The mechanics of corporal veno-occlusion in penile erection: a theory on the effect of stretch-associated luminal constrictability on outflow resistance

Abstract

In order to further our understanding of the physiology of corporal veno-occlusion, we developed a theory of a possible contribution to corporal venous outflow resistance which occurs as the result of venule stretching with resultant luminal narrowing when penile volume increases during the erection process. We stretched non-biological tubes and rabbit abdominal vena cava segments, performed flow-based and volume-based experiments to calculate the magnitude of N, the newly defined ‘stretch-associated luminal constrictability’ factor. We solved for (R_s/R_u), the ratio of the venule fluid resistance in the stretched state (R_s) to the unstretched state (R_u), to quantify the projected increases in fluid resistance as well as Q.R_u where Q is the subtunical venule flow rate.

For a given tube, N was found to be essentially constant for different amounts of stretch. A theory was formulated which predicted R_s andQ as a function of N, ΔP (intracavernosal pressure increase); V_E/V_F (tunical distensibility); X (cavernosal expandability) andR_u. Based on the magnitude ofN=2, this theory predicts that patients with the highest values of bothV_E/V_F andX would have maximalR_s values, approaching infinity (complete occlusion) at a low ΔP near 5 mmHg. In contrast, patients with low values of both V_E/V_F (eg Peyronie’s disease) and X (eg corporal fibrosis), would be predicted to have minimalR_s values. For example, a hypothetical patient with the lowest values of V_E/V_F and X would yieldR_s values only approaching 7.9 times that of unstretched values at a ΔP increase of 90 mmHg.

We concluded to that stretch-associated venule resistance may occur as a result of decreased sub-tunical venule diameter and increased sub-tunical venule length. In individual patients, stretch-associated venule resistance may either dominate or be a minor component of the overall mechanism of corporal veno-occlusion.