Electrophysiological aspects of human sphincter function

In order to investigate the electrophysiology of the human internal anal sphincter and two current concepts of sphincter function, simultaneous manometric and electrical recordings were made from circular smooth muscle of the internal anal sphincter in the resting state and during reflexly induced sphincter relaxation. Three groups were studied: seven normal subjects, 25 patients with functional bowel disease, and seven patients with external sphincter paralysis due to spinal cord lesions. In the resting state slow waves of alternating potential (basic electrical rhythm or BER) were recorded in all subjects. Two types of waves were present, a constant sinusoidal pattern or a spindleshaped pattern. Either pattern was consistent for a given individual. Frequency of BER in the internal sphincter was higher than that recorded in any other gastrointestinal muscle. Our findings indicate that the BER recorded from the internal anal sphincter originates in this muscle. This activity may represent a specialized feature of sphincteric muscle since BER cannot be recorded from isolated nonsphincteric circular muscle. Reproduction of the two patterns of BER by an electronic model suggests that BER, as recorded by this technique, results from a summation of a number of electrically active cells in contact with the recording electrodes. Inhibition of BER occurred when sphincter relaxation was reflexly induced by rectal distension. Both inhibition of BER and degree of sphincter relaxation were proportional to the strength of rectal stimulation, suggesting that strength of stimulus determines the number of active cells which are inhibited. The associations of high frequency of BER with high resting pressure, and of inhibition of BER with sphincter relaxation suggests that maintenance of sphincter tone is an active process that is governed by BER.