Study of the Mechanism of Rectal Motility: The ‘Mass Squeeze Contraction’

Abstract

The motor physiology of the rectum has remained largely obscure, especially concerning the mechanism of rectal motility. In the current communication we tested the possibility of characterizing the mechanism of rectal motility during filling and evacuation through the study of the rectal electric activity in 16 healthy volunteers (mean age 43.6 +/- 10.8 years; 11 men). Two monopolar silver-silver chloride electrodes were introduced per annum and fixed to the rectal mucosa by suction. The rectum was distended in 10 ml increments of water by means of a balloon-ended catheter inserted into the rectum. The rectal pressure was measured by one catheter placed above and a second one below the rectal balloon, and the 2 catheters were connected to 2 strain gauge pressure transducers. Regular triphasic slow waves or pacesetter potentials (PPs) were recorded from the 2 electrodes at rest. PPs were superimposed or followed randomly by action potentials (APs). APs but not PPs were coupled with elevated rectal pressure. Rectal distension with 10 ml of water caused no significant changes of the rectal pressure or EMG activity. Distension with a mean volume of 27.3 +/- 4.7 ml effected a significant increase (p < 0.05) of the rectal electromechanical activity proximally to the balloon and a decrease distally (p < 0.05) to it. With progressive increase of the rectal distension, the electromechanical activity continued to increase proximally and to decrease distally to the balloon, until, at a mean distending volume of 76.3 +/- 3.7 ml, the balloon was dispelled to the exterior. In conclusion, the identification of the modality of rectal motility during defecation was feasible by recording the rectal electromechanical activity. The rectal contraction is suggested to occur in a 'mass squeeze manner' which squeezes the rectal contents aborally into the anal canal. The recognition of the rectal motor modality appears to be important for the understanding of rectal motility disorders. However, further studies are required to confirm these findings.

Modulation of colonic function in irritable bowel syndrome rats by electroacupuncture at ST25 and the neurobiological links between ST25 and the colon

“…The slow wave is a local potential, which originates from the longitudinal muscle and is a relatively regular periodic electrical activity that controls the contraction rhythm of the intestine and is always present whether contracted or not. The action potential is generated on top of the slow wave, which is consistent with the smooth muscle contraction and is the main initiator of the propulsive contraction (Ahmed and Ali, 2000;Shafik et al, 2001). The frequency and amplitude of colonic slow waves can reflect colonic function.…”

Anorectal morphology and function: analysis of the Shafik legacy

“…From this work he proposed a mass squeeze action of the rectum aborally towards the anal canal [127,128] with a separable rectosigmoid pacemaker site [129,130] transmitted through the longitudinal muscle on distension and abrogated by longitudinal myotomy [131,132]. This work informed his suggestion for the treatment of severe constipation by colonic and rectal pacing using mucosally positioned pacing electrodes and home pacing with a subcutaneously implanted electrical stimulator.…”