Perineal nerve stimulation: role in penile erection

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1 International Journal of Impotence Research (1997) 9, 11±16 ß 1997 Stockton Press All rights reserved /97 $12.00 Perineal nerve stimulation: role in penile erection 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 paraanal 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 Most cases of erectile dysfunction (ED) have more than one cause which may work simultaneously. 1 The cause could be psychologic, hormonal, neurogenic, arterial and venous disorders. 2±6 Several procedures for the treatment of ED are well established; 7±10 however, the results are still unsatisfactory in many cases. The perineal nerve is one of the 2 terminal branches of the pudendal nerve. 11,12 It innervates the external urethral sphincter, levator ani as well as bulbo- and ischiocavernosus muscles. Contraction of the latter two muscles share in compression of the penile erectile tissue and the deep dorsal veins, thus helping to increase the intracavernosal pressure. 13±19 There is evidence that the bulbo- and ischiocavernosus muscles create rigidity by producing suprasystolic intracavernous pressures reaching values as high as 400 mmhg in man and 1000 mmhg in animals. 13±19 Furthermore, rhythmic contractions of these two muscles occur at orgasm and are believed to help in ejaculation. 15,18±22 The aim of this communication is to study the effect of stimulation of the perineal branch of the pudendal nerve on penile erection. Herein presented are the results of this study. The study was approved by our Faculty Review Board. Correspondence: Dr, 2 Talaat Harb Street, Cairo, Egypt. Received 15 June 1996; accepted 15 October 1996 Material and Methods The study was performed on ten male mongrel dogs of a mean weight of s.d. kg (range from 14± 26.2 kg). The dogs were given a one-week period to get accustomed to the facilities prior to inclusion in the study. They were housed in cages and supplied with water ad libitum, meat dog chow in the morning and dry chow throughout the day. The bipolar electrodes used were of a cuff type with a surface area of 2 mm 2 each (Avery Laboratory, Farmingdale, New York). Radiofrequency receivers (Avery) were implanted subcutaneously for activitation via an antenna by an externally adjustable stimulator. The dogs were premedicated with acepromazine (0.15 mg/kg body weight) subcutaneously. They were anesthetized with intravenous sodium pentobarbital (35 mg/kg body weight) with a bolus injection of 20±25 mg per hour to maintain adequate anesthesia with spontaneous respiration. All dogs were intubated to assist ventilation. Fluid maintenance consisted of intravenous infusion of normal saline solution (2 ml/kg body weight per hour). The technique of pudendal nerve exposure was described elsewhere, 23±25 and will be mentioned brie y. With the dog in the lateral position, a paraanal 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 when crossing the base of the ischiorectal fossa lateromedially. The nerve was hooked with the index nger and was followed to the pudendal nerve

12 in the pudendal canal. Pulling the inferior rectal nerve with the index nger, stretched tight the pudendal nerve which could be easily identi ed.

