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

Abstract

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¯ow-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 70.36); better correlation between compliance and expandability (r 70.72) and best correlation between dimensionless compliance and the dimensionless product of expandability with equilibrium pressure (r 70.88). 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 classi®cation system and diagnostic algorithm based on the determinants of penile rigidity and not exclusively on hemodynamic responses is proposed.

Hemodynamic Characterization of a Functional Erection

“…This fact also explains the relatively low percentage of patients who received a supplementary dose of vasoactive solution in order to achieve complete smooth muscle relaxation and/or bedroom quality erectile response. The wide range of circumference and length values observed in our study sample together with the wide equilibrium intracavernosal pressure values distribution (48–92 mm Hg) reflect the important role of the geometry of the penis and the mechanical properties of the tissues in the development of a rigid erectile response [14]. …”

“…Currently available sophisticated screening procedures, such as pharmacocavernosometry and duplex ultrasonography, offer valuable information on the hemodynamic integrity, but hemodynamic parameters are inadequate to differentiate normal from functional erectile capabilities. Intracavernosal pressure per se cannot be used as a parameter expressing penile rigidity, as its magnitude associated with rigidity varies widely and several other contributory factors have been recognized, such as the mechanical properties of the corporal tissue and the tunica albuginea, as well as penile geometry [14]. Objective assessment of the quality of erectile response during pharmacocavernosometry and determination of the lowest intracavernosal pressure associated with rigidity seems critical in the characterization of a patient as impotent.…”

“…Furthermore, the quality of the pharmacologic erectile response was compared to the best quality erection achieved by the patients in their own home privacy [8]. Finally, the last inclusion criterion was absence of Peyronie’s disease or congenital penile deviation, as in such patients axial loading forces may undergo regional redistribution [14]. …”

Reply

“…This condition can be identi®ed only through DICC with associated penile rigidometry; such conditions when recognized can be surgically cured, whereas if unrecognized can lead to an erroneous labelling of`psychogenic dysfunction'. 1,2 In our view, DICC is the gold-standard dynamic evaluation, when penile surgery is planned. For what concerns the`time-consuming' aspect of DICC, the present study provides a new methodology (VG-AVSS) that signi®cantly reduces the test time, by drastically decreasing the need of redosing'.…”

A Mathematical Model of Penile Vascular Dysfunction and Its Application to a New Diagnostic Technique

“…12 Only a few mathematical models were developed and used to study the erection process. In a three-part paper, [13][14][15] tissue properties and mechanics of penile erection were studied using an engineering approach. Mathematical models were developed to study tunica distensibility and cavernosal expandability as well as the effects of forces and pressures on buckling force of the erect penis.…”