U.S. patent number 3,650,275 [Application Number 04/752,352] was granted by the patent office on 1972-03-21 for method and apparatus for controlling anal incontinence.
This patent grant is currently assigned to Bio-Controls Corp.. Invention is credited to Hans A. Von Der Mozel.
United States Patent |
3,650,275 |
Von Der Mozel |
March 21, 1972 |
METHOD AND APPARATUS FOR CONTROLLING ANAL INCONTINENCE
Abstract
An electrostimulation probe comprising a suppository body formed
with a rounded bulbous head, a reduced neck, and a broadened hilt,
is inserted into the anus of a patient suffering from incontinence.
The rounded bulbous tip and reduced neck facilitate anal insertion
and subsequent retention. The rounded neck is clasped by the
sphincter rectalis, and is provided with a pair of spaced
electrical contacts which rest against the sphincter. The broadened
hilt limits insertion of the suppository body, and has a
substantially flat base so as to permit the patient to sit or lie
down comfortably with the device inserted. A pair of electrical
leads are connected respectively to the contacts, which are
energized by a square wave signal having an average value of zero
volts, a peak potential between 1 and 2 volts, and in the frequency
range from about 18 to Hertz. 20 hertz. Such electrostimulation
causes tonic and physiological contraction of the sphincter muscle,
with significant results in the control of incontinence.
Inventors: |
Von Der Mozel; Hans A.
(Cliffside Park, NJ) |
Assignee: |
Bio-Controls Corp. (New York,
NY)
|
Family
ID: |
25025950 |
Appl.
No.: |
04/752,352 |
Filed: |
August 13, 1968 |
Current U.S.
Class: |
607/76; 331/111;
607/138; 128/DIG.25 |
Current CPC
Class: |
A61N
1/36007 (20130101); A61N 1/0512 (20130101); Y10S
128/25 (20130101) |
Current International
Class: |
A61N
1/36 (20060101); A61N 1/05 (20060101); A61n
001/34 () |
Field of
Search: |
;128/404,407,408,419,421,422 ;331/51,111,113 ;307/261,291
;328/35,39 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,323,520 |
|
Mar 1963 |
|
FR |
|
794,908 |
|
May 1958 |
|
GB |
|
Other References
Turner, "Manual of Practical Medical Electricity," 3rd Edition,
1902, p. 300 relied on.
|
Primary Examiner: Kamm; William E.
Claims
The invention claimed is:
1. The method of controlling anal incontinence due to failure of
the sphincter rectalis function, comprising the steps of:
putting a pair of spaced electrodes against the sphincter
rectalis;
applying an alternating signal having an average value of about
zero across said spaced electrodes to contract said sphincter
rectalis, and
maintaining said sphincter in a steady contracted condition by
continuing to apply said signal to said electrodes.
2. The method of claim 1 wherein said signal is a voltage having a
frequency rate in the range from about 18 to about 90 Hertz.
3. The method of claim 2 wherein said signal is substantially a
square wave.
4. The method of claim 3 wherein the peak potential of said signal
is not greater than about 10 volts.
5. The method of claim 3 wherein the peak potential of said signal
is between about 1 and 2 volts.
6. In apparatus for use in controlling incontinence, a rectal probe
including:
a suppository body formed of an insulating material and including a
rounded bulbous tip adapted for insertion into and subsequent
retention within the anus of a patient, a reduced neck joined at
one end to said bulbous tip, and a broadened hilt joined to said
reduced neck at the other end thereof to limit anal insertion of
said suppository device so that said reduced neck rests against the
sphincter rectalis;
and a pair of spaced-apart electrical contacts energizable by an
external voltage source and secured to the external surface of said
reduced neck whereby to rest against said sphincter rectalis during
insertion;
a pair of electrical leads for connection to said external voltage
source and connected to said contacts respectively for energization
thereof; and
an electrical generator connected to said leads for energizing said
contacts, said generator comprising:
a time base oscillator for producing a series of timing pulses;
and a bistable circuit arranged to switch between alternate states
in response to successive ones of said timing pulses, and to apply
a substantially square wave output to said leads as a result of
said switching.
