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Research Related to the Development of an Artificial Electrical Stimulator for the Paralyzed Humanbladder: A Review
THE JOURNAL OF UROLOGY
Vol. 91, No. 1 January 1964 Copyright © 1964 by The Williams & Wilkins Co.
Printed in U.S.A.
RESEARCH RELATED TO THE DEVELOPMENT OF AN ARTIFICIAL ELECTRICAL STIMULATOR FOR THE PARALYZED HUMAN BLADDER: A REVIEW WILLIAM H. BOYCE, J. ERNEST LATHEM
AND
LOUIS D. HUNT
From the Section of Urology, Department of Surgery, The Bowman Gray School of Medicine, Winston-Salem, N. C.
The following unpublished data relafr.re to direct electrical stimulation of the human bladder have been collected since 1951. At that time, a series of experiments was in progress in an effort to record the bioelectric action potentials from smooth muscle of the detrusor in normaJ1- 3 and paraplegic 4 human subjects. Silver-silver chloride contact electrodes, 2 mm. in diameter, were found suitable for recording the action potentials from the detrusor when placed on either lateral bladder wall through a plastic urethral electrode carrier. Intravesical pressure changes were recorded through a third channel of the instrument with the aid of a Statham strain gauge. Utilizing the electrode placement described in these experiments, stimuli were applied to the bladder wall from a Grass stimulator, capable of delivering a wide range of monophasic and biphasic pulses as well as direct current stimuli. Direct current stimuli were ineffectual, but both sine and square wave stimuli gave prompt increases in intravesical pressure in both normal and paraplegic subjects. In the normal unanesthetized human, the maximal increase in intravesical pressure occurred with a 15 V. square wave, at a frequency of 20 cycles per second, applied for 1 to 2 seconds. Since it was impossible to accurately measure the resistance between the elec-
trodes, current flow could only be approximated, but was calculated to be within the range of 0.5 to 3 milliamperes. The paraplegic patients were found to respond to a wide range of stimuli, the optimum voltage varying from 10 to 40 volts, applied for 2 to 3 seconds and repeated at intervals of one second for a total of 20 to 30 seconds of stimulation. These experiments resulted in such severe abdominal pain in the normal subjects that they were discontinued. The intensity of the pain was unrelated to variation in voltage from 2 to 15 volts, to sine or square wave form, or duration of stimulus, but occurred whenever the stimulus was adequate to effect an increase in intravesicular pressure. The paraplegic patients commonly complained of unpleasant sensations in the lower abdomen and external genitalia, and frequently exhibited strong contractions of striated muscles of the extremities, and paravertebral musculature with extension of the spine. ANIMAL EXPERIMENTATION
In 1954, Dr. William F. JVIcGuire 5 performed a series of studies in three normal and five chordotomized dogs. The Grass model S-4 physiological stimulator utilized in these experi1nents provided a wide range of wave forms with a voltage of 0.0015 to 150 volts for a duration of 15 microseconds to 1 second at a repetition rate from 10,000 per second to one per 10 seconds. The electrical circuits and wave forms utilized in these experiments are illustrated (figs. 1 and 2). A variety of electrode shapes and sizes composed of copper, tantalum, and braided surgical steel wire were utilized (fig. 3). The effective positions for direct stimulation of the bladder are illustrated (fig. 4). Since a stimulus did not uniformly spread to the entire detrusor from a single pair of electrodes, it was found that multiple pairs of electrodes gave a more uniform increase in intra-
Read at annual meeting of American Association of Genito-Urinary Surgeons, Chicago, Ill., May 8-10, 1963. Supported in part by grants-in-aid from The John A. Hartford Foundation, Inc., New York, N. Y.; and The North Carolina Kidney Disease Foundation, Durham, N. C. 1 Corey, E. L., Boyce, W. H., Vest, S. A. and French, C.R.: Electropotential changes in human urinary bladder: A method of measurement. J. App. Physiol. 3: 631-636, 1951. 2 Boyce, W. H.: Bladder electromyography: A new approach to diagnosis of urinary bladder dysfunction. J. Urol., 67: 650-668, 1952. 3 Corey, E. L., Boyce, W. H. and French, C.R.: Electropotential and pressure variations in normal human urinary bladder. J. App. Physiol., 5: 38-42, 1952.
5 McGuire, W. F. : Response of the neurogenic bladder to various electrical stimuli. Research thesis submitted to Department of Surgery, Bowman Gray School of Medicine, Jan. 1955.
4 Boyce, W. H., Corey, E. L., Vest, S. A. and French, C. R.: Correlation of electromyographic records with neurogenic dysfunction of human urinary bladder. J. Urol., 70: 605-614, 1953.
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BOYCE, LATHEM AND HUNT
vesical pressure. For a single pair of electrodes positions 2 and 3 (fig. 4) gave the most consistently uniform response. Figures 5 and 6 illustrate the response of the normal and "dener-
0Jv :\Fu ~D~ ~ ~
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Fm. 1. Basic wave forms utilized in stimulation of detrusor musculature. A, sine wave (sinusoidal current). B, square wave (interrupted direct current with alternate polarity). C, surging uninterrupted direct current with alternate polarity. D, surging alternating current (modulated sine wave). D, surging alternating current (modulated sine wave). E, uninterrupted rectangular wave of alternate polarity. (Slope of plateaus illustrates changes observed with decrease in voltage when stimulus was adequate for muscular contraction. Accentuation of this slope could result in a near spike potention change such as F.) F, spike waves of alternate polarity with delayed regression of voltage. G, uninterrupted rectangular waves of direct current with alternate polarity and surge variation. In basic form this is antithesis of F. (Graph reproduced from thesis by W. F. McGuire.')
vated" dog bladder to stimulation through a single pair of electrodes applied as a "coil" of copper wire 1.0 cm. in diameter sutured into the detrusor muscle. These animal experiments were continued by the present authors, who found that two or more pairs of parallel wire electrodes placed so that one of each pair was attached to a positive and one to a negative lead produced a more uniform response than a single lead in each of the same positions. This arrangement provided multiple "small" electrical fields within the detrusor, rather than a single large field between two or more electrodes. Gold electrodes (22 carat) were also investigated and were not found to be significantly superior to braided surgical steel wire. Summary: It was demonstrated that the composition of the electrodes was not important in short-term experiments. The size of the electrode was important and should not exceed 1.0 to 1.5 cm. in diameter. The wire coil or perforated plate appeared equally effective, but the coil was more easily buried within the detrusor. With a single pair of electrodes the maximal response was obtained when the electrodes were placed on either lateral bladder wall so that a maximum of bladder muscle was encompassed between the points of stimulation. Muscular response was
110 volt, 60 cycle A. C. house circuit
28 volt, 60 cycle A. C.
