mode of
operation of a one-shot multivibrator. The time constant or period
of the multivibrator is determined by the relative values of
capacitor C1 and resistor R2 and is selected so as to provide, for
each triggering pulse, a square-wave output pulse of longer
duration than any contact bounce which might be expected from the
magnetic reed switch 21. This operation thus provides a pulse
shaping so that the resultant electrical pulse signals are suitable
for use with digital circuitry in conventional manner.
While magnetic pulse signals are presently preferred as a method of
communicating information to the implanted device, other types of
signals, appropriately selected to avoid interference from ambient
interference, may also be used. For example, bursts of acoustic
energy at preselected frequency can be transmitted through tissue
and detected. Likewise, bursts of electromagnetic energy at
relatively low r.f. frequencies can be detected and used to advance
the counters or registers of the present invention. Relatively low
r.f. frequencies, e.g., 15-150 kHz, have the advantage that they
can penetrate a shield around the implanted device which would
protect the circuitry from high frequency transients which might
affect the logic circuitry.
The pulse signals obtained from the multivibrator are applied,
through a diode D1, to a timing capacitor C2 which is shunted by a
resistor R3. The voltage on capacitor C2 is, in turn, applied to an
inverting gate 27. Gate 27 functions essentially as a voltage
threshold device, the output signal from gate 27 being positive or
a digital "one," except when the voltage on capacitor C2 is above a
predetermined voltage level or threshold which is the level of
actuation of the gate. Together with the capacitor C2 and resistor
R3, gate 27 thus operates as a rate detector. When pulses from the
one-shot multivibrator are applied through diode D1 to capacitor C2
so as to re-charge that capacitor faster than it is discharged by
the resistor R3, the output signal from gate 27 will remain
negative so as to constitute a logic "zero."
The output signal from gate 27 is applied as a reset signal to a
decade counter 31. Decade counter 31 is assumed to be of the
integrated digital circuit type having an integral decoder so that
separate output signals corresponding respectively to each of the
ten successive states of the counter are available without external
matrixing. In the embodiment illustrated, only the "6" and "7"
output signals are utilized.
The shaped input pulses obtained from the one-shot multivibrator
are applied to the input terminal of counter 31, through a NOR gate
35. The "7" output signal from the decade counter 31 is applied as
a second input to NOR gate 35 so as to selectively control the
application of these input pulses. As will be understood, this
connection will allow the counter to count up to its seventh state.
At this point, the "7" output signal becomes a digital "one."
Accordingly, the output signal from gate 35 will be held at a
digital "zero" and further counting is prevented.
The "7" signal from the decade counter 31 is also applied, through
an inverting gate 37, to a NOR gate 39. NOR gate 39 is connected so
as to control the application of the input pulses, obtained from
the one-shot multivibrator, to a binary counter 43. Since the "7"
signal from the decade counter 31 is inverted prior to its
application to the NOR gate 39, it will be seen that the binary
counter 43 is inhibited from counting until the decade counter 31
reaches its seventh state. The "6" output signal from the decade
counter 31 is applied as the reset signal to the binary counter
43.
Thus, when the decade counter 31 passes through its sixth state,
the binary counter 43 will be reset. Then, when the decimal counter
31 reaches its seventh state, it will stop counting and the binary
counter 43 will begin to count upwards from its reset or "zero"
state in response to any pulse input signals applied thereto by the
multivibrator circuit.
Counter 43 is a five-stage binary counter, an output signal being
provided from each stage. The output signals from the first four
stages, i.e., the "1," "2," "4" and "8" signals, are applied to
control the quad-bilateral switch 15. Thus, the value of the
repetition rate-controlling resistance will be a function of the
count held by the first four stages of binary counter 43. The "16"
output signal from binary counter 43, i.e., the signal from the
fifth stage, controls the gate 17 which, as noted previously,
affects the output current level of the stimulation
pulse-generating circuit 11. The counter 43 has 32 possible states,
16 in which the "16" signal is a logic "one" and 16 in which that
signal is a logic "zero." Accordingly, it will be seen that any of
the 16 different pulse repetition rates can be provided at either
of the two output current levels. In other words, there are 32
output parameter combinations which can be applied to the
stimulation pulse generator 11 and the selection of which of these
32 exists at any one time is under the control of the count
accumulated in the binary counter 43.
