Phosphodiesterase type 5 inhibitors: unmet needs.

Erectile dysfunction (ED) has been revolutionized during the last two decades, as several treatment options are available today. Phosphodiesterase type 5 (PDE5) inhibitors (sildenafil, tadalafil, vardenafil) are currently the first choice treatment option for ED by most physicians and patients due to their high efficacy rates and favourable safety profiles. Despite the fact that more than 50 million ED patients have been treated successfully worldwide with PDE5i several issues remain to be addressed. Patients with severe neurologic damage, diabetes mellitus, or severe vascular disease may be resistant to PDE5i. Inappropriate instructions, lack of follow-up and lack of patient-centered care models have been identified as main reasons for "nonresponse", leading to drop-out rates of even > 50%. Preservation of corporal smooth muscle with chronic administration of PDE5i has been reported and there is a substantial body of evidence for beneficial effects of these drugs on endothelium and cardiovascular function. Finally, improvement of lower urinary symptoms after PDE5i administration has been reported and a possible role on treatment of premature ejaculation has been proposed. Many new PDE5i are candidates to enter the market in the forthcoming years. However, pharmacokinetic differences should be obvious to consider a truly better option for patients. Patients must be aware of all treatment options since no ideal treatment exists and physicians must offer personalized medicine to their patients in the future. The development and adaptation of a patient-centered care model in sexual medicine will increase efficacy and safety of current and future treatments.

Protective role of the glans penis during coitus.

To examine the hypothesis that the glans penis acts protectively, absorbing forces, during coitus. Five potent patients (mean age 46.8+/-9.7 y), who had indication for surgical excision of the glans for penile carcinoma were included in the present study. Intraoperatively, intracavernosal pressure (ICP) was adjusted by saline infusion and maintained by a pressure feedback infusion pump to a pressure value of 70 mmHg. Using a dynamometer, an external compressive force of 0.5 kg was applied at the glans penis and the changes in ICP were monitored. Measurements were repeated after surgical excision of the glans. Significant ICP changes were noticed in all patients after excision of the glans. Mean preoperative ICP was 161+/-11.5 mmHg, while after glansectomy it reached 206.6+/-13 mmHg. DeltaICP was 45.8+/-10.57 mmHg. Two of the patients' partners reported pain during intercourse postoperatively, possibly due to the impact of the force applied by the rigid corpora cavernosa on the anterior vaginal wall without any absorption by the glans. The glans penis restricts the increase in ICP during sexual intercourse, playing a protective role for both the corpora cavernosa and the female genitalia.

Normal hemodynamic parameters do not always predict the presence of a rigid erection: a quantitative assessment of functional erectile impairment.

The purpose was to assess objectively and quantitatively the hemodynamic status and the degree of functional erectile impairment in a group of impotent patients. A clinical study was designed, incorporating pharmacocavernosometry (to evaluate arterial and veno-occlusive function) with axial buckling forces and penile geometry measurements in a group of impotent patients. The pressure gradient between the intracavernosal pressure associated with the presence of penile axial rigidity and the equilibrium intracavernosal pressure was calculated (axial rigidity gradient, ARG); such methodology allowed a quantitative characterization of functional impairment, as ARG expresses the intracavernosal pressure increase necessary to achieve axial rigidity and therefore potency. Penile geometry characteristics were also expressed by calculating the penile aspect ratio (diameter/length, D/L). In 83 consecutive patients tested (mean age 42.89+/-9.96), rigidity occurred at intracavernosal pressures between 50 and 100 mm Hg. A conversely proportional relation was noticed between penile aspect ratio values and the intracavernosal pressure associated with rigidity values, clearly demonstrating the important functional role of penile geometry. ARG demonstrated a wide range of values (3-69 mm Hg), reflective of the severity of the erectile dysfunction on each patient. Half (50.6%) of the patients had ARG values < or =20 mm Hg, indicative of minimal and minimal-to-moderate erectile impairment, while 20.48% had ARG between 21-30 and 28.92% >30 mm Hg, indicative of moderate and severe erectile dysfunction (ED) respectively. In all, 6% of the study group, all of them with primary ED, ARG <20 mm Hg had normal hemodynamics, but low penile aspect ratio values indicating that penile geometry may be the cause of insufficient rigidity. Hemodynamic integrity is the most critical, but not the only determinant of penile rigidity, as erectile impairment may be noticed in patients with normal arterial inflow and corporal veno-occlusive function. In such cases, unfavorable penile geometry should be considered as the possible etiological factor of impotence.

