Colonic motility in humans—a growing understanding

As yet, there is limited information about the relationship of colonic motility to colonic flow or transit. The overall flow in the colon is slow and highly variable. The measurement of total and segmental transit time is essential for the differentiation of motor disorders associated with delayed transit. Rapid movements of colonic contents (mass movements) occur only a few times during the day. Their motor equivalent is the giant contraction which migrates in the aborad direction at relatively high velocity. Motor activity in the colon is highly variable, with periods of contraction and motor quiescence. Contractions occur at different frequencies ranging from 2 to 13 cycles per minute. High frequency contractions are stationary. Their myo-electrical equivalent is short spike bursts. Long spike bursts result in sustained, low frequency contractions, which may migrate in both directions. Technological advances now make it possible to obtain ambulant manometric recordings from the colon for 24h. Such studies show a circadian variation in colonic motility with increases of activity after meals and after awakening. Motor disorders of the colon are not associated with specific abnormal motor patterns. Rather, they are due to changes in the occurrence of motor patterns seen in health. In constipated patients with slow colonic transit the suppression of strong peristaltic activity is the most plausible common pathogenetic mechanism. In diarrhoeal states, pro-pulsive activity such as the giant migrating contractions may be a major mechanism which promotes the passage of stools. There is no agreement that there is disordered basal colonic motor activity in IBS. There is, however, increasing evidence that in IBS the colon responds abnormally to eating, certain forms of stress and distension, and that this may relate to symptoms. The psychopathology of IBS patients is apparently the most important factor in the health care-seeking behaviour of the patients. No specific therapy has yet been shown to be convincingly effective.