JOURNAL OF SURGICAL RESEARCH 16, %-209 (1974)

A Prosthetic Sphincter for the Gastrointestinal Tract

JOHN DELANEY, M.D., PH.D., THOMAS BROADIE, M.D.,

GERALD TIMM, PH.D., AND WILLIAM BRADLEY, M.D.

A PROSTHETIC SPHINCTER SYSTEM, developed for use in the control of urinary incontinence, has now been implanted suc- cessfully in more than 70 human patients [2]. The purpose of this study was to test its applicability in the gastrointestinal tract. Experiments were carried out: (1) to determine the sphincter pressure necessary to restrain passage of intestinal contents, (2) to measure intraluminal pressure under- lying the cuff of the sphincter, (3) to measure blood flow changes in tissues under the cuff, (4) to determine short-term in- testinal tolerance to varying c,uff pressures, and (5) to observe chronic changes with long-term sphincter implantation.

METHODS

Description of the Prosthetic Sphincter

The device is constructed from silicone rubber and is composed of a reservoir, an inflatable cuff, and inflating-deflating pump mechanisms (Fig. 1). The back of the cuff is reinforced by Dacron mesh and is flexible but nonelastic. When sutures, which are in- corporated into the back of the cuff, are tied, a ring is formed. The inner lining is thin and elastic. When inflated, the inner lining applies circumferential pressure against the contained intestine. Each pumping mechanism is made up of a squeeze bulb and two valves. Repeated compression of one bub inflates the cuff by

From Departments of Surgery and Neurology, University of Minnesota Health Sciencrs Center, Minneapolis, Minnesota 55455.

Submitted for publication November 8, 1973.

delivering fluid from the reservoir to the cuff. The other bulb has the opposite func- tion. The valves serve to control the direc- tion of fluid flow and to allow a predeter- mined maximum pressure in the cuff. The fluid used is radiopaque so that it can be observed by means of roentgenography. The component parts of the sphincter system have been cycled 40,000 times without mechanical failure, equivalent to 6 cycles per day for approximately 20 years.

Pressure Studies

Large mongrel dogs were anesthetized, a midline incision made, and a loop of ileum delivered into the wound. The prosthetic sphincter device was placed about the ileum and the sutures tied. The intestine was di-

Fig. 1. Schematic representation of the prosthetic sphincter system.

204

Copyriybt 0 1974 by Academic Press, Inc. AU rights of reproduction in any form reserved.

DELAh-El- ET AL. : PROSTHETIC SPHINCTER 205

vided 5 cm beyond the edge of the cuff. Approximately 15 cm proximal to the cuff

the intestine was ligated over an infusion tubing which had been passed through a proximal stab wound (Fig. 2). Saline was delivered at a rate of 3.5 cc/‘min into the lumen. A side arm attached to a strain gauge permitted con&ant rccortiing of the pressure in the lumen. One of the tubes leading to the cuff was attached to a strain gauge and the pressure monitored. Saline was injected through the other tube until the desired intracuff pressure was reached and then the tubing clamped. The end point was when the saline began to leak from the intestine through the area compressed by the cuff. In this manner a series of values were obtained comparing pressure within the cuff with the intraluminal pressure at which leakage occurred.

A second study was aimed at determining

InfusIon Pump t 3 5 ct/min )

Pressure Transducer

the pressure underlying the cuff itself and was carried out in the same fashion as esophageal manometry. A I.&mm id. poly- ethylene tubing with an end opening and a side arm attached to a strain gauge was used to measure pressure. Saline was in- fused constantly at 1 cc per minute. The tip of the catheter was inserted into the cut end of the intestine and passed into the lumen underlying the cuff. Pressure within the cuff was varied and the pressure in the infusion tubing recorded as the dependent variable (Fig. 3).

Tissue Tolerance

Two animals u-ere used in this study. In one, cuffs wcrc applied at 125 and 200 cm H,O to two widely separated segments of the mid small bowel. In the other 175- and 275-cm cuff pressures were applied. All blood VCSSC~S were preserved including the

Fig. 2. Experimental arrangement for detrrmining the intrncuff pressures necessary to restrain inlraIumina1 fluid at varying prcesurrs.

