International Journal of Impotence Research (1997) 9, 11±16 ß 1997 Stockton Press All rights reserved 0955-9930/97 $12.00 Perineal nerve stimulation: role in penile erection A Sha®k Professor and Chairman, Department of Surgery and Experimental Research, Faculty of Medicine, Cairo University, Cairo, Egypt The effect of perineal nerve stimulation on penile erection was studied in ten dogs. Through a para- anal incision, the nerve was exposed in the ischiorectal fossa and a bipolar electrode was applied to it. A radiofrequency receiver was implanted subcutaneously in the abdomen. Upon perineal nerve stimulation, the corporeal pressure and EMG activity of the bulbo- and ischiocavernosus muscles increased; penile erection occured. With increased stimulus frequency up to 80 Hz, the pressure and muscles' response augmented while the latency and duration of response diminished. No further changes occurred above a frequency of 80 Hz (P > 0.05). Response was reproducible inde®nitely after an off-time of double the time of the stimulation phase. Penile erection upon perineal nerve stimulation is suggested to be an effect of corporeal pressure elevation resulting from cavernosus muscles' contraction. In terms of force and speed of contraction, a stimulus frequency of 80 Hz evokes the most adequate cavernosus muscles' contraction. Keywords: pudendal nerve; perineal nerve; penile erection; impotence; electrostimulation Introduction Material and Methods Most cases of erectile dysfunction (ED) have more The study was performed on ten male mongrel dogs than one cause which may work simultaneously.1 of a mean weight of 17.9 Æ 6.2 s.d. kg (range from 14± The cause could be psychologic, hormonal, neuro- 26.2 kg). The dogs were given a one-week period to genic, arterial and venous disorders.2±6 Several get accustomed to the facilities prior to inclusion in procedures for the treatment of ED are well the study. They were housed in cages and supplied established;7±10 however, the results are still unsatis- with water ad libitum, meat dog chow in the factory in many cases. morning and dry chow throughout the day. The perineal nerve is one of the 2 terminal The bipolar electrodes used were of a cuff type branches of the pudendal nerve.11,12 It innervates with a surface area of 2 mm2 each (Avery Laboratory, the external urethral sphincter, levator ani as well as Farmingdale, New York). Radiofrequency receivers bulbo- and ischiocavernosus muscles. Contraction (Avery) were implanted subcutaneously for activita- of the latter two muscles share in compression of the tion via an antenna by an externally adjustable penile erectile tissue and the deep dorsal veins, thus stimulator. helping to increase the intracavernosal pressure.13±19 The dogs were premedicated with acepromazine There is evidence that the bulbo- and ischiocaver- (0.15 mg/kg body weight) subcutaneously. They nosus muscles create rigidity by producing supra- were anesthetized with intravenous sodium pento- systolic intracavernous pressures reaching values as barbital (35 mg/kg body weight) with a bolus injec- high as 400 mmHg in man and 1000 mmHg in tion of 20±25 mg per hour to maintain adequate animals.13±19 Furthermore, rhythmic contractions of anesthesia with spontaneous respiration. All dogs these two muscles occur at orgasm and are believed were intubated to assist ventilation. Fluid main- to help in ejaculation.15,18±22 tenance consisted of intravenous infusion of normal The aim of this communication is to study the saline solution (2 ml/kg body weight per hour). The effect of stimulation of the perineal branch of the technique of pudendal nerve exposure was de- pudendal nerve on penile erection. Herein pre- scribed elsewhere,23±25 and will be mentioned sented are the results of this study. The study was brie¯y. With the dog in the lateral position, a para- approved by our Faculty Review Board. anal incision 1 cm from the anal ori®ce and at the base of the ischiorectal fossa was done, and the fossa was entered. The inferior rectal nerve was identi®ed Correspondence: Dr A Sha®k, 2 Talaat Harb Street, Cairo, when crossing the base of the ischiorectal fossa Egypt. lateromedially. The nerve was hooked with the Received 15 June 1996; accepted 15 October 1996 index ®nger and was followed to the pudendal nerve Perineal nerve stimulation in impotence A Sha®k 12 in the pudendal canal. Pulling the inferior rectal duced into the bulbo-cavernosus muscle which nerve with the index ®nger, stretched tight the overlay the bulb (Figure 1).26 Another needle pudendal nerve which could be easily identi®ed. electrode was introduced into the ischio-cavernosus The fascia of the pudendal canal was slit open, and muscle. The ischial ramus and overlying crus of the the pudendal nerve was freed from the canal. The penis were palpated and the needle electrode was perineal nerve was identi®ed with the