U.S. patent number 3,796,221 [Application Number 05/160,368] was granted by the patent office on 1974-03-12 for apparatus for delivering electrical stimulation energy to body-implanted apparatus with signal-receiving means.
Invention is credited to Norman R. Hagfors.
United States Patent |
3,796,221 |
Hagfors |
March 12, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
APPARATUS FOR DELIVERING ELECTRICAL STIMULATION ENERGY TO
BODY-IMPLANTED APPARATUS WITH SIGNAL-RECEIVING MEANS
Abstract
An apparatus for delivering electrical stimulation energy to
body-implanted apparatus with signal-receiving means is described
which is particularly useful in implanted devices, including nerve
and muscle stimulators, artificial organs, and certain
electro-mechanical devices such as implanted dispensers for the
administration of fluids to the body system. The electrical portion
of the system includes a transmitter and receiver, with the
transmitter normally being disposed or worn externally of the body
of the patient or user and being arranged to generate pulses of
predetermined amplitude at radio frequencies. The receiver includes
a pick-up, a receiver and an output electrode arrangement which is
normally subcutaneously implanted within the body of the patient.
Since variations in signal energy received by the receiver from its
coupled transmitter may occur due to relative positioning of the
transmitter-receiver pair, the receiver serves to regulate the
amount of energy delivered to the output electrodes such that
relatively uniform impulses are normally applied to the output
electrodes. Thus, even though there may be variations in the energy
coupled from the transmitter to the receiver, a uniform output
occurs; the arrangement providing a means for coupling an
electrical signal of variable magnitude to provide an output or
stimulation signal of constant energy amplitude or magnitude to an
implanted device.
Inventors: |
Hagfors; Norman R.
(Minneapolis, MN) |
Family
ID: |
22576592 |
Appl.
No.: |
05/160,368 |
Filed: |
July 7, 1971 |
Current U.S.
Class: |
607/59; 607/40;
607/42; 607/45; 607/64 |
Current CPC
Class: |
A61N
1/3787 (20130101); A61N 1/372 (20130101) |
Current International
Class: |
A61N
1/378 (20060101); A61N 1/372 (20060101); A61n
001/36 () |
Field of
Search: |
;128/419,421,422,2.1P |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Holcomb et al., "Medical & Biological Engineering" Vol. 7, No.
5, Sept. 1969, pp. 493-499. .
Parsonnet et al., "Surgical Forum," 1966, pp. 125-127. .
Cammilli et al., "Annals of the New York Academy of Science," Vol.
III, Art. 3, pp. 1007-1029, June 11, 1964 (pp. 1007-1013 relied
on)..
|
Primary Examiner: Kamm; William E.
Claims
I claim:
1. Apparatus for applying electrical stimulation signals of a
constant energy envelope to an object located within the human body
comprising:
a. a transmitter of pulse modulated radio frequency signals;
b. a radio receiver network means adapted to be subcutaneously
implanted in the body of a patient and responsive to said pulse
modulated signals for producing a demodulated output signal across
first and second junctions thereof;
c. a cource of reference potential connected between said first and
second junctions;
d. a controllable impedance means having an input coupled to said
first and second junctions, output terminals, and a control
terminal connected to said source of reference potential for
maintaining the voltage at said output terminal substantially
constant over a range of variations of said demodulated output
signals; and
e. stimulation electrodes adapted to be surgically implanted and
electrically coupled to said output terminals.
2. Apparatus as in claim 1 wherein said controllable impedance
means comprises a semiconductor current control means having input,
output and control electrodes, said input electrode being connected
to said first junction, said output electrode being connected
through a resistor to said second junction, and said control
electrode being coupled to said source of reference potential.
3. Apparatus as in claim 2 and further including magnetically
actuatable means for varying said source of reference potential
from a location outside of the body.
