Effect of straining on perineal muscles and their role in perineal support: Identification of the straining-perineal reflex

Objectives. The functional activity of the superficial (STPM) and deep (DTPM) transverse perineal muscles is poorly addressed in the literature. We investigated the hypothesis that these muscles act to support the perineum during increased intraabdominal pressure (LAP). Methods. 46 healthy volunteers (mean age 30.4 +/- 1.2 y, 20 nulliparous women) were studied. The UP was recorded by a manometric catheter introduced into the rectum. The response of the perineal muscles to straining (sudden by coughing and slow by Valsalva's maneuver) was registered by a needle electrode inserted into the STPM and DTPM separately. The response was recorded again after individual anesthetization of the perineal muscles and rectum using Xylocaine. The test was repeated using saline instead of Xylocaine and was performed on both sides. Results. Straining (sudden or slow sustained) effected increase of the rectal pressure and the motor unit action potentials of both perineal muscles. The higher rectal pressure was increased by straining, the higher the motor unit action potentials increased MUAPs. The latency showed a gradual decrease upon incremental rectal pressure elevation. The perineal muscles did not respond to straining after individual anesthetization of the rectum and perineal muscles, but did respond to saline administration. The response was similar from muscles on both sides. Conclusion. Perineal muscle contraction on straining postulates a reflex relationship that we call the straining-perineal reflex. We suggest that this reflex, which results in perineal muscle contraction, supports the perineum against the increased UP induced by straining and the tendency of the perineum to descend. The results warrant further study of the role of the straining-perineal reflex in the genesis of perineal functional disorders. (C) 2003 Elsevier Inc. All rights reserved.