A shared care approach to the management of erectile dysfunction in the community.

Erectile dysfunction (ED) affects men of all ages and results in considerable distress and impact on quality of life for those who suffer from it. As ED is associated with a wide variety of under-lying conditions and cardiovascular co-morbidities, there is a requirement for diversity of treatment options and several factors must be considered to customise and optimise therapy. In the ideal holistic approach to management of the ED patient, both primary care and specialist physicians have an important role to play. This article reports on a sequential approach for the diagnosis and treatment of ED, with an emphasis on 'shared care'. The deliberations are based on a pan-European inter-disciplinary group that met at the Lygon Arms, UK on 22 February 2002.

Sildenafil citrate: lessons learned from 3 years of clinical experience.

In the 3 y since its initial approval, sildenafil has become the most widely used treatment for erectile dysfunction (ED) and has been prescribed to more than 13 million patients worldwide. Significant improvements in erectile function have been demonstrated in double-blind, placebo-controlled studies in diverse patient populations. A significant treatment effect has been shown with sildenafil in men with ED and a history of diabetes, cardiovascular disease, minor depression, spinal cord injury and multiple sclerosis. In addition, promising results have been shown in patients with treated prostate cancer, end-stage renal disease, Parkinson's disease and spina bifida and in multiple-organ transplant recipients. Postmarketing data of the use of sildenafil in clinical practice confirm the efficacy and safety found in clinical trials and high satisfaction with treatment. Public awareness of the common occurrence of ED and the high likelihood of a potentially favorable response to an oral treatment increased dramatically with the introduction of sildenafil. Physicians, however, are still not comfortable with ED management, which negatively affects pharmacotherapy response rates and patients' compliance to treatment. Continuing medical education seems mandatory to overcome existing problems in ED management.

Glansectomy: an alternative surgical treatment for Buschke-Löwenstein tumors of the penis.

OBJECTIVES: To present the surgical excision of the glans penis (glansectomy) as an alternative surgical treatment to penectomy. Buschke-Löwenstein tumors of the penis include the entities described in published reports as verrucous carcinoma and giant condyloma acuminatum of the penis. Both types are well-differentiated tumors, typically confined to the glans penis, with distinctly rare metastatic activity. METHODS: The study included 7 patients, 40 to 63 years of age, with exophytic, papillary lesions involving the glans penis. Biopsy led to the diagnosis of verrucous carcinoma in 4 patients and giant condyloma acuminatum in 3 patients. All patients reported normal erectile function. Because of the low malignant potential of the tumor and its confinement to the glans penis, a simple glansectomy was performed in all patients to preserve the maximal penile length and functional integrity of the corpora cavernosa. RESULTS: The postoperative course was uncomplicated. With 18 to 65 months of follow-up, all patients were disease free. One patient required more aggressive treatment because of local recurrence of the tumor. All patients returned to normal sexual activity 1 month postoperatively. The only change during sexual activity, noted by two of the patients' partners, was vaginal pain, possibly due to the absence of the glans. CONCLUSIONS: Glansectomy may be considered the treatment of choice in patients with Buschke-Löwenstein tumors of the penis, with more radical techniques reserved for second-line treatment.

Effects of oral phentolamine, taken before sleep, on nocturnal erectile activity: a double-blind, placebo-controlled, crossover study.

The objective of this study was to determine the effects of oral phentolamine, administered before sleep, on nocturnal penile erectile activity of men with mild to moderate erectile dysfunction (ED). We studied five patients with mild to moderate ED (mean age 34.8 +/- 8.13 and mean duration of ED 31.8 +/- 23.5 months), in a double-blind, placebo-controlled, crossover study. All patients received oral phentolamine (Vasomax) at a dose of 40 mg and placebo for three consecutive nights respectively and were submitted to nocturnal penile tumescence and rigidity monitoring (NPTR) with the Rigiscan device. NPTR parameters of the two 3-night recordings were evaluated and compared. Administration of oral phentolamine before sleep was associated with a statistically significant increase in the number of erectile events with rigidity > or = 60% lasting > or = 10 min (P = 0.02), as well as the rigidity activity units (RAU) value per hour sleep, both at the base (P = 0.023) and the tip of the penis (P = 0.019). The number of events as measured by Rigiscan software (20% change in circumference), as well as tumescence activity units (TAU)/h values did not show any statistical difference. No adverse effects were recorded. It is concluded that oral phentolamine administered before sleep enhanced NPTR parameters associated with the quality of the erectile events. Such results provide a pathway for the development of a prevention strategy for ED. Future studies will elucidate whether vasoactive agents taken on a regular basis before sleep, can prevent ED in men at risk, protecting also minimally and moderately impotent patients to become moderately and severely impotent respectively.