Description
BACKGROUND OF THE INVENTION
Implanted devices have been used for some time for accomplishing a
variety of purposes. For example, implanted nerve and muscle
stimulators have been used for a substantial period of time, as
have artificial organs. In order to control these implanted
devices, an electrical signal is normally obtained with a
transmitter, which is coupled to an implanted receiver, with the
receiver having means for delivering an output or stimulation
signal to one or more output electrodes. By way of a specific
example, it has been known that relief of pain associated with
angina pectoris may be achieved in certain patients through the
manual stimulation of the carotid sinus, the stimulation resulting
in a general reduction in the peripheral vascular resistance
throughout the body, a significant drop in arterial pressure,
decreased cardiac rate, and diminished myocardical contractility. A
reduction in these factors results in a corresponding reduction in
the cardiac workload and the myocardial oxygen requirements.
Recently, however, it has been found that these results may be
achieved through the direct electrical stimulation of the carotid
sinus nerve bundle. The apparatus of the present invention is
particularly desirable for application to this type of
stimulation.
The present invention provides a system for delivering uniform
impulses of electrical energy to an output which may be coupled to
a nerve bundle, a muscle tissue, or to an artificial organ. The
input is derived from a source disposed externally to the body of
the patient which is coupled electrically to a surgically implanted
radio receiver and an associated electrode or electrodes which are
disposed within the body. In other words, a substantially uniform
energy envelope is delivered to the output of the system. The
transmitter includes a pulse wave form generator, preferably
battery-powered and adapted to deliver radio frequency pulses to an
antenna. The amplitude of the electrical signal available to the
receiver is variable because of the shifting of the relative
positions of the transmitter-receiver pair.
In one typical application, a subcutaneously implanted receiver
containing one or more electrically isolated receiving coils and
circuits is arranged to be operatively coupled to a transmitter and
is arranged to supply impulses to an appropriate nerve bundle by
means of an implanted electrode terminal. The antenna coil of the
transmitter is normally placed on or adjacent the skin of the
patient at a position disposed directly over the coils of the
receiving antenna contained within the implanted receiver.
Electrical impulses from the transmitter are thereby inductively
coupled through the skin of the patient and converted to a
stimulation impulse having a uniform energy envelope, with constant
characteristics of amplitude, pulse duration and frequency. The
transmitter is preferably and normally designed to permit the
physician to regulate the pulse rate and amplitude to a
predetermined desired level at the time of implant, and preferably
on occasion thereafter.
With the transmitter and transmitter coil located externally, it is
apparent that it is difficult to apply electrical pulses of
constant energy to the coils of the receiving antenna and
ultimately to the stimulation electrodes of the receiver. Such
problems do not normally occur when a direct electrical connection
is made between the pulse source and the stimulating electrodes,
however, such direct electrical connection is not always practical
or possible. For example, in the system utilizing a remote
transmitter, variations in stimulation or impulse may occur when
energy is coupled from the antenna of the transmitter to the
receiver and electrode assembly, since the transmitting antenna
frequently moves and becomes located in some different position or
assumes a different orientation relative to the coil of the
receiving antenna. The system of the present invention provides
means for accommodating these variations without varying the
magnitude or amplitude of the stimulation signal or impulse.
SUMMARY OF THE INVENTION
In accordance with the features of the present invention, circuit
means are provided in an implanted receiver for establishing an
energy envelope of constant characteristics at the output
electrodes. In this connection, the energy envelope will provide an
output with constant amplitude to the stimulation electrodes
irrespective (within pre-determined margins) of the relative
location of the antenna of the transmitter and the coil or coils of
the receiver so that the amount of energy delivered will be
regulated. In this arrangement, the amount of energy delivered may
be regulated by control of the amplitude, pulse duration, or
frequency.
Another feature of the apparatus of the present invention involves
the design of the receiver to permit the voltage amplitude to be
adjusted from a location externally of the body of the patient.
