Darrell A. Frohrib

The hemodynamic pathophysiology of impotence following blunt trauma to the erect penis.

A total of 19 patients provided a history of impotence following blunt trauma to the erect penis during intercourse or masturbation, or after accidents. Corporeal veno-occlusive dysfunction was the most common hemodynamic abnormality (16 of 19 patients, or 84%). A site-specific leak, which consisted of abrupt filling of the dorsal vein and/or corpus spongiosum from a focal site on the penile shaft, was demonstrated in 15 patients (79%). Cavernous artery insufficiency was found less often (7 of 19 patients, or 37%). A focal mid shaft cavernous artery occlusion was demonstrated in 5 patients (28%). It is hypothesized that the aforementioned hemodynamic abnormalities are caused by tunica and intracavernous vasculature injuries induced by the marked short-term pressure increases, which approach or exceed the tunica tensile strength during acute abrupt loading of the erect penis. This hypothesis is supported by direct recording of intracavernous pressures that exceeded 450 mm. Hg in response to angulation and manual compression of the penile shaft. Further evidence was created by a biomechanical model that was based on previously published intracavernous pressure--circumference patient data during dynamic infusion pharmacocavernosometry. Using a typical patient data set a 60% diminution of circumference at the site of abrupt loading was calculated to induce a 15% increase in circumference in the nonloaded portion of the penile shaft and an elevated intracavernous pressure exceeding 900 mm. Hg. The site-specific hemodynamic abnormalities were found to occur not only in patients with a classical penile fracture history but also in patients with injuries during masturbation or following accidents who had no acute penile swelling or ecchymosis. Thus, the erect penis is at risk for injury during any acute loading situation. It is likely that this erect trauma-induced hemodynamic pathology occurs more frequently than previously appreciated and that this type of impotence may be the underlying basis for many cases of idiopathic Peyronies disease.

Finite element approach to mathematical modeling of high-speed elastic linkages

Abstract A general approach is described for deriving the equations of motion of planar linkages in high-speed machinery. Based on the work of several current authors, well-known displacement finite element method is used to develop the mass and stiffness properties of an elastic linkage. To demonstrate the various steps in the analysis, a 4-bar linkage is utilized; however the method is readily extendible to other planar multi-loop linkages. Starting with a typical elastic planar beam element, the nodal displacement and acceleration expressions are derived including the terms coupling the elastic and rigid-body motions. The linkage is modeled as beam elements and its equations of motion are stated in matrix form. Methods are described for systematic assembly of all elements, resulting in the undamped equations of motion of the total system. Conventional forms of structural damping are reviewed and appended to this paper for inclusion in the equations of motion. This paper also includes assumptions made in order to simplify the analyses here as well as facilitate numerical solutions.