The study comprised 22 patients (study group, mean age 43.8 ± 5.9 SD years, range 37–52) with diminished CC EMG activity and with ED of a mean duration of 14.4 ± 2.2 SD years (range 10–16), and 15 healthy volunteers (control group, mean age 41.8 ± 5.1 SD years, range 34–50) who matched the patients in age and acted as controls. The volunteers had a normal sexual life and normal erection. All the subjects in the study gave an informed written consent after having been fully informed about the nature of the study, the tests to be done, and their role in the study.

The results of the physical examination including neurologic assessment were unremarkable. The laboratory work which comprised blood count, renal and hepatic function tests, and electrocardiogram recorded normal findings. The investigations for ED were done for the patients and healthy volunteers. These investigations included cavernosometry, cavernosography, penile arteriography, penile biothesiometry, penile Doppler and rigiscan. Duplex ultrasound scanning was performed in conjunction with a papaverine test 17. The mean arterial diameter increase was 88.2 % (range 82 – 93 %) of the flaccid value, and the mean peak flow velocity was 38.2 cm/s (range 33 – 48) after papaverine injection; these values represent adequate arterial capacity. During the 3 nights of testing the nocturnal penile tumescence (NPT), the greatest registered penile circumference was noted on the recorded data. If direct observation would estimate this circumference as a full erection, then episodes with a circumference of between 81 and 100 % of this greatest circumference would be considered to be a maximal episode 18. All of the studied patients had an average of 4 erectile episodes per night (range 3 – 5) with a mean maximal rigidity of 88.5 ± 3.2 % (range 84 – 92). Neurophysiologic studies were performed comprising of bulbocavernosus-evoked potential testing, dorsal nerve conduction velocity and dorsal nerve somatosensory-evoked potential testing. Neurogenic, vasculogenic, endocrinal and psychological causes of ED were excluded as a result of these investigations (table 1).

The study was approved by the Review Board and Ethics Committee of the Cairo University Faculty of Medicine.

The electric activity of the CC was recorded at rest (flaccid phase) and during erection and detumescence by means of a concentric electromyographic (EMG) needle electrode (Type 13L49 Disa, Copenhagen, Denmark) measuring 40 mm in length and 0.65 mm in diameter. Two needle electrodes were introduced into the CC: one in the upper and one in the lower third. A ground electrode was applied to the thigh and a strain-gauge respiratory transducer to the thoracic wall. After recording the electric activity, the upper electrode was transferred to the mid third of the CC and the recordings were repeated. The needle electrodes were then transferred to the contralateral CC and the electric activity was recorded.

A standard EMG apparatus (Type MES, Medelec, Woking, UK) was used to amplify and display the recorded potentials. Films of these potentials were taken on a light-sensitive paper (Linagraph type 1895, Kodak, London, UK) from which measurements of the duration of the motor unit action potentials were obtained. The EMG signals were in addition stored on an FM tape recorder (type 7758A, Hewlett-Packard, Waltham, MA) for further analysis as required. All filtered signals were collected and recorded using an online computer with a data acquisition and analysis software (Chart V 4.2, AD instruments, Castle Hill, Sydney, Australia). The acquisition rate was 10 Hz, and the EMG normal band width was 0.1 to 5.0 Hz.

Following the recording of the electric activity in the flaccid phase, erection was induced by administration of sildenafil citrate tablets and audiovisual sexual stimulation. One 50 mg tablet was given orally, and the EMG recording of the CC electric activity was performed as aforementioned after erection had occurred. If no erection had been achieved one hour after administration of 50 mg sildenafil, the EMG recording was discontinued and repeated 2 days later; if after 1 hour from administration of 100 mg of sildenafil and audiovisual sexual stimulation erection had as yet not been obtained, intracavernosus injection of papaverine was used to induce erection 19.

To ensure reproducibility of the results, the recordings were repeated at least twice in the individual subject. The results were analyzed statistically using the Student's t test, and values were given as the mean ± standard deviation (SD). Differences assumed significance at p < 0.05.

Penile implant was performed in the 22 patients of the study group who had all consented to do the penile implant. They also gave an informed consent for biopsies to be taken from each CC at operation. The obtained corporeal tissue was stained with hematoxylin and eosin and Mallory's trichrome stain. The healthy volunteers refused to do a CC biopsy for control.

Slow waves (SWs) were recorded in the flaccid phase from the two electrodes of each individual. The wave was negatively deflected (fig. 1) and had an invariable shape in all the recordings from the same site. The SWs in each individual exhibited the same frequency, amplitude and conduction velocity by the 2 electrodes (fig. 1) regardless of their location in the upper, middle or lower third of the penis. Frequency, amplitude and conduction velocity were constant in each subject. The SW variables in the flaccid phase are shown in table 2. These values were reproducible from the electrodes in the upper, middle or lower third of the penis and were identical from both CCs of the same subject. Bursts of fast activity spikes or action potentials (APs) superimposed or followed the SWs. They presented as negative deflections, and their frequency was inconsistent in each subject (fig. 1). The described SW pattern was identical from the 2 CC of the individual subject.

The ECG during rigid penile erection registered significantly diminished CC electric activity (fig. 2, table 3). The frequency, amplitude and conduction velocity showed a significant decrease when compared to the flaccid phase (p < 0.01, p < 0.01, p < 0.01, respectively; table 3). The APs occurred also randomly, but with diminished frequency. These findings were identical from the 2 electrodes of the same subject and from the upper, middle and lower third of the penis, and were reproducible. The recording of the electric activity after detumescence was not significantly different from that of the flaccid phase.

In the flaccid phase, the SWs were negatively deflected. The frequency, amplitude and velocity of conduction were significantly reduced (p < 0.05, p < 0.05, p < 0.05, respectively) in comparison to the normal controls (fig. 3, table 2). The wave rhythm was irregular, and the recordings from the 2 electrodes of the same individual were not identical (fig. 3). The irregular rhythm was consistent when the examination was repeated in the same subject. The APs occurred rarely and randomly; they were less frequent if compared to those of the healthy volunteers (fig. 3). The SW pattern was also recorded from the opposite CC of the same patient, although the SW variables were not identical.

Erection could not be initiated in any of the patients after 50 and 100 mg sildenafil administration and audiovisual sexual stimulation (fig. 4), nor did intracavernosal injection of papaverine effect erection (fig. 5). The ECG performed while the patients were under the effect of sildenafil or papaverine did not differ significantly from the ECG prior to treatment; the SW variables are shown in table 3.

The biopsies from the CC of the patients showed fragmented collagen and elastic fibers, degenerated muscle fibers and areas of fibrosis (fig. 6, 7). In some specimens, there were in addition non-specific inflammatory cells and thrombosed vessels. These histopathologic findings were present in the biopsies from both CCs of each individual and in all of the studied patients.