Tissue structure-specific distribution of glycosaminoglycans in the human penis.

The aim of this work was to isolate and characterise the glycosaminoglycans present in the different tissue structures of the human penis in view of their potentially significant role in the physiology of erection. Penile tissue samples were obtained from patients who underwent penectomy and were subsequently dissected into individual tissue structures. Total glycosaminoglycans were isolated and purified from tunica albuginea, corpora cavernosa and corpus spongiosum, following tissue mincing, ultrasonication, lipid extraction, extensive digestion with pronase and DNase, treatment with alkali-borohydride and ethanol precipitation. Isolated glycosaminoglycans were separated by cellulose acetate electrophoresis and fractionated by anion exchange chromatography on DEAE Sephacel columns. Different glycosaminoglycan fractions were identified using glycosaminoglycan-degrading enzymes of known specificity. Gradient polyacrylamide gel electrophoresis was used to determine the average molecular mass of the glycosaminoglycans. The corpus cavernosum and the corpus spongiosum extracts contained almost twice the amount of glycosaminoglycan-associated uronic acids as compared to the tunical extracts (1.47+/-0.09, and 1.49+/-0.15 as opposed to 0.75+/-0.15 microg/mg dry defatted tissue, respectively; S.E.M., n=5). With the exception of hyaluronic acid, the relative amount of individual glycosaminoglycan types varied significantly among extracts of different origin. Heparan sulphate was more abundant in cavernosal, dermatan sulphate in tunical, and chondroitin-6-sulphate in corpus spongiosum extracts. No structure-specific differences were detected with respect to the molecular mass distribution of each glycosaminoglycan type. Our study shows that the different structures of the human penis produce distinct profiles of glycosaminoglycans, which are well suited to the individual functional characteristics of these structures.

Sildenafil versus intracavernous injection therapy: efficacy and preference in patients on intracavernous injection for more than 1 year.

PURPOSE: To our knowledge comparative data on the effectiveness of and patient preference for intracavernous injection therapy and sildenafil are still not available. We evaluated the efficacy of sildenafil as well as patient preference in a group of impotent men on intracavernous injection for more than a year. MATERIALS AND METHODS: Patients on intracavernous injection therapy for more than a year without neurological disease and/or a contraindication to sildenafil treatment were recruited for study. In phase 1 we determined the efficacy of 50 and 100 mg. sildenafil citrate at home. In phase 2 responders to sildenafil were asked to use the preferred dose orally for a month and choose intracavernous injection or sildenafil. In phase 3 patients were asked to continue either treatment for 3 more months. Patient preferences were reported at the end of phases 2 and 3. RESULTS: Of the 180 men recruited 155 with a mean age of 56.4 +/- 12.6 years on intracavernous injection for a mean of 26 +/- 9 months accepted and were included in our series. Overall 116 men (74.8%) responded to sildenafil during study phase 1. After 1 month of treatment 71 responders (61.2%) preferred to continue with the oral drug, 31 (26.7%) returned to intracavernous injection and 14 (12.1%) used each drug alternately. Three months later 74 of the 116 responders (63.8%) preferred oral treatment and 38 (32.8%) chose intracavernous injection, while 4 (3. 4%) continued to use each treatment alternately. CONCLUSIONS: Sildenafil is highly effective in intracavernous injection responders, although a certain group prefer to continue intracavernous injection. While sildenafil should be considered first line treatment, men with erectile dysfunction should be aware of all treatment options available because nonresponders to sildenafil may respond to intracavernous injection.

Benign hyperplasia of the human prostate is associated with tissue enrichment in chondroitin sulphate of wide size distribution.

