Placement of a fine-bore rectal balloon catheter in the anal canal does not affect anal sphincter pressures: improving our understanding of physiological function with anal acoustic reflectometry.

Aim: The recto-anal inhibitory reflex (RAIR) is currently measured using anorectal manometry catheters, which may distort the anal canal. Anal acoustic reflectometry (AAR) is considered a catheter-free technique for evaluating the physiological function of the anal canal; however, it has yet to be used to elicit the RAIR. For the RAIR to be measured with AAR, the effect of placing an additional rectal balloon catheter on the measured AAR parameters needs to be investigated: that is the aim of this work.

Method: Patients aged over 18 years attending hospital for the investigation of pelvic floor disorders were included. AAR parameters were obtained before and after a rectal balloon catheter was placed alongside the AAR catheter. The following parameters were measured: opening pressure (Op, cmH O), opening elastance (Oe, cmH O/mm ), closing pressure (Cp, cmH O), closing elastance (Ce, cmH O/mm ), hysteresis (Hys, %), squeeze opening pressure (SqOp, cmH O) and squeeze opening elastance (SqOe, cmH O/mm ).

Results: Thirty-five patients were included in the analysis, of whom 28 were women. The median age was 58 years. Comparison of median AAR parameters before and after catheter placement showed no significant difference: Op (36.36 vs 33.42, P = 0.09), Oe (1.27 vs 1.39, P = 0.19), Cp (18.62 vs 19.73, P = 0.13), Ce (1.2 vs 1.28, P = 0.33), Hys (41.08 vs 40.11, P = 0.17), SqOp (81.85 vs 81.65, P = 0.93) and SqOe (1.44 vs 1.49, P = 0.55).

Discussion: Placement of a rectal balloon catheter alongside the AAR catheter has no significant effect on the measured AAR parameters. The results of this study add to the fundamental basic science and understanding of the physiological function of the anal canal.