AXIAL PENILE RIGIDITY - DETERMINANTS AND RELATION TO HEMODYNAMIC PARAMETERS

Erectile dysfunction may be defined in terms of axial penile rigidity, the physical property that enables the erection to be utilized as a p enetration tool during sexual activity. Erectile dysfunction occurs wh en inadequate axial penile rigidity results in buckling of the penile column when subjected to axial compressive loading situations during v aginal intromission. New multidisciplinary engineering studies of peni le hemodynamic and structural dynamic relationships are reviewed conce rning the determinants of axial penile rigidity. Axial penile rigidity develops as a continuum during the increases in intracavernosal press ure and volume changes from the flaccid state and is influenced by int racavernosal pressure, penile tissue mechanical properties and penile geometry. Two penile tissue mechanical properties are especially relev ant; cavernosal maximum volume at relatively low intracavernosal press ure, and tunical distensibility, the relative volume of the fully erec t to completely flaccid pendulous penis. Two penile geometric properti es are critical; the penile aspect ratio, defined as the diameter to l ength ratio of the pendulous penis, and the magnitude of the flaccid p enile diameter. Clinically measured values of axial buckling forces in patients undergoing dynamic pharmacocavernosometry strongly correlate d to theoretic-based analytic derived magnitudes of axial penile rigid ity based on these above pressure, tissue and geometric determinants. Since axial penile rigidity is not exclusively dependent upon intracav ernosal pressure, patients with normal erectile hemodynamics may be er roneously labelled as having psychogenic dysfunction where their true pathophysiology may be related to abnormal penile tissue properties an d/or penile geometric factors. Similarly, some patients may claim suff icient rigidity for penetration, but have abnormal hemodynamic erectil e function studies. They may have uniquely advantageous tissue mechani cal and/or geometric properties. More research is needed concerning ax ial penile ridigity, a most influential factor determining functional erectile quality, erectile potency and successful coitus.