2 12 in the pudendal canal. Pulling the inferior rectal nerve with the index nger, stretched tight the pudendal nerve which could be easily identi ed. The fascia of the pudendal canal was slit open, and the pudendal nerve was freed from the canal. The perineal nerve was identi ed with the help of a magnifying binocular loupe and bright light as the larger of the two terminal branches of the pudendal nerve. It ran forward below the internal pudendal artery which separated it from the dorsal nerve of the penis. Identi cation was con rmed by stimulation with a monopolar electrode connected to a stimulator (Urys 800 model) which generated square-wave DC current pulses with a pulse width of 200 m s. The bipolar electrode was applied to the perineal nerve in the ischiorectal fossa, and the skin incision was closed. The radiofrequency receiver was implanted subcutaneously through a skin incision in the abdomen of the animal. Stimulation was done with a pulse width of 200 m s. The charge density applied to the nerve ranged between 2±6 m Ci/cm 2 / phase. The response of the ischio- and bulbocavernosus muscles as well as the corporeal body pressure to perineal nerve stimulation was determined two weeks post-operatively. EMG studies The EMG activity of the bulbo- and ischio-cavernosus muscles was studied by means of a concentric needle electromyographic electrode (Type 13 L 49, DISA, Copenhagen, Denmark), 30 mm in length and 0.65 mm in diameter. With the dog lying in the left lateral positon, the bulb of the penis was identi ed by palpation, and the needle electrode was introduced into the bulbo-cavernosus muscle which overlay the bulb (Figure 1). 26 Another needle electrode was introduced into the ischio-cavernosus muscle. The ischial ramus and overlying crus of the penis were palpated and the needle electrode was introduced into the ischiocavernosus muscle which lies over the crus. A ground electrode was applied to the thigh. The entrance of the needles into the cavernosus muscles coincides with the appearance of EMG activity on the oscilloscopic screen and the burst of activity heard from the loudspeaker. The re ex response of the two cavernosus muscles on perineal nerve stimulation, recorded by the two needles, was displayed on the oscilloscope of a standard EMG apparatus (Type MES, Medelec, Woking, UK). Films of the potentials were taken on light-sensitive paper (Linagraph, Type 1895, Kodak) from which measurements of motor unit potential duration were made. The EMG signals were, in addition, stored on an FM tape recorder (Type 7758 A, Hewlett Packard, Waltham, Mass., USA) for further analysis as required. The normality of the myoelectric activity of the two cavernosus muscles had been tested in all dogs before performing the test. This was done by stimulating the muscle by one 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. Manometric studies The response of the corporeal pressure to perineal nerve stimulation was determined. The site of needle insertion in penile body was sterilized with 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 Christensen 26).

3 duced into the corpus cavernosus and was connected to a strain gauge pressure transducer (Statham 230b, Oxnard, Calif., USA). The aforementioned methods were repeated at least twice to assure reproducibility. The results were analysed statistically using ANOVA. 13 Results No complications were encountered in the dogs during the study. The corporeal pressure at rest varied from 3±8 mm Hg (mean s.d. mm Hg) (Table 1). The two cavernosus (bulbo- and ischiocavernosus) muscles showed no resting EMG activity (Figure 2, Table 2). Upon perineal nerve stimulation, the corporeal pressure and EMG activity of both cavernosus 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 frequency, a rising corporeal pressure and EMG activity as well as increase in penile length and diameter were recorded until a maximum rise was Table 1 Response of corporeal pressure to different frequencies of perineal nerve stimulation a Stimulus frequency (Hz) Corporeal pressure (mm Hg) Range Mean 0 (basal pressure) 3± ± * 40 35± * 60 50± ** 80 60± ** ± ** a Values are given as mean s.d. * P < 0.001; ** P < Figure 2 EMG activity of the bulbocavernosus muscle upon perineal nerve stimulation. The muscle activity increased with increased stimulus frequency. (a) basal activity; (b±d) EMG activity upon stimulation frequency of 20 Hz (b), 40 Hz (c) and 80 Hz (d). registered at a frequency of 80 Hz. Nerve stimulation exceeding this frequency failed to effect further increase in both the corporeal pressure or cavernosus muscles' EMG activity (Tables 1,2). The penis at this frequency was fully erected and rm to touch, and the glans penis was engorged. The duration of corporeal pressure and cavernosus muscles' response and penile erection varied according to the stimulation frquency. It diminished with increased frequency to reach the shortest duration at 80 Hz (Table 3, Figure 6) beyond which no reduction occurred although the stimulus frequency was further increased. The latency of the response also decreased with the increase of the stimulation frequency, but beyond 80 Hz showed insigni cant changes (P > 0.05) (Table 2, Figure 7). After dropping to the baseline, the response was resumed following an off-time which was found to be about twice the time of the stimulation phase. If re-stimulation was performed after a pause less than Table 2 EMG activity of the bulbo- and ischiocavernosus muscles upon perineal nerve stimulation at different frequencies. The latency is included a Stimulus frequency (Hz) Bulbocavernosus muscle Ischiocavernosus muscle Potentials (mv) Latency (ms) Potentials (mv) Latency (ms) Range Mean Range Mean Range Mean Range Mean Basal activity ± ** 2.2± ± ** 2.2± ± ** 2.0± * 92± ** 2.1± * ± *** 1.9± ** 145± *** 2.0± ** ± *** 1.7± ** 186± *** 1.8± ** ± *** 1.7± ** 172± *** 1.8± ** a Values are given as mean s.d. * P > 0.05; ** P < 0.05; *** P < 0.01.

