Megacolon is theresult of an extensive lesion of the mioenteric plexus, with lack of motor coordinationand achalasia of the anal sphincter. The motility disorder caused by the musclecontraction problems added to a mechanical obstacle results cause constipation.The defecation rectal pressure increases and reaches its peak with the startof fecal flow, exceeding the anal pressure. The objective of this work was toassess the ratio of rectal / anal pressure on 29 megacolon sufferers, comparedto normal subjects. Results have shown that defecation rectal pressure was higherthan expected for both men (72,2 ± 29,1 cm water) and women (64,5 ±20,1 cm water) exceeding the defecation anal pressure (66,4 ± 23,2 and62,1 ± 28,7 cm water, for men and women, respectively). The defecationpressures were much higher than those of the control group, what led to theconclusion that as an adaptive reaction, muscular effort increases to make evacuationpossible.
