A study of the effect of straining on the cavernosus muscles: identification of ‘straining‐cavernosus reflex’ and its clinical significance

Summary Bulbo/ischiocavernosus muscles (BCM, ICM) were found to contract on straining. We investigated the hypothesis that straining effects cavernosus muscles’ contraction through a reflex action. The response of the BCM and ICM electromyographic (EMG) activity to increased intra‐abdominal pressure (straining) as recorded by the intravesical pressure was registered in 32 healthy volunteers (age 39.2 ± 10.3 years, 20 men, 12 women). The latency of the response was recorded. Responses were registered again in 17 subjects after individual anaesthetisation of urinary bladder, BCM, and ICM. BCM and ICM EMG activity increased progressively with increasing straining. It was not evoked after frequent successive straining. Latency decreased gradually with increase of straining intensity. Cavernosus muscles did not respond to straining after bladder and cavernosus muscles had been individually anaesthetised. Straining appears to effect cavernosus muscles’ contraction through the ‘straining‐cavernosus reflex’. Cavernosus muscles’ contraction produces compression of the penile and clitoral cavernous tissue. BCM contraction, furthermore, causes narrowing or closure of the vaginal introitus. The vagina is suggested to become a high pressure closed cavity which counteracts the increased intra‐abdominal pressure and uterine tendency to prolapse. Meanwhile, the elevated intravaginal pressure presumably supports the rectovaginal septum against the concomitant high intrarectal pressure.