Consistency of Feces Affects Defecatory Function.

Background/aims: It is a common belief that constipated patients have hard feces that contributes to the difficulties defecating. To the best of our knowledge, no studies had been published on controlled evacuation of simulated feces with different consistencies.

Methods: Twelve normal subjects were recruited for studies with the simulated feces device "Fecobionics" of different consistency (silicone shore 0A-40A corresponding to Bristol stool form scale types 2-4). The subjects filled out questionnaires and had the balloon expulsion test and anorectal manometry done for reference. The Fecobionics probes were inserted in rectum in random order with +20 minutes between insertions. The bag was filled to urge-to-defecate and evacuations took place in privacy. Non-parametric statistics with median and quartiles are provided.

Results: One subject was excluded due to technical issues, and another had abnormal anorectal manometry-balloon expulsion test. The 4 females/6 males subjects were aged 23 (range 20-48) years. Most differences were observed between the 0A and 10A probe (duration, maximum bag pressure, duration x maximum bag pressure, and relaxation of the front pressure and the bend angle during evacuation), eg, the duration was 9 (8-12) seconds at 0A and 18 (12-21) seconds at 10A ( < 0.05), and maximum bag pressure was 107 (96-116) cmHO at 0A and 140 (117-162) cmHO at 10A ( < 0.05). The bend angle before evacuation differed between the probes whereas only the 10A differed from 40A during defecation. The 10A was harder to evacuate than the 0A probe. Except for the bend angles, no further significant change was observed from 10A to 40A.

Conclusion: Fecal consistency affects defecatory parameters.