Journal of Clinical InvestigationVol. 42, No. 2, 1963

THE INTERNAL ANAL SPHINCTERRESPONSE:MANOMETRICSTUDIES ON ITS NORMALPHYSIOLOGY, NEURAL

PATHWAYS,ANDALTERATION IN BOWELDISORDERS*

By MARVIN M. SCHUSTER,THOMASR. HENDRIX, ANDALBERT I. MENDELOFF

(From the Department of Medicine, The Johns Hopkins University School of Medicine,Baltimore, Md.)

(Submitted for publication July 6, 1962; accepted October 18, 1962)

Manometric recordings of lower bowel mo-tility have been difficult to interpret because 1)this segment frequently displays no spontaneousactivity for periods as long as 6 hours (1), 2)attempts to stimulate normal activity have beenmet with inconsistent results (2-4), and 3) theactivity observed has not been clearly related tothis segment's primary function, defecation (2-7).

Wehave described previously (8) an internalanal sphincteric response that can be elicited atwill, is regularly reproducible, and is analogous tothe physiological concomitants of defecation. Thisresponse is essentially that reported in 1877 byGowers, who found that insufflation of air intothe rectum produces relaxation of the internal analsphincter (9). Very few investigations of thisresponse, however, have subsequently been car-ried out.

This investigation was designed to define in thehuman 1) the normal physiology of the sphincterresponse, 2) the neural pathways involved, and3) the effect of various disorders of bowel func-tion upon this response.

MATERIAL AND METHODS

Sphincteric function was examined in the followinggroups of patients (Table I): a) normal controls; b)paraplegics with complete spinal cord transection atlevels ranging from C-7 to T-2; c) biopsy-proven casesof Hirschsprung's disease before surgery; d) patientswith Hirschsprung's disease who were asymptomatic af-ter proctosigmoidectomy; e) patients with Hirschsprung'sdisease in whom fecal incontinence appeared after proc-tosigmoidectomy; f) patients with functional megacolon("pseudo-Hirschsprung's disease") and fecal inconti-nence; g) patients who had undergone partial sigmoid-ectomy and partial proctectomy, the lower rectum being

* Work suported in part by training grant 2A-5095of the National Institute for Arthritis and Metabolic Dis-eases, Bethesda, Md.

left intact; h) a group of patients with various disturb-ances of bowel function, including the irritable colon syn-drome, diverticulitis, diabetic autonomic diarrhea, mega-colon secondary to intermittent volvulus, and posthemor-rhoidectomy diarrhea. The oldest patient studied was77 years old, the youngest, 10 weeks.

The apparatus used to measure sphincter function con-sisted of a balloon assembly attached via polyethylenetubes to Sanborn differential pressure transducers and adirect-writing electrical recorder. The tubes had an ex-ternal diameter of 6 mmand an internal diameter of 4mm; although somewhat flexible, they were rigid enoughnot to double on themselves in the rectum. The twocephalad tubes were taped together in tandem so thattheir tips were always 10 cm apart. Miller-Abbott bal-loons 4.5 cm long were attached to the end of the tubesas illustrated in Figure IA. When filled without stretch-ing, the balloons contained 50 ml air and were 4.0 cm indiameter. During recording in the resting stage, theballoons were kept inflated with 7 ml air to keep theirwalls slightly away from the side openings of the tube.This volume of air did not stimulate colonic motility inany of the patients, thus confirming the impression thatin routine studies of colonic motility, tracings obtainedwith a small balloon do not differ appreciably from thosetransmitted via fluid-filled open-tipped catheters (10).The caudad balloon was so constructed that when dis-tended with 17 ml air, it was 4 cm in diameter and 2.5cm long.

