Material and Method: Anorectal manometry with a conventional solid state manometric catheter was performed in 30 constipated patients in both the lying and sitting positions. Anorectal manometric variables at rest and during attempted defecation with empty rectum were assessed in both positions. A colonic transit study using Sitzmarks radiopaque markers and a 50-mL water-filled balloon expulsion test was also performed in all patients. Patients exhibiting an abnormal manometric pattern of defecation in either the sitting or lying position proceeded to a simulated defecation test. The anorectal pressure parameters of resting and during attempted defecation of the both positions were compared.

Results: The resting rectal pressure, maximum rectal straining pressure, and defecation index during attempted defecation were significantly higher in the sitting position than the lying position. A dyssynergic manometric pattern during attempted defecation with empty rectum was seen in 46% of the patients in the lying position, not significantly different from the 56% in the seated position (p = 0.58). Most patients (71%) who exhibited manometric dyssynergia with an empty rectum could relax their anal sphincter during the simulated defecation test. Only six (20%) constipated patients had abnormal dyssynergic anal sphincter contraction confirmed by a simulated defecation test.

Conclusion: Body position affects the results of manometric measurements related to the defecation mechanism.

Keywords: Anorectal manometry, Functional constipation, Body position