Erectile mechanisms in man.

Increases in penile circumference during sleep-related erections in human subjects closely reflected increases in penile blood flow, and bursts of activity in the bulbocavernosus and ischiocavernosus muscles were temporally related to these increases. The penile arterial system and the perineal muscles appear to have important coordinated roles in human penile erection. Monitoring sleep-related erections and penile blood flow holds promise for the study of erectile mechanisms and dysfunction and for screening of drugs.