An implantable incontinence device

AN IMPLANTABLE

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GERALD W. TIMMt and &kc&al E&neer& Univmity Center, MinnespoIis,Minn. 55455, U.S.A.

Departments ofNeuro@y

DEVICE* ofMinnesota

Medical

Aba@act-The shortcomings of previous electronic and surgical prosthetic devices in restoration of urinary incontinence have led to the development of an alternative treatment technique. A device is herein described that is comprised of an inflatable cuff to occlude an encirckd urethra and a totally implanted yet external& controiiabk hydraulic system that can maintain at a pressure and periodically remove a volume of fluid from the cuff. By pressurizing the cuff to 50 cm H*O no urethral kakage occurs for bladder pressures up to 50 cm HpO. The system was desiplcd so that kss than 6 x 1p dyns of force on the hydmuiic system is required to deftate the cuff. Urethral tissue viability in dogs was not impaired due to inaation of this apparatus after twomonthimpiants. _ -

URINARY incontinence is a frequent and distressing sequel to various neurologic diseases, surgical procedures and sljinal cord injury (Austin, 196 t ). Present treatment techniques aim at increasing bladder outlet resistance by electronic stimuiation of the muscles of the pelvic diaphragm (Caidwell, 1965), or implantation of surgical prosthetic devices (Berry. 196 1). Tonic stimulation of the muscles of the pelvic floor results in loss of contractile response (HaId et al. 1966) due to neuro-muscular transmitter depletion. Evaluation of results is further obscured, particularly in gynecoiogic cases of incontinence, by the psychological effects of the surgical procedure. Placement of prosthetic devices frequently evokes pain and may result in draining sinuses (Engie and Wade, 1969; Raney, 1969). This suggests a different approach to treatment of urinary incontinence be developed. Effective restoration of continence requires replacement or simulation of impaired sphincteric function (Timm and Bradley, 1970). Implantable hydraulic devices comprised of a deformable cuff encircling the urethra and an externally controlled pressure mechanism

provide a means for simuiating sphincteric contractions via prolongud inflation followed by periodic Mation of the cuff (T&m et al. 1970). A similar concept with an externally activated cti has been described by Foley ( 1947) but data on occlusive pressures rquiredwssnotgiven,maUugcvahrationof his results and comparison with those obtained in this study difficult. This investigation was aimedat determining: (a) minimum cuff pressure required to occlude urethra for continence restoration, (b) design of pressure mechanism so that minimal external force’ is required to deftate the cuff and (c) whether chronic implantation impairs viability of the urethral tissues. PRocEDtJRJz Experiments were conducted on adult male and female mongrel dogs (20-30 kg) anesthetized intravenously with sodium pentobarbital (Diabutai, 2540 mg/kg). In females the perivesicai space was entered through a lower abdominal mid-line incision, the bladder neck was exposed and the cuff positioned around the urethra near the urethrovesical

*Received 27 Augusr 1970.

iThis work was supported by research grants from the U.S. Public Health Service and from the University of Minnesota Graduate School.

214

G. W. TIMM

A

SILASTIC

TUBING

Fig. 1. A diagrammatic illustration of a deformable cuff showing (A) an uni&ted cuff around a section of urethra (B) the cuff inflated so that the urethra is occluded and (C) a cutaway view to show inner inflatable balloon attached to Silastic backing.

junction. In males a perineal incision exposed the junction of the anterior and posterior urethra. The urethra was then separated from surrounding tissues and the cuffpiaced around it. To permit chronic implantation, cuffs were constructed of silicone rubber sheeting (Siiastic, Dow Coming Corp.) (Fig. 1). Use of thin sheeting on the side to bc placed in contact

with the urethra permits the entire occlusive pressure to be ixerted on the urethra during cuff deformation. The length of the cuff was chosen to fit snugly around the urethra without constricting it and the width was chosen to approximate the urethral diameter. Figure 2 illustrates the experimental arrangement for determination of cuff prcssure required to prcvcnt fluid leakage from the I

CUFF< ANTERIOR __ URETHRA

Fig. 2. Illustration of placement of cuff and experimental set up for determining cuff pressures required to prevent urine leakage from the bladder.

