Hemodynamic mechanism of erection in the human penis

Current Techniques for the Objective Measures of Erectile Hardness

INTRODUCTION

One of the most discussed topics in the urology provider's office is that of the male penile erection. Moreover, this is also a frequent basis for consultation by primary care practitioners. As such, it is essential that urologists are familiar with the various means by which the male erection may be evaluated.

OBJECTIVES

This article describes several techniques presently available that may serve to objectively quantify the rigidity and hardness of the male erection. These techniques are meant to bolster information gathered from the patient interview and physical examination to better guide patient management.

METHODS

An extensive literature review was performed examining publications in PubMed on this subject, including corresponding contextual literature.

RESULTS

While validated patient questionnaires have been routinely employed, the urologist has many additional means available to uncover the extent of the patient's pathology. Many of these tools are noninvasive techniques that involve virtually no risk to the patient and take advantage of pre-existing physiologic properties of the phallus and its blood supply to estimate corresponding tissue stiffness. Specifically, Virtual Touch Tissue Quantification which precisely quantifies axial and radial rigidity, can provide continuous data on how these forces change over time, thus providing a promising comprehensive assessment.

CONCLUSION

Quantification of the erection allows for the patient and provider to assess response to therapy, aids the surgeon in choice of appropriate procedure, and guides effective patient counseling regarding expectation management. Rohrer GE, Premo H, Lentz AC. Current Techniques for the Objective Measures of Erectile Hardness. Sex Med Rev 2022;XX:XXX-XXX.

The biomechanics of erections: two- versus one-compartment pressurized vessel modeling of the penis

Previous biomechanical models of the penis simulated penile erections utilizing 2D geometry, simplified 3D geometry or made inaccurate assumptions altogether. These models designed the shaft of the penis as a one-compartment pressurized vessel fixed at one end when in reality it is a two-compartment pressurized vessel in which the compartments diverge as they enter the body and are fixed at two separate anatomic sites. This study utilizes the more anatomically correct two-compartment penile model to investigate erectile function. Simplified 2D and 3D models of the erect penis were developed using the finite element method with varying anatomical considerations for analyzing structural stresses, axial buckling, and lateral deformation. This study then validated the results by building and testing corresponding physical models. Finally, a more complex and anatomically accurate model of the penis was designed and analyzed. When subject to a lateral force of 0.5 N, the peak equivalent von Mises (EVM) stress in the two-compartment model increased by about 31.62%, while in the one-compartment model, the peak EVM stress increased by as high as 70.11%. The peak EVM stress was 149 kPa in the more complex and anatomically accurate penile model. When the perforated septum was removed, the peak EVM stress increased to 455 kPa. This study verified that there is significant difference between modeling the penis as a two- versus a one-compartment pressurized vessel. When subjected to external forces, a significant advantage was exhibited by two corporal based cavernosal bodies separated by a perforated septum as opposed to one corporal body. This is due to better structural integrity of the tunica albuginea when subjected to external forces.

Histologic study of the tunica albuginea of the penis and mode of cavernosus muscles' insertion in it

The tunica albuginea (TA) is the outer covering of the corpora cavernosa (CCs) and corpus spongiosum (CS) of the penile shaft. The different histoanatomical patterns of the TA, as well as the mode of attachment of the ischio-/bulbo-cavernosus muscles (ICM, BCM) to the TA, were studied, aiming at elucidating their role in the mechanism of erection. Twenty-eight cadaveric specimens (18 adults, 10 neonatal deaths) were studied morphologically and histologically after staining with hematoxylin and eosin and Verhoeff-van Gieson stains. The TA consisted in 20 specimens of 2 layers: inner circular and outer longitudinal, in 6 specimens of 3 layers: inner circular, longitudinal and outer circular, and in 2 of only one longitudinal layer. The CS TA was formed of one layer of longitudinal fibers. The mode of cavernosus muscles insertion into the TA revealed 3 patterns. The conjoint BCM and ICM formed a fibrous belt over the CCs in 18 specimens, a muscular belt in 6 and no belt in 4. The functional role of the variations in the TA morphological structure is not exactly known. We hypothesize that the 3-layered TA gives more penile rigidity than the double and single layers. Considering the type of cavernosus muscles insertion into the TA, it appears that the fibrous belt exerts more CC compression than the other 2 types of insertion.

