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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention presented herein relates to urinary control using in
intra-anal plug electrode assembly for applying a neuromuscular
stimulating signal from a battery-powered electronic circuit to the anal
sphincter of the user for causing reduction of urinary incontinence.
2. Description of the Prior Art
B. R. Hopkinson and R. Lightwood of England have reported the use of an
intra-anal plug electrode assembly constructed of electrically insulative
material having a central constricted portion. When positioned to extend
above and below the physiological anal sphincter, the constricted portion
allowed the assembly to be held in place by closure of the anal sphincter
muscle. The plug had circumferential ring electrodes laterally displaced
in both directions from the central constricted portion which were
connected to a portable battery-operated generator capable of delivering
25 microsecond pulses at a frequency of about 30 Hz. from 0 to 20 volts.
The pulses stimulated the sphincter causing it to close. The device was
used to treat persons with anal incontinence, urinary incontinence or
both. U.S. Pat. No. 3,749,100 to H.A. von der Mosel, indicates the method
of choice for functional electrical stimulation (FES) of the sphincter
using an intra-anal electrode unit is a square wave having a peak
potential not greater than about 10 volts (preferably between 1 and 2
volts) and a frequency in the range from 18 to 90 Hz. The patent indicates
that provision was made for adjustment of the load current by the user.
Cardiac Recorders, Ltd., has provided a system for FES using an intra-anal
electrode unit which delivers 1 millisecond pulses at a rate of 200 per
second with the output controlled by the user allowing the output to be
increased gradually when the unit is turned on.
The nature of an FES signal provided by the prior art devices results in a
phenomenon known as fatigue and habituation resulting in a decreasing
response to such an FES signal. While that FES signal may be effective
initially, its effectiveness diminishes quickly with time.
SUMMARY OF THE INVENTION
The fatigue and habituation problem presented by known systems providing
FES of the sphincter using an intra-anal electrode unit is minimized by
this invention, which provides for automatic changes in the duration and
frequency of the pulses in a pseudo-random fashion with provision made for
a relaxation or rest period when no pulses are supplied to the electrode
unit. In one embodiment, a urinary incontinence stimulator system of this
invention uses an intra-anal electrode and includes a generator means
providing a series of pulses of varying duration and frequency plus an
enabling means for providing a recurring enabling signal with an output
circuitry connected to receive the pulses from the generator means and the
enabling signals from the enabling means to provide a pulse to the
intra-anal electrode for each pulse received from the generator means for
a time determined by the enabling signal. The time periods between the
enabling signals provides the rest period when no pulses are applied to
the intra-anal electrode.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and its various advantages will
become apparent from the following description given in conjunction with
the accompanying drawings in which an embodiment of the invention is
illustrated by way of example and wherein:
FIG. 1 is a block diagram of a urinary incontinence stimulator system
embodying the invention; and
FIG. 2 is a schematic exemplary showing of circuit details for the circuit
portions shown in block diagram form in FIG. 1.
DESCRIPTION
FIG. 1 of the drawings shows in block diagram form a urinary incontinence
stimulator system embodying the invention which includes a pulse generator
20, output circuitry 30 and enabling circuitry 50. The generator 20
provides series of pulses of varying duration and frequency. The output of
the generator 20 is connected to output circuitry 30 which provides pulses
of the same varying duration and frequency to an intra-anal electrode 40
for the time the circuitry 30 is enabled by recurring enabling signals
supplied to it by the enabling circuitry 50.
The structure of a suitable intra-anal electrode for use in the system is
well known and may, for example, be of the type described in U.S. Pat. No.
3,749,100 to H. A. von der Mosel or of the type used by Cardiac Recorders,
Ltd.
Referring to FIG. 2, a detailed schematic is shown of exemplary circuits
which are interconnected for providing the above-described functions for
the pulse generator 20, the enabling circuitry 50 and the output circuitry
30.