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bladder via a Foley catheter cannulated through the dome. Intravesical and cuff pressures were monitored continuously during infusion with strain gauges (Model P23Db, Inc.), ampiifiers Statham Instruments, (Model 3 11A, Hewlett-Packard), and a dualchannel strip chart recorder (Model 7100 BM, Hewlett-Packard). Water was infused until fluid leakage from the external meatus was observed, the intravesical pressure at this time was noted and the cuff was then deflated. The infusion process was conducted: (a) with the animal under deep barbiturate anesthesia, (b) with the animal under deep barbiturate anesthesia plus curare-like agent (gallamine triethiodide, Flaxedil, 1 m&kg) and (c) after the animal was sacrificed. After administration of the curarizing agent the animal was maintained on a respirator pump (Model 607, Harvard Apparatus Co.).

A typical pressure tracing observed in a sacrificed animal during an infusion procedure is shown in Fig. 3. After positioning the cuff around the urethra it was infiated to a pressure of 30 cm Hz0 and water infusion was begun. The bT&i$er pressure rose slowly during filling and leveled off at a typical value of 25 cm H,O as urethral leakage began. Deflation of the cti was followed by a drop in bladder pressure to approximately 10 cm H?O. Plotting the bladder pressure required to induce urethral leakage as a function of the pressure in a cuff encircling the urethra of a male dog (a) under deep barbiturate anesthesia, (b) under deep barbiturate anesthesia plus curare-like agent and (c) after sacrificing is shown in Fig. 4. In all cases the cuff had little influence on urethral leakage for cuff pressures less than 20 cm H20. Above 20 cm Hz0 cuff pressure there is a direct retationship between the bladder pressure necessary to obtain urethral leakage and the cuff pressure. The intravesical pressure required to obtain urethral leakage without a cuff or with zero

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BLADDER PRESSURE fcm water)

CUFF PRESSURE (cm water)

;

(II

Fig. 3. Bladder pressure and cuff pressure tracings obtained during filling of bladder with warm tap water at constant till rate. The cuff prcssurc was held fixed until the firsr signs of urctbrai leakcgc and was then t&aced to zero. F Ming begus: 1. uruthral leakage begins; D. cuff &&ted.

pressure in a cti was the greatest when the animal was under barbiturate anesthesia only and was the least after sacrificing the animal. This difference was not as pronounced in female dogs. A totally implantable pressure mechanism suitable for maintaining the above derived cuff pressures is illustrated in Fig. 5. The chambers are made of stainless steel with an internal spring rate provided by the bellows action. With the cuff initially pressurized by chamber B3 sufficient force on chamber B, induces fluid flow into chamber Bp resulting in extension of the Bz-B3 concentric bellows combination and removal of the contents of the cuff. To determine the amount of force required to deflate a pressurized cuff introduce the following quantities: R 1= effective radius of bellows B, RZ = effective radius of bellows B2 R 3 = effective radius of bellows B3

G. W. TlMM

216 0 X a

I

Deep Diabutal anesthexir Deep Diabutrl and Flaxedil anesthesia Animal sacrificed

I

I

I

20

t

I

40

I

60

I

I

80

p2, cm H20 Fig. 4. Ruxure P, rquirrd in bladder to overcome occlusive effect of pressure Pr in inflatable cuff encircling the urethra with various prep%UiOnS.

Fig. 5. Pressure mechanism consisting of three stainless steel bellows chambers to be used in conjunction with deformable cuff of Fig. 1. The &-B3 bellows have their end plates in common.

AN IMPLANTABLE k=

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spring rate of pressure mechanism

xl = free length of bellows B,

x2 =x3 = free length of bellows Bz-B3 combination P, - cuff pressure V = volume of inWed cuff F1 = force on ends of bellows B1 F2 = force on ends of bellows B2-BJ combination. Assuming non-deformabIe walls for the bellows then any volume change in the bellows causes a separation of the end plates of, Ax= AVIAt

A 1 = wR 12* effective area of chamber B1 A2 = rr(Rsf-Rj) = effective area of chamber Bt A3 = aR I* = effective area of chamber Ba.

Let us first calcuiate the state of the bellows when the cuff is inflated to a pressure P,: P, = FzIAs = Ps

(2)

but, F? = P2A2 * PIA:!

