SPARC: Mechanophysiological analysis of anorectal function using simulated feces

Abstract

IntroductionDefecation is a complex process that may easily get disturbed. Defecatory disorders are commonly diagnosed with anorectal manometry and the balloon expulsion test. Recently we developed a simulated electronic stool named Fecobionics that integrates several tests and simultaneously assesses pressures, orientation, bending and geometry during expulsion of the device. The aim was to use new analytical tools to calculate frictional force and tension during expulsion of Fecobionics in normal subjects.MethodsThe 12‐cm‐long 12mm OD Fecobionics contained pressure sensors at the front, rear and inside a bag, two motion processor units for measurement of orientation and bending, and impedance rings for measurement of eight cross‐sectional areas/diameters. The geometry of the bag was computed from the cross‐sectional area measurements. Eight presumed normal subjects (4F/4M) defecated Fecobionics. High‐resolution anorectal manometry and the balloon expulsion test confirm that the subjects were normal. The bending angle of the device, the frictional force between the probe and the surrounding tissue, the membrane tension, and the probe expulsion velocity were calculated.ResultsData examples are shown in figure 1. The bending angle and pressures changed during expulsion of the device with the maximum pressure recorded at the rear. The change in bending angle during defecation was approximately 40 degrees. The averaged circumferential tension, longitudinal tension and friction force change were associated with the pressure difference between the rear and the front ends (R2=0.878±0.011, p<0.005; R2=0.885±0.01, p<0.005; R2=0.411±0.007, p<0.005; respectively). The peak tensions and friction force immediately before expulsion of the rear were significantly higher than that when the front entered into the anal canal (circumferential and longitudinal tension p<0.005, and friction force p<0.05).ConclusionsFecobionics obtained reliable data under physiological conditions. Mechanical features such as frictional force and membrane tension were assessable during Fecobionics expulsion using the developed analysis.Support or Funding InformationNIH SPARC FundingTop panels: The geometry and the membrane tension distributions of the Fecobionics during expulsion. Bottom panel: The recorded pressures and bending angles in the Fecobionics during expulsion.Figure 1Acknowledgements.Abbey Chen, Cherry Wong, Wingwah Leung, Kaori Futaba, Tony Mak and Simon Ng are thanked for providing data.