The corporo-glans ligament: description and functional significance of a ligament connecting the corpora cavernosa to the glans penis

The two corpora cavernosa (CC) end blindly under cover of the glans penis (GP). The method of attachment of the CC to the GP could not be traced in the literature. The current communication investigated the hypothesis of a ligamentous attachment existing between the two corporal ends and the GP. In all, 18 male cadaveric specimens were studied by direct dissection and histologically. Six were neonates and 12 adults (mean age 32.3+/-10.6 s.d. y). After examining and photographing the connection between the CC and GP, sagittal, parasagittal, and coronal sections of the connection were stained and studied microscopically. A triangular fibrous tissue band connected the distal blind ends of the two CC with the GP. The base of this band was attached to the tunica albuginea of the two CC, while the apex was continuous with the fibrous septa between the sinusoids of the cavernous tissue of the GP. Microscopically, the ligament consisted of collagen and elastic fibers; in some sections, the collagen fibers of the tunica albuginea were continuous with those of the band. A band of collagen and elastic fibers could be identified connecting the two CC to the GP; we term it the 'corporo-glans ligament'. This ligament presumably affords the connection with rigidity, flexibility, and tissue strength. We suggest that it firmly connects the GP to the CC during penile thrusting. Further studies are required to assess the possible role of this ligament in erectile dysfunction.

Response of the urethral and intracorporeal pressures to cavernosus muscle stimulation: role of the muscles in erection and ejaculation

OBJECTIVES

The role of the bulbocavernosus (BC) and ischiocavernosus (IC) muscles in erection and ejaculation was studied.

METHODS

The response of the urethral and intracorporeal pressure to cavernosus muscle stimulation was evaluated in 18 male volunteers (mean age, 36.6 years). A two-channel microtip catheter was placed in the prostatic and bulbous urethra. Muscle stimulation was done by two needle electrodes inserted into the BC and IC muscles.

RESULTS

BC muscle stimulation caused an increase in the pressure of the bulbous urethra (P < 0.001) and corpus spongiosum (P < 0.01) and an insignificant change in the prostatic and pendulous urethral and corpus cavernosal pressures (difference not significant). IC muscle stimulation effected an increase in the corpus cavernosal pressure (P < 0.001) without changing the urethral pressure (difference not significant).

CONCLUSIONS

The BC muscle contracts rhythmically at orgasm and this might help to eject the semen from the posterior to the anterior urethra. It is apparent that the muscle has minimal or no role in erection. IC muscle may have a role in erection by increasing the intracavernosal pressure. It seems that it has no role in ejaculation. BC may be considered the "muscle of ejaculation," and IC the "muscle of erection."

The use of duplex ultrasound in the assessment of arterial supply to the penis in vasculogenic impotence

Impotence may be caused by arterial disease affecting the vessels supplying the corpora cavernosa. Color duplex ultrasound was used to measure the peak systolic velocity and systolic rise time in the deep penile arteries in 22 impotent men following papaverine stimulation. The results were compared with the findings of selective internal pudendal pharmaco-arteriography. A further comparison was made using color duplex ultrasound with 37 impotent men who all responded well to papaverine. A systolic rise time of 110 msec. or more was found to be the best discriminant of disease in the arteries supplying the corpora giving a positive predictive value of 0.92. A long systolic rise time in a papaverine responder may indicate that the arterial supply is borderline or that the arterial flow is maximal and that the problem lies on the sinusoidal-venous side. It appears that in the absence of a pathological condition there is a large surplus arterial supply.

Corpus cavernosal relaxation in impotent men

OBJECTIVE

To investigate smooth muscle responsiveness in isolated preparations of corpus cavernosum from men with vasculogenic impotence.

PATIENTS AND METHODS

Biopsies of corpus cavernosum were obtained from 63 men undergoing penile surgery. These included a control group of eight men (mean age 59 years, range 38-82) undergoing penile amputation for carcinoma, 47 men with vasculogenic impotence (mean age 58, range 36-72) who were further sub-divided into arterial (n = 9), venous (n = 24) or mixed arterial/venous (n = 14) impotence according to the results of pre-operative haemodynamic investigation, and eight men with non-vasculogenic impotence (mean age 49 years, range 34-66). Smooth muscle contractile responses to alpha-adrenoceptor activation and relaxant responses to stimulation of intrinsic nerves and exposure to papaverine and sodium nitroprusside were recorded in tissue strips prepared from the biopsies. Morphology was assessed histologically using haematoxylin and eosin staining of tissue sections together with immunocytochemical labelling of intrinsic nerves.

