Effect of stool size and consistency on defecation

Transcription

1 GlCt, 1987, 28, () Effect of stool size and consistency on defecation J J BANNTER, P DAVON, J M TMM, C GBBON, AND N W READ From the Departments ofrgery and Physiology, Royal Hallamshire Hospital, heffield UMMARY The ability of sbjects to expel from the rectm objects simlating stools of different characteristics was assessed in paired stdies carried ot in a total of 58 normal sbjects and 25 yong women with severe constipation. Or reslts showed that a lower percentage of normal sbjects and a lower percentage of constipated patients were able to pass a 1 8 cm incompressible sphere compared with a 5 ml deformable balloon, althogh constipated patients fond it more difficlt than normal sbjects to expel both types of simlated stool. t was also more difficlt for normal sbjects to pass a soft compressible silicon rbber simlated stool than a stool made p of a similar volme of incompressible 1 cm wooden spheres contained in a cylindrical latex envelope, bt both objects were mch easier to pass than the same nmber of 1 cm spheres placed loose within the rectm. When normal sbjects were instrcted to expel single incompressible spheres of different sizes placed in the rectal amplla, the intrarectal pressre and the time needed to pass these objects varied inversely with their diameter. These reslts sggest that more effort is reqired to expel stools from the rectm if they are small and hard than if they are large and soft. Constipated patients or patients with the irritable bowel syndrome (B) often complain of difficlties with defecation. n recent stdies, 38% of patients with B' and 8% of women with severe idiopathic constipation' said they had to strain for long periods of time in order to defecate. These difficlties may be related at least in part to the natre of the stool passed. Over 8% of patients with constipation' pass separate hard pellets from the rectm. Proctoscopy often shows the presence of sch pellets in the rectm, sggesting that they are formed in the sigmoid and rectm and are not nolded to any large eytent dring passage throgh the ans. To investigate whether the natre of the stool has any effect on defecation we devised a series of stdies, in which we measred the ability of normal sbjects and constipated patients to expel from the rectm objects simlating stools of differing size and consistency. imilar stdies were carried ot in a grop of yong constipated patients to investigate whether these patients had any greater difficlty in expelling the same objects than normal sbjects. Addrcss t'or corrcsponlidcice: Dr N W Rceid b-elpairtmcn of Hman GaLstrointestin.al Physiology & Ntrition -Floor K. Roval H.ail.lmshirc Hospit.ill hcftic ld 1( 2J F. Rcccived for pblicition 19' Fehr.ary Methods UBJECT The normal sbjects consisted of 58 healthy volnteers (28 men, 3 women, aged 2-9 years) who had no history of difficlties with defecation, and who did not sffer from gastrointestinal problems. The constipated patients were 25 women (aged years) who complained of severe constipation refractory to treatment with dietary fibre (at least 3 g/day) and laxatives. EXPULON OF CYLNDRCAL WATER FLLED BALLOON AND A Pl ATC PHERE tdies were carried ot in 36 normal sbjects (25 women, 11 men) and 25 constipated patients. Cylindrical balloons containing 5 and 25 ml water simplated soft deformable stools of different sizes. The larger balloon was constrcted from 1 cm of nstretched latex condom and the smaller from an nstretched rbber finger cot. Each balloon was tied arond a polythethylene tbe (od 2 mm). The deflated balloon and its attached catheter was inserted digitally into the low rectm sing copios amonts of lbrication (KY Jelly, Johnson and Johnson), and was then filled with 5 ml or 25 ml 1246

2 Effect ofstool size anid consistencv on defecation warm (37 C) water. A hard polyethylene sphere 1 8 cm in diameter simlated the hard pellets that many constipated patients pass. Each object was inserted into the rectm on separate occasions and in random order, and was plled down gently so that it lay in the rectal amplla. The sbject was then allowed to sit p on a commode and left alone in a cbicle, althogh the technician remained within hailing distance in the adjacent room. When the sbject felt at ease he/she started a stop clock and attempted to expel the object from the rectm. The clock was stopped as soon as the simlated stool was passed. f the object was not expelled within 5 mintes, it was removed by traction on the manometric tbing or chain. The procedre was then repeated with the other simlated stools. EXPULON OF MULATED TOOL OF THE AME VOLUME, BUT DFFERENT COMPOTON AND CONTENCY tdies were carried ot in nine male normal volnteers. Having evacated the bowel before beginning the experiment, the sbject lay in the left lateral position. A narrow manometric catheter (od 2 mm) with a distal side opening port was inserted into the rectm and perfsed