Description
FIELD OF THE INVENTION
This invention relates generally to the area of prosthetic
assistance, and particularly concerns the control of anal
incontinence by electrical stimulation of the sphincter
rectalis.
THE PRIOR ART
The general idea of electrical stimulation of muscle tissue has a
long history, and recently has culminated in the impressive
successes now achieved in the area of cardiac pacemaking. In other
respects, however, electrical muscle stimulation is still largely
experimental, and has not become an established therapeutic
procedure.
Anal incontinence is a condition of considerable physical
inconvenience and psychological embarrassment which afflicts some
patients, generally as a result of neurogenic failure, or in some
cases senile atrophy of the sphincter muscle. It is highly
desirable that some way be found for controlling this
condition.
In experiments with electrical stimulation of the sphincter
rectalis to control this condition, it was discovered that the
techniques employed in the area of cardiac pacemaking and other
electrical muscle stimulation procedures are not applicable. Anal
incontinence presents a distinct problem calling for a different
kind of electrical muscle stimulation, if anal incontinence is to
be controlled effectively by this means.
In cardiac pacemaking, repeated short contractions of the heart
muscle are desired, followed by relatively long intervals of
relaxation between contractions. In contrast, if sphincter rectalis
stimulation is to control anal incontinence effectively, continuous
contraction over a long period of time must be achieved. Obviously,
even a single brief relaxation of the sphincter over a period of
many hours could result in incontinence when the patient relies
entirely upon the electrical stimulation.
SUMMARY AND OBJECTS OF THE INVENTION
Accordingly, the present invention is directed to controlling anal
incontinence and eliminating its physical inconvenience and
psychological embarrassment. The aim is to accomplish this by means
of electrical stimulation of the sphincter rectalis, resulting in
continuous tonic and physiological contraction of the sphincter
muscle without lapses over long periods of time so as to achieve
total continence.
At the same time, however, it is an object of the invention to
accomplish these results with minimal amounts of electrical power,
both for medical reasons and reasons of product design. The medical
reasons involve the avoidance of injury to the adjacent tissue
through electrical burns, as well as avoiding over-stimulation of
the tissue with consequent loss of muscle contraction response.
So far as product design is concerned, it would be quite desirable
to provide electrical stimulation apparatus for the control of anal
incontinence which will operate for long periods of time on the
energy available from a small battery power supply. This would make
the apparatus completely portable, allowing the patient to live as
normal a life as possible. This is another consideration which
dictates a design aiming at minimal power consumption.
The present method for the control of anal incontinence comprises
the steps of putting a pair of spaced electrodes against the
sphincter rectalis and applying a signal across these electrodes
which is effective to maintain the sphincter in a continuously
contracted condition for the duration of the signal. In more
specific terms, the signal is a voltage varying at a rate in the
range from about 18 to about 90 Hertz, having an average potential
of zero so as to avoid tissue polarization, and a substantially
square waveform with a peak potential of not more than about 2
volts.
The apparatus for practicing this invention comprises a probe
including a suppository body formed of a physiologically inert
insulating material, and including a rounded bulbous tip adapted
for insertion into and subsequent retention within the anus of the
patient. A reduced neck is joined at one end to the bulbous tip,
and a broadened hilt at the other end of the neck serves to limit
anal insertion of the device. The reduced neck rests against the
sphincter rectalis when the device is inserted, and has
spaced-apart electrical contacts mounted thereon. These contacts
are formed of a physiologically inert conductive material, and they
serve to stimulate the sphincter electrically during use of the
device. A pair of electrical leads is provided for the respective
contacts, the leads coming out of the probe and being connected to
the type of electrical drive described in the previous paragraph.
Additionally, the broadened hilt of the suppository body has a
substantially flat base to permit the patient to sit or lie down
comfortably when the device is inserted.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a side elevational view of a rectal probe according to
the present invention.
FIG. 2 is a front view partly in section and partly in elevation of
the same probe.
FIG. 3 is a schematic circuit diagram of the presently preferred
electrical generator for energizing the electrodes of the
probe.
FIG. 4 is a diagram showing the response of normal dogs to three
different types of electrical stimulation of the sphincter
rectalis.
