COMPARISON OF OBJECTIVE MEASUREMENT OF ANAL SPHINCTER STRENGTH WITH ANAL SPHINCTER PRESSURES AND LEVATOR ANI FUNCTION

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1 GASTROENTEROLOGY Cpyright 1969 by The Williams & Wilkins C. Vl. 56, N.1 Printed in U.S.A. COMPARISON OF OBJECTIVE MEASUREMENT OF ANAL SPHINCTER STRENGTH WITH ANAL SPHINCTER PRESSURES AND LEVATOR ANI FUNCTION NICHOLAS E. DIAMANT, M.D., AND LAURAN D. HARRIS, M.D. Evans Memrial Department f Clinical Research, University Hspital, and Department f Medicine, Bstn University Schl f Medicine, Bstn University Medical Center, Bstn, Massachusetts The fidelity with which anal sphincter intraluminal pressure can assess the strength f that sphincter cannt be determined withut a suitable bjective measurement f sphincter strength. This study details such a measurement and cmpares it with sphincter pressure. Sphincter strength was defined as the frce in grams required t pull a %-inch diameter firm rubber ball frm the rectum, thrugh the sphincter, t the utside. Cmparisn f this value with simultaneusly btained sphincter pressure shwed an excellent crrelatin (r = 0.955, P < 0.001). Crrelatin was equally gd fr changes f strength in an individual and as a cmparisn f strength amng individuals. It is emphasized that the device used t recrd sphincter pressure must incrprate a cntinuus infusin f fluid fr these measurements t be valid. A minr mdificatin f the apparatus used t measure sphincter strength als allwed levatr ani functin t be measured-inward mtin f the anus and the strength f this inward mtin. These tw functins crrelated well (r = 0.83, P < 0.001). Cmparisn f these values with sphincter strength, hwever, shwed n crrelatin. It is cncluded that n functinal relatinship exists between the levatr ani and the anal sphincter. Recently, anal sphincter pressure recrded frm a grup f patients with fecal incntinence was cmpared t the pressure recrded frm a grup f nrmal subjects. 1 This study shwed that a minr mdificatin f the cnventinal recrding system allwed cmplete separatin f these tw grups by the recrded sphincter pressure-all f the nrmal subjects had a higher pressure than all f the abnrmal patients. While these data suggest the lgical cnclusin that the magnitude f recrded sphincter pressure Received April 13, Accepted June 26, Address requests fr reprints t: Dr. Lauran D. Harris, University Hspital, 750 Harrisn Avenue, Bstn, Massachusetts This investigatin was supprted in part by Research Grant AM and Training Grant AM frm the Natinal Institute f Arthritis and Metablic Diseases, Natinal Institutes f Health, United States Public Health Service. 110 bears a direct relatinship t sphincter strength, the accuracy f this cnclusin cannt be tested withut a measurement f sphincter cmpetence mre precise than simple clinical definitins f "cntinent" and "incntinent" r "nrmal" and "abnrmal." Fr example, pressures recrded frm the nrmal anal sphincter during "tightening" ranged frm apprximately 100 mg Hg t ver 300 mm Hg. Hwever, since the presence r absence f cntinence was the nly available guide t sphincter strength, there was n apparent difference in sphincter strength despite this 3-fld difference in sphincter pressure. One must then assume either that pressures ranging frm 100 mm Hg t 300 mm Hg can be recrded frm sphincters f equal strength r that the 3-fld difference in sphincter pressure in fact indicates a 3-fld difference in sphincter strength that was masked by ur

