Measuring recto-anal Inhibitory reflex using functional lumen imaging probe: A pilot study

Faecal incontinence is a multi-factorial challenging problem. The maintenance of faecal continence relies on a complex voluntary and involuntary coordination between anal and colorectal activity. The aim of this study is to introduce a new method for measuring anal sphincter distensibility and function during voluntary manoeuvres like squeezing and straining as well as involuntary manoeuvres like recto-anal inhibitory reflex (RAIR) testing and slow rectal distension. A modified functional lumen imaging probe (FLIP) consisted of the rectal balloon to distend and measure the pressure in the rectum and the anal bag which contained 16 sensing electrode capable of measuring serial cross-sectional areas (CSA) of the anal bag. The CSAs were converted to functional images of the anal canal geometry. The bag pressure was also measured during anal distension. The probe was bench tested and the CSA measured by EndoFLIP system was calibrated. Four healthy volunteers (2 males/2 females) and one faecal incontinence patient were recruited for the studies. The probe was inserted in the anal canal with 2cm of the anal bag located outside the anal verge. The anal bag was distended from 0ml to 50ml, and then the volunteers were asked to rest, squeeze and strain voluntarily at specific step volumes in the anal bag. RAIR and slow rectal distension tests were also measured at three step distensions in the anal bag. The results showed that the distal end relaxed more than the proximal end during ramp distension. The anal canal length decreased as a linear function of the distending bag volume. The functional images measured during manoeuvres showed the contraction of the proximal part of the anal canal by 12mm² during squeezing and the relaxation by 10mm² during straining test. During the RAIR test, the distal part of the anal canal relaxed by 14mm². The distal part of the anal canal relaxed by 20mm² and the proximal part contracted by 10mm² during the slow rectal distension which mimics the defecation. In conclusion the modified EndoFLIP was capable of describing the anal distensibility and sphincteric function for different manoeuvres.