The relationship between external anal and external urethral sphincter activity in continent women

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Abstract
The relationship between the external anal sphincter and the periurethral sphincter muscles is an unresolved issue. Recordings of the external anal sphincter (EAS) are commonly used to indicate the responses of the urethral sphincter during urodynamic evaluations and in biofeedback procedures for the treatment of urinary incontinence. This study examined the validity of using anal sphincter training to teach control of the external urethral sphincter. Subjects were 5 continent women, aged 37–51 years, who reported being free of all urologic symptoms. Using visual biofeedback of anal sphincter pressure, subjects were trained to voluntarily contract the sphincter to four amplitudes: 5, 10, 15, and 20 mmHg (6.8, 13.6, 20.4, and 27.2 cmH2O). Then they were guided through a series of controlled anal sphincter contractions, while the response of the urethral sphincter was measured using surface electrodes embedded in a Foley catheter. At each of four bladder volumes, subjects performed 16 contractions (four contractions at each of the four amplitudes). The order of contractions was counterbalanced, using a Latin square design. The results show a strong, statistically significant, monotonic relationship between the magnitude of anal sphincter contraction (pressure) and the level of urethral sphincter electromyographic (EMG) activity. The results support the use of the external anal sphincter as an indicator of urethral sphincter activity for the purpose of conducting biofeedback in the treatment of urinary incontinence.