[Manometric and electrophysiologic study procedures for the functional diagnosis of the internal anal sphincter]

In 49 subjects, simultaneous manometric and electrical investigations of the internal anal sphincter were performed. In resting state slow potentials were recorded in all subjects at a mean frequency of 20.6 +/- 0.6 cpm for needle electrodes and 16.0 +/- 0.5 cpm for surface electrodes in bipolar technique. The mean amplitude amounted to 380.6 +/- 28.4 microV respectively 411.6 +/- 27.8 microV for both electrical derivations. Whereas frequency was fairly constant, amplitude of slow potentials changed interindividually and intraindividually. Anal sphincter pressure did not correlate with amplitude and frequency of slow potentials. Sphincter relaxation by rectal distension was associated with inhibition of slow potentials. Both, percentage of inhibition of slow potentials and of sphincter relaxation were proportional to the volume of rectal distension. There was also a direct correlation between volume of rectal distension, depth of sphincter relaxation and length of inhibition of slow potentials. When 10 ml, 25 ml and 50 ml of air were used for rectal distension, duration of inhibition of slow potentials were 8.5 +/- 1.5 s, 12.5 +/- 1.6 s and 15.1 +/- 1.2 s (p less than 0.05) for bipolar tracings, depth of relaxation respectively 15.0 +/- 1.2 mmHg, 26.1 +/- 2.3 mmHg and 36.6 +/- 2.2 mmHg (p less than 0.05). The association of inhibition of slow potentials with sphincter relaxation suggests that maintenance of sphincter tone is governed by slow potentials. This proves the diagnostic value of electromyography of the internal sphincter.