with distilled water at a rate of -2 ml/min sing a low compliance hydralic capillary perfsion system (Andorfer Medical pecialities nc., Greendale, Wisconsin, UA). A pressre transdcer (Drck Ltd, Groby, Leics, UK) sitated in the perfsion line measred rectal pressre and the signal was amplified and displayed on a chart recorder (Lectromed MT8 PX, Ormed Ltd, Welwyn Garden City, UK). A soft, deformable, cylindrical object made of silicon rbber tapered at either end (volme 3 ml by immersion) simlated a normal stool. A cord attached to one end facilitated its removal from the rectm. Thirty wooden beads, each 1 cm in diameter contained inside a doble layered envelope constrcted from two nstretched rbber finger cots simlated a hard stool. The individal components of this object were incompressible bt the object cold be deformed by moving the beads within the finger cots. A cord was attached to a bead inside the finger cots to enable this simlated stool to be withdrawn from the rectm. The packed bead volme (by immersion) was the same as the silicon stool and shape of the simlated hard stool was adjsted to match the shape of the simlated normal stool. The third and final simlation consisted of 3 loose 1 cm beads. Each simlation was inserted into the rectm sing generos amonts of lbrication (KY Jelly, Johnson and Johnson) and where appropriate plled down gently so that it lay in the rectal amplla. The sbject then sat on a commode in a private cbicle, althogh the technician was within hailing 1247 distance in an adjacent room. n the first part of the stdy, the sbject wais allowed to strain normally to expel the objects from the rectm. n the case of the loose beads, he was told to strain ntil he no longer had a desire to defecate, and the percentage of beads recovered was recorded. The sbject recorded the total time spent straining on a hand held stop watch. Each simlation was inserted into the rectm on at least two occasions, and the order of insertions was randomised. The shortest time taken to pass each object was recorded. The experiment was repeated in order to measre the minimm intrarectal pressre that was reqired to pass the simlated stools. The sbject was trained to increase his intra-abdominal pressre in 2 mmhg stages as indicated by lines drawn on the rectal pressre trace. The sbject maintained the rectal pressre at each prescribed level for a total of 3 seconds, and if he had not evacated the object within that time, he then increased the pressre by 2 mmhg and attempted to pass the object again. The whole procedre was repeated at increasing intraabdominal pressres ntil the object was evacated. f the sbject strained above the prescribed limits, the reslts were ignored and the test was repeated. EXPULON OF PHERE OF DFFERENT ZE tdies were carried ot in eight male and five female normal volnteers. With the sbject lying in the left lateral position, a narrow manometric catheter (od 2 mm), inserted into the rectm and pressres were recorded as described above. Hard polyethylene spheres, -5, 1-, 1-5, 1-8, and 2-5 cm in diameter, each with a nylon cord attached for ease of removal, were sed to simlate hard stool pellets of different sizes. Each sphere was placed in the rectm on separate occasions in random order and sing generos amonts of lbrication. The sbject then sat on a commode and raised the intraabdominal pressre stepwise by blowing into the tbing attached to a sphygmomanometer and raising the colmn of mercry in increments of 2 mmhg, taking care to maintain the pressre sing the abdominal mscles and the diaphragm and not by compressing the tonge against the palate. These increases in intra-abdominal pressre were recorded by the intrarectal pressre sensor and there was a highly significant correlation between the pressre in the manometer and the pressre recorded in the rectm (r= 85, p<1). The sbject was not allowed to strain and raise the intra-abdominal pressre above the prescribed limit and was allowed three mintes to expel the sphere at each level of pressre. The minimm intrarectal pressre reqired to pass each sphere was recorded. n a separate series of stdies, the sbjects were permitted to strain

3 1 248 normally, and the minimm time taken to pass each sphere was recorded. TATTCAL ANALY Data which cold be expressed in a 2x2 contingency table was analysed sing the X2 test with Yates correction for small nmbers. Normally distribted data were analysed sing the paired or npaired (as appropriate) tdent's t test. Non-parametric paired data was analysed sing the Wilcoxon's signed-ranksm test. Reslts EXPULON OF CYLNDRCAL WATER FLLED BALLOON VERU PLATC PHERE Normal patients A significantly lower nmber of normal sbjects cold expel the 1 8 cm sphere compared with the 5 ml balloon from the rectm within five mintes (p<1) (Fig. 1). There were no significant differences in the nmber of sbjects who cold expel the 25 ml balloon compared with either the 5 ml balloon or the 1*8 cm sphere (Fig. 1). No difference was fond in the ability of men compared with women to pass the simlated stools. Constipated patients A significantly lower nmber of constipated patients cold pass the 1-8 cm sphere than the 5 ml balloon from the rectm within five mintes (p<5) (Fig. 1). Again, there were no significant differences in the nmber of patients who cold expel the 25 ml balloon compared with either the larger balloon or the sphere. When the constipated patients were compared with normal volnteers of similar age and sex (19 women, aged 2-55 years), a significantly lower proportion of patients were able to expel either the 5 ml balloon (p<.5) or the 1*8 cm sphere (p<-1). 