Does Colonic Transit Time Affect Colonic pH?

Abstract

Purpose: Colonic luminal pH progressively rises from the cecum to the rectum and is affected by gut bacterial metabolism and colonic transport processes. Limited studies on small numbers of subjects using drugs to acutely alter colonic transit time (CTT) have suggested that pH in the distal colon increases with prolonged colonic transit. In the present study we have used a wireless manometry capsule containing pH, pressure, and temperature sensors to characterize the correlation between pH and transit time in the colon. Methods: 168 subjects were enrolled in a study comparing colonic transit time using the wireless motility capsule versus radioopaque markers (Clinical Gastroenterology and Hepatology 7:573, 2009). 87 subjects were healthy controls, and 81 had chronic constipation based on Rome II criteria. CTT was measured as previously described by defining capsule entry into the cecum by a rapid pH drop of >1 unit, and capsule exit from the body by a sharp temperature drop and characteristic pressure signature. 15 subjects (10 constipated, 5 normals) were excluded from analysis due to device malfunction or data loss, and 5 (3 constipated, 2 controls) were excluded because of inability to define the ileocecal transition, leaving 148 subjects (68 constipated, 80 normals for analysis). Mean pH was determined for each time quartile of colonic transit and in the 15 minute intervals after entry into the cecum (proximal colon) and prior to body exit (distal colon) using the manufacturer's software. An experimentally determined drift correction of the pH 0.01 pH units per hour was applied to the pH data to compensate for the inherent pH sensor drift. Constipated subjects were divided into normal (n=37) and slow transit (n=31) constipation based on the 95th percentile cutoff of 59 hours for the healthy controls. Spearman's correlation coefficient was used to assess the relationship between CTT and pH in different colonic segments. Results: There was a weak, but significant correlation (R=0.20, p=0.0137) between CTT and pH in the distal colon, but no correlation with pH in the more proximal colon. pH in the distal colon rose 0.1 pH units for every 24 hour increase in CTT. The mean rise in pH from the proximal to the distal colon was 0.5 in normal controls, 0.5 in normal transit constipation, and 0.8 in slow transit constipation [p<0.09] slow transit constipation vs. the other two groups. Conclusion: pH in the distal colon is positively, but weakly correlated with CTT. The effect of the higher distal colonic pH in patients with slow transit on important processes such as drug delivery, colonic flora, and colonocyte proliferation and transport merits further study. Disclosure: Dr Sitrin received research support from SmartPill, Inc. Dr Wilding is a consultant for SmartPill, Inc. Dr Semler is an employee of SmartPill, Inc. The study was supported by a grant from NYSTAR and SmartPill, Inc.Table