Three-dimensional static parametric modelling of phasic colonic contractions for the purpose of microprocessor-controlled functional stimulation

The study aimed at creating an integrated electromechanical model of invoked phasic contractions in canine colon during direct high frequency voltage stimulation. The model utilized data obtained from two large anaesthetized dogs that underwent laparotomy and serosal implantation of two circumferential electrode fairs into a distal segment of the left colon. The strength distribution of the stimulating electric field was analysed over a cylindrical mesh-surface grid modelling the interrogated colonic segment. Recordings of the stimulating current were utilized to model smooth, muscle depolarization using linearized macroscopic tissue conductivity. The invoked contractile stress was related to the stimulating electric field strength using an exponential sigmoid function. Artificially produced occlusion of the lumen was derived for a pair of 5 mm electrodes positioned on a cylindrical mesh-surface of 2 cm diameter and 15 cm length. The model simulated contractions invoked by stimuli of different amplitude (up to 12 V) with 98.6% accuracy of approximation. Macroscopic tissue conductivity was modelled as a combination of two first-order exponential terms involving a 3 ms time constant. Real-time simulation of the current drawn by the smooth muscle during 10 V/50 Hz bipolar voltage stimulation was performed. The integrated electromechanical model facilitates the quantification of microprocessor-controlled phasic colonic contractions.