Abstract
Background: Ingestible wireless motility capsules enable locoregional quantification of luminal pH and concentrations of hydrogen and carbon dioxide in the human colon.
Aim: To evaluate these measures in the colon of healthy adults.
Methods: Gas-sensing and pH-sensing wireless motility capsules were ingested tandemly and repeatedly over time. Measurements were analysed and compared in proximal and distal segments of the colon.
Results: In paired datasets from 37 participants, colonic pH rose from a median 6.3 (IQR 5.8-6.9) proximally to 7.0 (6.6-7.2) distally (p < 0.001). Concentrations of carbon dioxide rose in nearly all participants from 12.7 (9.1-18.6) proximally to 18.8 (11.9-28.1) %.h/h distally (p < 0.001) with a positive correlation between proximal and distal colon (r = 0.76; p < 0.001). Hydrogen concentrations showed widely varied proximal-to-distal gradients with an increase in 69% of participants, but no correlation between proximal and distal colon measures. No significant correlations between colonic pH, hydrogen concentrations, and carbon dioxide concentrations were observed. Comparison of hydrogen and carbon dioxide concentrations between tandem gas-sensing capsules by Bland-Altman analysis (n = 24) showed minimal (< 1.2%) bias for both measures, and gas metrics on repeat ingestion were similar (n = 20). However, there was greater variance in the distal colon.
Conclusions: Both wireless motility capsules evaluate different yet complementary aspects of colonic fermentation. Carbon dioxide concentrations that most likely reflect overall microbial metabolic activity were consistently greater distally, while proximal-to-distal gradients in hydrogen concentrations varied, likely due to inter-subject variations in dietary carbohydrate and/or methanogenesis. Luminal pH poorly reflects carbohydrate fermentation in the distal colon.
Trial registration: ACTRN12619001219178 and ACTRN12622000422729.