Anal acoustic reflectometry: a new technique for assessing anal sphincter function

Anal acoustic reflectometry (AAR) is a new technique that offers an assessment of anal sphincter function by the measurement of additional parameters not available with conventional manometry. The aim of this study is to describe the technique, methodology and initial pilot study results.

Wideband sounds (100 Hz to 16 kHz) are transmitted into a thin polyurethane bag placed within the anal canal. Calculation of cross-sectional area from reflected sound waves, over a range of pressures (0-200 cm H(2)O) during inflation/deflation of the bag, results in five physiological parameters of anal canal function. Five patients [three continent (two female) and two incontinent (both female)] were assessed with AAR and anal manometry.

Anal acoustic reflectometry parameters were reduced in incontinent when compared with continent patients. Resting Opening Pressures (cmH(2)O) were 27 and 16 in patients with faecal incontinence (FI) vs 44 and 72 in continent patients; Resting Opening Elastance (cmH(2)O/mm(2)) was 0.88 and 1.08 in FI patients vs 1.65 and 1.34 in continent patients. The Resting Opening Pressure of a similarly aged continent male (55 cmH(2)O) was greater than three of the females. During assessment of voluntary contraction (one FI female vs one continent female), Squeeze Opening Pressure (cmH(2)O) was 31 vs 100 and Elastance (cmH(2)O/mm(2)) 0.61 vs 2.07.

Anal acoustic reflectometry appears to be promising technique. Further work is in place to clarify whether it will be useful in clinical assessment of incontinent patients.