Mechanophysiological analysis of anorectal function using simulated feces in human subjects

INTRODUCTION: Defecation is a complex process that is difficult to study and analyze. OBJECTIVES: Here, we present new analytical tools to calculate frictional force and tension during expulsion of the Fecobionics simulated stool in human subjects. METHODS: The 12-cm-long Fecobionics device contained pressure sensors, motion processor units for measurement of orientation and bending, and impedance rings for measurement of cross-sectional areas. Eight normal subjects defecated Fecobionics. The bending angle of the device, frictional force between the device and the surrounding tissue, and the stretch tensions were calculated. RESULTS: The bending angle and pressures changed during expulsion with the maximum pressure recorded at the rear. The averaged circumferential tension, longitudinal tension and friction force in each subject were associated with the front-rear pressure difference (r > 0.7, p < 0.005). The peak circumferential tension, longitudinal tension, and friction force immediately before expulsion of the rear were significantly higher compared to when the front entered the anal canal (F = 164.7, p < 0.005; F = 152.1, p < 0.005; F = 71.4, p < 0.005; respectively.). CONCLUSION: This study shows that Fecobionics obtained reliable data under physiological conditions. Mechanical features such as frictional force and stretch tensions were assessable during Fecobionics expulsion.