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Background and aims: Invoked peristaltic contractions and movement of solid content have not been attempted in normal canine colon. The purpose of this study was to determine if movement of solid content through the colon could be produced by microprocessor controlled sequential stimulation. Methods: The study was performed on six anaesthetised dogs. At laparotomy, a 15 cm segment of descending colon was selected, the proximal end closed with a purse string suture, and the distal end opened into a collecting container. Four sets of subserosal stimulating electrodes were implanted at 3 cm intervals. The segment of bowel was filled with a mixture of dog food and 50 plastic pellets before each of 2-5 random sessions of non-stimulated or stimulated emptying. Propagated contractions were generated using microprocessor controlled bipolar trains of 50 Hz rectangular voltage having 20 V (peak to peak) amplitude, 18 second stimulus duration, and a nine second phase lag between stimulation trains in sequential electrode sets. Results: Electrical stimulation using the above mentioned parameters resulted in powerful phasic contractions that closed the lumen. By phase locking the stimulation voltage between adjacent sets of electrodes, propagated contractions could be produced in an aboral or orad direction. The number of evacuated pellets during the stimulation sessions was significantly higher than during the non-stimulated sessions (p<0.01). Conclusions: Microprocessor controlled electrical stimulation accelerated movement of colonic content suggesting the possibility of future implantable colonic stimulators.

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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 pairs 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 5mm 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 3ms time constant. Real-time simulation of the current drawn by the smooth muscle during 10 V/50Hz bipolar voltage stimulation was performed. The integrated electromechanical model facilitates the quantification of microprocessor-controlled phasic colonic contractions.

Three-dimensional (3-D) object-oriented models are needed for optimizing gastric electrical stimulation by performing virtual computer experiments. The aim of the study was to create a 3-D object-oriented electromechanical model of the stomach in vivo for the purpose of microprocessor controlled functional stimulation. The stomach was modeled using coaxial truncated conoids as objects. The strength of an external stimulating electric field generated by circumferentially implanted wire electrodes is related to artificial neurogenic and myogenic control of smooth muscle depolarization and contraction. Variation of the field strength modulates the frequency and concentration of acetylcholine release, as well as the transmembrane voltage of the muscle cells. Mechanical response of the stimulated tissue was quantified by two parametric functions of the electric field strength representing the relative contractile force and geometrical displacement of the gastric surface. Data from previously conducted canine experiments were used to test the validity of the model. The model was applied to simulate contractions with different positions, orientation and number of the circumferentially implanted stimulating electrodes. The model combined most of the existing theoretical and experimental findings concerning functional gastric stimulation and can be utilized as a flexible tool for virtual medical tests involving external high-frequency (50 Hz) neural stimulation.