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Fm. 2. Arrangement of current sources for application of either sinusoidal or square wave stimuli to bladder. Entire apparatus was mounted on standard laboratory cart.Note position of oscilloscope which served as monitor and accessory calibration device for every stimulus. (Graph reproduced from thesis by W. F. McGuire. 5)
43
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
TYPE OF ELECTRODE PRESENTLY IJSEO
(
TYPES OF ELECTRODES PREVIOUSLY USED AND EVALUATED
Frn. 3. Electrode configuration. A, braided surgical steel encased in non-conducting plastic lead with atraumatic needle. Used for permanent extracorporeal stimulator. B-E electrodes with plastic handles for surgical lo~alization of site for most effective stimulation and implantation of permanent ele~trode pairs. B, multiple leads which can be paired by color. Two main leads (positive and ground) to stimulus source each supply one contact pornt of all colors. Bare contact is ball with eye for temporary suture to bladder. C,. dual contacts may be used separately or as paired electrodes. This is most satisfactory for exploration of bladder during surgery. D, paddle (blank or perforated). E, coil. obtained within the voltage range of 2 to 40 volts, but 15 volts gave a maximum response in the majority of experiments. Variations in frequency between 15 and 60 cycles per second gave no significant variations in muscular response to stimuli but frequencies greater than 60 cycles per second resulted in decreased response. No significant difference was detected between stimuli of sine and rectangular shape, but surge variation of either stimulus gave a much better response than constant application of a similar current of peak voltage. It was noted that in many instances, the square wave stimulus tended to become distorted to approach a triangular or sinusoidal wave form during the stimulation, and that a very slight drop in voltage appeared as the bladder musculature contracted.
Frn. 4. Standard positions at which dual electrodes were applied to bladder. A, left lateral view. B, ventral or anterior view. Position 1 indicates application of one of pairs of electrodes on either lateral bladder wall. Thus, the pair of electrodes occupy positions at opposite poles of transverse axis of viscus. Similar arrangement applies to other positions referred to in text by number. (Diagram reproduced from thesis by W. F. McGuire.') These changes were not directly proportional to the voltage applied. The distortion of the wave form could not be corrected by any variation in electrode size or composition. It was noted that short circuiting of the electrode pairs by blood or saline in the pelvic cavity surrounding the bladder greatly distorted the square wave form. This suggested that the conducting surface of the electrode should be completely buried in the detrusor and should not penetrate into the bladder lumen. IMPLANTATION OF INDUCTION COILS IN HUMAN PARAPLEGIC PATIENTS
The only reliable source of electrical stimuli from a wholly implantable device available to us in 1954 was an induction coil. The single coil could supply only two points of stimuli, i.e. one field, and for practical purposes, the stimulus had to be sinusoidal and 60 cycles per second. A number of simple coils of iron core and copper wiring were prepared by Dr. William F. McGuire and by American Cystoscope J\fakers, Inc.* in 1954. These were coated with an experimental plastic material of low tissue reactivity. t These coils were tested in various field strengths, and coils with the following characteristics were selected for human implantation. Secondary coils were of two types. One type contained an elongated iron core of high permeability and 2 inches in length with copper winding to give an over-all diameter of ¾ inch.
* Courtesy of Mr. Frederick J. Wallace president, American Cystoscope :Makers, Inc., Pelham J\,lfanor, New York, New York. t Courtesy of the Research Division of General Electric Company.
44
BOYCE, LATHEM AND HUNT
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60 70
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Cystometrogram before denervation
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20 15
40
20 15 10
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150
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Volume in ml. H20
FIG. 5. A, effect of electrical stimulation of bladder of anesthetized animal prior to denervation. Surging sine wave stimulus of 40 volts, 60 cycles per second frequency, of 3 seconds' duration was applied to position 1 at each of indicated increments of bladder filling. Difference in pressure between base-line 0 and solid dot represents response at indicated bladder volume. Bladder filling was discontinued and base-line pressure stabilized prior to application of stimulus. B, effect of electrical stimulation of bladder of anesthetized animal 8 days after pelvic nerve resection. Stimulus and method of application were same as in A. Difference in pressure between open and solid squares indicates response to stimulus at indicated bladder volume. Stimulus of 10 volts produced essentially same response as did 40-volt stimulus. (Graphs reproduced from thesis by W. F. McGuire. 6)
The other type contained a special molybdenum core of ),~ inch in diameter and ~1 6 inch in length with sufficient fine copper winding to form a flat coil 2 inches in diameter. The latter coils were prepared by American Cystoscope Makers, Inc. These were impregnated in a molten polyethylene solution prior to implantation. The primary coils were large simple iron core coils designed to plug directly into 110 volt supply. The secondary iron core coils produced approximately 20 volts and the molybdenum core coils produced 40 volts in the 60 cycle per second fields of these primary coils. In 1954, three male patients with apparently complete paralysis of the detrusor muscle, greater than normal bladder capacity, and residual urine in spite of resection of the internal urethral sphincter and external pudendal neurectomy agreed to implantation of the induction coils. The leads from the coil were attached to braided steel surgical sutures which were sealed in plastic coatings with the exception of 7 cm. of bare end.
The bare suture was coiled (two turns) in the detrusor over an area approximately 1.5 cm. in diameter. This coil was anchored by a suture of 000 chromic absorbable suture and a fold of tissue was carried over the electrode to insure complete coverage by the bladder musculature. The position of the coil electrode was selected by stimulation of the bladder, but in each patient -the site approximated position 2 (fig. 3). The iron-core coil was implanted in the subcutaneous tissue of the lower abdominal wall, lateral to the midline and fastened to the fascia of the external oblique muscle with silk sutures. The results in these 3 patients were unqualified failure in one, partial success in one, and a highly successful response in one. The failure was due to the stimulus producing severe pain in the abdomen and penis with contractions of the adductor muscles of the thighs. There was also failure to empty the bladder. The patient classified as a partial success had no pain or other untowar
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
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Prestudy cystometrogrorn Prestimulus Pressure
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30 25 20 15 10 5 0 0
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100 Volume - ml.