This feature may be accomplished by an electrical bypass mechanism
which can eliminate the regulator portion of the receiver, thus
allowing for appropriate adjustment of the external source. As an
alternative, a magnetically adjustable potentiometer may be
provided in the receiver circuit to permit variation of the voltage
output level of the receiver at the output or stimulation
electrodes. Either a permanent magnet or an electromagnet may be
employed to accomplish the adjustment operation. In still another
alternate arrangement, a percutaneously adjustable potentiometer
may be employed.
It is accordingly a principle object of the present invention to
provide an improved apparatus for applying electrical stimulation
energy to body-implanted apparatus with signal-receiving means.
It is a further object of the present invention to provide an
improved apparatus for applying electrical stimulation energy to
implanted devices, including nerve and muscle stimulators,
artificial organs, and certain electromechanical devices.
It is still a further object of the present invention to provide a
system for delivering electrical stimulation energy to
body-implanted apparatus utilizing an implanted receiver coupled to
an externally worn transmitter, the apparatus being arranged to
deliver an energy envelope of constant characteristic to the output
electrodes of the receiver, this being achieved irrespective of the
precise location of the externally worn transmitter.
It is yet a further object of the present invention to provide an
apparatus for delivering electrical stimulation energy to
body-implanted apparatus with signal receiving means, the implanted
receiver being electrically coupled to an external transmitter, the
receiver being provided with means for controlably varying the
electrical characteristics of the receiver output from a point
external to the body.
These and other objects of the invention will become apparent to
those skilled in the art upon a reading of the following detailed
description of the various embodiments in light of the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates the manner in which one embodiment of the
present invention may be utilized in an application to stimulate
the carotid sinus nerve bundle, this figure showing the system as
implanted in a human being;
FIG. 2 illustrates the electrodes and receiver portion of the
embodiment of the invention as shown in FIG. 1;
FIG. 3 illustrates a typical transmitter enclosure and associated
antenna coil as utilized in the apparatus of FIG. 1, with the coil
being shown removed from the transmitter enclosure;
FIG. 4 illustrates, by means of an electrical schematic diagram, a
preferred embodiment of the receiver portion of the system;
FIG. 5 illustrates the wave forms existing at various points within
the circuit of FIG. 4;
FIGS. 6 and 7 illustrate alternative arrangements for producing a
constant amplitude output from the receiver in spite of input
variations;
FIG. 8 illustrates alternative embodiments whereby the constant
current circuitry can be switched out providing all controls
accessible from a point remote from the receiver package itself;
and
FIG. 9 illustrates a further alternative embodiment of a constant
current regulator which is adapted to function in conjunction with
a radio frequency receiver.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, there is shown a patient 10 having a
subcutaneously implanted apparatus for direct stimulation of
predetermined nerve bundles. Specifically, there is shown a radio
frequency impulse receiver 12 whose output is coupled by way of
electrodes 14 and 16 to the carotid sinus nerve bundles 18 and 20
of the patient 10.
Electrical stimulation energy passed along the carotid sinus nerves
proceeds generally centrally to the medullary cardiovascular
centers. It has been found that the affect achieved is a decrease
in the peripheral sympathetic stimuli to the arterioles, reflecting
in a lowering of blood pressure and a decrease in sympathetic
stimuli to the heart. In other applications, electrical stimulation
energy may be used for achieving entirely different affects, it
being understood that this application of the system is being shown
for purposes of explaining the various concepts of the present
invention.
Referring now to FIG. 2, it can be seen that the electrodes 14 and
16 terminate distally in cradle-shaped, polished-platinum
stimulation electrode structure 22, molded within a silicone rubber
head 24 and arranged to make direct physical contact with a nerve
bundle when in place, for example, the carotid sinus nerve bundle.
Flaps 26 extend from the head 24 and are normally sutured closed
during the implant operation to hold the conductive portions of the
electrode 22 in permanent contact with the nerve bundle. When
installed, only the platinum electrodes and the silicone rubber of
the electrode head come into physical contact with the nerve
bundle.
