Introduction The wireless motility capsule (WMC) allows investigation of regional gut transit times, intraluminal pH and pressure changes as it traverses the gastrointestinal tract. It is a useful diagnostic tool to confirm slow transit constipation (STC), which recent studies suggest is allied to dysregulated rather than impaired colonic motility (Dinning et al . NGM 2010). Whether luminal pH differs in STC is unknown. AIM: to compare colonic pressure and pH profiles between healthy volunteers (HV) and STC.

Method data from 18 WMC studies in STC (15 female, median age 37; colon transit time (CTT) >72h) were compared to those of 112 HV (48 female; median age 43). Pressure and pH profiles were analysed for: (1) the whole colon; (2) within the caecum and proximal colon (first 60 min following passage of WMC through the ICJ); and (3) within the distal colon (last 60 min prior to WMC expulsion).

Results overall frequency of colonic contractions was similar between STC and HV (STC: 3.0 ± 1.3/min vs. HV: 2.8 ± 1.2/min; P=NS). However, the colonic motility index (CMI) was significantly higher in STC than HV (STC: 330 ± 166 vs. HV: 184 ± 104; P < 0.0001). CMI and CTT were positively correlated (r = 0.38; P = 0.003). The proximal and distal colonic pressure profiles were similar between groups. For colonic pH profile, STC had a significantly more alkaline pH, both overall (STC: 7.7 ± 1.0 vs. HV: 6.8 ± 0.7; P < 0.0001), and in the distal colon (STC: 8.1 ± 1 vs. HV: 7.2 ± 0.9; P = 0.0004). Using linear regression modelling, alkaline pH was associated with an increase in the CMI when controlling for age and gender between groups (beta=62.1; P = 0.023). Conversely, proximal colonic pH was more acidic in STC, manifest as a greater difference in pH across the ICJ than in HV (STC delta ICJ: 1.8 ± 0.6 vs. HV: 1.3 ± 0.8; P < 0.005).

Conclusion the CMI was found to be higher in STC than HV, supporting a more contemporary acceptance of underlying dysregulation of colonic contractility rather than “inertia”. Differences in colonic pH in STC may reflect alterations in regional gut microbiota (i.e. dysbiosis), resulting in excessive production of acidic metabolites in the proximal colon (e.g. short-chain fatty acids) of STC patients, and more alkaline metabolites in the distal colon (perhaps related to methanogenic activity). The observed associations between colonic pH, CMI and CCT warrants further investigation; conceivably, this may represent a biomarker to sub-classify constipated patients, and identify those who may benefit from antibiotic and/or dietary interventions

Disclosure of interest None Declared.