Introduction: The sampling response describes reflex lowering of anal sphincter pressure allowing rectal content to come into contact with sensitive mucosa in the anal canal. Sampling events allow discrimination of faeces from flatus and may contribute to the perception of a rectal urge to defecate. Constipated patients can be classified according to whether they have a normal rectal urge to defecate (NUD) or reduced urge to defecate (RUD)[1]. Infrequent sampling events may cause RUD. Semi-ambulatory simultaneous anal and rectal manometry was used to record sampling events.
Method: Prospective study comparing frequency of sampling events in NUD patients with RUD patients. Ethical approval obtained. Power calculation to determine sample-size based on 4-hours of recording. Subjects with functional constipation (Rome II criteria) recruited. Colonic transit measured with radio-opaque markers. Resting anal pressure (RAP), anal squeeze pressure (ASP), rectal pressure (RP) and anal electromucosal sensation recorded. Rectal balloon distention to assess RAIR and rectal sensation (barostat controlled inflation). Semi-ambulatory anorectal manometry using a catheter with 2 solid-state transducers at 1cm and 5cm (Gaeltec). Catheter attached at anal verge with the transducers in the rectum and anal canal. The subject was ambulatory within the department during recording. Recordings reported by a researcher blinded to whether the subject had NUD or RUD.
Results: 22 female patients studied; 12 RUD;10 NUD. No differences between groups re: age; duration and severity of symptoms or mean duration of recording - NUD group 3.95 hrs, RUD 3.86 hrs (NS). Mean sampling event frequency: NUD group 8.71/hr (range 2-20/hr), RUD 8.95/hr (range 0-21/hr) (NS). NUD patients perceived 6% of sampling events; RUD patients perceived 9% of events (NS). No difference in total or segmental colonic transit time between groups. No association between sampling event frequency and segmental or total colonic transit time. No difference in RAP, ASP, RP or rectal and anal sensation between groups.
Conclusion: The cause of RUD in these patients was not infrequent sampling events. The factors determining whether patients have RUD or NUD remain unclear. Further study is required to evaluate rectal compliance, rectosigmoid motility and higher cerebral function in determining urge to defecate.
Reference:
[1]. Harraf F. Subtypes of constipation predominant irritable bowel syndrome based on rectal perception. Gut 1999;43.
Cowlam S, Saunders P, Wooff D, Yiannakou Y. The frequency of the sampling response does not determine urge to defecate in patients with constipation: A study using semi-ambulatory anorectal physiology. Joint International Society Meeting in Neurogastroenterology and GI Motility. Boston, Massachusetts, September 2006. Abstract in Neurogastroenterology and Motility. 18 (8); 676.
Mr. Phil Saunders, Durham Unit, Durham. Tel: +44 (0)191-333-2227.
Regional Medical Physics Department, Freeman Hospital, Newcastle upon Tyne, NE7 7DN, UK.
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