PHYSIOLOGY OF RECTAL SENSATIONS - A MATHEMATIC APPROACH

PURPOSE: The first awareness of balloon inflation (first sensation (FS )), flatus sensation (constant sensation (CS)), urge to defecate (UD), and maximum tolerated threshold (MTT) are the four commonly evaluated rectal sensations. The traditional view that these sensations are att ributable to pelvic floor mechanoreceptor stimulation is challenged by current evidence in favor of rectal wall mechanoreceptors. The aim of this study mas to determine the physiology of these sensations, using a dynamic mathematic model of the rectum METHODS: In a group of 15 he althy adult volunteers (11 female and 4 male; median age, 51.5 (range, 31-74) years), the polynomial behavior of the two smooth muscle compo nents of a dynamic mathematic model of the rectum was analyzed to find strain levels of smooth muscle activity in relation to corresponding strain levels of each of the four ''rectal'' sensations. RESULTS: Long itudinal and circular smooth muscle relaxation appeared to be the rate detection and signaling mechanisms, respectively. The latter triggere d sensations of CS, UD, and MTT. FS was an anal canal sensation, relat ed temporally with onset of rectoanal inhibitory reflex. In vitro vali dation of the model suggested MTT to be a physiologic protective mecha nism associated probably with tetanic smooth muscle contraction. CONCL USIONS: Evaluation of rectal sensations should be confined to CS and U D because MTT is painful and does not contribute any additional inform ation, and FS is not a true rectal phenomenon.