Topographic and manometric characterization of the recto‐anal inhibitory reflex

Abstract

INTRODUCTION (RAIR) Recto-anal inhibitory reflex is an integral part of normal defecation. The physiological characteristics of RAIR along anal length and anterior-posterior axis are unknown. AIM To perform topographic and vector-graphic evaluation of RAIR along anal canal using high definition manometry (HDM), and examine the role of various muscle components. METHODS Anorectal topography was assessed in 10 healthy volunteers using HDM probe with 256 sensors. RAIR data were analyzed every mm along the length of anal canal for topographic, baseline, residual, and plateau pressures during 5 mean volumes of balloon inflation (15cc, 40cc, 71cc, 101cc, 177cc), and in 3D by dividing anal canal into 4×2.1 mm grids. RESULTS Relaxation pressure progressively increases along anal canal with increasing balloon volume up to 71 cc and thereafter plateaus. In 3-D, RAIR is maximally seen at the middle and upper portions of anal canal (levels 1.2-3.2 cm) and posteriorly. Peak residual pressure was seen at proximal anal canal. CONCLUSION RAIR is characterized by differential anal relaxation along Anterior-Posterior axis, longitudinally along the length of anal canal, and it depends on the rectal distention volume. It is maximally seen at internal anal sphincter pressure zone. Multidimensional analyses indicate that external anal sphincter provides bulk of anal residual pressure. Our findings emphasize importance of sensor location and orientation; as anterior and more distal location may miss RAIR.

How to Perform and Interpret a High-resolution Anorectal Manometry Test

“…It seems intuitive that the pressure increment during squeeze probably reflects external anal sphincter function in the resting anal HPZ and the PRM in the region above the HPZ. 40,47,49 However, these inferences need to be confirmed by further studies in patients with selective dysfunction of a muscle or …”

“…It is manifest as a reduction in anal pressure during rectal balloon distention. 40 The amplitude and duration of the RAIR depend on the rate and volume of rectal distention. 41 RAIR is absent in several conditions, including dysganglionosis, postcircular myotomy, and lower anterior resections.…”

“…43 A recent HD-ARM study found that RAIR is characterized by a differential relaxation along the anteroposterior axis, the length of the anal canal, and at each vector, with the maximum change occurring at the level of the IAS. 40 There have been no studies assessing the RAIR with HR-ARM in Hirschsprung's disease.…”

Anorectal Physiology and Pathophysiology in the Elderly

“…Recent work shows that it is maximally seen at the internal anal sphincter pressure zone, and is characterized manometrically by the loss of anal canal pressure during rectal balloon distension (relaxation pressure), and the lowest anal canal pressure point of the reflex (residual pressure). [17] The SMR is a transient anal contraction that is primarily induced by the activation and contraction of the puborectalis muscle in response to sensation of a desire to defecate. [18] It usually overlies the initial relaxation phase of the RAIR, and normally coincides with the onset of a sensation to defecate.…”

Accuracy and Reproducibility of High-definition Anorectal Manometry and Pressure Topography Analyses in Healthy Subjects

“…A further refinement has been the introduction of 3-dimensional high definition anorectal manometry (HDAM-3D) that comprises of a rigid probe with 256 circumferentially arrayed pressure sensors that provides 3-D reconstruction of pressure profiles. Recent studies with HDAM-3D have provided novel information regarding the sensorimotor response, the recto-anal inhibitory reflex, and recto-anal contractile response (15, 16) and anal/vaginal functional morphology (17). …”