The pulse generator 20 is essentially a free-running multivibrator and
includes a comparator 21, the operation of which is controlled by the
voltage on a capacitor 22 connected between ground and the negative input
of the comparator. When the system is turned on by the operation of switch
60 to apply a D.C. voltage V+ from a battery 61 to the system, the voltage
across capacitor 22 is low allowing the comparator 21, due to the bias
presented by resistors 200, 201 and 202, to present a high signal at its
output. A charging circuit for capacitor 22 is provided by resistor 203,
diode 204 and resistor 205 connected in parallel with one or more of
resistors 206-209, as determined by the switching provided by the
semiconductor switching circuit 210. The switching circuit 210 is
commercially available, and may, for example, be a type 4016 device, which
is available from the RCA Corporation. The operation of the switching
circuit 210 is controlled by the outputs of a binary coded decimal up
counter 211 which changes with each input pulse supplied to the input 220
of counter 211. A type 4520 counter available from the RCA Corporation may
be used to provide counter 211. The form of the source for providing input
pulses to counter 211 is not critical and could, therefore, take on a
number of forms. For convenience, the output of the output circuitry 30 is
used to provide the input pulses to counter 211. Using the output of
output circuitry 30, the counter 211 is connected to respond to the
trailing edge of each pulse supplied to the counter 211. The resistor
206-209, have different values which are selected to provide 16 different
charging rates which may be spaced in essentially equal increments over
the range of charging rates provided. When capacitor 22 increases to about
2/3 of the voltage +V, the comparator 21 responds to provide a low signal
at its output which allows the capacitor 22 to discharge via diode 212 and
resistor 213 connected in parallel with one or more of resistors 214-217,
as determined by the switching provided by semiconductor switching circuit
218 which may be the same as the switching circuit 211. When the voltage
at capacitor 22 decreases to about 1/3 of the voltage V+, the comparator
21 again presents a high output. The operation of the switching circuit
218 is controlled by the outputs of a binary coded decimal up counter 219.
The counter 219 may be provided by the same type of counter used for
counter 211. An input for increasing the count of counter 219 is obtained
from one of the outputs of the counter 211 with the counter 219 connected
so as to respond to the leading edge of the output obtained from counter
211. The connection to an output of counter 211, for example, may be made
so the counter 219 provides a different output to present a different
dischage rate for capacitor 22 every fourth time the charge rate for
capacitor 22 is changed by the output of counter 211. Sixteen different
discharge rates, which may be spaced apart by essentially equal
increments, are provided. In a circuit constructed in accordance with this
invention, the values for capacitor 22 plus resistors 205-209 and 213-217
were selected causing the pulses presented at the output of the comparator
21 to have a duration which varied between about 0.5 milliseconds and 1.5
millseconds with a frequency which varied between about 10 and 55 Hz. With
the signal generator 20 just described, pseudo random variable frequency
and variable duration pulses are presented as an output from the
comparator 21 and are applied to output circuit 30.
Whether pulses corresponding to those from generator 20 appear at the
output of the circuit 30 is determined by enabling signals provided by the
enabling circuit 50 connected to circuit 30. The enabling circuit 50 is
also essentially a free-running multivibrator that is much like the
multivibrator described for the pulse generator 20, except that its on-off
times do not vary. The enabling circuit 50 includes a comparator 51, the
operation of which is controlled by the voltage on the capacitor 52
connected between ground and the negative input of the comparator. When
switch 60 is operated to provide the voltage V+ to the circuit 50, the
capacitor 52 presents a low voltage allowing comparator 51, due to the
bias presented by resistors 500, 501 and 502, to present a high signal at
its output. A charging circuit for capacitor 52 is provided by resistor
503, diode 504 and resistor 505 allowing the voltage on capacitor 52 to
increase after switch 60 is operated. When the voltage on capacitor 52
reaches about 2/3 of the voltage V+, the comparator 51 responds to provide
a low signal at its output allowing the capacitor 52 to then discharge via
resistor 506 and diode 507. When the voltage on capacitor 52 decreases to
a level that is about 1/3 the voltage V+, the comparator 51 responds to
again present a high signal at its output. The values of capacitor 52 and
resistors 505 and 506 determine the duration for the high and low signals
that are alternatively presented at the output of comparator 51. A high
signal from comparator 51 enables the output circuitry 30 for the duration
of such high signal so it can present a high signal to the load at the
intra-anal electrode 40 when a high signal is presented to circuitry 30
from the pulse generator 20. The control of urinary incontinence provided
by the system may deteriorate for some patients if the duration of the low
signal from the enabling circuit 50 is too long. Suitable values for
capacitor 52 and resistor 505 and 506 may be those which cause a high
signal to be presented at the output of the output circuitry 30 for about
the same time that a low signal is present with the maximum duration for
the low signal being about two seconds.