150
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Frn. 6. Effect of transection of spinal cord at third thoracic segment on response of dog bladder to electrical stimuli. Solid line represents base-line cystometrogram obtained under anesthesia on day of chordotomy but prior to operation. 0-0 represents base-line cystometrogram obtained 14 days after chordotomy and immediately prior to electrical stimulation. Difference in pressure between open and solid circles represents response of surging sine wave stimulus of 40 volts, 60 cycles per second of 3 seconds in duration applied at position 1 on bladder at each increment of filling. Similar stimuli of 10 to 15 volts produced essentially same response at each increment of filling. (Graph reproduced from thesis by W. F. McGuire. 5 ) void with the aid of the induced stimulation but only when the bladder was filled to 300 to 500 ml. volume. He continued to have residual urine of 150 to 200 ml. which could not be removed by induced voiding and this was not significantly different from the preoperative residual urine. He was considered to be somewhat improved in that the bladder could be partially emptied at regular intervals. The induction coils were removed from these 2 patients three and six months after implantation. No adverse effects attributable to the procedure were noted in either patient. The third patient was considered to be the more successful result and his case report is presented in detail. B.S., NCBH No. 1711 03, a 39-year-old man, was first examined on August 24, 1953 because of a complaint of progressive numbness in the back, left hip, and groin with difficult urination 3 months in duration. He was found to have a degenerative intramedullary spinal cord lesion on the right side just above the conus. The neurological progression of the lesion remained stabilized but the residual urine gradually increased from 150 cc to complete retention and a
45
bladder capacity of 850 cc bf May 1954. He then had in succession: a transurethral resection of the internal urethral orifice; a section of. the left pudendal nerve; and a section of the right pudendal nerve. These procedures resulted injmpro~ement of ability to empty the bladder .but (he residual urine progressively increased to. 300 ito 500 cc over the next 5 months. Numerous calculi formed in the bladder and were removed by litholapaxy on October 14. On October 21, an induction coil was in1planted in the lower abdomen as just described, with the exception that the coil was placed beneath the sheath of the rectus abdominis muscle, as there was insufficient subcutaneous tissue to cover it satisfactorily (fig. 7). The patient voided satisfactorily with residual urine from zero to 80 cc following activation of the induction coil. This state of affairs continued until February 1956, when he began to notice pain associated with the use of the induction coil. He was, however, still able to initiate urination by use of the apparatus. Cystoscopic examination on February 23, 1956 revealed no residual urine, but minimum fine trabeculations of the bladder were seen. In approximately a month the stimulator became completely ineffectual with regard to bladder stimulation. However, the patient was able to void in the squatting position without use of the stimulator. There had been no evidence of progression of his neurological lesion. On September 1, the induction coil and leads were removed. Roentgenograms had demonstrated a break in one of the leads near the point of attachment to the coil winding (fig. 7, B). Cicatricial tissue about the coil and electrode was minimal. Biopsy of the bladder indicated smooth muscle with minimal cicatrization surrounding the implanted electrodes. The patient was able to empty the bladder fairly well by squatting, dilatation of the anal sphincter and abdominal straining for 6 years. He was next admitted to the hospital on December 8, 1962 with chills, fever, and hematuria. A number of calculi were removed from the bladder by litholapaxy. He had neither formed calculi, nor had evidence of acute pyelonephritis during the 2 years in which the induction coil was in position" Hydronephrosis or ureteral reflux has not been demonstrated in any of the various examinations over the past 9 years. Sumrn.ary: Induction coils implanted in the
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BOYCE, LATHEM AND HUNT
Fm. 7. A, secondary (induction) coil in anterior abdominal wall with single pair of leads. Electrodes are coils of braided surgical steel suture embedded in bladder wall at position 2 in figure 4. Electrode was implanted October 21, 1954 and removed September 1, 1956. B, details of electrode emplacement and break in lead at point of attachment to coil winding. (Silver clips indicate sites of bilateral pudendal neurectomy.) abdominal wall were capable of delivering sine wave alternating current stimuli from a 60 cycle per second primary coil held over the abdominal wall. Such stimuli were capable of inducing muscular contractions of the detrusor and apparently aided in initiation of voiding. The implantable apparatus had the advantage of simplicity of structure. The disadvantages were associated pain and stimulation of adjacent motor nerves. Complete emptying of the bladder could not be uniformly achieved by repeated stimulation even when contractions could be initiated in a bladder filled to capacity. The greatest practical disadvantage for the paraplegic patient was the great weight of the primary coils which was 35 to 45 pounds, and the danger of the high voltage (110 volts) utilized. There were also unpleasant vibrations of the secondary coil in the abdominal wall in one patient. EXTERNAL STIMULATION OF THE HUMAN PARAPLEGIC BLADDER
The development of transistors and related miniaturization of electronic equipment suggested that an implantable stimulator capable of delivering adequate electrical stimuli to the human bladder was entirely possible. The only requirement was a knowledge of the optimal characteristics of the stimulus. In an effort to improve the
Fm. 8. Roentgenogram of patient with leads for extracorporeal bladder stimulation. Two pairs of type A leads (fig. 3) are shown in position 2 (fig. 4). Bladder is empty. bladder function, and simultaneously to obtain such information, three volunteer paraplegic patients have had electrodes implanted into the detrusor with the leads being exteriorized through the abdominal wall (fig. 8).
Fm. 9. Multiple exposure photograph during period of stimulation (oscilloscope Polaroid camera). A, wave and voltage immediately before stimulation (10 volts/cm. on x axis). B, voltage and changes in wave pattern during stimulation (1 volt/cm. on x axis). C, current flow through circuit during stirn.ulation (voltage recorded on x axis; cycles per second and pulse duration recorded on y axis). Apparatus (fig. 10) contains non-variable calibrated resistance for calculations involving current flow.
Hewlef!'-Pockard Oiclllo-scope (Mndel 120B)
G+.anuator
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Fm. 10. Portable console of electronic equipment used in bladder stimulation and other urological clinical investigation. Lower instrument panel introduces known resistance into selected points in circuitry for current flow.
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48
BOYCE, LATHEM AND HUNT
Fm. 11. Experimental model of portable stimulator, capable of producing impulses of variable characteristics. (See text for description.) The Hewlett-Packard model 202A low frequency generator provided electrical stimulation with a range of Oto 30 volts and at a frequency of 0.008 to 1200 cycles per second. Sine, square and triangular wave forms were available. A HewlettPackard model 120B oscilloscope with a grid screen over the cathode ray tube was utilized both as a continuous monitor and a calibration device. A Hewlett-Packard model 412A vacuum tube voltmeter was used for direct measure of the stimulus and to provide a check of the oscilloscope calibration. A Hewlett-Packard Polaroid model 196B oscilloscope camera was attached to the cathode ray tube for direct photography of the stimulus trace before and during stimulation (fig. 9). These components were assembled into a mobile cabinet which could be readily wheeled into the operating room or to the patients' bedside (fig. 10). The effectiveness of the stimulus has been determined by simple manometric recording of the intravesical pressure through a urethral catheter; by the volume voided from a known
intravesical content; and by cinefluoroscopy and cineradi0g-raphy of the bladder during stimulation. The electrodes have remained in place for as long as 3 months without infection or other adverse effects. Indeed, bladder function appears to be improved by even periodic application of the stimulus. An experimental external battery-powered stimulator with variable controls, transistorized circuitry, measuring approximately 4 by 3 by 1 inches has been provided through the courtesy of the Research Division of General Electric Company (fig. 11). This apparatus has proven more satisfactory in every respect as a source of external stimuli than the cumbersome apparatus (fig. 10). The many variations in stimuli which have been employed from these two sources are too voluminous to be recorded in detail. The essential characteristics of the external stimulation method are recorded i:n the following summary and in tables 1 and 2.
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER TABLE
49
1. Characteristics of effective stimulation in several patients
Optimum* Minimum Range of effective stimuli
Pre-Stimulus Voltage
Cycles/ Sec.
