Relationship between intra-abdominal and intrarectal pressure in the proctometrogram.

During normal defaecation the intrarectal pressure increases but, in the absence of a reference catheter in the pelvis, the contribution of abdominal straining and rectal contraction to this rise is unclear. Anorectal manometry was performed in ten consecutive women with no gastrointestinal symptoms in an attempt to measure intrapelvic pressure using a catheter in the bladder. During filling the mean (s.e.m.) rectal pressure increased from 2(1) to 18(4) cmH2O. The mean(s.e.m.) intravesical pressure remained unchanged at 2(1) cmH2O. Evacuation of the rectal balloon produced an increase in mean (s.e.m.) intrarectal pressure from 18(4) (end-filling pressure) to 68(15) cmH2O. The mean (s.e.m.) intravesical pressure increased from 2(1) to 51(18) cmH2O. The true intrarectal pressure (intrarectal minus intravesical) did not rise during defaecation. The rise in intrarectal pressure during rectal evacuation occurs by increased intrapelvic pressure alone.