A suitable output circuitry 30 includes two comparators 31 and 32 which are
connected to the pulse generator 20 and the enabling circuit 50 to control
the operation of two transmitters 33 and 34. The comparators 31 and 32,
like comparators 21 and 51, may be of a type having a transistor at its
output, the emitter of which is grounded with the collector providing the
output for the comparator. The comparator presents a high signal when its
output transistor is not conducting and presents a low when its output
transistor is conducting.
A variable resistive path is presented between the voltage V+ and the
output of comparator 32 by resistor 300 connected in series with a
potentiometer 301. The transistor 33 is an NPN type which has its emitter
connected to the emitter of a PNP type transistor 34. The collector of
transistor 33 is connected to voltage V+ while the collector of transistor
34 is connected to ground. The base of each transistor is connected to the
movable contact of potentiometer 301 so transistor 33 conducts when the
output of comparator 32 is high, at which time transistor 34 is not
conducting. When comparator 32 presents a low signal at its output, the
conducting state for the transistors is reversed, i.e., transistor 34 is
on and transistor 33 is off. A capacitor 302 is connected between one
input to the intra-anal electrode 40 and the emitter electrodes of
transistors 33 and 34. The other input of the electrode 40 is connected to
the collector of transistor 33. Charging of capacitor 302 occurs whenver
transistor 34 conducts to pass current through the load at electrode 40 in
one direction. The level to which the capacitor 302 charges is determined
by the setting of the potentiometer 301. When transistor 33 is turned on,
the capacitor 302 is effectively connected across the load at electrode 40
to apply substantially the full voltage on the capacitor 302 across the
load at the electrode 40. This current flow through the load is opposite
in direction to the charging current. The switch 60 is ganged to the
movable connector of potentiometer 301 so that the magnitude of the pulses
provided to load at electrode 40 will be at a low level when switch 60 is
moved to the on position by the user.
The negative inputs of comparators 31 and 32 are biased by series connected
resistors 303 and 304 which connect between voltage V+ and ground. The
negative input of comparators 31 and 32 is connected to the common
connection of resistors 303 and 304. A common connection is provided for
the outputs of comparators 21 and 31 plus the positive input of comparator
32. A high output will be presented at the output of comparator 31 when
the output of the enabling circuit 50 is high. A high signal is presented
to the comparator 32 only when the output of the pulse generator 20 and
the output of comparator 31 are both high. Accordingly, the pulses from
pulse generator 20 will be passed by the comparator 32 only for such times
as the enabling circuit 50 presents a high signal to the comparator 31.
With this arrangement, the user receives periods of bursts of pseudo
random variable frequency and variable duration pulses spaced by a rest
period of about equal duration when no pulses are received. The rest
period is provided when the output of the enabling circuit 50 is low.
In the light of the above teachings, alternative arrangements and
techniques embodying the invention will be suggested to those skilled in
the art. The scope of protection afforded the invention is not intended to
be limited to the specific embodiments disclosed, but is to be determined
only in accordance with the appended claims.
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