Assessment and modeling of the physical components of human corporovenous function.

To understand and quantify specific causes of venoocclusive dysfunction, an analog model of penile hemodynamics, including a mechanism of flow limitation by subtunical veins, was developed and a detailed analytic study was conducted in patients with erectile dysfunction. Computer simulations for steady-state and transient intracavernosal conditions were carried out to study graded changes in cavernosal smooth muscle tone, subtunical venular resistance, and cavernosal and tunical compliances. The model predicted a steady-state cavernosal pressure (Pca)-infusion flow relationship with two phases: an initial phase characterized by a gradual slope up to a critical flow and a second phase characterized by a much steeper slope after limitation of subtunical venular flow. Model predictions were compared with clinical data obtained during incremental saline cavernosometry (SaC) and pharmacocavernosometry (PhC) in 13 patients with erectile dysfunction with use of a computer-controlled infusion system that automatically changed from constant-flow to constant-pressure feedback control when Pca reached the threshold of 80 mmHg. Steady-state pressure-flow and pressure-circumference relationships of the penis were analyzed and interpreted in terms of specific components of the electrical analog model. These clinical studies demonstrated that patients with a functional venoocclusive mechanism (i.e., those able to achieve 100 mmHg Pca with infusion flow rates < 60 ml/min during PhC) had a steeper initial slope of the pressure-flow relationship during SaC and a greater increase in penile circumference and Pca after intracavernosal injection of papaverine-phentolamine than those with an impaired venoocclusive mechanism. From the electrical analog model, initial steepness of the pressure-flow relationship (slope) during SaC mainly represented subtunical venular resistance, whereas maintenance of flow during PhC depended on overall function of the different components, i.e., subtunical venular resistance, cavernosal and subtunical compliances, and full relaxation of cavernosal smooth muscle. We conclude that the proposed analog model can be used to interpret and characterize clinical penile hemodynamic data and may provide guidelines for more successful management of patients with erectile dysfunction.