5mrl Z5mi 1 8cm 5On 25ml 1 8cm Balloon phere -Badloon---' phere Fig. 1 Percentage ofnormal (left) and constipated (right) sbjects able to expel a 5 ml balloon, a 25 ml balloon or a 1-8 cm spherefrom the rectm withinfive mintes. Bannister, Davison, Timms, Gibbons, and Read Mean minimm time (sec) 12 1 Mean intrarectal 8 pressre 6 (mm Hg) n 2 o mh, 1 v~, v Ph % -~'j 1- PL.~ '%~~ '%~~ '%~~ 1%, ll%~~~11 Fig. 2 Mean minimm (a) time (mean±em) (pper graph) and (b) intrarectalpressre (mean±em) (lower graph) reqired to expel a 3 ml silicon rbbersimlated stool and a similar volme ofincompressible cm beads in a rbberfinger cot, in nine normal male sbjects. Also shown is the minimm time and intrarectal pressre reqiredfor sbjects to feel they had expelled all the loose beadsfrom the rectm. EXPULON OF TOOL OF DFFERENT CONTENCY All sbjects were able to pass the silicon rbber stool and the bag of beads, bt only one sbject was able to expel all the loose beads. Between 3 and 1% (median=67%) of the beads were recovered when the sbjects strained normally, and between 27 and 9% (median=68%) of the beads were recovered when intrarectal pressre was constrained. When sbjects strained normally, they took longer to expel the bag of beads than the silicon stool (p<-5) (Fig. 2a). These times were both mch shorter, however, than the times taken for sbjects to evacate sfficient loose beads to abolish the desire to defecate (p<-1) (Fig. 2a). When the intrarectal pressre was constrained, the minimm pressre reqired to pass the silicon stool or the bag of beads was significantly less than for the loose beads (p<-1) (Fig. 2b). There was no significant difference in the minimm pressre reqired to pass the bag of beads compared with the silicon stool (Fig. 2b).

4 Effect ofstool size atid co,lsistencv oni defecation EXPULON OF PHERF OF DFFERFNT DAMETER Only three of 13 sbjects (two men, one woman) managed to pass the smallest (diameter (5 cm) sphere, whereas 11 of 13 passed the 1 - cm sphere (p<(1 compared with -5 cm sphere) and all 13 passed the 2-5 cm sphere (p<(1 compared with the -5 cm sphere). No sex differences were fond in any part of this stdy. The minimm intrarectal pressres reqired to expel each sphere fell as the diameter rose (Fig. 3); the pressre reqired to expel the - cm sphere being significantly greater than that needed to expel the 2-5 cm sphere (p<5). Plotting the minimm intrarectal pressre needed to expel each sphere against the inverse of the radis of that sphere for each sbject yielded linear correlation coefficients ranging from 75 to -99 (median (82) (Fig. 4). The minimm time needed to pass each sphere also fell as the diameter rose (Fig. 5); the time needed to expel the 1- cm sphere being significantly greater than that needed to expel the 2-5 cm sphere (p<o-ol). Discssion These stdies indicate that people find it easier to expel large deformable stools from the rectm than small hard pellets. Althogh these differences appear to be predominantly becase of stool size, sbjects also passed a soft deformable silicon rbber stool in a shorter time, than they took to expel a similar volme of hard, incompressible spheres contained within a finger cot. Longer times and higher pressres were reqired, however, for sbjects to evacate sfficient 41 E a,, 2- -a Ld- 1- a Cs Radis of sphere (cm-') Fig. 4 Minimm intrarectal pressre reqired to expel spheres of varying diameters from the rectni in one normnal sbject plotted against the inverse ofthe radis ofthe sphere. Linear correlation coefficient=o-99 (p<<o()1). incompressible spheres lying loose in the rectm to abolish the desire to defecate. This particlar observation sggests that the sensation of incomplete evacation in some bt probably not all patients with irritable bowel syndrome may be related to retained faecal pellets. tdies sing spheres of different diameters showed that ease of defecation was directly related to the diameter of the sphere. A sphere of -5 cm in diameter cold only be expelled by three of ' E 3-3 UG3 2 U 1- C E * phere diameter (cm) Fig. 3 Minimm intrarectal pressres (mean ±EM) attained by normal sbjects whilst passing spheres of varying diameterfrom the rectm phere diameter (cm) Fig. 5 Minimm times in which.seven normal sbjects cold expel spheres of varying diameterfrom the rectm.