BACKGROUND: Benign prostatic hyperplasia (BPH) involves qualitative and quantitative alterations in extracellular matrix (ECM) components affecting stromal-epithelial interactions. Glycosaminoglycans (GAGs) are polysaccharide components of the ECM whose role in the development of BPH is under investigation. METHODS: GAGs were extracted from human prostates of normal and BPH origin and were subsequently fractionated through DEAE-sephacel anion exchange chromatography. The isolated GAG fractions were identified through electrophoresis on cellulose acetate membranes and treatment with GAG-degrading enzymes of known specificity. Their size distribution was determined through gradient polyacrylamide gel electrophoresis. RESULTS: Isolated prostatic GAGs included hyaluronic acid (HA), heparan sulphate (HS), and a mixture of dermatan sulphate (DS) and chondroitin sulphate (CS). The CS/DS ratio was significantly higher in hyperplastic as compared to normal prostates. A difference was also observed with respect to the apparent molecular mass of the DS-CS mixture, which reflects the CS enrichment in BPH. GAGs isolated from hyperplastic prostates were more diverse in size as compared to the corresponding glycans from normal prostates. CONCLUSIONS: The apparent increase in CS and decrease in DS content in prostates of patients with BPH is in good agreement with the pathological manifestation of increased cell proliferation in hyperplastic prostate tissue, since these glycan molecules have been reported to increase and decrease cell proliferation, respectively. Identification of the responsible enzymes involved in the homeostasis of CS and DS may provide alternative targets for pharmacological intervention.

Hemodynamic characterization of a functional erection. Arterial and corporeal veno-occlusive function in patients with a positive intracavernosal injection test.

OBJECTIVES: To characterize hemodynamically a functional/rigid erection and study the hypothesis that a positive intracavernosal injection test indicates normal arterial and corporeal veno-occlusive function. METHODS: 33 patients (mean age 39.5 +/- 9 years), who developed rigid erection during pharmacocavernosometry, included in the present study. The presence of axial rigidity was determined at steady state equilibrium intracavernosal pressure, by absence of buckling to axial force of 1 kg, applied to the erect penis and sustained for >/=15 min. Arterial and veno-occlusive hemodynamic parameters were analyzed. RESULTS: Flow-to-maintain at intracavernosal pressure 150 mm Hg and mean pressure decay values ranged between 0.5-13 ml/min and 5-85 mm Hg, respectively. Flow-to-maintain values >5 ml/min were noticed in 8 patients (24. 24%), while pressure decay values >45 mm Hg in 13 patients (39.39%). Pharmacocavernosography revealed moderate opacification of venous structures in 7 cases (21.21%). Abnormal systemic-cavernosal systolic arterial pressure gradients in both cavernosal arteries were noticed in 9 patients (27.27%). All patients with flow-to-maintain values >5 ml/min had normal arterial function. CONCLUSIONS: A functional/rigid erectile response may coexist with arterial insufficiency or corporeal veno-occlusive dysfunction. Presence of normal or borderline arterial inflow may compensate minimal or moderate veno-occlusive dysfunction, resulting in a functional - but not normal - erection. Such information is critical when the intracavernosal injection test is used for diagnostic purposes.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part III--Clinical considerations of penile hemodynamic and rigidity erectile responses.

PURPOSE: The extent to which hemodynamic erectile responses predict penile buckling forces has not previously been analytically investigated. An engineering study was performed to compare hemodynamic data with penile buckling force values. METHODS: Dynamic infusion pharmacocavernosometry studies in 21 impotent patients (age 43, range 24-62 y) were accomplished to obtain information during penile erection concerning hemodynamic values, penile buckling forces and their determinants: intracavernosal pressure, erectile tissue mechanical properties and penile geometry. RESULTS: In the 21 patients, discrepancies existed in several patients who demonstrated normal hemodynamic values (low flow-to-maintain and high equilibrium intracavernosal pressures) but elevated cavernosal compliance values and diminished penile buckling forces. There was poor correlation between cavernosal compliance and equilibrium intracavernosal pressure (r = -0.36); better correlation between compliance and expandability (r = -0.72) and best correlation between dimensionless compliance and the dimensionless product of expandability with equilibrium pressure (r = -0.88). These data implied that cavernosal compliance was dependent on multiple factors, not only equilibrium intracavernosal pressure. CONCLUSIONS: Hemodynamic indices which correlate with intracavernosal pressure alone do not predict penile buckling forces since the latter are dependent not only on intracavernosal pressure but also on penile geometry and erectile tissue properties. The most relevant tissue property in predicting adequate penile buckling forces is cavernosal expandability. A new impotence classification system and diagnostic algorithm based on the determinants of penile rigidity and not exclusively on hemodynamic responses in proposed.

Current treatment and future perspectives for erectile dysfunction.