help of a introduced into the ischiocavernosus muscle which magnifying binocular loupe and bright light as the lies over the crus. A ground electrode was applied to larger of the two terminal branches of the pudendal the thigh. The entrance of the needles into the nerve. It ran forward below the internal pudendal cavernosus muscles coincides with the appearance artery which separated it from the dorsal nerve of of EMG activity on the oscilloscopic screen and the the penis. Identi®cation was con®rmed by stimula- burst of activity heard from the loudspeaker. tion with a monopolar electrode connected to a The re¯ex response of the two cavernosus stimulator (Urys 800 model) which generated muscles on perineal nerve stimulation, recorded by square-wave DC current pulses with a pulse width the two needles, was displayed on the oscilloscope of 200 m s. of a standard EMG apparatus (Type MES, Medelec, The bipolar electrode was applied to the perineal Woking, UK). Films of the potentials were taken on nerve in the ischiorectal fossa, and the skin incision light-sensitive paper (Linagraph, Type 1895, Kodak) was closed. The radiofrequency receiver was im- from which measurements of motor unit potential planted subcutaneously through a skin incision in duration were made. The EMG signals were, in the abdomen of the animal. Stimulation was done addition, stored on an FM tape recorder (Type 7758 with a pulse width of 200 m s. The charge density A, Hewlett Packard, Waltham, Mass., USA) for applied to the nerve ranged between 2±6 m Ci/cm2/ further analysis as required. The normality of the phase. The response of the ischio- and bulbo- myoelectric activity of the two cavernosus muscles cavernosus muscles as well as the corporeal body had been tested in all dogs before performing the pressure to perineal nerve stimulation was deter- test. This was done by stimulating the muscle by one mined two weeks post-operatively. needle electrode and recording the response by another one which had already been inserted into the muscle. All dogs showed normal EMG activity of the two cavernosus muscles. EMG studies The EMG activity of the bulbo- and ischio-caverno- Manometric studies sus muscles was studied by means of a concentric needle electromyographic electrode (Type 13 L 49, DISA, Copenhagen, Denmark), 30 mm in length and The response of the corporeal pressure to perineal 0.65 mm in diameter. With the dog lying in the left nerve stimulation was determined. The site of lateral positon, the bulb of the penis was identi®ed needle insertion in penile body was sterilized with by palpation, and the needle electrode was intro- alcohol. A 21-gauge scalp vein needle was intro- Figure 1 Diagram illustrating the erectile skeletal muscle of the dog. Dorsal view (from Evans and Christensen26). Perineal nerve stimulation in impotence A Sha®k 13 duced into the corpus cavernosus and was con- nected to a strain gauge pressure transducer (Sta- tham 230b, Oxnard, Calif., USA). The aforementioned methods were repeated at least twice to assure reproducibility. The results were analysed statistically using ANOVA. Results No complications were encountered in the dogs during the study. The corporeal pressure at rest varied from 3±8 mm Hg (mean 4.2 Æ 1.1 s.d. mm Hg) (Table 1). The two cavernosus (bulbo- and ischio- cavernosus) muscles showed no resting EMG activ- Figure 2 EMG activity of the bulbocavernosus muscle upon ity (Figure 2, Table 2). perineal nerve stimulation. The muscle activity increased with Upon perineal nerve stimulation, the corporeal increased stimulus frequency. (a) basal activity; (b±d) EMG pressure and EMG activity of both cavernosus activity upon stimulation frequency of 20 Hz (b), 40 Hz (c) and 80 Hz (d). muscles increased and the penis lengthened and increased in diameter (Tables 1,2; Figures 2±5); the degree of increase was dependent on the frequency of electrical stimulation. With increasing stimulus registered at a frequency of 80 Hz. Nerve stimulation frequency, a rising corporeal pressure and EMG exceeding this frequency failed to effect further activity as well as increase in penile length and increase in both the corporeal pressure or caverno- diameter were recorded until a maximum rise was sus muscles' EMG activity (Tables 1,2). The penis at this frequency was fully erected and ®rm to touch, and the glans penis was engorged. Table 1 Response of corporeal pressure to different frequencies The duration of corporeal pressure and caverno- of perineal nerve stimulationa sus muscles' response and penile erection varied according to the stimulation frquency. It diminished Stimulus frequency (Hz) Corporeal pressure (mm Hg) with increased frequency to reach the shortest Range Mean duration at 80 Hz (Table 3, Figure 6) beyond which no reduction occurred although the stimulus fre- 0 (basal pressure) 3±8 4.2 Æ 1.1 quency was further increased.