Ejaculation induced by penile vibratory stimulation in men with spinal cord injuries. The importance of the vibratory amplitude

A total of 66 men with a spinal cord injury (SCI) and ejaculatory dysfunction were included in two different but comparable study populations I (n = 25) and II (n = 41). The level of lesion ranged from C2 to L1 (44 complete). Penile vibratory stimulation (PVS) to induce ejaculation was performed with two different types of vibrators in population I and considerably different ejaculation rates (antegrade+retrograde) occurred depending on the vibrator used. Our experience suggested discrepancies between the manufacturers' specifications and the actual vibrator outputs concerning frequencies and peak-to-peak amplitudes. Retrospectively performed determinations revealed that the manufacturers' specifications regarding the frequencies were accurate whereas the peak-to-peak amplitudes were inaccurate. With a frequency of 100 Hz and determined peak-to-peak amplitudes of 1 mm and 2.5 mm, ejaculation rates of 32% and 96%, respectively, were obtained in population I. This indicates that an adequate peak-to-peak amplitude is essential to exceed an 'ejaculatory threshold' in the majority of SCI men. Furthermore, an ejaculation rate of 83% obtained in a subsequent prospective study of 41 SCI men (population II) verified that a frequency of 100 Hz and a peak-to-peak amplitude of 2.5 mm seems to approach the ideal vibrator output. The ejaculation responses obtained by JS (first author) were reproduced when the PVS was performed by the patient or his partner, indicating that the vibrator output is more important than PVS experience. No major adverse reactions due to autonomic dysreflexia were observed. The lowest level of SCI where antegrade or retrograde ejaculation occurred was T9 and L1, respectively. No absolute predictors for ejaculatory success or failure in relation to patient age, years since lesion, completeness of SCI, urinary bladder management method, hip flexion and bulbocavernous reflexes were observed. Therefore, most SCI men with ejaculatory dysfunction should be considered candidates for PVS.