RESULTS

Nerve-evoked relaxation was markedly impaired in tissue from men with venous or mixed arterial/venous impotence. A lesser degree of impairment was found in tissue from men with arterial impotence alone. Tissue from men with all types of vasculogenic impotence also showed a decreased contractile response to alpha-adrenoceptor stimulation. The magnitude of relaxant responses to papaverine and sodium nitroprusside in the vasculogenic group was similar to that of the control. There were no differences in smooth muscle content or nerve density between the vasculogenic group and the control. In the non-vasculogenic group responses to relaxant nerve stimulation, alpha-adrenoceptor activation and relaxant drugs were similar to those of the control. Nerve density in this group was similar to the control but smooth muscle content was reduced.

CONCLUSIONS

The results of this study demonstrate a functional impairment of smooth muscle contractility and neurogenic relaxation in corpus cavernosum from impotent men with abnormal penile haemodynamics. Altered smooth muscle responsiveness is likely to be a factor in the aetiology of impotence in such men and may contribute to the relatively poor results of vascular surgery for impotence.

Colour flow and spectral Doppler imaging after papaverine-induced penile erection in 220 impotent men: study of temporal patterns and the importance of repeated sampling, velocity asymmetry and vascular anomalies

Of 220 impotent men studied, 52 demonstrated venous leakage, 85 had arterial insufficiency and 65 showed normal vascular response. Persistent diastolic velocity > 7 cm/s diagnosed venous leakage with a sensitivity of 94% and a specificity of 69%, using cavernosography as the reference standard. Using clinical response as the reference standard maximal systolic velocity of 30 cm/s identified normal penile arterial response with a sensitivity of 96% and specificity of 82%. There was a good correlation between penile arterial insufficiency and a strong history of arteriopathy. Time to peak systole > 0.1 s was a reliable predictor of arteriogenic impotence and Pulsatility Index (PI) < 300 was discovered only in patients with either venous leakage or arteriogenic impotence. Peak systolic velocity (Tmax) occurred between 5.2 and 6.5 min after injection, and diastolic velocity was minimal at 9 min with only the normal responders showing reversed diastolic flow. However, 22% had a delayed response (Tmax range 1-18 min). Velocity asymmetry was equally common in the three groups and unilateral sampling would have misdiagnosed 6% of patients studied. Vascular anomalies were seen in 13%, particularly a single feeding artery, dorsal vein flow or collateral arterial flow.

Drug-induced male sexual dysfunction. An update

Impotence, defined as the consistent inability to maintain an erect penis of sufficient rigidity for sexual intercourse, has been estimated to affect 10 million American men. An age dependence has been shown to exist, with 25% of men over age 65 affected. A large body of clinical experience and published reports in the literature link many commonly prescribed drugs with sexual dysfunction. Drugs can affect sexual function at a variety of points such as inhibition of ejaculation or sedation/depression leading to reduced libido. Antihypertensive drugs have been most commonly associated with impotence. There have been reports of sexual dysfunction with almost all classes of antipsychotics, but little clinical investigation has been performed. Other drugs associated with sexual dysfunction include digoxin, clofibrate, cimetidine and various hormonal agents and antineoplastics. An important first step in approaching all impotent patients is the taking of a detailed medical, surgical, sexual and drug/substance abuse history. The least invasive form of therapy should be employed. Recent studies have shown intracavernous injections of alprostadil (prostaglandin E1) to be safe and effective for long term use. Vacuum constriction devices may also be of help. Better and more durable prostheses are now available should other treatment be unsuccessful.

Evaluation of vasculogenic impotence by monitoring of cavernous oxygen tension

Color coded duplex sonography, regarded as the gold standard in penile vascular evaluation, does not yield data on cavernous oxygenation itself. In addition to using color coded duplex sonography to measure peak flow velocity in cavernous arteries after injection of 20 micrograms. prostaglandin E1 in 34 unselected patients with impotence, we monitored cavernous oxygen tension with oxygen-sensitive Eppendorf needle electrode. During flaccidity the mean cavernous oxygen tension of 38 mm. Hg increased to 61 mm. Hg after injection of prostaglandin E1. Peak flow shown with color coded duplex sonography and maximal oxygen tension correlated well in 24 men (71%). However, in 10 men (29%) normal peak flow did not result in a cavernous oxygen tension of greater than 65 mm. Hg, so this might have been isolated cavernous perfusion defects. In contrast, there was no case of impaired arterial inflow and high oxygen tension. Monitoring of cavernous oxygen tension allows for characterization of patients with cavernous perfusion deficiency. This new and simple diagnostic method might help to improve diagnosis and followup after penile vascular surgery. However, more data on patients and controls will be required to define normal ranges.

