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

Abstract

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.

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

“…This latter version of cavernosal compliance C H comp was previously calculated (Equation 11 instead of Equation 22 of Part I). 5 The incorrect assumption used for the derivation of cavernosal compliance in the previous literature was that compliance was constant over the range of intracavernosal pressures. 6 In Figure 4b, the dimensionless variables selected were C H comp aXV E and XP eq, the same as in Figure 4a.…”

“…In all cases, complete smooth muscle relaxation was felt to exist on the basis of pressure±¯ow-to-maintain and pressure±venous out¯ow resistance relationships. Modi®cations in technique concerning geometric (Part I) 5 and buckling force data (Part II) 2 were previously reported. In all cases, intracavernosal pressures P are expressed as DP, the pressure rise above the¯accid pressure.…”

“…Cavernosal compliance values were similarly plotted against equilibrium intracavernosal pressure values (Figure 1; cavernosal compliance vs equilibrium pressure data were also reported in previous literature studies). Cavernosal compliance was previously calculated (Equation 22 of Part 1) 5 where it was shown that at a given pressure, compliance was determined in terms of tissue mechanical properties, penile geometry and intracavernosal pressure (similar factors were used to determine the theoretical penile buckling forces). The correlation in our study was poor (r 70.36).…”

“…A newly described mathematically derived model of hemodynamic and structural-dynamic characteristics of penile erection was developed which incorporated penile tissue mechanical properties (Part I) 5 and penile buckling forces (Part II). 2 A series of analyses were performed (Part III) to further examine the relationship between the erectile hemodynamic variables described above and the constituents of penile buckling force.…”

“…, Part I in which cavernosal compliance has dependency upon pressure and expandability). 5 To further examine these relationships, cavernosal expandability, in units of inverse pressure, was multiplied by equilibrium pressure, thus creating a new dimensionless variable XP eq . Cavernosal compliance, in units of mlammHg, was divided by cavernosal expandability times the erect volume, thus creating a second new dimensionless variable C comp aXV E .…”