2 January 1969 ANAL SPHINCTER STRENGTH AND PRESSURE 111 crude clinical criterin f sphincter cmpetence. T explre the relatinship between sphincter pressure and strength, we have devised a simple bjective measurement f anal sphincter strength and have cmpared this measurement with sphincter pressure. During the curse f this study, it was fund that a minr mdificatin f the prcedure als allwed measurement f levatr ani functin. Methds Fifty-ne nrmal adults were studied withut prir bwel preparatin. Figure 1 diagrams the essential features f the apparatus used t measure sphincter strength. Subjects were studied while they were lying in the left lateral psitin with their buttcks placed firmly against a backbard having a central pening apprximately 4 inches square. A firm rubber ball % inches in diameter was inserted int the rectum and attached by a line t a mtrized reel. Except fr 3 inches next t the ball, the line was made f light weight cpper chain t minimize artifacts caused by stretching f the line. Sphincter strength was defined as the maximum frce necessary fr the reel t pull the ball at a cnstant rate f 0.25 cm per sec frm the rectum, thrugh the anal sphincter t the utside. This rate was chsen primarily fr cnvenience. FIG. 1. Diagram f apparatus. (1) Measurement f anal sphincter strength. The rubber ball in the rectum t the left f the illustratin was attached by a line t a mtrized reel (C). T recrd the frce develped as the reel pulled the ball frm the rectum thrugh the anal sphincter, the frce transducer (B), munted n a lw frictin track, was interpsed in the line. (2) Measurement f levatr ani {unctin. The mtrized reel (C) was discnnected and the transducer designed t measure linear mtin (A) was placed between the ball in the rectum and the frce transducer (B). With the frce transducer mving freely n its track, inward mvement culd be measured by the linear mtin transducer. With the frce transducer lcked in psitin, the strength f the ptential inward mvement was recrded by the frce transducer. The same results were btained with rates f 0.1 cm per sec and 0.5 cm per sec. A frce transducer (B) (Grass Mdel FT. 10) munted n a lw frictin track was interpsed in the line t recrd this frce. T measure levatr ani functin, the mtrized reel (C) was discnnected, and a transducer (A) designed t measure linear mtin (Sanbrn Mdel 585DT) was placed between the ball and the frce transducer (B). When the subjects tightened their anal sphincters, any inward mtin f the anus (presumably due t cntractin f the levatr ani muscles) als mved the ball inward, and this mvement was recrded by the linear mtin transducer. The frce transducer was allwed t mve freely n its track. The strength f this inward mvement r levatr ani strength was recrded by lcking the frce transducer in psitin. Then, when the subjects tightened their anal sphincters, the lcked frce transducer prevented inward mtin and instead measured the strength f this ptential mvement. Sphincter pressure was simultaneusly recrded by a single plyvinyl tube placed in the anal canal. This pressure recrding tube, 2.5 mm in utside diameter, had a side pening apprximately 1.2 mm in diameter and was cntinuusly infused with water at a rate f 7 /lliters per sec. Pressure was transmitted t a Sanbrn Transducer (267A) leveled with the anal rifice as the zer reference pint. Outputs frm all f the transducers were graphed n a direct-writing recrder. Results Sphincter strength, i.e., the maximum frce in grams required t pull the ball frm the rectum t the utside, was cmpared with the sphincter pressure recrded at the same time. Figure 2 shws all f the 111 bservatins btained frm 51 subjects during maximum vluntary cntractin f their anal sphincters. Gd crrelatin (r = 0.74, P < 0.001) between sphincter pressure and strength was fund. T see if this same pressure-strength relatinship existed with changes in sphincter strength in an individual, studies were als perfrmed during less than maximal tightening. Figure 3 illustrates several such bservatins in an individual subject. As he maintained sphincter cntractin at varius levels, pressure and

3 112 DIAMANT AND HARRIS Vl. 56, N. 1 MM HG ,--... ). I -.,... - I - - t. I I \ -,. -.,.- r=0.74 (P=< OOI) FiG. 2. Cmparisn f the simultaneusly determined anal sphincter pressure (mm Hg) and sphincter strength (grams) during maximum vluntary cntractin f the anal sphincter. The pints represent all f the 111 bservatins btained frm 51 nrmal male subjects. MM HG FiG. 3. The relatin f anal sphincter pressure t changes f sphincter strength in an individual. The bservatins were made as the subject vluntarily maintained sphincter cntractin at varius levels.

