The pathophysiology of structurally based corporeal veno-occlusive dysfunction is related to elevated corporeal connective tissue content. Based on our data and those in the literature corporeal fibrosis is hypothesized to develop secondary to abnormalities in the regulation of normal collagen synthesis and degradation, most likely associated with adverse influences of chronic ischemia.

Purpose: The least investigated physical determinant of penile rigidity has been penile tissue material properties. The goals in this study (Part I) were to de®ne two penile mechanical parameters, cavernosal expandability X and tunical distensibility V E /V F , 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 AE 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 V E /V F denoted the maximal erect to¯accid penile volume ratio. The magnitudes of X and V E /V F in the study population were 0.04±0.17 mmHg 71 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.

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.

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 in¯uence 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 AE 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¯accid 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 ®rst time, to theoretically predict the magnitude of clinically-measured penile buckling forces.

Aim: An improved understanding of the relationship between radial and axial rigdity values would enable better appreciation of the clinical usefulness of RigiScan TM , the most widely utilized determination of erectile rigidity testing. Previous studies have shown that axial rigidity (measured by buckling forces) correlated well with radial rigidity (measured by RigiScan TM ) for radial rigidity values below 60%. For radial rigidity exceeding 60%, there was poor correlation. Heretofore, there has been no physiologic explanation of this phenomenon. Methods: During dynamic pharmacocavernosometry in 36 impotent patients, we investigated the relationship between axial buckling forces and RigiScan TM radial rigidity and, for the ®rst time, how they both vary with pressure, (which we varied over over a wide functional range). In addition, we recorded multiple penile length and diameter values enabling us to relate, also for the ®rst time, axial and radial rigidity to individual mechanical erectile tissue and penile geometric properties. Results: Marked differences were found in the manner RigiScan TM radial rigidity units and axial buckling force magnitudes increased with increases in intracavernosal pressure values in each individual. The former asymptotically approached a maximum ®nite value while the latter increased continuously towards in®nity. Based on data in this study, RigiScan TM radial rigidity values greater than 55% may be considered a necessary criteria for vaginal intromission capability in all partners but it is not a suf®cient one. Conclusions: Axial and radial rigidity share a common dependency upon intracavernosal pressure, however, they are also dependent upon other unique physical determinants. For axial rigidity, additional dependent variables include cavernosal erectile tissue properties and penile geometry, while for radial rigidity, this may include tunical surface wall tension properties. Clinical devices which assess functional penile rigidity should utilize axial and not radial rigidity testing.