During the last fifteen years the field of erectile dysfunction has grown tremendously, offering several treatment options to impotent patients, such as intracavernosal pharmacotherapy, vacuum therapy, penile vascular surgery and penile prosthetic surgery. Several multicenter clinical trials have been undertaken and numerous studies have been published, showing that the 'gold standard' treatment does not exist. As new oral, intraurethral and intracavernosal medications are added to the armamentarium of physicians and even more will be available for physicians and patients in the near future, the question becomes apparent: which treatment and when? The present paper critically reviews the existing information on currently available treatment options, and discusses future perspectives based on data from ongoing clinical trials. Considerations for the development of a new management strategy are also discussed.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part I--Clinical implications of penile tissue mechanical properties.

PURPOSE: The least investigated physical determinant of penile rigidity has been penile tissue material properties. The goals in this study (Part I) were to define two penile mechanical parameters, cavernosal expandability X and tunical distensibility VE/VF, determine their magnitudes in humans and develop an analytical expression for penile volume as a function of these two tissue characteristics and intracavernosal pressure. METHODS: Dynamic infusion pharmacocavernosometry was performed in 21 impotent patients (age 43 +/- 19 y) to provide human geometric, hemodynamic and structural data. A mathematically derived model of hemodynamic and structural-dynamic characteristics of penile erection was developed (Parts I, II, III) incorporating penile tissue mechanical qualities. RESULTS: Cavernosal expandability X provided a measure of the ability to approach maximum volume at relatively low intracavernosal pressures. Tunical distensibility VE/VF denoted the maximal erect to flaccid penile volume ratio. The magnitudes of X and VE/VF in the study population were 0.04-0.17 mmHg-1 and 1.7-5.0 respectively. CONCLUSIONS: Enabling penile volume to be derived as a function of tissue mechanical characteristics and pressure, allows for penile rigidity to be expressed (in Part II) as a function of pressure, geometry and tissue qualities.

Engineering analysis of penile hemodynamic and structural-dynamic relationships: Part II--Clinical implications of penile buckling.

PURPOSE: Penile buckling force was analytically described in terms of its constituents. In addition, theoretically-derived buckling force data were compared to clinically measured data and the influence of each constituent on penile buckling force data was assessed. METHODS: Using engineering buckling theory for a column, a mathematically-derived penile buckling model was developed which incorporated geometric and hemodynamic data obtained by dynamic infusion pharmacocavernosometry studies in 21 impotent patients (age 43, range 24-62 y) as well as penile tissue mechanical characteristics previously developed (Part I). RESULTS: In 17 of 21 patients the mean difference between theoretically derived and clinically measured buckling force data was 0.33 +/- 0.25 kg (r = 0.96). Factors which increased penile buckling forces were: (1) high intracavernosal pressure values (rigidity was related to pressure in an exponential-like fashion); (2) high penile aspect ratio (D/L) values (relatively large diameter/short length penile geometry) and high flaccid diameter; and (3) high cavernosal expandability values (a measure of the ability of the corpora to approach its erect volume with relatively low intracavernosal pressures). CONCLUSIONS: Pressure-volume data (pressure, geometry and tissue characteristics) obtained during erectile function testing have been shown, for the first time, to theoretically predict the magnitude of clinically-measured penile buckling forces.

Nocturnal penile tumescence and rigidity monitoring in young potent volunteers: reproducibility, evaluation criteria and the effect of sexual intercourse.

PURPOSE: We studied the reproducibility of nocturnal penile tumescence, rigidity evaluation criteria and the possible effects of sexual intercourse in young, healthy, potent male volunteers. MATERIALS AND METHODS: We recruited 12 male medical students 21 to 24 years old into the study. A disorder-free medical history, availability of a sexual partner and normal erectile function were the inclusion criteria. All subjects completed 3 sessions of 3 nights of recording using the RigiScan* device with at least a 3-day interval between recordings. During the last 3-night recording subjects were asked to have sexual intercourse at least once. Analysis of the recordings was focused on the best erectile event as well as on rigidity and tumescence activity units normalized per hour. RESULTS: The subjects completed 36, 3-night recordings. Of the total of 108 sessions 18 occurred after sexual intercourse. We analyzed 562 erectile episodes. All 3-night recordings included at least 1 episode of rigidity at the penile tip greater than 60% and more than 10 minutes in duration. Sexual intercourse did not significantly affect nocturnal penile tumescence and rigidity. When rigidity and tumescence activity unit values were normalized by the hour and expressed as mean values of the 3-night sessions, documented values became reproducible. CONCLUSIONS: At least 2 consecutive nights of recording are necessary to evaluate nocturnal penile tumescence and rigidity recordings. Nocturnal penile tumescence and rigidity with at least 1 erectile episode of tip penile rigidity greater than 60% and 10 minutes in duration may be associated with potency. Mean rigidity and tumescence activity unit values per hour of a recording may be used as objective parameters to measure overall erectile activity. In addition, sexual intercourse seems to decrease nocturnal penile tumescence and rigidity measurements, although not statistically significant. We anticipate that application of these criteria for nocturnal penile tumescence and rigidity evaluation will improve the diagnostic validity of the test. Future research will determine whether these criteria are too strict for the evaluation of aging men.