4 January 1969 ANAL SPHINCTER STRENGTH AND PRESSURE 113 strength changed in a linear fashin. Further bservatins f this type were made in 27 subjects. Figure 4 shws these additinal values (pen circles) superimpsed n the values btained during maximum vluntary cntractin (clsed circles). Sphincter pressure seemed t be an excellent index f sphincter strength (r = 0.955, P < 0.001) ver the range f pressures measured frm as lw as 60 mm Hg t ver 300 mm Hg. The rubber ball % inches in diameter was chsen fr its cnvenient size and firm cnsistency. Since the high frictin surface might have influenced ur results, studies were repeated using a ball the same size but made f Tefln and therefre with a smth, lw frictin surface. Identical results were btained using either ball, 100 mm Hg sphincter pressure being equivalent t apprximately 600 g f sphincter strength. Obviusly, this pressure-strength relatinship is quantitative nly fr a %-inch diameter ball and wuld nt be expected t be the same if balls f different size were used t determine sphincter strength. T see if the pressure-strength relatinship was als linear fr a different sized ball, a Tefln ball V2 inch in diameter was used in 68 studies n 29 subjects. As expected, the frce necessary t pull this smaller ball frm the rectum t the utside was less than that required fr the larger ball, apprximately 300 g per 100 mm Hg sphincter pressure as cntrasted with apprximately 600 g per 100 mm Hg sphincter pressure. Greater variatin in sphincter strength measurements was fund when the V2-inch ball was used, but crrelatin f these results with simultaneusly btained sphincter pressure. was still reasnably gd (r = 0.562, P < 0.001). Sn after beginning these studies, it MM HG ~ 0 0_. e._... ~. I.,.. '0. i ~..A. e 'i 0\. 0:.0 g 0.i 0., I r ( p.<.ool) FIG. 4. The relatin f anal sphincter pressure t sphincter strength cmbining all f the bservatins made during maximum vluntary cntractin f the anal sphincter (.) and during less than maximal tightening(o).

5 114 DIAMANT AND HARRIS Vl. 56, N.1 became apparent that as the subjects tightened their anal sphincters, the anus mved inward. The recrded extent f this inward mvement during maximum tightening f the anal sphincter-presumably due t cntractin f the levatr ani muscles-was remarkably cnstant in each individual, varying by less than ± 10%. As figure 5 shws, hwever, there was a wide range amng individuals. N relatinship was apparent between the extent f this inward mvement and the height, bdy build, r general muscular develpment f the individuals. The strength f this inward mvement (r levatr ani strength) als shwed wide variatin frm subject t subject, ranging frm under g t ver 1000 g in the I I I I I I I I I I em. INWARD MOVEMENT FIG. 5. Extent f the inward mvement f the anus that ccurred as the anal sphincter was tightened. Each pint represents the maximum value recrded fr a single subject. 19 subjects studied. Figure 6 shws that the tw measurements f levatr ani functin-extent f the inward mvement and strength f the inward mvementcrrelate well (r = 0.83, P < 0.001). Thus, either measurement wuld appear t be a suitable index f levatr ani functin. Discussin It seems clear that anal sphincter pressure measurements are an accurate indicatin f that sphincter's ability t cntain a slid blus. A difference in sphincter strength was assciated with a prprtinal difference in sphincter pressure nt nly in an individual but als when cmparisn was made amng individuals. It shuld be emphasized that sphincter pressures shwn in this study were btained while the recrding tubes were cntinuusly infused with water. Sphincter pressures btained by either the cnventinal uninfused system r with small fluid-filled ballns shw n crrelatin with pressures recrded by the cntinuusly infused system. J - 3 Sphincter pressures btained with these systems d nt seem t be suitable fr use as an index f sphincter strength. The range f sphincter pressures shwn in figure 4 (60 mm Hg t ver 300 mm r 0.83 (p.<.l) LEVATOR ANI STRENGTH (GRAMS) FIG. 6. Cmparisn f the tw indices f levatr ani muscle functin, the extent f the inward mvement and strength f this inward mvement (levatr ani strength).

