| Summary: | Anal Acoustic Reflectometry (AAR) is a novel technique providing a dynamic physiological assessment of anal sphincter function. In AAR wide band sound waves are transmitted into a thin polyurethane bag placed within the anal canal. The reflection of these sound waves allows calculation of the cross-sectional area of the anal canal. The bag is slowly inflated and deflated, during which simultaneous cross-sectional area and pressure measurements are taken along the entire length of the anal canal. This allows Opening Pressure, Opening Elastance, Closing Pressure, Closing Elastance and Hysteresis to be calculated, representing a physiological assessment of anal canal function at rest. During voluntary contraction Squeeze Opening Pressure and Squeeze Opening Elastance can be measured. AAR has been shown to be a reproducible and clinically reliable technique in the assessment of women with faecal incontinence. The aims of this study were to: (i) compare AAR with conventional anal manometry in the assessment of women with faecal incontinence, (ii) evaluate the use of AAR in patients undergoing percutaneous nerve evaluation (PNE) and sacral nerve stimulation (SNS), (iii) determine whether male patients with faecal leakage have an identifiable abnormality in anal sphincter function using AAR and (iv) determine the relative contributions of the EAS and IAS to anal tone by using AAR to study anal sphincter function during general anaesthesia with and without neuromuscular blockade. In a comparative study of AAR and anal manometry, AAR provided a more sensitive assessment of anal sphincter function in women with faecal incontinence. Unlike anal manometry, AAR variables correlated with symptom severity and were able to distinguish between different symptomatic subgroups of incontinence. Patients undergoing PNE for faecal incontinence were assessed pre-operatively. The AAR variable Opening Pressure was significantly greater in those patients with a successful outcome than in those with an unsuccessful outcome, whereas no difference was seen with the manometric equivalent of maximum resting pressure (MRP). Furthermore, Opening Pressure was shown to be an independent predictor of success in PNE, which suggests that AAR may allow better patient selection for this expensive treatment. In patients undergoing insertion of a permanent sacral nerve stimulator no change in anal sphincter function was identified at follow up and the exact mode of action of SNS remains unclear. Male patients with faecal leakage were compared with continent controls. No difference in anal manometry was found, but AAR was sensitive enough to detect a measurable difference in anal sphincter function. Both Opening and Closing Pressure were significantly lower in the male leakers which suggest that reduced anal closing forces may account for the post-defaecatory leakage. The relative contributions of the anal sphincter muscles to resting anal canal function was investigated by measuring male subjects while conscious and while under general anaesthesia with and without neuromuscular blockade. General anaesthesia resulted in a significant reduction in resting sphincter function. Neuromuscular blockade resulted in a significant increase in Opening Pressure, which has not been previously reported. AAR is a promising new technique which has advantages over conventional anal manometry and allows a sensitive assessment of anal sphincter function.
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