Electrophysiology of human colon motility in health and disease.
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Recent years have seen a number of studies measuring electrical activities of the human colon muscle layers. In vitro studies have enhanced our understanding of myogenic control of colon motility. In vivo studies have suggested a relationship between patterns of electrical activities and the transport of colon contents. This chapter describes the patterns of electrical and motor activity that the human colon can perform depending on the nature and intensity of the stimulus, using recent in vitro and in vivo data. In vitro studies with human tissue have shown differences between the electrical activity of the longitudinal and circular muscles. They have also revealed the unique nature of the electrical control activity of the circular muscle of human colon. The electrical oscillatory activity of this layer is variable in frequency from 1 to 60 cpm, variable in amplitude, and not omnipresent. Furthermore, the activity is sensitive to stretch and markedly altered by excitatory and inhibitory substances. In vivo data, especially spike action potential recordings for 24 h, have revealed patterns of electrical activity related to intake of meals, sleep, and also constipation. The limitations of some intraluminal techniques to record electrical activity are discussed. Further studies are needed to accurately relate in vivo activities to cellular events recorded in vitro, and to relate these to altered patterns of activity in disease. The suggestion is made that a relevant in vivo assessment of the colonic motility of a patient can only be achieved by long-lasting (24-h) studies, because of the large variability in the hour-to-hour colonic activity. Timing of experimental drug intervention is important since colonic motility undergoes diurnal changes. Recent studies into profiles of electrical and motor activity in irritable bowel syndrome (IBS) suggest that there is not a typical IBS myogenic activity. Rather, patterns of electrical activity can be related to the symptoms of IBS: diarrhea and constipation. Recent electrophysiologic data on Hirschsprung's disease reveal absence of intrinsic inhibitory innervation in the aganglionic segment. In vitro studies on tissue from diverticular disease patients show abnormal myogenic activity.
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