The combined intracavernous injection and stimulation test: diagnostic accuracy

A retrospective review was done of the results of the combined intracavernous injection and stimulation test, an office based functional test for impotence. In this procedure the quality of erection is assessed 15 minutes after injection of a vasoactive drug. In our series 90 patients did not achieve full rigidity and were instructed to perform genital self-stimulation for 5 minutes before reevaluation. Of the 90 patients 67 (74%) improved with stimulation and 23 (26%) showed no improvement. At 5 minutes after stimulation a decrease in the quality of the erection was found in 25 patients--a finding suggestive of venogenic impotence. When cavernosometry and cavernosography were performed 21 patients (84%) had moderate to severe venous leakage and 4 (16%) showed none. Self-stimulation after diagnostic injection of intracavernous agents can improve patient response, and may better predict the potential success of a therapeutic self-injection program and the diagnosis of suspected venogenic impotence.

Nuclear medicine in problems of fertility and impotence

Nuclear medicine techniques may be used to test fallopian tube patency and penile vascular inflow and outflow. Radionuclide hysterosalpingography (HSP) is a readily performed method of evaluating fallopian tube patency, and is believed to be more physiologic and functionally informative than the accepted radiologic method of contrast HSP. The test is simple to perform and interpret and offers an accurate alternative to the contrast examination. For scintigraphic evaluation of impotence, blood pool studies are most useful in assessing the integrity of arterial inflow, but may also be used to generate indices of venous leak. Washout of xenon after subcutaneous injection, in the flaccid state, has been used as a measure of baseline penile perfusion, as has intracavernosal injections in the flaccid penis. Intracavernosal xenon washout during erection seems the most useful method of testing venous integrity. Washout using technetium-99m (99mTc)-labeled red blood cells (99mTc-RBC) may emerge as a convenient alternative to the more technically difficult xenon examinations.

Venous leaks: anatomical and physiological observations

A total of 50 patients with impotence underwent cavernosometry and cavernosography with intracavernous injection of vasoactive drugs. Several hemodynamic parameters were analyzed, including the pressure response curve after injection of vasoactive drugs and infusion of saline, the volume required to achieve erection, venous outflow resistance, erection maintenance infusion rate, rate of pressure decrease after discontinuation of infusion and post-infusion steady state pressure. On the basis of cavernosometric findings, venous leakage was ruled out in 4 patients. In the remaining 46 patients leak sites visualized during cavernosography included superficial dorsal vein in 1 (2.2%), deep dorsal vein in all 46 (100%), cavernous veins in 32 (69.6%), glans in 19 (41.3%) and corpus spongiosum in 14 (30.4%). Aberrant veins were documented in 7 patients (15.2%) communicating with the saphenous vein in 4 (8.9%), scrotal veins in 2 (4.4%) and femoral veins in 1 (2.2%). Eight patients (17.4%) had leakage through the deep dorsal vein as the only venous site, 17 (36.9%) had leakage through 2 venous sites, 14 (30.4%) had leakage through 3 venous sites and 7 (15.2%) had leakage through 4 venous sites. Correlations among hemodynamic and radiographic observations allowed the identification of 4 different types of cavernosometric findings. While type I represented normal penile vascular findings, types III and IV represented venous leakage. Type II could represent no leak, a mild leak or an undetected arterial problem. Accuracy of interpretation of a study may be improved by taking more than 1 parameter into consideration, including erection maintenance infusion rate, intracavernous pressure decrease within the first 5 seconds after discontinuation of infusion and the final steady state intracavernous pressure. The majority of patients have more than 1 leak site (82.6%). The most commonly combined sites of leakage are the deep dorsal and cavernous veins.

Evaluation and treatment of erectile dysfunction following spinal cord injury: a review

The majority of spinal cord injured (SCI) men with upper motor neuron lesions have reflex erections. However, these erections are often not adequately sustained making it difficult if not impossible to have intercourse. The majority of SCI men with lower motor neuron lesions do not have erections. Penile implants are effective in producing erections following SCI. However, they have the disadvantages of being a surgical procedure and of having the risk of infections and erosion of the implant through the skin. Intracavernous injections of papaverine and phentolamine and vacuum erection devices have recently been added to our armamentarium of ways to treat erectile dysfunction. A major concern particularly in SCI men is that papaverine and phentolamine may cause prolonged erections in SCI men. We presently have little data on the use of vacuum devices in SCI men, but preliminary reports on those who are using FDA-approved devices appear promising.