No premedication was administered, and no laxativesor enemas were given to normal subjects. Eight pa-tients received hypertonic phosphate enemas to facilitaterecording when impaction or watery stool was present.The recordings from patients who received such enemaswere similar to those in patients who required none. Thishas also been the experience reported by others in rou-tine studies of colon motility (2). With the patient inthe knee-chest position, the tubes were passed throughthe proctoscope so that the cephalad balloon lay in therectosigmoid colon with the tip of the tube at 22 to 25cm, while the middle balloon lay in the rectum with itstip 40 cm caudad to the cephalad balloon. The third tube,also in the rectum, was unattached to the other two.The proctoscope was then withdrawn over the tubes.Finally, the caudad balloon was pulled against the in-ternal anal sphincter and held there snugly by a string

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THE INTERNAL ANAL SPHINCTER RESPONSE

TABLE I

Patients

SexNo. Time

Classification subjects Age Postop. Male Female

yearsA. Controls 10 < I yr 2 1

1-2 yrs 1< 20 yrs 6

B. Paraplegics 3 20, 21, 25 yrs 3 0

C. Hirschsprung's disease, 5 2 mos; 4 mos; 4 1preoperative 4 mos; 14 mos;

22 mosD. Hirschsprung's disease,

postoperative, asymptomatic 2 13 yrs 24 2 028 yrs 7

E. Hirschsprung's disease, 5 14 yrs* 2postoperative, with fecal incontinence 3 2 3 2

5 37 29 7

F. Functional megacolon, with fecal incontinence 6 4, 10, 11, 15, 16, 4 21 7 yrs

G. Sigmoidectomy and partial proctectomy 2 57 yrs 13 1 157 2

H. Miscellaneous bowel disturbancesPosthemorrhoidectomy diarrhea 77, 66 yrs 1 1Irritable colon 51, 41 1 1Functional constipation 10 7, 28 1 1Diverticulitis 55, 65 0 2Diabetic autonomic diarrhea 50 0 1Megacolon secondary to intermittent volvulus 60 1 0

Total 43 30 13

* This patient is grouped among those with incontinence because she had incessant dribbling of stool and severelymacerated buttocks.

from the tube to a pulley system with a 200-g counter-weight (Figure 1B). Accurate placement against thesphincter was indicated by a rise in pressure in thetracing from the caudad balloon as it was pulled into theanal canal (Figure 2). The mean increase in pressureupon entry into the anal canal was 12 mmHg, rangingfrom 5 to 22 mmHg. The balloon was not visible atthe anal orifice under these circumstances. During thetest, the subject was placed in the left lateral semiproneposition, and was unable to view the actual recording(Figure 1B). Subjects were informed simply that colonicmotility was being studied by the use of plastic tubes.Subj ective sensations were recorded as reported. Apneumograph monitored respiration and body movements.

After a short period of recording in the resting state,one of the two cephalad balloons was rapidly inflatedwith 50 ml air and quickly deflated, by a hand syringeattached to a 3-way stopcock. During this procedure,which required about 2.5 seconds, recording from thedistending balloon was interrupted. After this, theother cephalad balloon was inflated momentarily in simi-lar fashion. The technic of transient inflation was insome instances compared with prolonged distension, dur-ing which the balloon was inflated for 30 to 90 seconds.

In infants, only two balloons were used and were in-serted without use of the proctoscope. The cephalad tipwas inserted to 10 cm while the caudad balloon was heldagainst the sphincter by manual traction. Tubes usedfor infants had an external diameter of 3 mmand an in-ternal diameter of 1.5 mm. The sphincteric balloon,when distended with 15 ml air, assumed a diameter of 3cm and a length of 2.5 cm. Infants were held supine dur-ing the test with the legs flexed at hip and knee.

RESULTS

Table II summarizes the results for all groupsstudied.

A. Normal subjects. In all, distension of therectal or rectosigmoid balloon produced relaxationof the internal anal sphincter, as manifested by atransient fall in pressure within the caudad bal-loon (Figure 3, A-D). The mean duration ofthis relaxation was 12.8 seconds, with a rangeof 4 to 18 seconds. This same range of variationamong subjects was also seen in a single subject.