FIG. 5 is a graph showing corresponding data in relation to dogs
suffering from experimentally induced loss of sphincter rectalis
function.
And FIG. 6 is a graph of sphincter rectalis response as a function
of the electrical stimulation frequency.
The same reference characters refer to the same elements throughout
the several views of the drawing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The sphincter rectalis stimulation apparatus of this invention
includes a rectal probe 8 of the type illustrated in FIGS. 1 and 2.
This probe comprises a suppository body 10 integrally molded of a
physiologically inert material such as silicone rubber, medical
grade, to avoid tissue necrosis. This material is available from
the Dow Chemical Company under the trademark Elastomer. The
suppository body 10, which is inserted into the anus of the
patient, is formed with a rounded bulbous tip 12 adapted for smooth
insertion with a minimum of discomfort to the patient. The bulbous
tip 12 tapers to a reduced neck 14, which then widens out again to
a broadened hilt 16, terminating in a substantially flat base 18.
After anal insertion has been accomplished, the fact that the
bulbous tip 12 has a larger diameter than the reduced neck 14
facilitates retention of the suppository body 10 by causing the
body 10 to be cammed inwardly instead of being expelled in response
to sphincter contraction. The broadened hilt 16, which is also
wider than the reduced neck 14, serves to limit insertion of the
suppository body 10 so that it is not intruded too far into the
anal opening.
As a result, the body 10 comes to rest with the reduced neck 14
clasped by the sphincter rectalis, the bulbous tip 12 protruding
into the rectum, and the broadened hilt 16 remaining outside the
ans. When it is necessary to remove the probe 8, the external
portion 16 is thus readily accessible to facilitate withdrawal. As
an additional feature of the suppository body 10, the flat base 18
thereof permits the patient to sit or to lie down upon his back in
relative comfort when the device is in use.
The probe 8 also includes a pair of electrodes 20 and 22 mounted on
opposite sides of the reduced neck 14 for electrical stimulation of
the sphincter rectalis. Each of these electrodes is a thin leaf of
physiologically inert but electrically conductive material, such as
gold, although stainless steel and other relatively inert
conductors may be used. Preferably, the leaves 20 and 22 are formed
of a plurality of side-by-side wires 23 although satisfactory
results can be obtained with thin continuous leaf material. The
choice of silicone rubber as the material for the suppository body
10 is of course entirely compatible with the use of stainless steel
for the contacts 20 and 22, and in addition provides electrical
insulation between the contacts. While there are a number of
possible methods for securing the contacts 20 and 22 in place upon
the suppository body 10 the presently preferred method is to form
the contacts of thin leaves of gold which are bent to match the
curvature of the reduced neck 14 and are then simply glued in
place. Any method will do, however, if it results in contacts 20
and 22 which lie relatively flat against the surface of the reduced
neck 14 so as to avoid injury to the patient upon insertion.
In order to provide individual electrical connections to the
contacts 20 and 22, the suppository body 10 may be provided with a
hole 24 drilled transversely through the reduced neck 14, and
another hole 26 drilled longitudinally upward from the base 18 and
intersecting the transverse hole 24. A pair of leads 28 and 30
enter the longitudinal hole 26 from outside the base 18, and extend
upwardly through the length of the longitudinal hole to the
transverse hole 24. Then the leads 28 and 30 extend in opposite
directions through the transverse hole 24 to reach their respective
electrical contacts 20 and 22, to which they are soldered. When
mounting the electrical contacts 20 and 22 upon the suppository
body 10, the leads 28 and 30 can first be inserted into the holes
26 and 24, and pulled sidewardly from the ends of the hole 24 so
that a length of each lead protrudes from the reduced neck 14 to
facilitate soldering to the associated contact. Afterwards, the
leads 28 and 30 can be pulled back down through the longitudinal
hole 26 while the contacts 20 and 22 are placed adjacent the
reduced neck 14 and glued in place.