Summary of Operation
Briefly then, the operation of the embodiment illustrated is as
follows. The output parameters of the stimulation pulse generator
11 are determined in correspondence with the count held in the
binary counter 43. The existing parameter values persist until the
counter 43 is set to some different value. Pulse signals for
changing the count held in counter 43 are introduced by applying,
through the patient's body, bursts or trains of magnetic pulses
which will actuate the magnetic reed switch 21. Each operation of
the reed switch triggers the one-shot multivibrator comprising
gates 23 and 25 so that a squarewave pulse, suitable for use with
digital circuitry, is generated. If successive pulses follow at a
rate which is within the time constant determined by capacitor C2
and resistor R3, the gate 27 resets the counter 31 and this counter
begins to count the shaped input pulses. After the counter 31
receives six of the succeeding pulses, the binary counter 43 is
reset. When the decade counter reaches its seventh state, it is
stopped from further counting and subsequent shaped input pulses
are applied to the binary counter 43 so that this counter is then
advanced from its initial or all "zero" state. The total length of
the pulse train is selected so that the new count introduced into
the binary counter 43 corresponds to that state of the counter
which will produce the desired output parameters, i.e., through the
quadbilateral switch 15 and the gate 17. For example, if it is
desired to set the stimulation pulse generator output parameters to
values corresponding to the seventh state of the binary counter 43,
the applied pulse train should produce fifteen actuations of the
magnetic reed switch 21. The first actuation causes the gate 27 to
release the reset signal from the counter 31, the next seven counts
advance the decade counter 31 and the last seven counts advance the
binary counter 43 to the desired state. Since magnetic reed
switches can operate at frequencies of several hundred Hz and the
digital counting circuitry will operate much faster, a complete
resetting cycle can be accomplished in less than a typical
heartbeat period. If even faster parameter resetting is sought,
semi-conductor magnetic or electric sensing devices may be
used.
In addition to providing timed resetting of the output control
counter 43, the count threshold established by the decade counter
31 also provides the additional desirable function of establishing
a count threshold which must be exceeded before any change in
output parameter will be effected. Thus, a short burst of
electrical noise pulses which might find their way into the
circuitry at the proper repetition rate to actuate the
rate-sensitive circuitry, still would not typically advance the
counter 31 sufficiently far to erase the output parameter
information previously stored in the binary counter 43.
Accordingly, a very high degree of noise immunity is provided.
Apparatus in accordance with the embodiment illustrated was
constructed using components having the values and/or
manufacturer's part designation as given in the following table and
this apparatus operated in the manner described.
TABLE
Ohms R1 100,000 R2 1,000,000 R3 1,000,000 R4 176,000 R5 232,000 R6
564,000 R7 1,024,000 R8 1,863,000 R9 10,000 R10 27,000 R11 5,600
R12 2,200,000 R13 22,000 R14 3,300,000 R15 10,000 R16 10,000 R17
1,000 Microfarads C1 0.0047 C2 0.047 C3 4.7 C4 0.1 C5 0.22 NOR
Gates RCA CD 4001 23, 25, 35 and 39 Decade Counter RCA CD 4017
Binary Counter RCA CD 4004 Quad Bilateral Switch RCA CD 4016 Gates
27, 37 and 17 RCA CD 4007
with regard to the inverting gates 27 and 37, it may be noted that
these gates, in the RCA integrated circuit designated, are in fact
pairs of separable field-effect transistors on the same chip and a
remaining one of the transistors on the same integrated circuit
chip is employed as the switching gate 17. While this particular
embodiment was made up using commercially available integrated
circuit devices, it should be understood that essentially the same
circuitry can be formed as a single special purpose integrated
circuit using so-called large scale integrated circuit (LSI)
techniques, as can other embodiments falling within the scope of
the appended claims. The particular integrated circuits designated
are of the complementary MOSFET (metal oxide semiconductor,
field-effect transistor) type. An advantage of this type of
circuitry in implantable stimulation devices is that the logic
gates employed draw very little current except in actual switching
and thus average current drain is very low.
While the parameter-controlling apparatus of the present invention
has been illustrated in conjunction with stimulation pulse
generating circuitry using analog timing and output current
control, it should be understood that, the functional parameters of
other types of stimulation pulse-generating circuitry may also be
controlled in accordance with the count held in a digital storage
register such as the binary counter 43. For example, apparatus of
the present invention might also be used in conjunction with a
digitally timed implantable cardiac pacer, e.g., of the type
disclosed in U.S. Pat. No. 3,557,796 Keller et al. Similarly, the
operating parameters of other types of tissue stimulators, e.g.,
bladder, phrenic nerve, or carotid sinus, may also be controlled in
accordance with the present invention.
In view of the foregoing, it may be seen that several objects of
the present invention are achieved and other advantageous results
have been attained.
As various changes could be made in the above constructions without
departing from the scope of the invention, it should be understood
that all matter contained in the above description or shown in the
accompanying drawings shall be interpreted as illustrative and not
in a limiting sense.
* * * * *