Continuous vs stepwise anal acoustic reflectometry: An improved technique for physiological measurement of anal sphincter function?

Abstract

Anal acoustic reflectometry (AAR) is a technique for measuring the physiological profile of the anal canal, primarily the internal anal sphincter. Evaluation of a new continuous method, recently developed for the urethra, would enable its future application for investigation of rectal reflexes. Patients aged 18 and over with fecal incontinence (FI) were included. Stepwise AAR parameters were compared with continuous opening pressure (Op, cmH2 O), opening elastance (Oe, cmH2 O/mm2 ), closing pressure (Cp, cmH2 O), closing elastance (Ce, cmH2 O/mm2 ), hysteresis (Hys, [%]), squeeze opening pressure (SqOp, cmH2 O), and squeeze opening elastance (SqOe, cmH2 O/mm2 ). Vaizey incontinence and Manchester Health Questionnaire scores were also collected. Thirty-two patients, 26 females were analyzed. Median age: 60 (range, 32-75). Median AAR parameters of Op (37.50 vs 35.15, P = .031), Oe (1.31 vs 0.84, P < .0001), Ce (1.11 vs 0.88, P < .0001), Hys (37.75 vs 19.04, P < .0001), and SqOe (1.27 vs 1.06, P = .005) were significantly higher with the continuous method. Cp (22.70 vs 27.22, P = .003) is lower and SqOp (96.87 vs 59.47, P = .71) not significantly different. The continuous technique had superior repeatability between cycles for all AAR parameters except Oe, which was equivalent and continuous SqOp had a stronger negative correlation with Vaizey score than stepwise (-0.46, P = .009 vs -0.37, P = .038). The differences seen between the two techniques are likely to be related to the rate of stretch. The continuous technique appears to represent a more physiological measurement of anal sphincter function than the stepwise technique particularly in the assessment of voluntary squeeze function.