Diagnostic value of the radioisotope erection penogram for vasculogenic impotence

Radioisotope erection penography of 113 consecutive impotent patients (41 with psychogenic and 72 with vasculogenic impotence) and 15 normal potent men were obtained. Twenty minutes after intracavernous injection of 99mtechnetium-pertechnetate 40 mg. papaverine hydrochloride were administered into the corpus cavernosum to induce erection. A gamma camera with a pinhole collimator was used to monitor the radioactivity. Various penogram indexes were calculated from the time activity curve and their usefulness was evaluated. Index A1 was useful to differentiate vasculogenic and psychogenic importance. Indexes V1 and V2 were useful to differentiate arteriogenic and venogenic impotence. The radioisotope erection penogram is a simple, less invasive and valuable screening test in the identification of vasculogenic impotence, and is effective in differentiating arteriogenic and venogenic impotence.

The effect of venous incompetence and arterial insufficiency on erectile function: an animal model

We designed an animal model to elucidate the effect of venous leakage and arterial insufficiency on erectile function. In 10 dogs, electrodes were implanted around the cavernous nerves for electroerection and blood flow in the internal pudendal artery was recorded. Venous leakage was mimicked by inserting needles of varying gauges (30 to 16G) into the corpus cavernosum and the erectile response to neurostimulation was recorded before and after the creation of the leak. The relationship between the size and the amount of the venous leakage, the changes in the intracavernous pressure (peak and drop), and the changes in the peak and maintenance arterial blood flow were documented. Arterial blood flow was then reduced by 25 and 50 per cent by means of a screw clamp on the terminal aorta. The erectile response to neurostimulation was again determined, with the same electrical parameters, first with reduced blood flow alone, then in combination with leakage of varying size. Our results showed that minor cavernous vein leakage in the presence of normal arterial flow and a healthy sinusoidal system had a minimal effect on erectile function owing to a compensatory increase in penile blood flow. However, when reduction of arterial blood flow was superimposed on venous leakage, even of a minor degree, the erectile response to neurostimulation was markedly impaired.

Comparison of penile duplex ultrasonography with nocturnal penile tumescence monitoring for the evaluation of erectile impotence

A total of 50 patients with erectile dysfunction underwent comprehensive evaluation, including vascular evaluation with penile duplex ultrasonography and papaverine injection, as well as nocturnal penile tumescence monitoring. The latter was performed in a sleep laboratory setting in all patients. The results of penile duplex ultrasonography with papaverine injection were classified as 18 patients with normal vascular findings, 22 with arterial insufficiency, 3 with the pelvic steal syndrome and 7 with isolated venous leakage. Of the patients 15 had normal ultrasonographic and nocturnal penile tumescence findings, 29 had abnormal ultrasonographic vascular and nocturnal penile tumescence findings, 3 had abnormal ultrasonographic vascular findings and normal nocturnal penile tumescence (including 1 with the pelvic steal syndrome as evidenced by penile brachial index) and 3 had normal ultrasonographic vascular findings and abnormal nocturnal penile tumescence (including 2 with neurogenic erectile dysfunction). Penile duplex ultrasonography with papaverine injection appears to be a useful objective method to evaluate vasculogenic impotence and to correlate favorably with nocturnal penile tumescence monitoring. It also may have a higher yield than nocturnal penile tumescence monitoring in patients with the pelvic steal syndrome. While nocturnal penile tumescence is impaired in patients with neurogenic impotence, penile duplex ultrasonography with papaverine injection reveals, as expected, normal findings in patients with neurogenic impotence and normal vascular systems.

Evaluation of vasculogenic erectile impotence using penile duplex ultrasonography

A total of 140 patients underwent penile vascular evaluation with intracavernous papaverine injection combined with duplex ultrasonography. Of these patients 8 were potent men who were evaluated for reasons other than erectile failure. These potent men were used as controls to obtain normal values. The remaining 132 patients had erectile impotence of various etiologies. Real-time imaging with high resolution, high frequency probes allowed for visualization of the cavernous arteries along the entire length in addition to accurate measurement of the diameter. Simultaneous selectively focused Doppler ultrasonography was used to measure the blood velocity and other vascular parameters in the cavernous and dorsal arteries. Comparison of measurements before and after papaverine injection allowed for objective interpretation of the injection results. The results were analyzed and compared to other data available on the same patients, such as history and physical examination, nocturnal penile tumescence, penile blood pressures, selective arteriography and dynamic cavernosography. In addition to the 8 potent men, there were 35 patients (27% of the impotent patients) whose vascular findings were normal. A total of 78 patients (59% of the impotent patients) had arterial insufficiency; a subgroup of 13 patients had the pelvic arterial steal syndrome. Dynamic cavernosography confirmed venous leak in all 19 patients (14% of the impotent patients) whose penile duplex ultrasonography suggested the possibility of a venous leak. Ten patients (7%) had prolonged erection after papaverine injection and they were managed without consequences. One patient had a small hematoma that resolved uneventfully. Penile duplex ultrasonography was a helpful and objective method to evaluate vasculogenic impotence.