4 14 Table 3 Relation of frequency of stimulus to stimulation phase a Stimulus frequency (Hz) Contraction time (s) Range Mean 20 6± ± * 60 2± ** 80 1± ** 100 1± ** a Values are given as mean s.d. * P < 0.05; ** P < Figure 3 EMG activity of the ischio-cavernosus muscle upon perineal nerve stimulation. The muscle activity increased with incrreased stimulus frequency. (a) basal activity; (b±d) EMG activity upon stimulation frequency of 20 Hz (b), 40 Hz (c) and 80 Hz (d). that time, the response was weaker. With repetition of the stimulus, the response was reproducible inde nitely, provided that the period of off-time was double the time of the stimulation phase. Discussion Figure 4 Corporeal pressure response to perineal nerve stimulation at different frequencies. The pressure increased with increased frequency up to 80 Hz, above which there was no signi cant pressure rise. Perineal nerve stimulation led to increase of both the corporeal pressure and EMG activity of the bulbo- and ischio-cavernosus muscles. It seems that the increased corporeal pressure is an effect of cavernosus muscles' contraction. Upon contraction, the cavernosus muscles compress the crura as well as the bulb of the penis. Furthermore, the hair-pin arrangement of the ischiocavernosus muscles functions to compress not only the penile corpora but also the dorsal penile veins, 27 with a resulting diminution of venous drainage along the dorsal penile veins. The corporeal pressure rise and cavernosus muscles contraction led to penile erection. They increased with the increase of the stimulation frequency up to 80 Hz, above which no further rise occurred. Moreover, the latency and stimulation phase decreased with the increase of the stimulation frequency. These results indicate that the quality of cavernosus muscles' contraction and consequently the corporeal pressure is dependent on the stimulation frequency and that the muscles respond more rapid and fatigue earlier with increased frequency. Furthermore, the study has shown that in terms of force and speed of contraction, a stimulus frequency of 80 Hz evokes the most adequate cavernosus muscles' contraction. Meanwhile, an off-time of double the stimulation phase allows re-stimulation inde nitely without fatigue. Conclusions Figure 5 Motor unit action potentials of the bulbo- and ischiocavernosus muscle upon perineal nerve stimulation at different frequencies. The activity increased with increased frequency up to 80 Hz, above which there was no signi cant increase of activity. Perineal nerve stimulation initiates penile erection by means of cavernosus muscles' contraction and consequent corporeal pressure elevation. The re-