Referring again to FIG. 1, the nerve stimulating apparatus of this
invention further includes a transmitter or source of radio
frequency impulses 38 which may be affixed to the body of the
patient by an convenient means such as a belt 30. Alternatively,
the transmitter 38 may be carried by the patient in this shirt
pocket, or any other convenient location on or adjacent the body.
The transmitter assembly 38 consists of a battery-powered pulse
generator and an attached antenna coil 32. The coil 32 is connected
to the transmitter 38 by way of conductive wires encased or
encapsulated within a flexible tube or conduit 34.
As is indicated by the broken line 36 in FIG. 1, in use, the
transmitter antenna coil 32 is placed on the skin directly over the
receiver 12 such that pulses of radio frequency energy are
inductively coupled through the skin of the patient from
transmitter antenna coil 32 to the receiving coils (not shown in
FIG. 1) located within the surgically implanted receiver package
12.
As is shown in FIG. 3, the transmitter is provided with controls
which can be adjusted to fix the characteristics of the energy
envelope, including such parameters as amplitude, pulse duration,
and frequency of the impulses to be produced by the transmitter for
required or optimum response.
With continued attention being directed to FIG. 3, the transmitter
circuits are enclosed within a rugged, light weight container 38a,
the container preferably being sealed to prevent ingress of
moisture, dirt, or other contamination. Within this container is a
power source in the form of a battery 40.
The cable 34 is adapted to be connected to the transmitter 38 by
means of a connector 44 which mates with a socket 46 on the
transmitter case. The transmitter is also provided with an on-off
switch 48 which is accessible to the patient so that he can switch
the transmitter into operation when a need is indicated, such as
upon the onset of anginal pain or prophylactically when he
anticipates that a given activity will precipitate an anginal
attack.
Referring again to FIG. 2, the implantable portion of the nerve
stimulating apparatus of this invention consists of a wafer-like
receiver package 12. The receiver electrical components 50 are
preferably embeded in epoxy resin, with the entire assembly being
encased in an inert medium such as transparent silicone rubber or
the like.
With the physical construction of the transmitter, transmitting
antenna, receiver and electrodes having been described, attention
will now be given to the various circuits which may be included
within the receiver package 12 and which function to provide
impulses with an energy envelope of constant characteristics, with
the impulse energy being regulated through control of the pulse
amplitude, the pulse duration, or the pulse frequency delivered to
the stimulation electrodes which are in turn coupled to the nerve
bundle. Referring to FIG. 4, there is shown a tuned circuit 66
comprising an inductor 68 and a capacitor 70. The component values
of the inductor and capacitor are such that the circuit resonates
at the transmitter frequency. Coupled to the output of the tuned
circuit 66 at the terminal 71 is a diode detector network including
a semiconductor diode 72 and a filter capacitor 74. The output of
the diode detector appearing at the junction 76 is coupled through
a current limiting diode 78 and a coupling capacitor 80 to the
output terminals 82, 84 to which the conductors 54 (FIG. 2) are
attached. A load resistor 86 is connected to the junction 88 formed
between the current limiting diode 78 and the coupling capacitor
80.
FIG. 5 illustrates the wave form of the signals occurring at
various points in the circuit of FIG. 4 when the transmitter
antenna coil is placed in close proximity to the coil 68 of the
receiver. Specifically, the wave form of FIG. 5, waveform a shows
the form of the output appearing at the junction 71. The radio
frequency signal when applied to the diode detector 72 causes
rectification to take place so that only the positive going portion
of the envelope results at the junction 76. The capacitor 74 acts
as a filter capacitor or band-pass filter for smoothing the signal
and removing the RF components of the signal. The diode 78 is a
constant current diode of a pre-selected value. Its function is to
regulate the current flow, providing a desired current flow
independent of the input signal as long as the input signal is
above the threshold value of the diode 78. The dotted line in the
wave form shown at b in FIG. 5 illustrates this threshold level and
the wave form shown at c in FIG. 5 results at the junction 88. The
wave form d of FIG. 5 illustrates the pulse which is AC coupled to
the electrode load. The electrode assembly can be considered as a
resistive element but in practice, it does not exhibit some degree
of capacitance causing the voltage wave forms to differ slightly
from those illustrated in FIG. 5.
