Method for determining individual contributions of voluntary and involuntary anal sphincters to resting tone

With simultaneous recordings of the external anal sphincter EMG activity and the anal resting pressure, it is possible to estimate the isolated part played by the internal anal sphincter on the resting pressure by means of a correlation calculation with extrapolation to zero EMG amplitude. The value of the method was proven by comparative investigations in conscious and curarized patients under general anesthesia. In a group of 20 normal people we found that the part the internal sphincter has in the total resting pressure was 75 per cent. Because of the very low standard deviation of +/- 5.5 per cent the method is superior to others for comparing various anal disorders.