Background: Studying colonic motility currently involves intubation which patients dislike and inevitably disrupts normal colonic physiology. Our aim was to use a novel, non-invasive MRI method of assessing colonic motility, validating it by comparing to our established MRI motility index (MMI) which assesses wall movement over a 10 minute period with free breathing, using image registration to correct for breathing artefact as previously described (1).
Methods: Randomised, double-blind cross-over trials in otherwise healthy subjects who suffered from occasional constipation (needing to take laxative no more than 4X/ month) entered trials of either A) a single dose of 5mg Bisacodyl vs identical appearing Placebo on Day 1 or B) a single dose of 5mg Bisacodyl taken during three consecutive days, Days 1-3, vs placebo. Study A had serial MRI every 75 minutes on Day 1 with a fasting scan on Day 4 ; Study B had serial scans on Day 3 with fasting scans on Day 1 and 4 . Primary endpoint: T1 of ascending colon (AC), (an established measure of colonic chyme water content). Secondary endpoints included: whole gut transit (WGTT), small bowel water content (SBWC), MMI, serial segmental (ascending, transverse, descending and rectosigmoid) colonic volumes and their variability, number of “epochs” when segmental volume change between scans was >20% of baseline volume, time to defecate after dosing and stool consistency using Bristol Stool Form Score (BSFS).
Results: While a single dose of Bisacodyl did not significantly alter AC T1, 3 doses did (Table). Both treatments significantly accelerated WGTT however only 3 doses increased SBWC and decreased AC volume. MMI proved technically difficult owing to substantial changes in colon images associated with “mass movements” making image registration (required to correct for breathing artefact) difficult. Movement of colonic contents was more easily assessed from the variability of colonic segmental volumes which both doses increased (Figure1). This variability with 3 doses was significantly greater in the distal segments. Only the 3 doses increased the number of epochs with >20% change in volume (Figure 2), changes which we believe are indication of movement “en mass” also known as “mass movements”.
Conclusion
MMI is technically difficult in unprepared colon when wall movements are erratic and substantial. Variability in serial MRI measured segmental volumes allows reliable, non-invasively assessment of colonic motility stimulation by bisacodyl. Low dose (5mg) bisacodyl has both prosecretory and prokinetic effects resulting in substantial “mass movements”. MRI can visualise these important and distinctive colonic motor patterns.
Key words
Constipation, laxative, MRI
Funding: Supported by a research grant from Sanofi GmbH
References
Menys et al Phys Med Biol 2014;59(16):4603-19.

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Emily Gaudoin

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