ASSESSMENT AND MODELING OF THE PHYSICAL COMPONENTS OF HUMAN CORPOROVENOUS FUNCTION

To understand and quantify specific causes of venoocclusive dysfunctio n, an analog model of penile hemodynamics, including a mechanism of fl ow limitation by subtunical veins, was developed and a detailed analyt ic 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 compli ances. The model predicted a steady-state cavernosal pressure (P-ca)-i nfusion flow relationship with two phases: an initial phase characteri zed by a gradual slope up to a critical flow and a second phase charac terized by a much steeper slope after limitation of subtunical venular flow. Model predictions were compared with clinical data obtained dur ing 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-f low to constant-pressure feedback control when P-ca reached the thresh old of 80 mmHg. Steady-state pressure-flow and pressure-circumference relationships of the penis were analyzed and interpreted in terms of s pecific components of the electrical analog model. These clinical stud ies demonstrated that patients with a functional venoocclusive mechani sm (i.e., those able to achieve 100 mmHg P-ca with infusion flow rates <60 ml/min during PhC) had a steeper initial slope of the pressure-fl ow relationship during SaC and a greater increase in penile circumfere nce and P-ca after intracavernosal injection of papaverine-phentolamin e than those with an impaired venoocclusive mechanism. From the electr ical 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, cavern osal and subtunical compliances, and full relaxation of cavernosal smo oth muscle. We conclude that the proposed analog model can be used to interpret and characterize clinical penile hemodynamic data and may pr ovide guidelines for more successful management of patients with erect ile dysfunction.