IN-VIVO EVALUATION OF VISCOELASTICITY IN A BIOLOGICAL TUBE .1. STRESS-RELAXATION IN THE FEMALE URETHRA STUDIED BY CROSS-SECTIONAL AREA AND PRESSURE MEASUREMENTS

The urethral response to a sudden forced dilatation was studied by a m athematical analysis of the pressure response in ten healthy women. A total of 60 dilatations, using various sizes and velocities of deforma tion, were performed in the high-pressure zone. The decay in pressure during relaxation proved to follow an exponential equation of the foll owing form: Y=Z+C(alpha)e(-t/tau alpha)+C(beta)e(-t/tau beta), where Z is the equilibrium pressure, C-alpha and C-beta are pressure decay, a nd T-alpha and T-beta are time constants. The time constants were unaf fected by the circumstances of dilatation, whereas all the other param eters were correlated to size or velocity of dilatation, or both. The time constants showed a fairly high reproducibility when repeated afte r one weak. The method is presumed to characterise the tissue composit ion of the preiluminal tissue layers and may prove useful in the evalu ation of the normal urethal sphincter function. Furthermore, it may pr ove of value in the elucidation of the pathophysiology of stress urina ry incontinence.