Anorectal manometry: are fatigue rate and fatigue rate index of any clinical importance?

BACKGROUND

Loss of voluntary contraction of the external anal sphincter is thought to be a factor in fecal incontinence. During anal manometry, computerized systems produce several parameters including fatigue rate (FR), which is the basis for calculating the fatigue rate index (FRI). Our aim was to evaluate FR and FRI and their clinical importance in patients suffering from fecal incontinence or severe constipation.

MATERIALS AND METHODS

All patients scheduled for an anal physiology work-up were included in the study. FR was determined by a computer program and FRI was calculated manually with the following equation: FRI (minutes) = [squeeze pressure (mm Hg) - resting pressure (mmHg)] / - FR (mmHg/min). FR and FRI were compared in patients suffering from fecal incontinence (group I) and severe constipation (group II). Furthermore, subgroups (<50 and > or = 50 years of age) were compared. Lastly, a possible relation between length of the high-pressure zone (HPZ) and FR and FRI was assessed.

RESULTS

Between January 2000 and December 2004, 131 patients (96 with fecal incontinence, 35 with constipation) were studied. Both FR and FRI were similar between groups I and II; no significant differences were found when younger and older patients were compared within the same group. We also did not find any relation between HPZ length and either FR or FRI.

CONCLUSIONS

FR and FRI do not seem to be helpful in routine colorectal practice for evaluating the strength of the external anal sphincter.