Pulse Duration
10-15 1.8 1.8-38
20-30 5-10 5-200
0.5-1.0 0.5 0.5-4.0
Wave Form
Rectangular Triangular Square, sine triangular and rectangular
*. The optimum stimuli are those which consistently produce 70 to 100 ml. H 2 0 increase in intravesical pressure~. Generally, increases in voltage above those listed did not produce any significant response. Lowermg of the cycles per second below 10 tended to enhance any painful effects of stimulus. TABLE
PreStimulus Voltage
2. Example of responses to variation in voltage of stimuli applied for 5 seconds to two pairs of electrodes in the bladder of a single paraplegic patient
Voltage Pulse During Cycles/ Duration Sec. Stimulams. tion
Bladder Volume (cc)
Manometric (cm. of H,O)
Motor
Sensory
--- --- ---
10 10 7 15 18
7 7 4.7 9.0 15
50 25 25 25
0.5 0.5 0.5 0.5
200 200 200 200
15 75 5 100
25
0.5
225
100
SUMMARY
Bladder response. The increase in intravesical pressure of the paraplegic patient may be made to exceed that of the normal voiding bladder. The response is prompt and may be sustained or reproduced over intervals of time sufficient to : permit complete emptying of the bladder contents through a urethra of normal caliber. Resistance to urine flow along the course of the urethra should be less than that of the normal since it is desirable to effect voiding at a minimal increase in intravesical pressure. This serves to protect the kidneys and ureters from reflux of urine, and by reducing the current strength of the stimulus minimizes the local injury to tissue at the site of electrode implantation, and, incidentally, conserves the energy of the power pack. Relief of obstruction or reduction of urethral resistance by pudendal nerve resection, surgical revision of the internal urethral orifice, external sphincterotomy, and other techniques is well established. Patient discomfort appears to arise from several sources: a) spasm of the detrusor, especially when there is no flow of urine through the urethra; b) stimulation of adjacent major somatic nerve
Desire to void Desire to void Minimal discomfort Slight discomfort; desire to void Pain; desire to void
Erection Erection Erection; leg movement Erection; leg movement
trunks with striated muscle spasm or sensory excitation; c) stimulation of pelvic parasympathetic or sensory components of the autonomic nerves with the resultant sensations of an urge to defecate, "gas pains," "stomach ache" or testicular pain; d) penile erections may occur with or without pain. Such patient discomfort can be reduced to a level which is virtually absent or at the most is readily tolerable. This is accomplished by individualization of the characteristics of the stimulus and proper placement of the electrodes. Electrode placement. The number of electrodes required to produce adequate increase in intravesical pressure is related to the degenerative changes which have occurred in the musculature and intrinsic innervation of the detrusor. There is no evidence that conduction pathways exist in the human bladder other than the intrinsic nerve-net of the bladder wall. In the absence of detrusor hypertrophy, fibrosis, or decompensation by chronic over-distension, a single pair of electrodes on either lateral bladder wall will be adequate and even one such pair may be sufficient. More than three additional pairs of electrodes spaced at maximal intervals from the
50
I
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BOYCE, LATHEM AND HUNT
aforementioned pair will not enhance the response of the irreparably degenerated detrusor. The electrodes should be of braided stainless steel and enclosed in an insulation which is biologically inert. The exposed segment of electrode should be an inch in length and completely buried within the detrusor musculature where it is securely anchored by an embedding suture. The lead from each electrode is brought through the skin at a point separate from the incision and other electrode leads. The electrodes are placed in pairs, one active (negative) and one ground (positive). The pairs are placed so that each electrode lies parallel to the other and no closer together than an inch in the empty bladder. Application of a current flow results in an electrical field of greatest intensity between these two electrodes and prevents dissipation of the stimulus. The prime site for electrode placement is on either lateral bladder wall so as to encompass between each pair the sheaf of parasympathetic nerves as they separate from the middle vesical artery and begin to fan out over the detrusor. One branch of the middle vesical artery is usually included in the electrical field along with the accompanying veins and lymphatics. In bladders with excessive muscular hypertrophy and interstitial fibrosis, or in excessively large bladders, additional pairs of electrodes may be placed on the ventral bladder wall or on the dorsum near the base of the extraperitonealized bladder. Electrode pairs in the exact vertex of the bladder dome have been least effective. Adequate response to stimulation is quite difficult to obtain in the bladder so severely damaged as to require more than the two prime pairs of electrodes. Characteristics of the stimulus. The range of characteristics of effective stimuli for the human bladder and the values currently considered as optimal are presented (table I). These values apply for the well preserved paraplegic bladder which has minimal hypertrophy of the musculature, has a residual urine in the range of 200 ml., but has not been chronically overdistended. Much individual variation in the requirements of the stimulus will result from degenerative changes in the bladder. Future requirements. The mechanical feasibility of a totally implantable effective bladder stimulator appears unequivocal. Much clinical investi-
gation must precede its general usage. For the present, the external lead stimulator will be the most productive tool, and may never completely disappear from the field. Perhaps the first question is when in the course of central nervous system disease or injury should bladder stimulation be considered. There is general agreement that the patient with paralysis of the bladder resulting from trauma to the central nervous system should be greatly benefited by a program which completely eliminates the need for urethral catheterization. Whether the external stimulator can serve this purpose remains to be evaluated. Recovery of bladder function is unpredictable in the majority of traumatized patients. Since the complications of urinary dysfunction remain the major causes of death in paralyzed patients any procedure which can significantly improve or preserve function of the bladder deserves an adequate clinical evaluation. Among other significant problems requiring investigation are the following: a) Methods to circumvent the apparent physiological obstruction at the internal urethral orifice and within the urethra which impairs the outflow of urine at a time when stimulation is producing an intravesical pressure sufficient for normal voiding. b) Methods for prevention of excitation of other somatic and visceral structures. c) Adaptation and variation of sources of etimuli to meet the various requirements encountered in patients with neurogenic dysfunction of the bladder. Developing interest in this field has been evidenced by several preliminary reports from other investigators. 5 - 9 Hopefully, the investigations in this field will continue at an advanced pace. 6 Bunghele, T., Ichim, V. and Demetrescu, M.: Experimental study of emptying of cord bladder. Transcutaneous stimulation of pelvic nerves by electromagnetic induction apparatus. Therapeutic deductions. Digest of the 1962 15th Annual Conference on Engineering in Medicine and Biology, November 5-7, 1962. (Read by title.) 7 Bradley, W. E., Wingrove, R. and Chou, S. N.: Use of an implantable R. F. powered receiver for evacuation of the neurogenic bladder. Digest of the 1962 15th Annual Conference on Engineering in Medicine and Biology, November 5---7, 1962. 8 Bradley, W. S.: Implantable bladder stimulator developed. Med. Tribune, 3: 1, 24, 1962. 9 Schoenberg, H. W., Young, D. G. and Murphy, J. J.: Electrical stimulation of urinary bladder. Surgical Forum, 13: 509, 1962.
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
The authors acknowledge valuable assistance and participation of the following individuals: E. L. Corey, M.D.,* professor of physiology, University of Virginia School of Medicine, Charlottesville, Virginia. S. A. Vest, M.D.,* professor of urology, University of Virginia School of Medicine, Charlottesville, Virginia.
* Deceased.
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William F. McGuire, M.D., Pulaski, Virginia. Mr. D. L. Bowers, Mr. H. G. Taus, and Mr. A. W. Schwalm, Advanced Medical Projects, General Electric Company. C. H. Davis, JVI.D ., associate professor of neurosurgey, The Bowman Gray School of Medicine, Winston-Salem, North Carolina. Mr. Frederick J. Wallace, president, American Cystoscope Makers, Inc., Pelham Manor, New York.
Vol. 91, No. 1 January 1964 Copyright © 1964 by The Williams & Wilkins Co.
Printed in U.S.A.
RESEARCH RELATED TO THE DEVELOPMENT OF AN ARTIFICIAL ELECTRICAL STIMULATOR FOR THE PARALYZED HUMAN BLADDER: A REVIEW WILLIAM H. BOYCE, J. ERNEST LATHEM
AND
LOUIS D. HUNT
From the Section of Urology, Department of Surgery, The Bowman Gray School of Medicine, Winston-Salem, N. C.
