Evaluation of the Fast Fill Technique for Anal Acoustic Reflectometry (AAR) in the Incontinent Anal Sphincter

Anal Acoustic Reflectometry (AAR) is a technique that has been studied in our department over the last 6 years. Sound waves pass into a balloon placed in the anal canal and are used to measure the cross-sectional area. By gradually increasing and decreasing the pressure in the balloon the investigators can measure the pressure at which the cross-sectional area starts to increase and decrease, and the anal canal starts to open and close. This assessment mimics the natural opening and closing of the anal canal and the effect of squeezing the muscles.

The gold standard investigation of the anal sphincter muscles has been manometry which measures anal canal pressure at rest and during squeeze. However, it has limitations. Despite the two measurements being within the normal range, some patients can have significant faecal incontinence. This has prompted clinicians to search for a better investigation to guide the management of this condition.

AAR is a reproducible and repeatable technique that has been used as a research technique in the assessment of faecal incontinence. It has been shown to correlate with symptom severity and, unlike manometry, is able to distinguish between different symptomatic subgroups with faceal incontinence. In our studies so far the investigators have increased the bag inflation pressure a step at a time which means that each study takes about 20 minutes to perform. The limitation of this method is that during the measurement of squeeze pressure the sphincter muscle is subject to fatigue. A recent study using the acoustic technique in the urethra has demonstrated a faster method of recording measurements over an 8 minute period. The investigators propose to study the fatiguability effects of this faster technique and validate the method against the existing step-wise technique and standard anal manometry.

Patients will be randomised into two groups:

1. Stepwise then fast-fill
2. Fast-fill then stepwise