In order to enable workers in the field to practice this invention
readily, it will be helpful to have some idea of the dimension of
the rectal probe 8 which enable it to fit comfortably and
functionally within the rectal opening of a patient. In a
particular preferred embodiment, the overall length of the
suppository body 10 from the base 18 to the tip of the rounded
bulbous tip 12, was about 3 inches. The measurement from the
extremity of the rounded bulbous tip 12 to the thinnest portion of
the reduced neck 14 was approximately 17/8 inches. The maximum
diameter of the tip 12 was approximately 11/4 inches, and the
minimum diameter of the reduced neck 14 was approximately one-half
inch. The maximum diameter of the broadened hilt 16 should be
somewhat in excess of the maximum diameter of the rounded bulbous
tip 12. The contacts 20 and 22 were approximately one-quarter inch
wide and 11/2 inches long. They were so placed upon the reduced
neck 14 that they extended to within about half an inch of the base
18.
Best experimental results were achieved with an electrical signal
of square wave shape applied across the contacts 20 and 22 by means
of the leads 28 and 30. One illustrative circuit which has been
found to accomplish this successfully is illustrated in FIG. 3.
There it is seen that a battery 32 energizes a positive bus 40 and
a negative bus 42 through an on-off switch 38.
A conventional unijunction relaxation oscillator 56 energized from
busses 38 and 42 serves to generate repetitive pulses for timing
the square wave output signal. The time base is an RC circuit
comprising a capacitor 58 charging through a series resistance 60.
The switching function for the relaxation oscillator is
accomplished by a unijunction transistor 64, the emitter E
(switching electrode) of which is connected to the positive side of
the timing capacitor 58. Load current for the unijunction is drawn
through a resistor 66 in series with base B2 and a resistor 68 in
series with base B1.
The relaxation oscillator operates in the following well known
manner. Initially, the unijunction 64 is cut off, and the timing
capacitor 58 charges through the resistance 60. When the capacitor
voltage reaches the threshold switching potential of the
unijunction 64, the unijunction turns on, and timing capacitor 58
then discharges through the emitter and base 1 of the unijunction
and the resistor 68. When the discharging process drops the
unijunction emitter voltage below the cutoff level, the unijunction
64 ceases conducting and the charging cycle starts again. Since the
value of the resistor 60 determines the RC timing constant, it
determines the capacitor charging time, which in turn determines
the pulse repetition rate.
The output of the unijunction relaxation oscillator 56 is a train
of positive pulses developed across the load resistor 68 by the
successive discharges of the timing capacitor 58 through the
emitter-base 1 circuit of the unijunction 64. This pulse train has
good frequency stability, which is one of the characteristic
advantages of unijunction time base circuits.
The unijunction output pulse train is applied over a lead 70 to a
bistable circuit or flip-flop 72. Each successive output pulse from
the relaxation oscillator 56 reverses the state of the bistable
circuit 72 in the following manner. The bistable circuit comprises
two NPN-transistors 74 and 76, and two PNP-transistors 78 and 80.
These are grouped into two diagonal pairs 74, 80 and 76, 78, with
each diagonal pair of transistors conducting simultaneously, and
alternating conduction with the other diagonal pair. Assume that at
a given moment transistor 80 is conducting. Its collector load
current flows through a pair of resistors 82 and 84 which form a
voltage divider. The potential at the center point of the voltage
divider 82, 84 drives the base of transistor 74 high to make the
latter transistor conduct at the same time that transistor 80 is
conducting.
When the next output pulse from relaxation oscillator 56 appears on
the lead 70, it is applied through an isolating diode 86 to the
base of transistor 74, but has no effect on that transistor because
it is already conducting. The same output pulse however is also
applied through another isolating diode 88 to the base of
transistor 76, turning that transistor on. When this happens, the
collector potential of transistor 80 drops due to the low impedance
path presented by the now conducting transistor 76, and as a result
the positive base drive formerly transmitted to transistor 74
through resistor 82, is now terminated, and as a result transistor
74 turns off. When transistor 74 turns off, it ceases to draw
collector current through the voltage divider formed by resistors
90 and 92. This removes the negative base drive from transistor 80,
which consequently also shuts off. At the same time, the collector
current now drawn by transistor 76 traverses the voltage divider
formed by the resistors 94 and 96. The resulting negative base
drive to the transistor 78 turns that transistor on. It will
therefore be appreciated that the effect of the oscillator output
pulse appearing on lead 70 and coming through the diode 88, is to
turn transistors 76 and 78 on, while cutting transistors 74 and 80
off. In effect, the flip-flop 72 is switched.