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THE INTERNAL ANAL SPHINCTERRESPONSE

TABLE II

Sphincter response

Classification Positive Negative Abnormal

A. Controls 10 0 0B. Paraplegics 3 0 0C. Hirschsprung's disease, 5 0 0

preoperativeD. Hirschsprung's disease, 0 2 0

postoperative, asymptomaticE. Hirschsprung's disease, 0 0 5*

postoperative, with fecalincontinence

F. Functional megacolon, 6 0 0with fecal incontinence

G. Partial proctectomy1. Distension cephalad to 0 2 0

anastomosis2. Distension caudad to 2 0 0

anastomosisH. Miscellaneous bowel disturbances 10 0 0

Total 36 4 5

* An abnormal sphincter response was also found in a 7-year-old boy with functional megacolon who had undergonea proctosigmoidectomy and still had encopresis 3 years postoperatively. An additional patient, age 5 months, had anabnormal response shortly after proctosigmoidectomy at a time when fecal dribbling was prominent. An incompleteresection of aganglionic segment had been performed so that aganglionic colon was anastomosed to anus.

Failure of sphincteric relaxation occurred only 5times in 97 distensions in these subjects (and only8 times in 600 distensions in all subjects withoutsphincter abnormality). After prolonged dis-tension, the sphincter rapidly regained its tone

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even though rectal distension was maintained(Figure 4A). Occasionally the sphincter main-tained a state of partial relaxation as long as therectum remained distended (Figure 4B).

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FIG. 2. HIGH PRESSUREZONE IN INTERNAL ANAL SPHINCTER. In this and in subsequent figures, Roman numeralsrefer to location of recording balloons as indicated in the drawing in Figure 3. A downward arrow indicates inflation andan upward arrow deflation of the distending balloon. "C" designates contraction around a recording balloon. "R"represents sphincteric relaxation. A. Distension of the rectosigmoid colon (arrows) fails to produce pressure decreasein caudad balloon (III) which lies immediately cephalad to the sphincter. B. Rise in baseline (heavy arrow) appearswhen the caudad balloon is pulled into the sphincter. Distension (arrows) now produces sphincteric relaxation.

FIG. 3. FOURTYPES OF COLONICRESPONSEIN NORMALSUBJECTS. A. No colonic contractions and sphincter relaxesnormally (R), in 77 per cent of distensions. B. Colonic contraction around distending balloon (C), in 16 per cent.C. Synchronous contraction (C) in rectosigmoid colon (I) and rectum (III), in 13 per cent. D. Progressive wave ofcontraction (C) from rectosigmoid colon (I) to rectum (II), in 4 per cent of distensions.

199

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sphincter and levatores ani produced a rise inpressure in the sphincteric balloon; it was notpossible, however, to inhibit internal anal sphincterrelaxation by voluntary effort (Figure 5). Therewas no subjective awareness of changes in sphinc-ter tone. Age did not appear to affect the re-

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FIG. 5. FAILURE OF VOLUNTARY INHIBITION TO IN-

FLUENCEINTERNAL ANAL SPHINCTER RESPONSE. A. Nor-mal sphincter relaxation (R). B. Voluntary contractionof external anal sphincter and levatores ani (heavy ar-

row) results in elevation of baseline in caudad balloon(III), but fails to inhibit relaxation of internal sphincter(R).

Four types of colonic response were elicited,and are seen in Fig 3 as A, B, C, and D. In 77per cent of the distensions, no pressure change oc-

curred in either the rectal or rectosigmoid bal-loon (Figure 3, A). In 16 per cent, there was a

contraction around the distending balloon (Figure3, B), and in 13 per cent, synchronous contrac-tions were seen with simultaneous pressure ele-vations in both cephalad balloons (Figure 3, C).

In 9 per cent, coordinated contractions of peri-staltic type were recorded in the distending balloonin the rectosigmoid colon and the recording bal-loon in the rectum (Figure 3, D). In all in-stances, the pressure decrease in the sphinctericballoon (i.e., sphincteric relaxation) appeared si-multaneously with distension of the rectosigmoidballoon. When peristalsis was present in thecolon, sphincteric relaxation preceded arrival ofthe wave of contraction in the rectal balloon;sphincteric tonus often had returned to normal bythe time the wave of contraction was recorded inthe rectum.