Local and systemic effects of chronic intracavernous injection of papaverine, prostaglandin E1, and saline in primates

To compare the local and systemic effects of chronic intracavernous injection of papaverine, prostaglandin E1, and saline on erectile tissue, eight pigtail monkeys underwent 75 injections over a nine-month period. Monkeys were divided into three groups; each group received papaverine (10 mg.), prostaglandin E1 (20 micrograms.), or saline (one ml.). The erectile response was closely observed for two hours after each injection to monitor the onset, degree, and duration of erection. Liver function tests were performed every three months to detect early systemic metabolic changes. After sacrifice, the simian penises were perfused in situ and examined histologically with both light and electron microscopy. Papaverine resulted in an initially strong erectile response, but this was maintained throughout the length of the study in only two monkeys. In contrast, prostaglandin E1 resulted in tumescence that was maintained in all monkeys over the nine-month period. In addition, the papaverine group had elevated liver enzymes and significant histologic changes with loss of normal architecture on both light and electron microscopy. The other two groups showed only minimal histologic changes or none.

Penile venous drainage in erectile dysfunction. Anatomical, radiological and functional considerations

To elucidate further the penile venous anatomy and its role in the haemodynamics of erection, we performed pharmacological cavernometry and cavernography in 95 patients with venogenic impotence and in 12 patients with psychogenic impotence. The findings were correlated with those of dissection in 10 adult male cadavers. Cavernography confirmed that the main venous drainage of the corpora cavernosa is via the cavernous veins, with additional drainage through the crural, circumflex and deep dorsal veins and demonstrated that, in patients with venogenic impotence, the cavernous veins are the common site of leakage. Cavernometry provided valuable parameters for the quantification of the degree of venous leakage. Detailed knowledge of the penile venous system and cavernometry and cavernography are essential for the proper diagnosis and treatment of patients with venogenic impotence.

The vascular anatomy of the cavernous body of green monkeys

The cavernous body of monkeys was studied by light and electron microscopy. The intima of the deep artery contained longitudinal muscle cells, but cushions or valve-like structures were not found. Some branches of the deep artery directly connected to subtunical veins. Only the helicine arteries which drained into the cavernous sinuses displayed subendothelial cushions. The "epitheloid cells" forming the cushions unequivocally were smooth muscle cells. It is suggested that the helicine arteries open during tumescence, thereby diverting blood from the shunt vessels into the dilating sinuses, and that the rising intracavernosal pressure eventually occludes the shunt vessels. The endothelium of the sinuses contained many intermediate filaments, but there was no morphological evidence for the hypothesis that the cells are contractile.

Quantitative analysis of outflow pathway of corpora cavernosa by pressure flow technique

Using a pressure flow technique, quantitative analysis of the physiological characteristics of the outflow pathway of the corpus cavernosum was carried out in 19 male dogs weighing 7.5 to 23.0 kg. Pressure flow curves were made on dogs whose pelvic nerve was stimulated electrically and on dogs left unstimulated. When a cyclical change in saline perfusion rate was applied without nerve stimulation, the variable of the intracorporeal pressure showed a large hysteretic loop, indicating that the resistance of the outflow canals to flow was altered by the distension of the sinusoidal space. In dogs whose pelvic nerve was stimulated, the pressure flow curves shifted to the left side in comparison with the outward phase of the pressure flow curve of animals without pelvic nerve stimulation, and this curve piled on the returning phase. No hysteretic relation was observed between the outward and returning phase of the pressure flow curve with pelvic nerve stimulation, but in the detailed analysis, in which the % flow rate was used instead of actual flow rate of saline perfusion, a small hysteretic loop based on the difference of the elasticity of the outlet canals was found. The distension of the corpora cavernosa and the pelvic nerve electrostimulation probably act as the triggers of the same occlusive mechanism in the outflow pathway. The percentage decrease in the blood flow in the outflow canal of the corpus cavernosum induced by the distension of the sinusoidal space or by the pelvic nerve electrostimulation was 69.6 +/- 14.4% (mean +/- SD).