(3)

since, Pz = PI.

Also, PI = F,A,

(4)

V== A3Ax9

A& =A&

where x is the length of B1 in compression, after assuming the spring rate k of the entire system is lumped into B1. Then, F, = P,A, = A ,FZ/A2 = A,A,P,IAz

(7)

(9)

and AnA+ = AlAx;

(10)

where A.$ is the additional compression B,. Then, Ax; = ArAxzlA 1 = A2VlA1A3.

of (

1)

The total force exerted on B, required to defMe the cuff is then given by, F = k(AxI+Ax;) =A,A3P,/A2+AskV/A1A3.

f

2)

(13)

When the units are A cm2, P dynlcm2, k dynlcm and V cc, the force F is dynes. Experiments are presently being set up and conducted to determine whether placement of a cuff around the urethra impairs viability of the urethral tissues. Preliminary results indicate no loss of viability after two month implants in male dogs with cuff pressures less than 80 cm Hz0 and in female dogs with cuff pressures less than 40 cm H20. Above 80 cm H,O cuff pressure in the males penis engorgement was observed. and in females tissue necrosis occurred at cuff pressures above 40 cm H,O.

(9

(6)

(8)

where Ax3 is the increase in length of BJ. But,

DISCUSSION Use

F, = k(x, -x) = khx,

217

is the force being exerted on the ends of B, to maintain the pressure P, in the cuff. To deflate the cuff a volume V must be removed from it. Thus,

(1)

where Ax is the change in separation for a volume change of AV in a chamber with effective area Ai. The effective areas for the chambers here are,

DEVICE

of an inflatable cuff begirding the urethra as an ocdusion technique to increase bladder outlet resistance and thereby restore urinary continence requires knowledge of internal cuff pressure necessary to prevent urine outflow. Our experiments indicate that urethral leakage wilt occur only when intravesical pressure exceeds cuff prespure. Ure-

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G. W. TIMM

thral contraction studies show bladder pressures as high as 50 cm H20 are achieved during a normal bladder filling phase (Lenaghan, 1970: Tanagho and Smith. 1968) and so inflating a cuff encircling the urethra to this pressure is expected to be adequate in restoration of urinary continence. This pressure requirement may restrict use of this device in females. Knowledge of the pressure and size requirements for an occlusive cuff permits design of the hydraulic pressure activation mechanism so that a minimal force is required to deflate the cuff. It was previously determined in ( 13) that a force

indicate that a combination of physiologic and anatomic parameters are normally involved in maintaining continence. Incontinence or loss of urinary function may be classified in the following manner: (A) Loss of volitional detrusor reflex control. A principal manifestation of normal urinary bladder control is the capacity to depress a reflex detrusor contractile response (Denny-Brown and Robertson,, 1933). This capacity is impaired in many neurologic diseases such as multiple sclerosis (Bradley et al. 1967) and trauma., and involves d&rent target sites in the nervous system including spinal cord, cerebellum and areas of the frontal cortex. In these cases the reflex eliciF = A1A,P,IAz+A2kVIA,A3 (13) ted by bladder filling is sudden, shortened in duration and lacks volitional control. must be exerted on B1 to remove a volume of (B) Disordered spread of excitation within fluid V from a cuff inflated to a pressure the detrusor muscle. A prime consideration in P,, in a bellows system having a linear spring orderly sequential opening of the urethrovesical junction is adequate and coordinated conrate of k. Introduce traction of the derrusor muscle (Conway and y = AtAsiA (14) Bradley, 1969; Lapides, 1958). This orderly contraction may be impaired by both central and take the derivative F’(y): and peripheral neurological lesions (Bradley and Teague, 1969). F’(y) - P, - Vkly*. (C) Loss of detrusor contractile function. (15) Detrusor contractile function may be impaired Then for F = minimum set F’ - 0 which as a result of peripheral denervating processes yields, such as diabetes, meRitus or processes which y* = VA/P, (16) result in smooth muscle destruction and fibrous tissue replacement such as recurrent so that from (13). infection (Bradley, 1967; Swaiman and F m,n = 2(VkP,)‘n. (17) Bradley, 1967). (D) Loss of urethral resistance and ureIn a typical situation V = 5 cc, k = 3 x 105 thral guarding reflex (Garry et al. 1959). dyn/cm and P, = 6 X l(rdyn/cm* so that This may occur after surgical resection of the prostate, or in patients with congenital F,,,(typ) = 6 x 1p dyn. (18) defects of the spinal cord producing atrophy of the pelvic door musculature. Varying the experimental preparation Of these classifications, category (D) is through use of anesthetizing and curarizing proposed as the primary indication for agents produced variations in the bladder application of this device. The other sources pressure required to obtain urethral leakage at of incontinence require other treatment low cuff pressures. Although the significance schedules. of these *results is presently unclear, they Potential sources of complications that may