B. Paraplegic subjects. In the three patientstested, the sphincter responded in normal fash-ion. None of these patients had voluntary con-

trol of defecation and each suffered rare episodesof fecal incontinence. For years, all had beentaking enemas regularly in order to produce au-

tomatic defecation. Perianal scratching in thesepatients failed to produce reflex contraction ofthe external anal sphincter ("anal reflex").

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THE INTERNAL ANAL SPHINCTERRESPONSE

C. Patients with Hirschsprung's disease studiedpreoperatively. Five patients were studied. Allexhibited the normal sphincter relaxation pattern.

D. Patients with Hirschsprung's disease studiedpostoperatively who were asyimptomatic after proc-tosigmoidectomy (Swenson procedure). Two pa-

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FIG. 6. ABNORMALRESPONSES IN PATIENTS WITH INCONTINENCE FOLLOWING

PROCTOSIGMOIDECTOMY. A. Progressive wave of contraction (C) proceeds fromcolon (II) to sphincter (III). Sphincter fails to relax. B. Colonic distensionproduces synchronous waves of contraction (C) in rectal (II) and sphincter (III)balloon superimposed upon increase in baseline tonus (broken line). Sphincterfails to relax. C. Transient distension of the colon produces multiple spasmodiccontractions (C) around the sphincter balloon superimposed upon an increase intonus, manifested by elevated baseline (broken line). Sphincter fails to relax. D.Multiple spasmodic contractions (C) simultaneously in colonic (II) and sphincterballoon (III) after a single transient distension (arrows). Sphincter fails torelax. E and F. Multiple sphincteric relaxations appear with a single distensionof the colon.

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201

SCHUSTER, HENDRIX, AND MENDELOFF

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duces normal sphincter response (R).

tomy. Of the five subjects, all showed abnormalresponses. In four this abnormality consisted ofrepetitive contractions recorded in the sphinctericballoon when the rectum was distended above(Figure 6 A-D). One patient exhibited multiplesphincteric relaxations in response to a singledistension (Figure 6 E, F).

F. Patients with functional megacolon and en-

copresis. All had normal sphincteric responses.G. Patients who had undergone partial proc-

tectomy and sigmoidectomy (one for sigmoid car-

cinonia and one for "acquired megacolon"). Bothpatients had anastomosis of the descending colonto the mid-rectum. Both showed a normalsphincteric response when distension was ap-

plied to the intact lower rectum caudad to the anas-

tomosis, whereas distension cephalad to the anas-

tomosis had no effect on sphincteric tone(Figure 7).

H. Patients with various bowel disorders. Nonehad any symptoms related to sphincteric dysfunc-tion, and all had normal responses.

DISCUSSION

A. Results. Rapid balloon distension of therectum has been shown to produce relaxation of

the internal anal sphincter. In our experiments,as in the classic studies by Denny-Brown on thenervous control of defecation (11), a normal re-sponse in patients with spinal cord transectionindicates that centers higher than the spinal cordare not required for the mediation of this response.A normal response was, however, also found inpatients with aganglionosis coli (Hirschsprung'sdisease). Thus the intramural ganglion cells ofthe myenteric plexus are not required either in thetransmission of impulses, as has been suggested(11-16), or in the effector organ (the internalanal sphincter) (12-14), since myenteric gang-lion cells are absent from this organ as well asfrom the rectum in Hirschsprung's disease (13,14, 16-23). These findings contradict the gen-erally accepted concepts that an intact myentericplexus is essential for internal anal sphincteric re-laxation (12, 16), and that the internal analsphincter, because it is spastic, fails to relax inHirschsprung's disease (13-15, 17, 18, 22, 24).Denny-Brown suggested in his monograph that"the nervous mechanism for the 'reflex' reactionappears to be related solely to the peripheralnervous plexus. . . . The mechanism of posturaltone of sphincter ani is local and probably is re-lated to the peripheral ( ? intramural) [sic] nerv-ous plexus" (11). In his textbooks, Kuntz statesthat peristalsis is coordinated by "myenteric re-flexes" transmitted by synaptic connections be-tween enteric neurons (12, 16), and that thepersistence of sphincteric response accompanyingrectal contraction in man after destruction of sac-ral innervation is evidence that "this reciprocalreaction is mediated through intrinsic reflexmechanisms that are activated by tension on therectal wall" (12). Our findings demonstratethat myenteric ganglion cells are not essential forthis response.

