Gradient of pressure and time between proximal anal canal and high-pressure zone during internal anal sphincter relaxation. Its role in the fecal continence mechanism.
OBJECTIVE
The normal response to rectal distention is a relaxation of the proximal anal canal (PAC). We hypothesized that this mechanism would require a gradient of pressure and time to preserve continence.


METHODS
Sixteen volunteers (10 male), mean age, 41.5 (range, 24-60) years, were studied using an eight port axial catheter with a compliant balloon at its tip. Relaxation was induced by a small volume of rectal distention (15-30 ml of air) and was recorded until recovery of resting anal pressure (RAP). Duration of relaxation was measured until recovery of RAP. Amplitude of relaxation was determined between RAP before rectal distention (RAP-BR) and pressure at the point of maximum relaxation (RAP-PMR). Gradient of pressure was determined by comparing RAP-PMR in the high-pressure zone (HPZ) and PAC. Contraction in the distal anal canal was interpreted as external anal sphincter contraction (EASC) and was compared with RAP-PMR in the HPZ.


RESULTS
Relaxation was significantly greater in PAC than in HPZ (50 vs. 36 percent; P = 0.001). RAP-PMR was significantly higher in HPZ than in PAC (30.7 vs. 12.6 mmHg; P = 0.001). EASC was observed in six patients and did not show significant difference with RAP-PMR in HPZ (39.7 vs. 36.3 mmHg; not significant). Relaxation began at the same time in all levels but lasted significantly longer in PAC compared with HPZ (13.5 vs. 9.4 sec; P = 0.003).


CONCLUSIONS
Anal relaxation induced by small volume rectal distention involves a gradient in the pressure and time of relaxation between PAC and the HPZ.
Goes
R N
RN
Department of Surgery, University of Southern California, Los Angeles, USA.
Simons
A J
AJ
Masri
L
L
Beart
R W
RW
D000328:Adult; D001003:Anal Canal / Q000503:physiopathology*; D005242:Fecal Incontinence / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011312:Pressure; D013997:Time Factors