Impotence in diabetic men

Studies relating to pathogenetic mechanisms resulting in impotence in diabetic subjects have been reviewed. Erectile dysfunction was reported to occur in 50 to 75 percent of diabetic patients and the prevalence appeared to increase with age. Contributions of vascular, endocrine, and neurologic system alterations result in this disturbing condition, but a detailed analysis of all the parameters was not found in any individual study. In our review of 301 veterans presenting to a sexual dysfunction clinic, the clinical and hormonal alterations in the diabetic patients closely resemble those seen in nondiabetic impotent subjects. Atherosclerotic vascular changes play an important predisposing role in the development of impotence. A difference exists between the prevalences of associated medical conditions in diabetic patients taking insulin, compared with those receiving oral agents or receiving dietary management. The high prevalence of impotence in diabetic patients seems to be due to the high prevalence of its vascular complications. Considering the availability of useful therapeutic approaches, it is mandatory to evaluate all diabetic men for the presence of impotence.

Penile pharmacocavernosography and cavernosometry in the evaluation of impotence

Within the past few years, veno-occlusion of the corpora cavernosa has become generally recognized as an essential prerequisite for adequate penile erection. Veno-occlusive incompetence is suspected to be a frequent cause of impotence. Our recent experience with cavernosography in two normal volunteers and 36 impotent patients indicates that angiography is reliable in evaluating the competence of the veno-occlusive mechanism only if both pharmacocavernosography (PCG) and pharmacocavernosometry (PCM) are applied. Twenty minutes after intracavernosal (IC) injection of a mixture of 60 mg. papaverine and one mg. phentolamine (regitine), 100 ml. of diluted radiographic contrast medium are infused at the rate of one or two ml./sec. while pressure is recorded, and radiographic films are exposed at the rate of one every eight to 15 seconds. PCM and PCG of the corpora cavernosa indicated the overall degree of competence of the cavernosal veno-occlusive mechanisms, and the sites of veno-occlusive incompetence; non-pharmacologic studies were unreliable in these regards. During non-pharmacologic infusion in normals, pressures rose to 40 to 45 mm. Hg, and free efflux could be visualized from multiple venous systems. After pharmacologic injection in normals, all venous channels closed, and pressures rapidly rose toward or above 200 mm. Hg, at which time the infusion was stopped. Veno-occlusive incompetence was defined angiographically when more than minimal efflux occurred during pharmacocavernosography from any venous system. The incompetence could involve the deep penile system, the deep dorsal system, or the spongiosal system, alone or in combination. Severe veno-occlusive incompetence was considered diagnostic of venogenic impotence, and was defined manometrically when IC pressures failed to exceed 100 mm. Hg during infusion of 100 ml. of fluid at 2 mm./second after IC papaverine and phentolamine injection. We believe these angiographic methods will improve the criteria against which other diagnostic and therapeutic methods can be assessed.

Human penile hemodynamics studied by a polarographic method

Observations of the tissue oxygen tension alteration were made using an open tip type oxygen electrode polarographic method as an index of blood flow change in the penile skin, corpus cavernosum and thigh skin of 16 males aged 20-26 years (average age: 20.5 years). In another five males aged 18-21 (average age: 19.8 years) the relationship between corpus cavernosum tissue oxygen tension alteration and penile circumference change in the erection process was observed. This relation was obtained in the penile circulation model, and penile hemodynamics were ascertained. In the flaccid penis the corpus cavernosum contains low-oxygen blood and there is a blockade at the vascular tree in the corpus cavernosum. In the tumescence phase the blood flow of the corpus cavernosum increased suddenly by the relief of cavernosum vascular blockade. During the penile tumescence phase the increased inflow and outflow persisted in corpus cavernosum, and in penile skin the blood also increased initially, but gradually decreased as penile circumference increased. After erection was attained it is thought that resistance to inflow occurred by outflow pathway contraction. In the detumescence phase, a decrease of inflow and a concomitant increase of outflow occurred and the reopening of outflow is thought to be necessary for prompt penile detumescence.

Functional evaluation of penile veins by cavernosography in papaverine-induced erection

Of 49 patients in whom cavernosography was performed after papaverine-induced erection 38 had abnormal venous leakage to various drainage systems (corpus spongiosum, cavernous vein or superficial and deep dorsal veins). Because the effect of papaverine on penile arteries, sinusoids and veins is similar to that caused by electrostimulation, we believe that this technique is better than other reported means of evaluating the functional status of the penile veins. However, we recommend that only patients with a normal arterial response but poor erection after papaverine injection be considered candidates for erection cavernosography, since they most likely will benefit.