When using a direct wire connection which passes through the skin
of the patient from a transmitter to the nerve rather than
inductive coupling as in this invention, it is relatively simple to
maintain a constant energy pulse for application to the nerve
bundle. When the coupling is inductive in nature, however, such as
is the case where the pulse generator is external to the body and
the receiver and stimulation electrodes are implanted, it is more
difficult to maintain or predict accurately the amount of energy
being transferred. This is particularly true when the distance
between the transmitting antenna coil and the receiving antenna
coil varies or a concentricity displacement occurs. The use of the
constant current diode 78 in the receiver of FIG. 4 obviates this
problem. Specifically, by supplying an excess of energy to the
receiving coil and limiting the receiver output with the constant
current diode 78, the amount of energy transferred is maintained at
a constant value which can be controlled by varying the pulse
duration periods.
As an alternate structure, the current limiting diode 78 as
illustrated in FIG. 4 may be replaced with a field effect
transistor and associated bias potentiometer. In its operation, the
field effect transistor functions as a current regulator with the
current flow being determined by the bias voltage existing between
the source and gate electrodes of the field effect transistor. The
voltage of the field effect transistor is independent of the
voltage signal applied to its input so long as the input voltage
exceeds the sum of the voltage drop across the associated bias
potentiometer and the voltage drop across the load being applied to
the terminals, such as the load terminals 82 and 84 of FIG. 4. The
output current can, of course, be adjusted in view of the provision
of the bias potentiometer.
In another embodiment, FIG. 7 illustrates a receiver suitable for
use in the nerve stimulating system of this invention, wherein the
output signal level is controlled through the use of a series type
voltage regulator. Again, those components having similar function
to the components in FIG. 4 are given identical identifying
numerals in FIG. 7. The circuit if FIG. 7 is substantially
identical to that of FIG. 4 except that the current limiting diode
78 of FIG. 4 is replaced by a conventional NPN transistor 102
connected in an emitter follower configuration. Specifically, the
transistor 102 includes a base electrode 104, an emitter electrode
106, and a collector electrode 108. The collector electrode is
connected to the junction point 76 which is the output from the
diode detector network. The emitter electrode 106 is directly
connected to the junction 88. A voltage divider including a
resistor 110 and a potentiometer 112 is connected in parallel with
the output of the detector network. Connected in parallel with the
resistive element of the potentiometer is a Zener diode 114. This
diode serves to maintain the junction 116 at a constant voltage. By
adjusting the wiper arm 118 with respect to the potentiometer
resistance 112, the bias applied to the base electrode 104 of the
transistor can be varied. Of course, variation of this bias affects
the resistance presented between the emitter and collector
electrodes of the transistor 102 and therefore the output signal
amplitude appearing across the terminals 82, 84.
A further improvement in the receiver circuit is illustrated in
FIG. 8. The circuit of FIG. 8 is identical to that of FIG. 4 except
that a normally open magnetically actuated reed type switch is
connected in parallel with the constant current diode 78. This
switch is identified in FIG. 8 by numeral 120. The switch is placed
in the receiver circuitry in such a manner so as to remove the
current limiting circuitry, thereby allowing full control of the
amplitude and pulse width parameters from the external transmitter
without the benefit of the receiver regulating circuit. Because the
receiver package is located from one to two centimeters beneath the
surface of the skin of the patient, the switch can be actuated by a
permanent magnet positioned on the surface of the skin in proximity
to the location of the implanted receiver.