5 References 15 Figure 6 The stimulation phase upon perineal nerve stimulation. It diminished with increased frequency up to 80Hz, above which there was insigni cant decrease. Figure 7 The latency of the bulbo- and ischiocavernosus muscle response to perineal nerve stimulation. It diminished with increased frequency up to 80 Hz, above which there was insigni cant decrease. corded corporeal pressure could achieve an adequate penile rigidity and vaginal penetration. However, further studies are needed to evaluate the condition of the smooth musculature surrounding the cavernosus spaces of the corpora cavernosa, and the degree of penile rigidity. The role of perineal nerve stimulation in evoking erection in man is an ongoing study and will be reported later on. Acknowledgements Waltraut Reichelt and Margot Yehia assisted in preparing the manuscript. 1 Lo Piccolo J. Management of psychologic erectile failure. In: Tanagho EA, Lue TF, Dale McClure R (eds). Contemporary Management of Impotence and Infertility. Williams & Wilkins: Baltimore, USA, 1988, pp Lo Piccolo J. Diagnosis and treatment of male sexual dysfunction. J Sex Marital Ther 1986; 11: 215± Bors E, Comarr AE. Neurological disturbance of sexual function with special reference to 529 patients with special cord injury. Urol Surv 1960; 10: 191± Bancroft J, Wu FCW. Changes in erectile responsiveness during androgen therapy. Arch Sex Behav 1983; 12: 59±66. 5 Michal V, Kovac J, Belan A. Arterial lesions in impotence. Phalloarteriography Int Angiol 1984; 3: 247± Ebbehoj I, Wagner G. Insuf cient penile erection due to abnormal drainage of cavernous bodies. Urology 1979; 12: 507± Virag R. Intracavernous injection of papaverine for erectile failure. Lancet 1982; 2: Goldstein I. Arterial revascularization procedures. Semin Urol 1986; 4: 252± Fishman IJ, Shabsign R, Scott PB. A comparison of the hydro ex and in atable penile prothesis. J Urol 1986; 135: 358± Padma-Nathan H, Payton T, Goldstein I. Treatment of organic impotence: alternatives to the penile prothesis. American Urological Association Update Series, Vol. 10±11, Warwick R, Williams PL. Neurology. In: Warwick R, Williams PL (eds). Gray's Anatomy, 35th edn, Longman: London, 1975, pp Sha k A, El-Sherif MB, Youssef AE, El-Sibai Olfat. Surgical Anatomy of the Pudendal Nerve and its Clinical Implications. Clin Anat 1995; 8: 110± Karacan I, Aslan C, Hirshkowitz M. Erectile mechanism in man. Science 1983; 220: 1080± Schmidt MH et al. Corpus spongiosum penis pressure and perineal muscle activity during re exive erections in the rat. Amer J Physiol 1995; 269: 904± Sha k A. Response of the urethral and intracorporeal pressure to cavernosus muscle stimulation: role of the muscles in erection and ejaculation. Urology 1995; 46: 85± Lavoisier P, Aloui R, Iwaz J, Kokkidis MJ. The physiology of penile rigidity. Prog Urol 1992; 2: 119± Schmidt MH, Schmidt HS. The ischiocavernosus and bulbospongiosus muscles in mammalian penile rigidity. Sleep 1993; 16: 171± Gerstenberg TC, Levin RJ, Wagner G. Erection and ejaculation in man. Assessment of the electromyographic activity of the bulbocavernosus and ischiocavernosus muscles. Br J Urol 1990; 65: 395± Claes H, Bijnens B, Baert L. The hemodynamic in uence of the ischiocavernosus muscles on erectile function. J Urol 1996; 156: 986± Semans JH, Langworthy DR. Observations on the neurophysiology of sexual function in the male cat. J Urol 1938; 40: 836± Whitelaw GP, Smithwick RH. Some secondary effects of sympathectomy: with particular reference to disturbance of sexual function. New Engl J Med 1951; 245: 121± Bancroft J. The biological basis of human sexuality. In: Bancroft J (ed). Human Sexuality and its Problems, 2nd edn, Churchill Livingstone: London, UK, 1989, pp Sha k A. Pudendal canal syndrome. Description of a new syndrome and its treatment. Report of 7 cases. Coloproctology 1991; 13: 102± Sha k A. Pudendal canal decompression in the treatment of idiopathic fecal incontinence. Dig Surg 1992; 9: 265± Sha k A. Pudendal canal decompression in the treatment of idiopathic fecal incontinence. Dis. Colon Rectum, 1993; 36: 17 (abstract).

6 16 26 Evans HE, Christensen GC. The reproductive organs. In: Evans HE, Christensen GC (eds). Miller's Anatomy of the Dog. WB Saunders Company: Philadelphia, 1979, pp Sha k A. Vaginocavernosus re ex: clinical signi cance and role in sexual act. Gynecol Obstet Invest 1993; 35: 114±117.

The anocavernosal erectile dysfunction syndrome II Anal ssure and erectile dysfunction

(2000) 12, 279±283 ß 2000 Macmillan Publishers Ltd All rights reserved 0955-9930/00 $15.00 www.nature.com/ijir The anocavernosal erectile dysfunction syndrome II Anal ssure and erectile dysfunction A Sha