Pressure Transducer h’

Fig. S. Experimental arrangement for measuring intraluminal pressure in the intestine under- lying the cuff. Note the similarit!- to esophageal manometry.

206 JOURNAL OF SURGICAL RESEARCH, VOL. 16, NO. 3, MARCH 1974

marginal arteries and veins. The tubing leading to the cuffs was occluded and the incision closed. Eighteen hours later the dogs were sacrificed, pressures rechecked, cuffs removed, and the underlying tissue in- spected for gross damage. Each segment of intestine was fixed in formalin and sec- tioned for microscopic examination.

Blood Flow

Six dogs were used in the blood flow study. The method was the radiorubidium distribution technique previously used in our laboratory [l]. Briefly, each animal was anesthetized with pentobarbital and catheters threaded into the aorta and the vena cava. After the animal was stabilized with respect to blood pressure, cardiac out- put, and arterial blood gases, a b,)lus of radiorubidium was injected rapidly through the caval catheter. At the same time arte- rial blood was withdrawn through a beta scintillation detector whose output was re- corded to provide an isotope di!ut:on curve for calculation of cardiac output. Thirty seconds after the radiorubidium injection, the animal was sacrificed by a rapid injec- tion of saturated potassium chloride. The tissues of interest were then assayed for radioactivity, which was expressed as a fraction of the total injected radioactivity. This fraction represents the percentage of the cardiac output perfusing each tissue. Perfusion, expressed in terms of cubic cen- timeters per gram per minute, was calcu- lated by multiplying this fraction times the cardiac output and dividing by the tissue weight. Four cuffs were applied at widely spaced intervals in the mid intestine of each animal. Pressures in the cuffs tvere set at 0, 40, 80, and 120 cm of water. After ap- proximately 15 min, radiorubidium was in- jected and the animal sacrificed. Each seg- ment of intestine underlying the cuff was removed and dissected into mucosa, submucosa, and muscularis. A comparable control segment of intestine with no over- lying cuff was also assayed for radioac- tivity.

Long-Term in Vivo Implantation

Ten dogs were used in this study. The sphincters employed had maximum in- tracuff pressures ranging from 70 to 90 cm of water. At laparotomy the distal ileum was divided approximately 12-15 cm proxi- mal to the ileocecal valve, with careful preservation of the mesenteric blood ves- sels. An area in the mesentery proximal to the last arcade was opened and the cuff placed around the intestine without divid- ing any blood vessels. The sutures on the back of the cuff were tied and the sphincter tested to establish that proper occlusion could be accomplished. A right lower-quad- rant ileostomy was then constructed in such a manner that the cuff lay in the abdomen flush with the peritoneum, the axis of the cuff and intestine at right angles to the ab- dominal wall. The cuff was sutured at 3 or 4 points to the peritoneum and wrapped with omentum. A pocket for the fluid reser- voir was developed between the peritoneum and the muscles of the abdominal wall. The reservoir thus lay in an extraperitoneal position but was subjected to intraab- dominal pressures. The fluid transfer tubes were tunneled in an extraperitoneal plane to an incision in the suprapubic area whence they were tunneled into the scro- tum, one bulb on each side. After the inci- sions were closed, the ileostomy was opened and everted and a mucosa to skin approxi- mation made with catgut sutures. For 3-5 days after operation, the dog was given in- travenous fluids and was then progressed through a liquid to a regular diet. After 2-3 weeks for recovery and healing of the stoma, the prosthetic sphincter was acti- vated for short periods. After proper func- tion was verified, the sphincter was oc- cluded each day for 8 hr and left open for 16 hr.

