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

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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).

CONCLUSIONS: 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.