Anatomical localization and some pharmacological effects of vasoactive intestinal polypeptide in human and monkey corpus cavernosum

Vasoactive intestinal polypeptide is hypothesized to be a nonadrenergic, noncholinergic neurotransmitter important in the physiology of penile erection. To further explore this concept, anatomical localization of vasoactive intestinal polypeptide, in vitro muscle bath studies and in vivo injection experiments were undertaken in the monkey and man. Using immunohistochemical techniques vasoactive intestinal polypeptide was localized at the light microscopic level to nerves within the monkey and human penis. Ultrastructurally, a modified peroxidase-antiperoxidase technique was used to identify large vasoactive intestinal polypeptide-positive vesicles within peptidergic and cholinergic varicosities. In the in vitro muscle bath, the addition of 10(-7) M vasoactive intestinal polypeptide did not alter the baseline tension of strips of monkey and human corpus cavernosum. During contraction produced by norepinephrine stimulation, however, vasoactive intestinal polypeptide (10(-7) M) caused relaxation of the monkey (41 +/- 18 per cent, no. = 8) and human (23 +/- 8 per cent, no. = 5) corpus cavernosum. Intracorporal injection of vasoactive intestinal polypeptide (0.75 X 10(-9) to 3.75 X 10(-9) moles/kg.) had no effect on the monkey penis. Administration of vasoactive intestinal polypeptide (1.25 X 10(-9) to 2.5 X 10(-9) moles/kg.) into the internal iliac artery of the monkey, while having no effect on the flaccid penis, caused detumescence of the erect penis obtained by cavernous nerve stimulation (2-5 V, 40 Hz, 2 msec.). Although vasoactive intestinal polypeptide can be found within the nerves of the penis, its apparent in vitro and in vivo effects raise further questions concerning the role of this peptide in penile erection.

Penile xenon (133Xe) washout: a rapid method of screening for vasculogenic impotence

The radioactive inert gas xenon (133Xe) is a well-established isotopic indicator used to assess vascular status in many organ systems. We employed xenon-133 to evaluate male impotence. Xenon-133 was injected subcutaneously at the level of the coronal sulcus in the detumescent state. Using the gamma camera, sequential images were obtained and computer-generated curves calculated. The clearance time for 50 per cent washout of the injected 133Xe (T1/2) was then calculated for each patient, as well as a control group. Preliminary findings indicate a correlation with such established techniques of evaluating erectile impotence as history, physical examination, penile pulse Doppler tracings, and brachial-penile blood pressure index. The xenon-133 washout study was a rapid, minimally invasive, reproducible, and cost-effective method of screening those impotent patients for vasculogenic etiology of their erectile impotence. We recommend the addition of this method to the surgeon engaged in the care of impotent males.

Hemodynamics of erection in the monkey

Being able to induce controlled erection in dogs and monkeys, we investigated the hemodynamics and mechanism of penile erection. 'Chronic' monkey models, having had electrodes implanted around the cavernous nerves for electroerection, were studied to evaluate the details of the hemodynamic changes. The studies included: 1) arterial blood flow, 2) corporeal pressure, 3) blood gases, 4) venous flow and 5) radiography. Tumescence of the corpora cavernosa was found to be a result of: 1) active relaxation of the sinusoidal spaces, 2) active arteriolar dilatation and 3) active venous outflow constriction. At full erection there is adequate but reduced blood flow into and out of the corpora cavernosa for metabolic exchange.

Hemodynamics of erection in man

Inquiry was made into the theory that closure of the efferent vein from the corpora cavernosa is essential for erection of the human penis. To determine whether the venous closure is indeed a prerequisite to human penile erection, two tests were carried out in men: (1) direct infusion in 133Xe into corpora cavernosa and (2) performance of carvernosography. In each case, penile erection was induced by providing the subject with sexual stimulation. The behavioral changes were studied through the 133Xe clearance curve and the contrast medium, respectively. When the penis remained flaccid, the 133Xe clearance curve followed a gentle path and the contrast medium could be noted within the penis for a relatively long period. However, on erection with sexual stimulation, the 133Xe clearance curve fell rapidly instead of following the gentle course expected in the case of venous closure. Also, the contrast medium quickly flowed out of the corpora cavernosa. The human penis therefore can well erect without closure of the efferent vein from the corpora cavernosa.