The cough response of the anal sphincter.

Rises in intra-abdominal pressure are common and are accompanied by reflex contraction of the external sphincter. Voluntary contraction of the sphincter is an uncommon event but is routinely used as a measure of sphincter strength. Cough pressure and squeeze pressure were compared in 75 patients using a 4 channel perfused catheter (3 anal and 1 rectal side-hole). Maximum anal cough pressure was higher than squeeze pressure (mean 158 vs 133 cm H2O, P = 0.0015). Intra-individual variance was less using cough pressure (mean 20% vs 29%, P = 0.005). There was significant overall correlation between cough pressure and squeeze pressure (P < 0.001) although in some cases there were wide differences, suggesting that use of both cough and squeeze pressure in manometry will assess sphincter strength more reliably. Measurement of the recto-anal pressure gradient during coughing correlated significantly better with degree of incontinence than cough or squeeze pressure (P = 0.005). The presence of a positive gradient was 100% specific for incontinence but the sensitivity was only 43% suggesting that factors other than simple mechanical sphincter weakness are involved in incontinence. Measurement of cough pressure has both clinical and research importance and should be added to standard manometric protocols.