The following unpublished data relafr.re to direct electrical stimulation of the human bladder have been collected since 1951. At that time, a series of experiments was in progress in an effort to record the bioelectric action potentials from smooth muscle of the detrusor in normaJ1- 3 and paraplegic 4 human subjects. Silver-silver chloride contact electrodes, 2 mm. in diameter, were found suitable for recording the action potentials from the detrusor when placed on either lateral bladder wall through a plastic urethral electrode carrier. Intravesical pressure changes were recorded through a third channel of the instrument with the aid of a Statham strain gauge. Utilizing the electrode placement described in these experiments, stimuli were applied to the bladder wall from a Grass stimulator, capable of delivering a wide range of monophasic and biphasic pulses as well as direct current stimuli. Direct current stimuli were ineffectual, but both sine and square wave stimuli gave prompt increases in intravesical pressure in both normal and paraplegic subjects. In the normal unanesthetized human, the maximal increase in intravesical pressure occurred with a 15 V. square wave, at a frequency of 20 cycles per second, applied for 1 to 2 seconds. Since it was impossible to accurately measure the resistance between the elec-
trodes, current flow could only be approximated, but was calculated to be within the range of 0.5 to 3 milliamperes. The paraplegic patients were found to respond to a wide range of stimuli, the optimum voltage varying from 10 to 40 volts, applied for 2 to 3 seconds and repeated at intervals of one second for a total of 20 to 30 seconds of stimulation. These experiments resulted in such severe abdominal pain in the normal subjects that they were discontinued. The intensity of the pain was unrelated to variation in voltage from 2 to 15 volts, to sine or square wave form, or duration of stimulus, but occurred whenever the stimulus was adequate to effect an increase in intravesicular pressure. The paraplegic patients commonly complained of unpleasant sensations in the lower abdomen and external genitalia, and frequently exhibited strong contractions of striated muscles of the extremities, and paravertebral musculature with extension of the spine. ANIMAL EXPERIMENTATION
In 1954, Dr. William F. JVIcGuire 5 performed a series of studies in three normal and five chordotomized dogs. The Grass model S-4 physiological stimulator utilized in these experi1nents provided a wide range of wave forms with a voltage of 0.0015 to 150 volts for a duration of 15 microseconds to 1 second at a repetition rate from 10,000 per second to one per 10 seconds. The electrical circuits and wave forms utilized in these experiments are illustrated (figs. 1 and 2). A variety of electrode shapes and sizes composed of copper, tantalum, and braided surgical steel wire were utilized (fig. 3). The effective positions for direct stimulation of the bladder are illustrated (fig. 4). Since a stimulus did not uniformly spread to the entire detrusor from a single pair of electrodes, it was found that multiple pairs of electrodes gave a more uniform increase in intra-
Read at annual meeting of American Association of Genito-Urinary Surgeons, Chicago, Ill., May 8-10, 1963. Supported in part by grants-in-aid from The John A. Hartford Foundation, Inc., New York, N. Y.; and The North Carolina Kidney Disease Foundation, Durham, N. C. 1 Corey, E. L., Boyce, W. H., Vest, S. A. and French, C.R.: Electropotential changes in human urinary bladder: A method of measurement. J. App. Physiol. 3: 631-636, 1951. 2 Boyce, W. H.: Bladder electromyography: A new approach to diagnosis of urinary bladder dysfunction. J. Urol., 67: 650-668, 1952. 3 Corey, E. L., Boyce, W. H. and French, C.R.: Electropotential and pressure variations in normal human urinary bladder. J. App. Physiol., 5: 38-42, 1952.
5 McGuire, W. F. : Response of the neurogenic bladder to various electrical stimuli. Research thesis submitted to Department of Surgery, Bowman Gray School of Medicine, Jan. 1955.
4 Boyce, W. H., Corey, E. L., Vest, S. A. and French, C. R.: Correlation of electromyographic records with neurogenic dysfunction of human urinary bladder. J. Urol., 70: 605-614, 1953.
41
42
BOYCE, LATHEM AND HUNT
vesical pressure. For a single pair of electrodes positions 2 and 3 (fig. 4) gave the most consistently uniform response. Figures 5 and 6 illustrate the response of the normal and "dener-
0Jv :\Fu ~D~ ~ ~
0J\J
Fm. 1. Basic wave forms utilized in stimulation of detrusor musculature. A, sine wave (sinusoidal current). B, square wave (interrupted direct current with alternate polarity). C, surging uninterrupted direct current with alternate polarity. D, surging alternating current (modulated sine wave). D, surging alternating current (modulated sine wave). E, uninterrupted rectangular wave of alternate polarity. (Slope of plateaus illustrates changes observed with decrease in voltage when stimulus was adequate for muscular contraction. Accentuation of this slope could result in a near spike potention change such as F.) F, spike waves of alternate polarity with delayed regression of voltage. G, uninterrupted rectangular waves of direct current with alternate polarity and surge variation. In basic form this is antithesis of F. (Graph reproduced from thesis by W. F. McGuire.')
vated" dog bladder to stimulation through a single pair of electrodes applied as a "coil" of copper wire 1.0 cm. in diameter sutured into the detrusor muscle. These animal experiments were continued by the present authors, who found that two or more pairs of parallel wire electrodes placed so that one of each pair was attached to a positive and one to a negative lead produced a more uniform response than a single lead in each of the same positions. This arrangement provided multiple "small" electrical fields within the detrusor, rather than a single large field between two or more electrodes. Gold electrodes (22 carat) were also investigated and were not found to be significantly superior to braided surgical steel wire. Summary: It was demonstrated that the composition of the electrodes was not important in short-term experiments. The size of the electrode was important and should not exceed 1.0 to 1.5 cm. in diameter. The wire coil or perforated plate appeared equally effective, but the coil was more easily buried within the detrusor. With a single pair of electrodes the maximal response was obtained when the electrodes were placed on either lateral bladder wall so that a maximum of bladder muscle was encompassed between the points of stimulation. Muscular response was
110 volt, 60 cycle A. C. house circuit
28 volt, 60 cycle A. C.
,-----~,I -~----~:::L_ 1
I
====
--1
Oscilloscope
Vibrator
Variable transformer
J~_--lr_-_.,..~ 45v.dry-==-bottery
45v. dry --battery _ _ Isolation
---+--1000 ohm
~
variable
resistor
transformer
~ Voll meter
Togqle switch
l1
-""' ,['===tr-'""" Foot
B
.
