Sensations of gas and pain and their relationship with compliance during distension in human colon

Background Colonic mechanosensory afferents 'in parallel' to circular muscle activate prevertebral ganglion reflexes; 'in series', afferents convey visceral sensation to the central nervous system; and pain receptors are activated with muscle distension. Our aim was to analyze the relationships of gas and pain sensations during graded distensions, and the association of sensations with colonic compliance in conscious humans. Methods The data were acquired in a prior study performed on 60 healthy volunteers (aged 18-75years) under baseline conditions... Colonic compliance was measured in response to 4mmHg stepwise balloon distensions to estimate pressure at half-maximum volume (Pr_50%). Sensation ratings for gas and pain were averaged over distensions at 16, 24, 30 and 36mmHg above baseline operating pressure. Associations between mean gas and pain ratings, and colonic compliance were assessed with Pearson correlations. Key Results Gas and pain sensations were significantly correlated at all levels of distension (all P<0.001). Significant inverse correlations between Pr_50% and sensations of gas and pain were observed, suggesting that lower compliance was associated with lower sensations. Up to 25% of the variance in sensation may be attributed to colonic compliance. Conclusions & Inferences These data are consistent with the hypothesis that, if circumferential colonic receptors are stimulated by distension to mediate gas and pain in humans, they are, at least partly, arranged 'in parallel' to the muscle layer.