Intermittent bursts of motor activity in the human rectum and absence of propagation

Manometric recordings from multiple sites were performed to determine the propagating properties of intermittent bursts of motor activity in the human rectum. Pressure changes were recorded simultaneously at 12.5 cm, 10 cm and 7.5 cm from the anal verge in nine healthy subjects for a total recording time of 32 hours, each study lasting 2.7-4.8 hours. The burst motor activity was identified on 19 occasions in 7 of 9 subjects at 12.5 cm; 26 occasions in all subjects at 10 cm; and 11 occasions in 3 of 9 subjects at 7.5 cm. In most cases, the burst motor activity was observed at a single recording site while other recording sites were quiescent. It did not appear to migrate in either an oral or aboral direction. The burst motor activity contained in part runs of pressure waves with a regular frequency: at 12.5 and 10 cm of the recording site, runs of regular pressure waves were dominated by a frequency of 2.5-5 cycle per minute, whereas those at 7.5 cm occurred with a higher frequency and a lower amplitude as compared with the more proximal recording sites. No evidence of propagation of each pressure wave was seen even when the burst occurred simultaneously at more than two recording sites. These results suggest that the intermittent bursts of rectal motor activity occur locally and do not propagate in either on oral or aboral direction. They appear dissimilar to the interdigestive migrating motor complex observed in the more proximal part of the gut.