6 January 1969 ANAL SPHINCTER STRENGTH AND PRESSURE (ii ~ C2 800 S :r I- z (!) ~600 I- Ul Z ~ a:: ~400 ::> w...j ' FIG. 7. The relatin f levatr ani functin (levatr ani strength) t anal sphincter strength. Hg) was btained while the subjects tightened their anal sphincters with varying degrees f vluntary effrt. Values belw 60 mm Hg presumably represent the cntributin f resting r invluntary sphincter tne, and thus sphincter pressure, which is always present. Therefre, sphincter pressures belw 60 mm Hg culd nt be recrded. Are the human levatr ani muscles anatmically distinct frm the external anal sphincter, r d the levatr ani muscles frm the external anal sphincter? This basic and seemingly straightfrward questin is surprisingly hard t answer. The external sphincter has been described as being frmed by and therefre indistinguishable frm the levatr ani,4-6 and als as being cmpletely separate and distinct frm the levatr ani.7 Between these tw extremes are descriptins f varying degrees f intermingling f therwise distinct muscle grups.8-12 Frm meticulus dissectin f many examples, the authr f an excellent recent treatise n the subject takes the latter view. 13 It is hardly surprising that pinin abut the functinal relatinships f levatr ani and anal sphincter als varies.4-12, Chiefly respnsible fr this cnfusin has been the lack f a quantitative measurement f these functins. Our study allws us t quantitate bth a functin f the muscles cncerned with lifting the anus (r levatr ani functin) and the strength f the anal sphincter. Therefre, it wuld als seem t allw a meaningful cmparisn f these tw functins (fig. 7). Regardless f the anatmical relatinships f levatr ani and anal sphincter, there appears t be n functinal relatinship between the tw. REFERENCES 1. Harris, L. D., C. S. Winans, and C. E. Ppe, II Determinatin f yield pressures: a methd fr measuring anal sphincter cmpetence. Gastrenterlgy 50: Winans, C. S., and L. D. Harris Quantitatin f lwer esphageal sphincter cmpetence. Gastrenterlgy 52: Ppe, C. E., II A dynamic test f sphincter strength: its applicatin t the lwer esphageal sphincter. Gastrenterlgy 52:

7 116 DIAMANT AND HARRIS Vl. 56, N Curtney, H Anatmy f the pelvic diaphragm and anrectal musculature as related t sphincter preservatin in anrectal surgery. Amer. J. Surg. 79: Gligher, J. C., A. G. Leacck, and J.-J. Brssy The surgical anatmy f the anal canal. Brit. J. Surg. 43: Hllinshead, W. H The rectum and anal canal, p In Anatmy fr surgens, Vl. 2. Paul B. Heber, Inc., New Yrk. 7. Grant, J. C. B., and C. G. Smith Musculature f the pelvic utlet, p In J. P. Schaeffer [ed.), Mrris' human anatmy, Ed. 11. Blakistn Divisin, McGraw-Hill Bk Cmpany, New Yrk. 8. Lckhart, R. D Muscles and fasciae f the abdminal wall, perineum, and pelvis, p In G. J. Rmanes [ed.), Cunningham's textbk f anatmy, Ed. 10. Oxfrd University Press, New Yrk. 9. Gray, H Anatmy f the human bdy, Ed. 26. Lea and Febiger, Philadelphia, 1480 pp. 10. Milligan, E. T. C., and C. N. Mrgan Surgical anatmy f the anal canal. Lancet 2: Shackelfrd, R. T The anrectal tract, p In Surgery f the alimentary tract. W. B. Saunders Cmpany, Philadelphia. 12. Smith, W. C The levatr ani muscle: its structure in man, and its cmparative relatinships. Anat. Rec. 26: Wilsn, P. M Anchring mechanisms f the an-rectal regin. S. Afr. Med. J. 41: , Berglas, B., and I. C. Rubin Study f the supprtive structures f the uterus by levatr mygraphy. Surg. Gynec. Obstet. 97: Hiatt, R. B., and T. V. Santulli Imprtant factrs influencing the treatment f imperfrate anus. Dis. Cln Rectum 5: Kiesewetter, W. B Imperfrate anus: the rle and results f the sacr-abdmin-perineal peratin. Ann. Surg. 164: Kttmeier, P. K A physilgical apprach t the prblem f anal incntinence thrugh use f the levatr ani as a sling. Surgery 60: