Prolonged anorectal manometry and external anal sphincter electromyography in ambulant human subjects

We have developed a method for prolonged combined anorectal manometry and electromyography (EMG) of the external anal sphincter in ambulant subjects. Fourteen healthy volunteers were studied for a total of 284 hr (mean of 20.3 hr/subject). Anorectal manometry was performed using a probe with twin pressure sensors. EMG was recorded by one indifferent and two differential silver-silver chloride surface electrodes positioned 0.5-0.75 cm from the anus on either side. The sampling reflex occurred frequently and was significantly (P less than 0.001) more common during wakefulness than during sleep and also following meals than during fasting (P less than 0.01). The passage of flatus was associated with transient relaxation of the anal canal in 19% of episodes. In contrast, there was a contractile episode with no preceding relaxation in 75% of episodes. The anal sphincter had significantly (P less than 0.05) more action potentials (APs) during the day (12.8 +/- 3.2 APs/10 min) than at night (1.6 +/- 1.3 APs/10 min). During micturition, anal canal pressure rose (mean 15 mm Hg) in association with powerful external anal sphincter contractions. Our data show that, normally, contractile activity both in the anal canal and external anal sphincter maintains fecal continence during micturition and the passage of flatus. The technique should lead to a better understanding of the normal mechanisms of fecal continence during waking and sleep and of the pathophysiology of disorders of anorectal function.