To stimulatinq electrode
Fm. 2. Arrangement of current sources for application of either sinusoidal or square wave stimuli to bladder. Entire apparatus was mounted on standard laboratory cart.Note position of oscilloscope which served as monitor and accessory calibration device for every stimulus. (Graph reproduced from thesis by W. F. McGuire. 5)
43
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
TYPE OF ELECTRODE PRESENTLY IJSEO
(
TYPES OF ELECTRODES PREVIOUSLY USED AND EVALUATED
Frn. 3. Electrode configuration. A, braided surgical steel encased in non-conducting plastic lead with atraumatic needle. Used for permanent extracorporeal stimulator. B-E electrodes with plastic handles for surgical lo~alization of site for most effective stimulation and implantation of permanent ele~trode pairs. B, multiple leads which can be paired by color. Two main leads (positive and ground) to stimulus source each supply one contact pornt of all colors. Bare contact is ball with eye for temporary suture to bladder. C,. dual contacts may be used separately or as paired electrodes. This is most satisfactory for exploration of bladder during surgery. D, paddle (blank or perforated). E, coil. obtained within the voltage range of 2 to 40 volts, but 15 volts gave a maximum response in the majority of experiments. Variations in frequency between 15 and 60 cycles per second gave no significant variations in muscular response to stimuli but frequencies greater than 60 cycles per second resulted in decreased response. No significant difference was detected between stimuli of sine and rectangular shape, but surge variation of either stimulus gave a much better response than constant application of a similar current of peak voltage. It was noted that in many instances, the square wave stimulus tended to become distorted to approach a triangular or sinusoidal wave form during the stimulation, and that a very slight drop in voltage appeared as the bladder musculature contracted.
Frn. 4. Standard positions at which dual electrodes were applied to bladder. A, left lateral view. B, ventral or anterior view. Position 1 indicates application of one of pairs of electrodes on either lateral bladder wall. Thus, the pair of electrodes occupy positions at opposite poles of transverse axis of viscus. Similar arrangement applies to other positions referred to in text by number. (Diagram reproduced from thesis by W. F. McGuire.') These changes were not directly proportional to the voltage applied. The distortion of the wave form could not be corrected by any variation in electrode size or composition. It was noted that short circuiting of the electrode pairs by blood or saline in the pelvic cavity surrounding the bladder greatly distorted the square wave form. This suggested that the conducting surface of the electrode should be completely buried in the detrusor and should not penetrate into the bladder lumen. IMPLANTATION OF INDUCTION COILS IN HUMAN PARAPLEGIC PATIENTS
The only reliable source of electrical stimuli from a wholly implantable device available to us in 1954 was an induction coil. The single coil could supply only two points of stimuli, i.e. one field, and for practical purposes, the stimulus had to be sinusoidal and 60 cycles per second. A number of simple coils of iron core and copper wiring were prepared by Dr. William F. McGuire and by American Cystoscope J\fakers, Inc.* in 1954. These were coated with an experimental plastic material of low tissue reactivity. t These coils were tested in various field strengths, and coils with the following characteristics were selected for human implantation. Secondary coils were of two types. One type contained an elongated iron core of high permeability and 2 inches in length with copper winding to give an over-all diameter of ¾ inch.
* Courtesy of Mr. Frederick J. Wallace president, American Cystoscope :Makers, Inc., Pelham J\,lfanor, New York, New York. t Courtesy of the Research Division of General Electric Company.
44
BOYCE, LATHEM AND HUNT
B 70 65
A
50 0 (\)45 J:
50
E
;t' 45
e 40
... Best response to electrical stimulus before denervation
"
.!: 35 ~
::,
a:
denervation
55
65 60 55
..,
a-a Cystometrogram after
60 70
0
. . Best response after denervation
C>-O
Cystometrogram before denervation
30 25
0 C
35
...
30
"'"'
25
QJ
::,
~
Q.
20 15
40
20 15 10
10
5 0
5 0 0
50
100
150
200
Volume in ml. H 20
0
50
100
150
200
Volume in ml. H20
FIG. 5. A, effect of electrical stimulation of bladder of anesthetized animal prior to denervation. Surging sine wave stimulus of 40 volts, 60 cycles per second frequency, of 3 seconds' duration was applied to position 1 at each of indicated increments of bladder filling. Difference in pressure between base-line 0 and solid dot represents response at indicated bladder volume. Bladder filling was discontinued and base-line pressure stabilized prior to application of stimulus. B, effect of electrical stimulation of bladder of anesthetized animal 8 days after pelvic nerve resection. Stimulus and method of application were same as in A. Difference in pressure between open and solid squares indicates response to stimulus at indicated bladder volume. Stimulus of 10 volts produced essentially same response as did 40-volt stimulus. (Graphs reproduced from thesis by W. F. McGuire. 6)
The other type contained a special molybdenum core of ),~ inch in diameter and ~1 6 inch in length with sufficient fine copper winding to form a flat coil 2 inches in diameter. The latter coils were prepared by American Cystoscope Makers, Inc. These were impregnated in a molten polyethylene solution prior to implantation. The primary coils were large simple iron core coils designed to plug directly into 110 volt supply. The secondary iron core coils produced approximately 20 volts and the molybdenum core coils produced 40 volts in the 60 cycle per second fields of these primary coils. In 1954, three male patients with apparently complete paralysis of the detrusor muscle, greater than normal bladder capacity, and residual urine in spite of resection of the internal urethral sphincter and external pudendal neurectomy agreed to implantation of the induction coils. The leads from the coil were attached to braided steel surgical sutures which were sealed in plastic coatings with the exception of 7 cm. of bare end.
The bare suture was coiled (two turns) in the detrusor over an area approximately 1.5 cm. in diameter. This coil was anchored by a suture of 000 chromic absorbable suture and a fold of tissue was carried over the electrode to insure complete coverage by the bladder musculature. The position of the coil electrode was selected by stimulation of the bladder, but in each patient -the site approximated position 2 (fig. 3). The iron-core coil was implanted in the subcutaneous tissue of the lower abdominal wall, lateral to the midline and fastened to the fascia of the external oblique muscle with silk sutures. The results in these 3 patients were unqualified failure in one, partial success in one, and a highly successful response in one. The failure was due to the stimulus producing severe pain in the abdomen and penis with contractions of the adductor muscles of the thighs. There was also failure to empty the bladder. The patient classified as a partial success had no pain or other untowar
