Simultaneous pressure waves (SPWs) in manometry recordings of the human colon have been associated with gas expulsion. Our hypothesis was that the SPW might be a critical component of most colonic motor functions, and hence might act as a biomarker for healthy colon motility. To that end, we performed high-resolution colonic manometry (HRCM), for the first time using an 84-sensor (1 cm spaced) water-perfused catheter, in 17 healthy volunteers. Intraluminal pressure patterns were recorded during baseline, proximal and rectal balloon distention, after a meal and following proximal and rectal luminal bisacodyl administration. Quantification was performed using software, based on Image J, developed during this study. Gas expulsion was always associated with SPWs, furthermore, SPWs were associated with water or balloon expulsion. SPWs were prominently emerging at the termination of proximal high amplitude propagating pressure waves (HAPWs); we termed this motor pattern HAPW-SPWs; hence, SPWs were often not a pan-colonic event. SPWs and HAPW-SPWs were observed at baseline with SPW amplitudes of 12.0 ± 8.5 mmHg and 20.2 ± 7.2 mmHg respectively. The SPW occurrence and amplitude significantly increased in response to meal, balloon distention and luminal bisacodyl, associated with 50.3% anal sphincter relaxation at baseline, which significantly increased to 59.0% after a meal, and 69.1% after bisacodyl. Often, full relaxation was achieved. The SPWs associated with gas expulsion had a significantly higher amplitude compared to SPWs without gas expulsion. SPWs could be seen to consist of clusters of high frequency pressure waves, likely associated with a cluster of fast propagating, circular muscle contractions. SPWs were occasionally observed in a highly rhythmic pattern at 1.8 ± 1.2 cycles/min. Unlike HAPWs, the SPWs did not obliterate haustral boundaries thereby explaining how gas can be expelled while solid content can remain restrained by the haustral boundaries. In conclusion, the SPW may become a biomarker for normal gas transit, the gastrocolonic reflex and extrinsic neural reflexes. The SPW assessment reveals coordination of activities in the colon, rectum and anal sphincters. SPWs may become of diagnostic value in patients with colonic dysmotility.

The role of short-chain fatty acids (SCFAs) in colonic motility is controversial. Germ free (GF) mice are unable to produce these metabolites and serve as a model to study how their absence affects colonic motility. GF transit is slower than controls and colonization of these mice improves transit and serotonin (5-HT) levels. Our aim was to determine the role SCFAs play in improving transit, and whether this is dependent on mucosal 5-HT signaling. Motility was assessed in GF mice via spatiotemporal mapping using two techniques. The first measured motor patterns under intraluminal perfusion of phosphate buffer (PBS) with or without SCFA. In addition, outflow from the colon was recorded to quantify outflow due to individual propulsive contractions. The second technique measured fecal pellet propulsion using artificial pellets. Motility was then assessed in TPH1 KO mice, devoid of mucosal 5-HT, with PBS, butyrate and propionate intraluminal perfusion. GF mice exhibited a lower proportion of propulsive contractions, lower volume of outflow/contraction, slower velocity of contractions and slower propulsion of fecal pellets compared to controls. SCFAs changed motility patterns to that of the controls in all parameters. Butyrate administration increased the proportion of propulsive contractions in controls, yet failed to in TPH1 KO mice. Propionate inhibited propulsive contractions in all mice. Our results reveal significant abnormalities in the propulsive nature of colonic motor patterns in GF mice, explaining the decreased transit time in in vivo studies. We show that butyrate, and not propionate, activates propulsive motility and that this may require mucosal 5-HT.

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