RESULTS

Pressure Studies

Table 1 relates intracuff pressure to the intraluminal pressure at which the fluid

DELANEY ET AL.: PROSTHETIC SPHINCTER 207

Table 1. Comparing Pressure with the Cuff (cm H,O) with the Intraintestinal Lumen Pressure at Which Leakage Occurred

Cuff A

cuff I!,

Intracuff pressure (cm H&) 4,; 50 70 93 Intraluminal leaking pressure 40 40 60 65

Intracuff pressure (cm H?(1) 50 70 90 100 Intraluminal leaking pressure 40 33 40 80

leaked through the occluded segment. The cuff pressure which permitted passage of fluid depended in part upon the exact gco- metric arrangement, the fit of the cuff, and the angle of the intestine entering and leav- ing the cuff. Generally the luminal pressure at which leakage occurred was IO-20 cm less than t’he pressure recorded within the cuff. For example, a cuff pressure of 50 cm of water restrained the intraluminal fluid until the intraluminal pressure reached 40 cm of water, at which point leakage occurred.

Manometry of the luminal pressure underlying the cuff was not entirely consis- tent; rising intracuff pressure did not lead to a linear rise in intraluminal pressure. The data points are shown in Fig. 4. The intraluminal pressure ranged from 20-55 cm of lyater less than the pressure recorded within the cuff. As a very rough approxima- tion, intraluminal pressure was 30 cm less than intracuff pressure.

Tissu,e Tolerance

Aft’er 18 hr of compression by a cuff with 125 cm H,O pressure no gross damage was apparent,. Cuff pressures of 175 and 200 led

f 8\1!- 3 0 0

,“g 60- X

Er”

: 5 / 3 401 xal O

$ 1.x

x 0

3 20

i- 0 O : 11 50 75 100 125 150 175

lntm cuff pressure (cm Hz01

Fig. 4. Intraluminal pressures as a function of pressures in the cuff.

to a slight reddening of the mucosa ; 275 cm of pressure caused gross mucosal ulcera- tion. Microscopic examination confirmed the gross observations, 125 cm cuff pressure led to no detectable changes; 175 and 200 cm were associated with some small vessel dilatation; 275 cm pressure in the cuff caused frank necrosis of underlying bowel.

Blood Flotu

Blood flow data are presented in Fig. 5. Although the difference was not significant from control, the mean blood flow in mucosa underlying the cuff with zero pres- sure was slightly reduced. Perfusions of submucosa and muscularis were not signifi- cantly altered by intracuff pressures of ul) to 120 cm of water. Mucosal blood flow was sensitive to pressure changes, such that the perfusion rates at 40, 80, and 120 cm of water were all significantly reduced from that of the control intestine. It should be noted that even with 120 cm H,O cuff prcs- sure mean mucosal blood flow was still 0.37 cc/g/min or approximately half the control value.

I I I / I noCUff 0 40 80 120

Cuff pressure LcmH,O)

Fig. 6. Mean tissue perfusions (cc/g/min) as a function of cuff pressures. Note the lack of change in submucosa and muscularis. Bars on mucosal blood flow points represent % Standard Error of the mean.

208 JOURNAL OF SURGICAL RESEARCH, VOL. 16, NO. 3, MARCH 1974

Long-Term in Vivo Studies

In one animal the cuff, placed in the extraperitoneal position, encircling the ileum as it passed through the abdominal wall, eventually eroded through the skin. Twice the placement was done with the long axes of the cuff and intestine lying parallel with the abdominal wall. This led to kinking, intestinal obstruction, and death of the animal. In three instances, the dogs injured the ileostomies and succumbed to the ensuing hemorrhage or were sacri- ficed. Infections around the reservoir and/or pumps developed in three animals. Fibrous rings between the sphincter and peritoneum caused partial obstruction in two dogs. The animals exhibited no signs of discomfort or symptoms of intestinal ob- struction with 8 hr of sphincter occlusion. Mechanical function was uniformly good and continence was accomplished in every instance. The longest in vivo observation, to date, was 3 months.

DISCUSSION

Measurement of pressure within an clas- tic system, such as the cuff of this prosthe- sis, has meaning only for the individual characteristics of each balloon. Pressure is a function of the elasticity of the balloon as well as the volume of fluid injected and the volume of tissue enclosed. Observations regarding continence, which compared the pressure of the cuff with the pressure that could be restrained in the lumen, indicated that intracuff pressures in the 50- to 70-cm H,O range readily restrain passage of in- testinal contents. Seldom does the intra- luminal pressure of the bowel exceed 40 cm of water, even in the obstructed situation. Long-term in viva experiments with dog ileostomies verified the in vitro observa- tions. With the prosthetic device closed, there was virtually no leakage of intestinal contents.

