Spontaneous Anorectal Pressure Activity: Evidence of Internal Anal Sphincter Contractions in Response to Rectal Pressure Waves

Abstract

To characterize spontaneous anorectal pressure activity and a possible relation between the activity in the rectum and the anal canal, 11 healthy female volunteers were investigated. Resting activities were obtained during 1-h recordings with a multichannel perfused catheter measuring the pressure 1, 2, 3, 7, and 8 cm from the anal verge. in five subjects sequences of rhythmic rectal pressure waves with amplitudes exceeding the maximal anal resting pressure coincided with a similar internal anal sphincter activity, preventing rectal pressure from exceeding the anal pressure at any point. the mean frequency was 5 × min⁻¹ (range, 3–6 × min⁻¹). This may well be a reflex mechanism by which the internal anal sphincter prevents incontinence in the resting state. Low-frequency pressure waves, not previously described, were detected in four women. These pressure waves were attributed to the internal anal sphincter and were named ultra-slow waves type II. the mean frequency and amplitude were 0.16 × min⁻¹ (range, 0.15–0.17 × min₋₁) and 24cm H₂O (range, 11–41 cm H₂O), respectively. the function of these pressure waves is unknown.

Key Words:

• Anorectal manometry
• anorectal pressure and motility
• pressure recordings of the anorectum