AN IMPLANTABLE

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limit clinical application but have not been observed in our animal experiments indude: ( 1) development of fibrous tissue productive of urethral stricture or rendering device ineffectual, (2) intolerable pain, (3) tissue necrosis as a result of impeded blood flow in the urethra and (4) momentarv hinh levels of bladder press&i induced in &es&i situations causing slight leakage. Acknowledgements -The

author wishes to thank Drs.

WiBiam E. Bradley and Daniel C. Merrill for their advice and assistance in performing the experiments. REFERENCES Austin. G. (1966) The Spinal Cord: Basic Aspects and Surgical Considerations. Thomas, Springfield. Illinois. Berry, J. L. ( 1961) A new procedure for correction of urinary incontinence: a preliminary report. J. Ural. 85,771-775.

Bradley. W. E. (1967) Neurologic aspects of smooth muscle disease: Dysfunction of the urinary bladder. Postgrad. Med. 41.260-262. Bradley, W. E., Chou. S. and Ma&and+ c. (1967) Neurologic dysfunction of the urinary bladder in demyelinating disease of the central nervous system. The Nrnrogenic Bladder, pp. 158-164. Williams and Wilkins, Baltimore. Md. Bradley. W. E. and Teague, C. T. (1%9) Cerebelhu influence on the micturition reflex. Expr. Neural. 23, 399-411. CaMweB. K. P. S., Flack, F. C. and Broad, A. F. (1965) Urinary incontinence folIowing spinal cord injury treated by electronic implant. Lancrt 1.846847.

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Conway, C. J. and Btadiey, W. E. (1969) Measumment of spread of excitation in the urinary detrusor muscle duringreflexinduction.J. Uroi. 101.533-538. ~y_B~wn, D. and Robemmn, E. G. (1933) On the physiology of mictutition. Bruin #, 149- 190. Engel. R M. and Wade, J. C. (1969) Experience with the Berry prosthesis. J. Ural. 102.78-80. Foley, F. E. B. ( 1947) An artificial sphincter: a new device and operation for control of enuresis and urinary incontinence~ J. Ural. S&250-259. Garry, R C.. Roberts, T. D. M. and Todd, J. K. (1959) Reflexes involving the external urethrai sphincter in the cat. J. Physiol. 149.653-665. Haki, T., Freed. P. S.. Agrawal, G. and Kantmwitx. A. ( 1966) Urethral resistance during electrical stimulation. Invest. Ural. 4.247-256. Lapides. J. ( 1958) Structure and function of the internal vesicai sphincter. J. Ural. 80.341-353. Lenaghan. D. (1970) The diagnosis of prostatic obstruction by measurement of urethral resistance to flow. 1. Uroi. 103.320-326. Ranev. A. M. ( 1969) Reevahtation of post pmstatectomy m&u-y incontinence with Ben-y procedure. J. Uroi. 102.81-83.

Swaiman. K. F. and Bradley, W. E. (1967) Quantitation of collagen in the wall of the human urinary bladder. J. appl. Physiol. 22. 122- 124. Tanagho, E. A. and Smith, D. R. ( 1968) Mechanism of urinary commence. 1. Embryologic, anatomic and pathologic considerations. J. Ural. l@, 640-646. Timm. G. W. and Bradlev. W. E. (1970) Electronic mictutition rdIex sit&&n. Proc. 17th spinal Cord Injtqv Co& of the Vetetws Adtninistratim.

Timm. G. W., Merrill, D. C. and Bradley. W. E. ( 1970) Intermittent occlusion system. IEEE Trans. on BioMedical Engng BME-17.352.