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
i
60 55
-
50 0 I
N
0
Best response to electrical
stimulus ofter cordotomy
Prestudy cystometrogrorn Prestimulus Pressure
45
~ 40 35 C
.., ~
CL
30 25 20 15 10 5 0 0
50
100 Volume - ml.
150
200
H20
Frn. 6. Effect of transection of spinal cord at third thoracic segment on response of dog bladder to electrical stimuli. Solid line represents base-line cystometrogram obtained under anesthesia on day of chordotomy but prior to operation. 0-0 represents base-line cystometrogram obtained 14 days after chordotomy and immediately prior to electrical stimulation. Difference in pressure between open and solid circles represents response of surging sine wave stimulus of 40 volts, 60 cycles per second of 3 seconds in duration applied at position 1 on bladder at each increment of filling. Similar stimuli of 10 to 15 volts produced essentially same response at each increment of filling. (Graph reproduced from thesis by W. F. McGuire. 5 ) void with the aid of the induced stimulation but only when the bladder was filled to 300 to 500 ml. volume. He continued to have residual urine of 150 to 200 ml. which could not be removed by induced voiding and this was not significantly different from the preoperative residual urine. He was considered to be somewhat improved in that the bladder could be partially emptied at regular intervals. The induction coils were removed from these 2 patients three and six months after implantation. No adverse effects attributable to the procedure were noted in either patient. The third patient was considered to be the more successful result and his case report is presented in detail. B.S., NCBH No. 1711 03, a 39-year-old man, was first examined on August 24, 1953 because of a complaint of progressive numbness in the back, left hip, and groin with difficult urination 3 months in duration. He was found to have a degenerative intramedullary spinal cord lesion on the right side just above the conus. The neurological progression of the lesion remained stabilized but the residual urine gradually increased from 150 cc to complete retention and a
45
bladder capacity of 850 cc bf May 1954. He then had in succession: a transurethral resection of the internal urethral orifice; a section of. the left pudendal nerve; and a section of the right pudendal nerve. These procedures resulted injmpro~ement of ability to empty the bladder .but (he residual urine progressively increased to. 300 ito 500 cc over the next 5 months. Numerous calculi formed in the bladder and were removed by litholapaxy on October 14. On October 21, an induction coil was in1planted in the lower abdomen as just described, with the exception that the coil was placed beneath the sheath of the rectus abdominis muscle, as there was insufficient subcutaneous tissue to cover it satisfactorily (fig. 7). The patient voided satisfactorily with residual urine from zero to 80 cc following activation of the induction coil. This state of affairs continued until February 1956, when he began to notice pain associated with the use of the induction coil. He was, however, still able to initiate urination by use of the apparatus. Cystoscopic examination on February 23, 1956 revealed no residual urine, but minimum fine trabeculations of the bladder were seen. In approximately a month the stimulator became completely ineffectual with regard to bladder stimulation. However, the patient was able to void in the squatting position without use of the stimulator. There had been no evidence of progression of his neurological lesion. On September 1, the induction coil and leads were removed. Roentgenograms had demonstrated a break in one of the leads near the point of attachment to the coil winding (fig. 7, B). Cicatricial tissue about the coil and electrode was minimal. Biopsy of the bladder indicated smooth muscle with minimal cicatrization surrounding the implanted electrodes. The patient was able to empty the bladder fairly well by squatting, dilatation of the anal sphincter and abdominal straining for 6 years. He was next admitted to the hospital on December 8, 1962 with chills, fever, and hematuria. A number of calculi were removed from the bladder by litholapaxy. He had neither formed calculi, nor had evidence of acute pyelonephritis during the 2 years in which the induction coil was in position" Hydronephrosis or ureteral reflux has not been demonstrated in any of the various examinations over the past 9 years. Sumrn.ary: Induction coils implanted in the
46
BOYCE, LATHEM AND HUNT
Fm. 7. A, secondary (induction) coil in anterior abdominal wall with single pair of leads. Electrodes are coils of braided surgical steel suture embedded in bladder wall at position 2 in figure 4. Electrode was implanted October 21, 1954 and removed September 1, 1956. B, details of electrode emplacement and break in lead at point of attachment to coil winding. (Silver clips indicate sites of bilateral pudendal neurectomy.) abdominal wall were capable of delivering sine wave alternating current stimuli from a 60 cycle per second primary coil held over the abdominal wall. Such stimuli were capable of inducing muscular contractions of the detrusor and apparently aided in initiation of voiding. The implantable apparatus had the advantage of simplicity of structure. The disadvantages were associated pain and stimulation of adjacent motor nerves. Complete emptying of the bladder could not be uniformly achieved by repeated stimulation even when contractions could be initiated in a bladder filled to capacity. The greatest practical disadvantage for the paraplegic patient was the great weight of the primary coils which was 35 to 45 pounds, and the danger of the high voltage (110 volts) utilized. There were also unpleasant vibrations of the secondary coil in the abdominal wall in one patient. EXTERNAL STIMULATION OF THE HUMAN PARAPLEGIC BLADDER
The development of transistors and related miniaturization of electronic equipment suggested that an implantable stimulator capable of delivering adequate electrical stimuli to the human bladder was entirely possible. The only requirement was a knowledge of the optimal characteristics of the stimulus. In an effort to improve the
Fm. 8. Roentgenogram of patient with leads for extracorporeal bladder stimulation. Two pairs of type A leads (fig. 3) are shown in position 2 (fig. 4). Bladder is empty. bladder function, and simultaneously to obtain such information, three volunteer paraplegic patients have had electrodes implanted into the detrusor with the leads being exteriorized through the abdominal wall (fig. 8).
Fm. 9. Multiple exposure photograph during period of stimulation (oscilloscope Polaroid camera). A, wave and voltage immediately before stimulation (10 volts/cm. on x axis). B, voltage and changes in wave pattern during stimulation (1 volt/cm. on x axis). C, current flow through circuit during stirn.ulation (voltage recorded on x axis; cycles per second and pulse duration recorded on y axis). Apparatus (fig. 10) contains non-variable calibrated resistance for calculations involving current flow.
Hewlef!'-Pockard Oiclllo-scope (Mndel 120B)
G+.anuator
202A)
Fm. 10. Portable console of electronic equipment used in bladder stimulation and other urological clinical investigation. Lower instrument panel introduces known resistance into selected points in circuitry for current flow.
47
48
BOYCE, LATHEM AND HUNT
Fm. 11. Experimental model of portable stimulator, capable of producing impulses of variable characteristics. (See text for description.) The Hewlett-Packard model 202A low frequency generator provided electrical stimulation with a range of Oto 30 volts and at a frequency of 0.008 to 1200 cycles per second. Sine, square and triangular wave forms were available. A HewlettPackard model 120B oscilloscope with a grid screen over the cathode ray tube was utilized both as a continuous monitor and a calibration device. A Hewlett-Packard model 412A vacuum tube voltmeter was used for direct measure of the stimulus and to provide a check of the oscilloscope calibration. A Hewlett-Packard Polaroid model 196B oscilloscope camera was attached to the cathode ray tube for direct photography of the stimulus trace before and during stimulation (fig. 9). These components were assembled into a mobile cabinet which could be readily wheeled into the operating room or to the patients' bedside (fig. 10). The effectiveness of the stimulus has been determined by simple manometric recording of the intravesical pressure through a urethral catheter; by the volume voided from a known
intravesical content; and by cinefluoroscopy and cineradi0g-raphy of the bladder during stimulation. The electrodes have remained in place for as long as 3 months without infection or other adverse effects. Indeed, bladder function appears to be improved by even periodic application of the stimulus. An experimental external battery-powered stimulator with variable controls, transistorized circuitry, measuring approximately 4 by 3 by 1 inches has been provided through the courtesy of the Research Division of General Electric Company (fig. 11). This apparatus has proven more satisfactory in every respect as a source of external stimuli than the cumbersome apparatus (fig. 10). The many variations in stimuli which have been employed from these two sources are too voluminous to be recorded in detail. The essential characteristics of the external stimulation method are recorded i:n the following summary and in tables 1 and 2.
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER TABLE
49
1. Characteristics of effective stimulation in several patients
Optimum* Minimum Range of effective stimuli
Pre-Stimulus Voltage
Cycles/ Sec.
