Investigation of anal motor characteristics of the sensorimotor response (SMR) using 3-D anorectal pressure topography

Abstract

Desire to defecate is associated with a unique anal contractile response, the sensorimotor response (SMR). However, the precise muscle(s) involved is not known. We aimed to examine the role of external and internal anal sphincter and the puborectalis muscle in the genesis of SMR. Anorectal 3-D pressure topography was performed in 10 healthy subjects during graded rectal balloon distention using a novel high-definition manometry system consisting of a probe with 256 pressure sensors arranged circumferentially. The anal pressure changes before, during, and after the onset of SMR were measured at every millimeter along the length of anal canal and in 3-D by dividing the anal canal into 4 ϫ 2.1-mm grids. Pressures were assessed in the longitudinal and anterior-posterior axis. Anal ultrasound was performed to assess puborectalis morphology. 3-D topography demonstrated that rectal distention produced an SMR coinciding with desire to defecate and predominantly induced by contraction of puborectalis. Anal ultrasound showed that the puborectalis was located at mean distance of 3.5 cm from anal verge, which corresponded with peak pressure difference between the anterior and posterior vectors observed at 3.4 cm with 3-D topography (r ϭ 0.77). The highest absolute and percentage increases in pressure during SMR were seen in the superior-posterior portion of anal canal, reaffirming the role of puborectalis. The SMR anal pressure profile showed a peak pressure at 1.6 cm from anal verge in the anterior and posterior vectors and distinct increase in pressure only posteriorly at 3.2 cm corresponding to puborectalis. We concluded that SMR is primarily induced by the activation and contraction of the puborectalis muscle in response to a sensation of a desire to defecate. anal manometry; puborectalis IN HUMANS, BALLOON DISTENTION of the rectum normally induces the recto-anal inhibitory reflex (RAIR) (6, 11) as well as the recto-anal contractile reflex (RACR) (9, 10, 21). RAIR is an enteric neuronal reflex that is mediated by nitric oxide, vasoactive intestinal peptide, and adenosine triphosphate and causes relaxation of internal anal sphincter (IAS) (18). The rate and method of rectal distention (intermittent vs. ramp) affect the properties of the RAIR, and this reflex response is classically absent in Hirschsprung's disease and other conditions such as after circular rectal myotomy and after lower anterior resection (4,12,22).In addition to the aforementioned reflexes, recently, we have described the sensorimotor response (SMR) (5) that is also seen during balloon distention of the rectum. The SMR is a transient anal contraction that is usually seen overlying the initial relaxation phase of the RAIR (5). In healthy subjects, it coincides with the onset of a sensation for defecation (5). A recent study showed that the SMR was abnormal in patients with rectal hyposensitivity, suggesting a pathophysiological role for this response in anorectal disorders (19). However, the precise origin of the anal contractile response, in particular...

On The Etiology of the Electric Activity of the External Anal and Urethral Sphincters

“…These results were obtained after internal anal sphincter excision performed experimentally and as a part of mobilization operation for lower third rectal cancer [4,5].…”

“…Following complete excision of the internal anal sphincter the anal pressure declined. Monthly biopsies of EAS showed proliferation of the smooth muscle fibers which, by the 10th postoperative month, clearly outnumbered the striated fibers and was associated with anal pressure elevation [4]. These results were obtained after internal anal sphincter excision in anorectal mobilization operation performed for lower third rectal cancer [5].…”

“…In a previous study [4], the EAS in dogs, known to consist of skeletal muscle fibers, was found to contain smooth fibers. Following complete excision of the internal anal sphincter the anal pressure declined.…”

Purse-string morphology of external anal sphincter revealed by novel imaging techniques

“…Figure 6B shows a significant decrease (21 Ϯ 5%) in anal canal squeeze pressures after lidocaine injection. Furthermore, anal canal pressure decreased in the caudal half of the anal canal region, which is under the influence of EAS muscle (5).…”

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 …”