Measuring intraluminal pressure under the cuff provides a reasonable estimate of the pressure to which the tissue is sub-

jected. Pressure impinging on the mucosa is probably of the same order of magnitude as the pressure measured in the adjacent lumen. With a cuff pressure 50 cm H,O the intraluminal pressure was 20 cm; at 70- to 75-cm intracuff pressure, the intraluminal pressure was 25-30 cm of water. Clearly these tissue pressures are tolerable on a long-term basis.

The influence of intraluminal distention and pressure on intestinal blood flow has been previously studied. To the best of our knowledge no one has looked at the rcla- tionship of external compression and blood flow alterations. Cuff pressure well in excess of that needed to restrain passage of lu- minal contents reduced mucosal blocd flow by only 50%. Half-normal blood flow is very likely adequate to sustain viability. This supposition is supported by the experi- ments in which 125 cm intracuff pressure was applied for a period of 18 hr with no detectable damage to the intestinal wall.

Long-term in viva studies supported con- clusions surmised from the acute experi- ments, namely, that cuff pressures sufficient to completely restrain intestinal contents were not injurious to the underlying tissues and were well tolerated for extended periods of time.

The long-term experience in the dog pro- vided a number of lessons. The first was that infection around a foreign body in the extraperitoneal position is a significant problem. This will likely be more important in the gastrointestinal tract, which is heavily laden with bacteria, than in the urinary tract. In human applications it will be prudent to construct the stoma first and apply the cuff at a later date, as some con- tamination is inevit’able when bowel is transected. Another notable finding was that infection did not develop around the cuff, which lay intraperitoneally. Dense adhesions did form in reaction to the intra- peritoneal foreign body. Our observations suggest that silicone rubber is quite reac- tive within the peritoneal cavity. At post- mortem examination the cuff was dissected

DELANEY ET AL. : PROSTHETIC SPHINCTER 209

out of the surrounding fibrous tissue only with considerable difficulty. In the early experiments intestinal obstruction was seen resulting from adhesion of loops of intestine directly to the cuff itself. Subsequently, omentum was wrapped around the device to obviate this problem.

Two animals developed partial obstruc- tion secondary to formation of a fibrous ring at the point where the intestine passctl through the parietal peritoneum. A single attempt to place the cuff in the subcutanc- ous position failed because of erosion of the device through the skin. Intestinal obstruc- tion due to angulation occurred when the long axes of the cuff and bowel were paral- lel to the abdominal wall.

Potential uses for an implantablc pros- thetic sphincter in the gastrointestinal tract are numerous. The two most obvious appli- cations are for anal incontinence and for control of ileostomy efflux. Other possible uses are in the short-bowel syndrome, the postgastrectomy dumping syndrome, and gastroesophageal reflux. With continuctl mechan’cal improvcmcnts and better tech-

niques for avoiding infection, this pros- thetic sphincter system may well find clini- cal applicat’ion.

SUMMARY

A totally implantable prosthetic sphinc- ter was tested on dog small bowel and on dog ileostomies. External pressure sufficient to completely restrain passage of intestinal contents caused some reduction in mucosal blood flow but no gross or microscopic in- jury to the intestinal wall. Long-term in vivo studies pointed out two major prob- lems, infection around the foreign body and fibrotic reaction, leading to intestinal ob- struction. The in Go prosthetic sphincter functioned perfectly and caused no injury to the underlying intestine. This system has promise for future clinical applications.

1.

2.

REFERENCES

Delaney, J. P., and Cust)er, J. Gastrointestinal blood flow in the dog. Circ. Res. 17:394, 1965. Scott, F. B., Bradley, W. E., and Timm, G. W. Treatment of urinary incontinence by im- &mtable prosthetic sphinctrr. Urology 1:252, 1973.