Pulse Duration
10-15 1.8 1.8-38
20-30 5-10 5-200
0.5-1.0 0.5 0.5-4.0
Wave Form
Rectangular Triangular Square, sine triangular and rectangular
*. The optimum stimuli are those which consistently produce 70 to 100 ml. H 2 0 increase in intravesical pressure~. Generally, increases in voltage above those listed did not produce any significant response. Lowermg of the cycles per second below 10 tended to enhance any painful effects of stimulus. TABLE
PreStimulus Voltage
2. Example of responses to variation in voltage of stimuli applied for 5 seconds to two pairs of electrodes in the bladder of a single paraplegic patient
Voltage Pulse During Cycles/ Duration Sec. Stimulams. tion
Bladder Volume (cc)
Manometric (cm. of H,O)
Motor
Sensory
--- --- ---
10 10 7 15 18
7 7 4.7 9.0 15
50 25 25 25
0.5 0.5 0.5 0.5
200 200 200 200
15 75 5 100
25
0.5
225
100
SUMMARY
Bladder response. The increase in intravesical pressure of the paraplegic patient may be made to exceed that of the normal voiding bladder. The response is prompt and may be sustained or reproduced over intervals of time sufficient to : permit complete emptying of the bladder contents through a urethra of normal caliber. Resistance to urine flow along the course of the urethra should be less than that of the normal since it is desirable to effect voiding at a minimal increase in intravesical pressure. This serves to protect the kidneys and ureters from reflux of urine, and by reducing the current strength of the stimulus minimizes the local injury to tissue at the site of electrode implantation, and, incidentally, conserves the energy of the power pack. Relief of obstruction or reduction of urethral resistance by pudendal nerve resection, surgical revision of the internal urethral orifice, external sphincterotomy, and other techniques is well established. Patient discomfort appears to arise from several sources: a) spasm of the detrusor, especially when there is no flow of urine through the urethra; b) stimulation of adjacent major somatic nerve
Desire to void Desire to void Minimal discomfort Slight discomfort; desire to void Pain; desire to void
Erection Erection Erection; leg movement Erection; leg movement
trunks with striated muscle spasm or sensory excitation; c) stimulation of pelvic parasympathetic or sensory components of the autonomic nerves with the resultant sensations of an urge to defecate, "gas pains," "stomach ache" or testicular pain; d) penile erections may occur with or without pain. Such patient discomfort can be reduced to a level which is virtually absent or at the most is readily tolerable. This is accomplished by individualization of the characteristics of the stimulus and proper placement of the electrodes. Electrode placement. The number of electrodes required to produce adequate increase in intravesical pressure is related to the degenerative changes which have occurred in the musculature and intrinsic innervation of the detrusor. There is no evidence that conduction pathways exist in the human bladder other than the intrinsic nerve-net of the bladder wall. In the absence of detrusor hypertrophy, fibrosis, or decompensation by chronic over-distension, a single pair of electrodes on either lateral bladder wall will be adequate and even one such pair may be sufficient. More than three additional pairs of electrodes spaced at maximal intervals from the
50
I
'
BOYCE, LATHEM AND HUNT
aforementioned pair will not enhance the response of the irreparably degenerated detrusor. The electrodes should be of braided stainless steel and enclosed in an insulation which is biologically inert. The exposed segment of electrode should be an inch in length and completely buried within the detrusor musculature where it is securely anchored by an embedding suture. The lead from each electrode is brought through the skin at a point separate from the incision and other electrode leads. The electrodes are placed in pairs, one active (negative) and one ground (positive). The pairs are placed so that each electrode lies parallel to the other and no closer together than an inch in the empty bladder. Application of a current flow results in an electrical field of greatest intensity between these two electrodes and prevents dissipation of the stimulus. The prime site for electrode placement is on either lateral bladder wall so as to encompass between each pair the sheaf of parasympathetic nerves as they separate from the middle vesical artery and begin to fan out over the detrusor. One branch of the middle vesical artery is usually included in the electrical field along with the accompanying veins and lymphatics. In bladders with excessive muscular hypertrophy and interstitial fibrosis, or in excessively large bladders, additional pairs of electrodes may be placed on the ventral bladder wall or on the dorsum near the base of the extraperitonealized bladder. Electrode pairs in the exact vertex of the bladder dome have been least effective. Adequate response to stimulation is quite difficult to obtain in the bladder so severely damaged as to require more than the two prime pairs of electrodes. Characteristics of the stimulus. The range of characteristics of effective stimuli for the human bladder and the values currently considered as optimal are presented (table I). These values apply for the well preserved paraplegic bladder which has minimal hypertrophy of the musculature, has a residual urine in the range of 200 ml., but has not been chronically overdistended. Much individual variation in the requirements of the stimulus will result from degenerative changes in the bladder. Future requirements. The mechanical feasibility of a totally implantable effective bladder stimulator appears unequivocal. Much clinical investi-
gation must precede its general usage. For the present, the external lead stimulator will be the most productive tool, and may never completely disappear from the field. Perhaps the first question is when in the course of central nervous system disease or injury should bladder stimulation be considered. There is general agreement that the patient with paralysis of the bladder resulting from trauma to the central nervous system should be greatly benefited by a program which completely eliminates the need for urethral catheterization. Whether the external stimulator can serve this purpose remains to be evaluated. Recovery of bladder function is unpredictable in the majority of traumatized patients. Since the complications of urinary dysfunction remain the major causes of death in paralyzed patients any procedure which can significantly improve or preserve function of the bladder deserves an adequate clinical evaluation. Among other significant problems requiring investigation are the following: a) Methods to circumvent the apparent physiological obstruction at the internal urethral orifice and within the urethra which impairs the outflow of urine at a time when stimulation is producing an intravesical pressure sufficient for normal voiding. b) Methods for prevention of excitation of other somatic and visceral structures. c) Adaptation and variation of sources of etimuli to meet the various requirements encountered in patients with neurogenic dysfunction of the bladder. Developing interest in this field has been evidenced by several preliminary reports from other investigators. 5 - 9 Hopefully, the investigations in this field will continue at an advanced pace. 6 Bunghele, T., Ichim, V. and Demetrescu, M.: Experimental study of emptying of cord bladder. Transcutaneous stimulation of pelvic nerves by electromagnetic induction apparatus. Therapeutic deductions. Digest of the 1962 15th Annual Conference on Engineering in Medicine and Biology, November 5-7, 1962. (Read by title.) 7 Bradley, W. E., Wingrove, R. and Chou, S. N.: Use of an implantable R. F. powered receiver for evacuation of the neurogenic bladder. Digest of the 1962 15th Annual Conference on Engineering in Medicine and Biology, November 5---7, 1962. 8 Bradley, W. S.: Implantable bladder stimulator developed. Med. Tribune, 3: 1, 24, 1962. 9 Schoenberg, H. W., Young, D. G. and Murphy, J. J.: Electrical stimulation of urinary bladder. Surgical Forum, 13: 509, 1962.
ARTIFICIAL ELECTRICAL STIMULATOR FOR PARALYZED HUMAN BLADDER
The authors acknowledge valuable assistance and participation of the following individuals: E. L. Corey, M.D.,* professor of physiology, University of Virginia School of Medicine, Charlottesville, Virginia. S. A. Vest, M.D.,* professor of urology, University of Virginia School of Medicine, Charlottesville, Virginia.
* Deceased.
51
William F. McGuire, M.D., Pulaski, Virginia. Mr. D. L. Bowers, Mr. H. G. Taus, and Mr. A. W. Schwalm, Advanced Medical Projects, General Electric Company. C. H. Davis, JVI.D ., associate professor of neurosurgey, The Bowman Gray School of Medicine, Winston-Salem, North Carolina. Mr. Frederick J. Wallace, president, American Cystoscope Makers, Inc., Pelham Manor, New York.