Thereafter, the flip-flop remains in the state to which it has been
switched, because the collector current of transistor 78 flows
through the voltage divider comprising resistors 98 and 100, and
the resulting voltage developed across resistor 100 provides the
necessary positive base drive to transistor 76 to keep the latter
in conduction. At the same time, the collector current of
transistor 76 flows through the voltage divider comprising
resistors 94 and 96, so that the voltage developed across resistor
94 provides the necessary negative base drive to keep transistor 78
in conduction.
The next positive output pulse from the oscillator 56 appearing on
lead 70 will switch the flip-flop 72 back again. This pulse passes
through the diode 88 but has no effect on transistor 76 because the
latter is already conducting. However the pulse, in passing through
diode 86 as well, turns on transistor 74. This in turn causes
transistor 80 to turn on and transistors 76 and 78 to turn off.
This state also is stable, continuing until the next oscillator
pulse occurs. The process need not be described in detail because
it is precisely the complement of the switching operation described
above.
Since the bistable circuit 72 stays in each of its two conducting
states until the occurrence of the next output pulse from the
relaxation oscillator 56, the circuit 72 will spend equal time (on
the average) in each of its two stable states, provided the
consecutive output pulses from the oscillator 56 are evenly spaced
(on the average). Since unijunction relaxation oscillators are
noted for their frequency stability, this condition is met. As a
result, over any substantial number of full cycles of operation,
each state of the bistable circuit 72 will average out to
substantially a 50 percent duty cycle. This is important, because
it permits the average potential of the electrical stimulation
applied to the sphincter rectalis to be zero. This avoids
electrical polarization of the biological tissue, which would have
quite undesirable effects as described subsequently. It should also
be noted that the value of the resistor 60 determines the pulse
repetition rate of the relaxation oscillator 56 so as to select the
desired operating frequency, but does not affect the 50 percent
duty cycle. The output pulses from the relaxation oscillator 56 can
be closer together or further apart in time as determined by the
value of the resistor 60, but as long as they occur at a steady
rate for any given resistance value, the interval between
successive reversals of the bistable circuit 72 will be equal.
When the transistors 78 and 76 are conducting, output lead 30 is
connected through a resistor 102 to the high collector potential of
transistor 78, while output lead 28 is connected through a
potentiometer 104 and resistor 106 to the substantially lower
potential developed across resistors 94 and 96 by the collector
current of transistor 76. Accordingly, in this state of the
bistable circuit 72, the output lead 30 is driven high and the
output lead 28 is driven low. After the bistable circuit 72 is
switched to its opposite state, transistors 74 and 80 are
conducting and transistors 76 and 78 are cut off. At that time the
polarities of the output leads 28 and 30 are reversed because lead
28 assumes the high collector potential of transistor 80, while
output lead 30 assumes the low potential developed across resistors
90 and 92 as a result of the collector current of transistor 74. It
will therefore be understood that the output on the leads 28 and 30
is a square wave synchronous with the switching frequency of the
bistable circuit 72. The output leads 28 and 30 of FIG. 3 are the
same as the input leads 28 and 30 to the contacts 20 and 22 of
FIGS. 1 and 2. Accordingly, the square wave output of the circuit
of FIG. 3 is the electrical drive used for stimulating the
sphincter rectalis of the patient.
The potentiometer 104, which is wired as a rheostat, serves to
adjust the load current drawn by the body tissues of the patient.
The circuit is designed to have an output impedance such that even
under short circuit conditions, the load current is of the order of
a couple of milliamperes; therefore it is obvious that the current
actually drawn through the impedance represented by the body
tissues of the patient will be substantially less, and therefore at
a safe level. The resistors 106 and 102 are in series with the
output, and contribute to the limiting of the output current. The
capacitors 108 and 110 are included in the circuit to bypass base
transients of the transistors 78 and 80 respectively.
