Nocturnal penile rigidity measured by the snap-gauge band.

Nocturnal penile tumescence is used commonly to evaluate erectile dysfunction. However, this test is not equivalent to erection since it measures circumferential change only rather than the crucial variable of penile rigidity. We present a new concept in the measurement of penile rigidity--the capability of a patient during sleep to break a band furnished with pre-set snap-gauges with different release-force constants applied around the penile shaft. The snap-gauge band was tested simultaneously with the recording of nocturnal penile tumescence measuring penile rigidity rather than tumescence.