A novel method for measurement of the recto‐anal inhibitory reflex using anal acoustic reflectometry

Abstract

Aim The recto-anal inhibitory reflex (RAIR) is currently measured using manometry catheters, which potentially distort the anal canal. Anal acoustic reflectometry (AAR) is considered to be a catheter-free technique and primarily measures the function of the internal anal sphincter. We sought to determine if RAIR could be measured using AAR. Method Patients aged 18 and over attending the hospital for investigation of pelvic floor dysfunction were included. AAR parameters were obtained before (prerectal distension) and after (postrectal distension) inflation of a rectal balloon catheter with 100 ml of air. Minimum opening pressure (Op, cmH 2 O), opening elastance (Oe, cmH 2 O/mm 2), closing pressure (Cp, cmH 2 O), closing elastance (Ce, cmH 2 O/mm 2) and hysteresis (Hys, %) were recorded. The presence of RAIR was defined by a reduction of prerectal distension Op by 20% or more. Results Thirty-two patients were included, 26 of whom were women. The mean age of patients was 57.5 years (SD 11.3 years). Nine patients had faecal incontinence, six patients had obstructive defaecation and 17 patients had both. RAIR was seen in 30/32 patients. The mean reduction in Op was 58.8% (range À59.18% to 100%). Three patients had 100% reduction. Comparison of pre-and post-RAIR parameters showed a significant difference in Op (34.44 vs 15.41, P < 0.0001), Oe (1.39 vs 1.1, P = 0.004), Cp (20.06 vs 8.00, P < 0.0001) and Ce (1.31 vs 1.13, P < 0.0001) but not Hys (39.71 vs 39.90, P = 0.88). Conclusion We describe a novel method for the measurement of RAIR. Rectal distension appears to alter resting pressure and the resistance of the anal canal to opening and closing, with complete inhibition of the sphincter complex in three patients.

Current and future perspectives on the utility of provocative tests of anal sphincter function: A state‐of‐the‐art summary

“…Parameters are calculated from the mean of rest cycles two to ten and from all five squeeze cycles. The measurements obtained from the first cycle at rest are significantly higher than the subsequent nine cycles because of tissue preconditioning and are, therefore, excluded with the first cycle instead used to ensure the bag is unfolded correctly 27,28 . With the addition of a rectal balloon, AAR has been shown to have the ability to measure the recto‐anal inhibitory reflex expanding its utility in the assessment of the anorectum 28 …”

“…The measurements obtained from the first cycle at rest are significantly higher than the subsequent nine cycles because of tissue preconditioning and are, therefore, excluded with the first cycle instead used to ensure the bag is unfolded correctly. 27,28 With the addition of a rectal balloon, AAR has been shown to have the ability to measure the recto-anal inhibitory reflex expanding its utility in the assessment of the anorectum. 28 AAR obtains both CSA and pressure measurements during inflation and deflation of the bag allowing the identification of the point of minimum measurable CSA, which represents the highpressure zone (HPZ) (Figure 2).…”

“…27,28 With the addition of a rectal balloon, AAR has been shown to have the ability to measure the recto-anal inhibitory reflex expanding its utility in the assessment of the anorectum. 28 AAR obtains both CSA and pressure measurements during inflation and deflation of the bag allowing the identification of the point of minimum measurable CSA, which represents the highpressure zone (HPZ) (Figure 2). Physiologically, this is the point of most resistance to opening, and identifying the pressure at which the bag starts to open is considered the pressure providing continence.…”