While the circuits for the electrical generator of FIG. 3 are a
matter of design choice, and the choice of parameters for and types
of circuit elements in the illustrated electrical generator of FIG.
3 are within the ability of the skilled art worker, a highly
desirable electrical generator in accordance with FIG. 3 has been
employed in working the present invention using the following
circuit parameters and element designations.
Circuit Element Parameters or Designation
__________________________________________________________________________
Battery 32 5.6 v. Capacitor 58 47 Microfarad 35 v. Resistor 60 68
Kohms 1/2 w. Unijunction Transistor 64 2N4853 Resistor 66 680 ohms
1/2 w. Resistor 68 82 ohms 1/2 w. Transistor 74 MPF 6552 Transistor
76 MPF 6552 Transistor 78 2N 5087 Transistor 80 2N 5087 Resistor 82
47 Kohms 1/2 w. Resistor 84 47 Kohms 1/2 w. Diode 86 IN 914 Diode
88 IN 914 Resistor 90 47 Kohms 1/2 w. Resistor 92 47 Kohms 1/2 w.
Resistor 94 47 kohms Resistor 96 47 Kohms 1/2 w. Resistor 98 47
Kohms 1/2 w. Resistor 100 47 Kohms 1/2 w. Resistor 102 270 ohms 1/2
w. Potentiometer 104 Max R=5 Kohms Resistor 106 270 ohms 1/2 w.
Capacitor 108 .02 microfarad 50 v. Capacitor 110 .02 microfarad 50
v.
__________________________________________________________________________
It will be understood that the above defined circuit elements are
incorporated herein by way of illustration and not by way of
limitation.
The therapeutic effect of the apparatus of FIGS. 1 through 3 is
best described in terms of the experimental results actually
obtained. Comparative studies have been performed on normal and
paraplegic dogs, the normal group serving as a scientific control
while the paraplegic dogs gave an indication of the ability of this
invention to restore lost function of the sphincter rectalis. In
the test group, paraplegia of the sphincter was experimentally
induced by either of two methods, spinal anesthesia with xylocaine,
or transsection of the spinal cord in the lumbar area. In both
cases, fecal incontinence appeared quite promptly as a result, and
this was thought to be analogous to naturally occurring neurogenic
sphincter rectalis dysfunction.
An electrical stimulation device similar to that of FIGS. 1 aNd 2,
but proportioned to the experimental animals, was inserted into the
rectal opening so that the sphincter rectalis clasped the reduced
neck 14 thereof, thereby coming in contact with the spaced
electrodes 20 and 22. In other cases, the output electrodes used
for the purpose of electrical stimulation were in the form of
needles inserted directly into the sphincter muscle on opposite
sides of the anus of the experimental animal. In the terminology
used for the purposes of this patent application and the appended
claims, any reference to an electrode placed "against" the
sphincter rectalis, or similar terminology, should be understood to
apply generically to both types of electrode placement, i.e.,
placement of the electrode in contact with the epidermis overlying
the sphincter rectalis, as well as insertion of the electrodes
through the epidermis and directly into the sphincter muscle
itself.
Pressure changes within the anal canal of the experimental animals,
just inside the sphincter rectalis, were monitored by insertion of
a small rubber balloon filled with water and connected to a water
manometer. In the first series of tests, the stimulation frequency
was 20 Hertz throughout, and water pressure changes were plotted as
a function of peak voltage for three different types of wave forms:
low duty cycle pulses, sine wave, and square wave. FIG. 4
graphically illustrates the results obtained with normal dogs.
Trace 112 shows that, for square wave energization, the water
pressure obtained increased from a low value at an energization
level of 1 volt peak, to over 115 millimeters of water at an
energization potential of somewhat more than 5 volts peak. Trace
114 shows the corresponding results for sine wave stimulation as
the peak voltage was varied. Trace 116 is the corresponding curve
for a low duty cycle pulse wave form. The conclusion drawn from the
graph of FIG. 4 is that with normal dogs, the square wave (trace
112) gives maximum results with minimum power consumption and
lowest peak voltage levels.