A view that takes exception to the concept ofintrinsic reflex transmission was expressed in1900 by Bayliss and Starling, who, on the basisof mechanical and electrical stimulation of nakednerve endings in dogs and rabbits, concluded thatlocal nervous mechanisms become less importantand external innervation more important as eitherend of the gut was reached (25). Moreover,Garry was able to show in decerebrate and de-capitated cats that pudendal nerves were not in-volved in the internal anal sphincteric reflex,

202

THE INTERNAL ANAL SPHINCTER RESPONSE

whereas the pelvic hypogastric nerves were (26).Learmonth and M\arkowitz (27) further clarifiedthe functions of these hypogastric nerves as in-hibitory to the internal anal sphincter by demon-strating that, after intravenous administration ofergotoxin, electrical stimulation of hypogastricnerves produced relaxation of the sphincter,whereas contraction of the sphincter followednerve stimulation without previous administra-tion of ergotoxin. This was presumed to be dueto the selective effect of ergotoxin in eliminatingmotor responses without affecting inhibitory re-sponses.

The question then arises as to whether an al-ternate idiomnuscular pathway might not exist.For example. experiments on the urinary bladderhave been cited (28) in favor of a myogenic basisfor sphincteric relaxation and against the theoryof reciprocal innervation. In these studies, smoothmuscle sphincters were plastically constructed di-rectly from the detrusor substance. When thedetrusor contracted, the "sphincter" activelyopened, presumably because of activation byspread of smooth muscle contraction. Our ex-periments clearly demonstrate that sphinctericopening occurs most frequently without associ-ated rectal or sigmoid contraction, as recordedby this technic (Figure 3, A). Therefore, theresponse is not necessarily dependent upon spreadof smooth muscle contraction for its activation.Furthermore, when peristalsis does appear, thesphincter relaxes at the moment of distension ofthe rectosigmoid colon before the wave of con-traction reaches even the mid-rectum (Figure3, D).

It therefore becomes necessary to account. ona basis other than muscular contraction, for thenormal sphincteric relaxation that occurs whenmyenteric ganglion cells are absent from thesphincter, as in our patients with Hirschsprung'sdisease. Our studies do not exclude the possi-bility that inhibition of the internal sphincter fol-lows noncontractile events in rectal smoothmuscle, although this mechanism seems unlikely.There is some ultramicroscopic (29) and physio-logic (30) evidence that transmission of impulsesfrom muscle fiber to muscle fiber may occur in theabsence of neural elements, but there is no indi-cation that this can occur without muscular con-traction. Since velocity of conduction in ganglion-

free intestinal muscle is 3 to 5 cm per second (30),an impulse, under conditions of our experiment,would require 5 to 8 seconds to travel 25 cm fromthe distending balloon to the sphincter. The im-mediate sphincteric relaxation with rectosigmoiddistension in our studies argues against the ap-plicability of the theory of muscular transmissionin this instance. Another possible explanationlies in the demonstration by both chemical andhistochemical technics that there is no decrease inthe content of either true cholinesterase or pseu-docholinesterase in the aganglionic bowel ofHirschsprung's disease (31). These enzymeshave been shown to be concentrated in hyper-trophied nerve fibers (axons) that are present innormal or increased numbers in the aganglionicsegment (31-33). It is possible that the sphinctermuscle may be actively fired by acetylcholine de-rived from naked nerve endings in the absence ofganglion cells.

Recently, a study employing special stainingtechnics for cholinesterase has raised the questionof the persistence of a few light-staining ganglioncells in the spastic segment in Hirschsprung's dis-ease. In addition, the outer muscular layer of thatsegment showed markedly increased staining forcholinesterase (33).

