Anorectal tightening reflex: role in fecal incontinence

The present study describes the clinical significance of the anorectal tightening reflex (ATR) in normal and incontinent subjects. It was examined in 16 healthy volunteers and 11 subjects incontinent to flatus and fluid stools; 5 of the latter had in addition fecal soiling. The rectum was distended by a condom inflated with carbon dioxide, while the rectal and rectal neck (RN) (anal canal) pressures were measured, and the external (EAS) and internal anal sphincter (IAS) EMG activity was recorded. The rectum was inflated at two rates: slow and rapid. In normal subjects, the RN pressure increased upon slow rectal inflation; the IAS EMG was augmented. Pudendal nerve block and phentolamine administration revealed that this pressure increase is due to increased IAS tone which tightens the RN against the slow rectal filling by the time adaptive reaction occurs. Rapid rectal filling evoked Gower's rectoinhibitory reflex. Thus, while increased IAS tone in the ATR protects against involuntary incontinence upon 'slow' rectal filling, the increased EAS tone of Gower's reflex protects in the case of 'rapid' filling. Of the 11 incontinent patients, the 5 with fecal soiling did not show ATR, and investigative results pointed to the IAS as being responsible for incontinence. The other 6 patients had normal ATR but nonresponsive EAS on rapid filling. Findings suggest that the ATR plays a role in maintaining continence during slow rectal distension and that a disordered ATR due to IAS dysfunction leads to fecal incontinence. Thus ATR may be useful as an investigative tool in anorectal disorders.