The results were somewhat different for the paraplegic dogs, as
shown in the graph of FIG. 5. The onset of reaction to stimulation
with all three kinds of signals, the square wave signal represented
by trace 118, the sine wave signal represented by trace 120, and
the low duty cycle pulse wave form represented by trace 122,
occurred at a lower voltage level, and hence a lower power level.
In addition, above 2 volts the trace 120 corresponding to the sine
wave rises steeply and after a certain point exceeds the response
represented by the square wave trace 118. This however does not
necessarily lead to the conclusion that sine wave stimulation is
superior.
In the treatment of fecal incontinence by means of
electrostimulation of the sphincter rectalis muscle, the goal is to
restore normal muscular contraction in order to close the anal
opening in a physiological manner. In the course of the experiments
performed on dogs, it was observed that the difference in anal
canal pressure before and after the experimental induction of
paraplegia, was only between 12 and 15 millimeters of water. (This
value might be slightly greater in cases of chronic paraplegia, as
a result of progressive atrophy of the sphincter muscle.) Since
this is not a very great pressure difference, it is not necessary
to produce a muscular contraction which would increase the anal
pressure to the extreme values achieved by the sine wave trace 120
when the peak potential rises much above 2 volts. Moreover, such
pressures would be unphysiological. For effective anal pressures
not exceeding 35 millimeters of water, square wave stimulation
(represented by trace 118) allows for the lowest electrical power
and voltage levels for a given pressure response. Since it is
desirable to keep the electrical energy level as low as possible in
order to avoid tissue damage or overstimulation and consequent
fatigue of the muscle, it follows that a square wave output is the
method of choice.
In fact the application of excessive electrical voltage and power
levels resulted in clonic contractions, not only of the sphincter
rectalis muscle, but over the entire perineal area, and extending
into the extremities. The onset of such spasms is marked with x's
and indicated by arrows 124 on the graph traces 112, 114, 118 and
122 (FIGS. 4 and 5). Such contractions are of course undesirable in
themselves, and in addition the graphs of FIGS. 4 and 5 show that
after the onset of clonic contractions the degree of response to
the applied stimulus had a tendency to fall off.
FIG. 6 demonstrates the variation of pressure response as a
function of changes in frequency. As the graph of FIG. 6 shows, the
response fell off rapidly below 18 Hertz, while at frequencies
above 90 Hertz the response was short muscular twitches followed by
intervals of relaxation, rather than the desired tonic contraction.
At frequencies between 18 and 90 Hertz, the response was
substantially uniform, and the results not greatly affected by the
specific choice of frequency within that range.
Accordingly, it appears that the method of choice for the present
purpose is electrical stimulation of the sphincter rectalis by
means of a square wave having a peak potential not greater than
about 10 volts and preferably between about 1 and 2 volts, and a
frequency in the range from 18 to 90 Hertz.
It is important to note that one of the advantages of square wave
stimulation is the fact that such a wave form has an average
potential of zero. This avoids polarization of the muscle tissue to
which the electrical stimulation is applied. If a direct current is
conducted through muscle tissue and continued for upwards of about
4 minutes, the muscle becomes polarized and relaxes. Then a new
contraction cannot be produced by the same method for an interval
of about 10 minutes. The control of incontinence, however, requires
constant muscular contraction over long periods of time. A gap of
10 minutes in the protection afforded by electrical stimulation can
easily result in fecal incontinence, thereby defeating the
purpose.
Moreover, it has been noted that a device constructed and used in
the manner described controls urinary incontinence as well as anal
incontinence. Thus with paraplegic patients who generally exhibit
both anal and urinary incontinence, the use of the one device will
control both conditions. Accordingly, when a patient using the
device deenergizes it for the purposes of eliminating feces, he can
expect simultaneous urination.
It will now be realized that the method and apparatus of the
present invention provide significant advantages in the control of
rectal incontinence and the obvious physical inconvenience and
psychological embarrassment which such a condition entails.
Since the foregoing description and drawings are merely
illustrative, the scope of protection of the invention has been
more broadly stated in the following claims, and these should be
liberally interpreted so as to obtain the benefit of all
equivalents to which the invention is fairly entitled.
* * * * *