Finally, an investigation of possible sensorypathways for the sphincter reflex was carried outby a study of patients who had had resection ofthe rectosigmoid colon. Surgical excision of thissegment abolished the normal response in all pa-tients. Gaston reported similar findings thatled him to conclude that the rectosigmoid colonmay serve as part of the afferent limb of a reflexarc extending from rectum to anal sphincter viathe spinal cord (34). Further support for thissupposition is obtained in the motility patternnoted in our patients who have undergone par-tial proctosigmoidectomy. In such subjects, dis-tension of the intact rectum produced sphinctericopening, whereas distension above the anastomosisdid not. A spinal pathway as the only route forthis reflex, however, is effectively ruled out bythe evidence adduced by Denny-Brown (11), whodemonstrated that a normal reflex exists in hu-mans after destruction of sacral nerve roots bycauda equina lesions and after hypogastric nerveresections. Denny-Brown explained the dis-crepancy between his human results and those

203

SCHUSTER, HENDRIX, AND MENDELOFF

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FIG. 8. SIMULTANEOUSRELAXATION (R) OF AGANGLIONIC RECTUM(II) AND

INTERNAL ANAL SPHINCTER (III). Rectal balloon lies in spastic aganglionicsegment of a patient with Hirschsprung's disease.

reported in decerebrate cats by Garry (26) onthe basis of spinal shock in the latter's acute ani-mal experiments. Wehave also found a normalresponse in a patient with inferior mesentericneurectomy. A recently proposed theory, whichis particularly intriguing in the light of thesefacts, holds that enteric contractions are due toa true local reflex with sensory impulses origi-nating in the mucous membranes being transmittedby direct nervous connections between mucosaand muscle coats (35). For obvious reasons, nopatients with simple transection of the rectumwithout resection were available for study of thishypothesis.

Intramural ganglion cells play no role in theafferent limb of the sphincteric reflex, as shown bythe existence of a normal response in patientswith Hirschsprung's disease studied preopera-tively, when the rectum, later proved histologicallyto be aganglionic, was distended.

The mechanisms by which abnormal repetitiveresponses are evoked after proctosigmoidectomyremain unexplained. This interesting abnormalresponse was seen only in patients who demon-strated fecal soiling postoperatively, whereas noresponse at all could be elicited in patients whowere asymptomatic postoperatively. Two in-

fants with Hirschsprung's disease were studiedbefore and after proctosigmoidectomy. Both hadnormal sphincteric responses pre- and abnormalresponses postoperatively, at a time when fecaldribbling was prominent. When dribbling laterceased in one of these infants, a follow-up studyshowed absence of any sphincteric response, indi-cating that an abnormal sphincteric reflex may becausally related to fecal incontinence in the post-operative cases.

Three patterns were observed in response todistension of the aganglionic segment in Hirsch-sprung's disease. One, the normal response, con-sisted in sphincteric relaxation without rectalrelaxation. The second was rectal relaxationwithout sphincteric relaxation. Neither of thesetwo responses was frequent, but a third response,distinctly unexpected and unexplained, was foundin every patient with Hirschsprung's disease stud-ied preoperatively, but in only 5 of the remaining38 patients in the entire study group. This re-sponse consisted of relaxation of the aganglionicsegment concomitant with sphincteric relaxation(Figure 8). This test, therefore, may be valu-able in establishing the diagnosis of aganglionicmegacolon.

B. Methodology. A brief discussion seems ap-

204

THE INTERNAL ANAL SPHINCTER RESPONSE

propriate concerning the technic employed for thisstudy. First of all, the internal anal sphincter hasbeen demonstrated to be in a state of constanttonic contraction. This is shown by the pressurerise seen in the caudad balloon as it is withdrawninto the anal sphincteric area (Figure 2). Themagnitude of this pressure increase, as well as thepressure fall during relaxation, depends upon theforce with which the caudad balloon is held againstthe sphincter, as well as upon the distance thatthe balloon penetrates the sphincteric area, pro-vided that the counterweight force is kept con-stant. This can be accounted for, first, on thesimple mechanical basis of increased tractionagainst an unyielding sphincter, and second, bythe progressively greater number of circular fibersof sphincteric muscle involved as the balloon ispulled further into the sphincteric area. Re-corded pressures, therefore, have only relative sig-nificance. When traction was held constant, pres-sure remained constant at an elevated level. Onlywhen the caudad balloon enters the high pressurezone can the sphincter response be demonstrated(Figure 2), and then only in a very limited seg-ment of the distal rectum, since placement of thecaudad balloon could not be varied more than 1cm if the sphincteric response were to be elicited.This correlates well with the anatomy of the in-ternal anal sphincter, which has been shown toconsist of a firm white band of concentric musclefibers, a direct continuation of the circular smoothmuscle fibers of the rectum (16, 18, 36-39).Sphincteric relaxation therefore occurs as a re-sult of inhibition of normal sphincter tone whenthe rectum or rectosigmoid colon is distended.This relaxation is apparently reflex in nature andcannot be inhibited by voluntary effort.

