Role of the Perineal Muscles in Micturition

Abstract

Abstract The role of the superficial (STPM) and deep (DTPM) transverse perineal muscles during micturition is poorly addressed in the literature. We investigated the hypothesis that, at micturition, reflex contraction of the 4 perineal muscles occurs, which acts to fix the perineal body in its anatomic position and support the perineal floor and prevent its descent. The electromyographic (EMG) activity of STPMs and DTPMs as well as vesical pressure response to vesical balloon distension with carbon dioxide in increments of 20 mL were recorded in 26 healthy volunteers (16 men, 10 women, age 34.6 ± 6.7 years [mean ± standard deviation]). The test was repeated after individual anesthetization of the urinary bladder and perineal muscles with lidocaine and again after using saline instead of lidocaine. Big volumes of vesical balloon distension produced an increase of perineal muscles’ EMG activity and vesical pressure, both of which rose progressively with incremental increase of vesical distension. The latency exhibited gradual decrease on progressive increase of vesical distension. Perineal muscles did not respond to vesical distension after individual anesthetization of urinary bladder or perineal muscles but did respond to saline administration. Muscle response was similar from both sides. Vesical contraction at micturition appears to effect perineal muscles’ contraction. This action is suggested to be mediated through a reflex which we call “vesicoperineal reflex.” Perineal muscles’ contraction at micturition presumably supports perineal floor and protects perineal muscles from the high pressure induced by straining.