Peripheral pacemakers and patterns of slow wave propagation in the canine small intestine in vivo

In an anesthetized, open-abdomen, canine model, the propagation pattern of the slow wave and its direction, velocity, amplitude, and frequency were investigated in the small intestine of 8 dogs. Electrical recordings were made using a 240-electrode array from 5 different sites, spanning the length of the small intestine. The majority of slow waves propagated uniformly and aborally (84%). In several cases, however, other patterns were found including propagation in the oral direction (11%) and propagation block (2%). In addition, in 69 cases (3%), a slow wave was initiated at a local site beneath the electrode array. Such peripheral pacemakers were found throughout the entire intestine. The frequency, velocity, and amplitude of slow waves were highest in the duodenum and gradually declined along the intestine reaching lowest values in the distal ileum (from 17.4 +/- 1.7 c/min to 12.2 +/- 0.7 c/min; 10.5 +/- 2.4 cm/s to 0.8 +/- 0.2 cm/s, and 1.20 +/- 0.35 mV to 0.31 +/- 0.10 mV, respectively; all p < 0.001). Consequently, the wavelength of the slow wave was strongly reduced from 36.4 +/- 0.8 cm to 3.7 +/- 0.1 cm (p < 0.001). We conclude that the patterns of slow wave propagation are usually, though not always, uniform in the canine small intestine and that the gradient in the wavelength will influence the patterns of local contractions.