Two of the variables that influenced the mag-nitude of pressure fall during sphincteric relaxationwere the distance that the balloon had penetratedinto the sphincter area and the amount of air usedto distend the cephalad balloons. As decreasingincrements of air were employed for distension,the drop in pressure diminished proportionatelyuntil no further sphincteric response occurred.The threshold for this minimal response was 10 to15 ml of injected air. The establishment of arange, rather than a definite value, for the amountof air needed to produce the response suggestedthat the response is not an "all-or-none" phenome-

non, but rather that either a larger number ofsphincteric muscle fibers are called into play withincreasing distension of the rectum, or, less likely,that each individual muscle fiber can vary itstonus depending upon the strength of the stimulus.

In our experiments, sigmoid distension (25 to35 cm from the anus) proved an effective stimulusfor sphincteric relaxation. Gaston, in contrast,found distension above the rectum ineffective (34).

The initial spike deflection (Figure 3, C) thatsometimes precedes the pressure drop in thecaudad recording balloon is not caused by reflexcontraction of the external anal sphincter, whichhas been reported to occur with distension of therectum (39), since this spike was seen in para-plegics who had complete paralysis of the externalsphincter. It was also recorded in the middle bal-loon 10 cm cephalad to the anus. It is thereforeevident that the spike cannot result from externalsphincteric contraction. Wefound that, when thedistending balloon was kept inflated for varying,generally brief periods, the duration of the spikecoincided with that of distension and disappearedrapidly (Figure 9) as the distending balloon wasrapidly deflated. It seems likely, therefore, thatthis spike represents increasing pressure in aclosed container (the lower colon) in those pa-tients in whom plastic adaptation of the colonto the balloon was either totally insufficient or tooslow to accommodate the increasing intraluminalmass. The passive spike differs from contractionaround the distending balloon; the pressure in-crease seen with contraction persists after thedistending balloon is deflated (Figure 3, C).The minute, spontaneous decrease in pressureseen occasionally in the distending balloon beforedeflation (Figure 9) probably represents earlyplastic adaptation of the rectum. As might have

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FIG. 9. "SPIKE" OF DISTENSION. The sharp spike ofbrisk distension (A) is compared with the border spikeseen when the distension is prolonged (B and C).

205

SCHUSTER, HENDRIX, AND MENDELOFF

been anticipated, the spike of distension was pres-ent in all cases of Hirschsprung's disease whenthe distending balloon lay in the spastic segment.

SUMMARY

1. An involuntary internal anal sphinctericreflex has been identified by balloon manometrictechnics. Studies were performed to investigatethe normal physiology and neural pathways ofthis response, and the effect of various patho-logical states upon it.

2. Evidence is presented by means of thesetechnics to indicate that, while an intact rectosig-moid colon is needed for this response, neitherintramural ganglia nor spinal cord connections arerequired for its mediation; nor does an idiomus-cular transmission appear to be involved.

3. Normal sphincteric relaxation was found inunoperated cases of Hirschsprung's disease, indi-cating that constipation and megacolon in thisdisorder are not due to an unyielding internalanal sphincter.

4. A correlation is demonstrated between ab-normal sphincter response and fecal incontinenceafter proctosigmoidectomy. A normal responseis found in patients who are incontinent on thebasis of functional megacolon.

5. The possible application of this test to thediagnosis of Hirschsprung's disease is suggested.

ACKNOWLEDGMENT

The authors wish to acknowledge with thanks the sug-gestions and advice of Dr. John Magladery.

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