In the embodiments of FIG. 6 it is also possible to provide means
for adjusting the voltage or current limiting circuitry of the
implanted receiver from an external location without surgical
intervention. Specifically, the positionable wiper arms on the
potentiometers used in the circuit of FIG. 6 may be moved by means
of an external magnet. That is, by coupling the wiper arm of the
potentiometer directly or through a gear reduction to a permanent
magnet 91, it is possible to drive the assembly by means of an
external magnet (not shown). Alternatively, by coupling the
potentiometer wiper arm to a ratchet, which in turn, is coupled
directly to a permanent magnet, it is possible to adjust the
resistance value of the potentiometer by electro-magnetic pulses
which cause the ratchet to rotate.
Still additional alternatives are available by the use of a
potentiometer adjustable by a percutaneous needle, or the like. A
mechanical pressure ratchet may also be used.
Attention is now directed to FIG. 9 of the drawings wherein a
constant current regulator is shown in combination with the radio
frequency receiver, and having certain modified features from those
shown in the circuitry of FIGS. 4-8. A receiving coil is provided
having segments 122 and 124 center tapped at 126. Capacitor 128 is
used to tune the receiver to resonance at the carrier frequency.
Diodes 130 and 132 are provided in such a manner so as to provide
full-wave rectification as an alternate to the half-wave
rectification provided on previous illustrations. This feature is
provided in order to achieve greater power transfer efficiency.
Capacitor 134 functions as a filter capacitor to remove the carrier
frequency from the stimulus signal. Variable resistor 136 is
provided along with constant current diode 138 to form the
reference standard for the regulator device. The current flowing
through resistance element 136 is held constant by constant current
diode 138, and adjustment of the value of resistance element 136
will adjust the reference voltage developed across resistance
element 136. The voltage reference is converted into a current
reference by use of resistor 140, resistor 140 having a large ohmic
value. Transistor 142 is utilized as a current amplifier with the
collector current applied to the load being approximately equal to
the base current, multiplied by the amplification factor B Beta, of
the transistor. Capacitor 144 is utilized to block the DC component
of the stimulus signal while resistor 146 provides a discharge path
for capacitor 144 between pulses. The circuitry as shown in FIG. 9
minimizes variations in output delivered to electrodes 148 and 150
due to changes in input signal as well as load impedance. The
stimulus current may be readily adjusted by controlling the
resistance value of variable resistor 136.
In addition to application as a carotid sinus nerve stimulator, the
concept of the present invention is readily adaptable for use in
electroanalgesia. In particular, one such area of electroanalgesia
may involve dorsal column stimulators which stimulators may include
an implanted dorsal column electrode and receiver system. The
control of the amplitude of the signal being delivered to the
electrodes may be controlled in the manner illustrated hereinabove,
with the same electrical principles being applied. Other specific
applications includes the use as a phrenic nerve stimulator,
cardiac pacing, or peripheral nerve stimulation. The apparatus may
find further application as a muscle stimulator, such as in bladder
stimulation, or the like. The apparatus may also find application
as a brain stimulator. For electro-mechanical applications, the
device may be used to controlably inject quantities of a particular
fluid into the system, such as insulin or the like.
The apparatus of the present invention is arranged to deliver
electrical stimulation energy to body-implanted apparatus with an
energy envelope of constant characteristic. As such, the range of
applications are wide and varied.
As used herein, the stimulation electrodes may be applied to either
an animate or inanimate structure. When used for nerve or muscle
stimulation, the stimulation or electrodes are coupled to an
animate object, however when coupled to an implanted
electro-mechanical device, the stimulation electrodes will be
coupled to an inanimate object. The definition of the term
"stimulation electrode" will, therefore, be readily comprehended
and understood.
Thus, it can be seen that there is provided by this invention a
means whereby pulses which are accurately controlled in amplitude,
duration and frequency can be applied to a nerve bundle within the
body of a patient by inductively coupling electrical energy from an
externally located transmitter to a subcutaneously located receiver
and electrode assembly. Variations of this invention will occur to
those skilled in the art upon a reading of the specification and
accordingly, the scope of the invention is to be determined by the
appended claims.
* * * * *