New method for direct stiffness measurement of the corpora cavernosa.

We describe a new methodology for direct ex vivo measurements of corporal stiffness. Using a new biosensor, stiffness of the corpora cavernosa was measured in 32 mature male Spraque Dawley rats. Mean stiffness (+/- se) value of the corpora was 8.186 +/- 0.318 gm/cm. The corpora was numerically the stiffest organ, when compared to the bladder and the prostate. Values measured at different points from both corpora showed a quite uniform stiffness (range 7.576-8.835 gm/cm). Hormonal stimulation with DHT was shown to significantly increase prostatic stiffness but not corpora stiffness. Similarly alpha-adrenergic antagonists did not affect corporal stiffness in a statistically significant manner. These results suggest that the influence of hormones and adrenergic stimulation on the passive properties of the corpora is negligible. It is concluded that this new method provides a reproducible new parameter for the measurement of corporal stiffness. It is anticipated that in the future this kind of stiffness measurement may be of use for the evaluation of the biomechanical properties of the corpora and its response to pharmacologic manipulation of the trabecular smooth muscle tone in vivo.

In vivo assessment of trabecular smooth muscle tone, its application in pharmaco-cavernosometry and analysis of intracavernous pressure determinants.

A pharmaco-cavernosometry based clinical study was designed to define hemodynamic parameters consistent with complete trabecular smooth muscle relaxation, establish a methodology for overcoming incomplete trabecular smooth muscle relaxation, and determine under controlled conditions the contribution of venous outflow and arterial inflow to the steady-state equilibrium intracavernous pressure. Flow-pressure relationships were analyzed in 21 patients each of whom was assumed to have complete smooth muscle relaxation by virtue of the full, rigid and maintained erectile response following intracavernous vasodilator administration, which required intracavernous adrenergic agonists to achieve detumescence. Flow-to-maintain values increased linearly with intracavernous pressure while venous outflow resistance values were high and constant. Based on these relationships, trabecular smooth muscle tone was assessed in 123 impotent patients. In 14%, 63% and 14% of the patients (112 of 123 overall), respectively, 1, 2 and 3 doses of vasoactive agents were required to achieve hemodynamic relationships consistent with complete trabecular smooth muscle relaxation. In 9% of the patients such hemodynamic relationships were unable to be reached. In the 112 patients the influence of different engineering based measures of corporeal veno-occlusive function, including flow-to-maintain, pressure decay, venous outflow resistance and corporeal capacitance, was analyzed against the spectrum of equilibrium steady-state intracavernous pressures. Two distinct equilibrium pressure groups were identified reflecting different capacitance states: pressures greater than 60 mm. Hg (associated with low capacitance values) and pressures less than 50 mm. Hg (associated with high capacitance values), with pressures 50 to 59 mm. Hg representing a hemodynamic transition zone. When analyzed during complete trabecular smooth muscle relaxation, corporeal veno-occlusive hemodynamic variables in conjunction with cavernous arterial perfusion pressure determine the steady-state equilibrium intracavernous pressure. Failure to assess corporeal veno-occlusive function under such conditions will overestimate the degree of suspected corporeal structural disease.

Construction of a surrogate variable for impotence in the Massachusetts Male Aging Study.

Uncollected data must be filled in after the fact in many epidemiological studies. We compared several methods for constructing a surrogate variable for erectile potency, based on responses to related questions, in the Massachusetts Male Aging Study (MMAS). Quadratic discriminant analysis performed best among the procedures tested, achieving high rates of correct classification in cross-validation of training data and (according to posterior estimates) in classification of MMAS subjects. Two versions of the surrogate variable were constructed, one involving a discrete classification and the other involving a set of continuous probabilities. The two versions were used to investigate medical correlates of impotence in MMAS and produced similar results, although the continuous version appeared to provide higher statistical power. We conclude that construction of a surrogate variable is a viable and potentially beneficial option in epidemiological investigations.