5 125 Bannister, Davison, Tirnins, Gibbons, and Read normal volnteers: a sphere of 1 cm in diameter cold be passed by most volnteers, bt larger intraabdominal pressres and longer times were reqired to pass this object compared with - for example, a 2 5 cm sphere. The reslts are spported by theoretical considerations. Dring defecation, inhibition of the external anal sphincter (EA) is probably modlated by cortical mechanisms and is thoght to be independent of the diameter of the stool. n fact, the electrical activity of the EA can be inhibited by 'bearing down' even with no stool in the rectm.`- nhibition of the internal anal sphincter (A), on the other hand, is directly related to the degree of rectal distension,7 and is probably mediated by the degree of stimlation of circmferential stretch receptors in the rectal wall.' f this is so, then there shold be an inverse relationship between stool circmference (or stool radis) and anal pressre dring defecation, and hence the minimm intrarectal pressre reqired to expel a sphere shold also be inversely related to the radis of the stool as observed in or sbjects. The same relationship wold apply to a cylindrical or sasage shaped stool provided that object approaches the sphincter end on Ṫhe reslts of this stdy therefore sggest that the difficlty in defecation experienced by many patients with constipation or B may be related in part to the size and consistency of the stool in the rectm; small, hard stools being harder to expel than large soft stools. This wold explain how ingestion of a high fibre diet might facilitate defecation in sch patients by increasing stool size and making the stool softer and more deformable.9 The patients with severe diet and laxative resistant constipation, that we investigated, however, fond it more difficlt than normal sbjects to pass each of the simlated stools. This is presmably related to the observation that many of these patients do not relax their pelvic floor as they attempt to defecate, bt obstrct defecation by contracting their external sphincter and pborectalis." The force reqired to propel a solid stool arond a sharp anorectal angle and expel it throgh a contracted sphincter wold be extremely high and may be impossible to achieve by normal contraction of abdominal mscles. References 1 Cann PA. Thesis: Leeds Bannister JJ, Timms JM, Barfield LJ, Donnelly TC, Read NW. Physiological stdies in yong women with chronic constipation. nt J Colorectal Dis 1986; 1: hre T. tdies on anal fnction in continent and incontinent patients. cand J Gastroenterol 1974; 9: sppl: Floyd WF, Walls EW. Electromyography of the sphincter ani externs in man. J Physiol 1953; 122: Parks AG, Porter NH, Melzak J. Experimental stdy of the reflex mechanism controlling the mscles of the pelvic floor. Dis Colon Rectm 1962; 5: Preston DM, Lennard-Jones JE. Anisms in chronic constipation. Dig Dis ci 1985; 3: Menier P, Marechal JM, De Beaje MJ. Rectoanal pressres and rectal sensitivity stdies in chronic childhood constipation. Gastroenterology 1979; 77: Martelli H, Devroede G, Arhan P, Dgay C, Dornic C, Faverdin C. ome parameters of large bowel motility in normal man. Gastroenterology 1978; 75: Davies GJ, Crowder M, Reid B, Dickerson JWT. Bowel fnction measrements of individals with different eating patterns. Gt 1986; 27: Read NW, Timms JM, Barfield LJ, Donnelly TC, Bannister JJ. mpairment of defecation in yong women with severe constipation. (Ga.siroenietrology 1986; 9: 53-6.