MECHANICAL CHARACTERISTICS OF TUBULAR AND DETUBULARIZED BOWEL FOR BLADDER SUBSTITUTION - THEORY, URODYNAMICS AND CLINICAL-RESULTS

A theoretical analysis of the mechanics of tubular and detubularised b owel bladders is presented. The results are compared with clinical fin dings following bladder substitution with the tubular ileocaecal and t he detubularised urethral Kock reservoir. The theoretical results are consistent with clinical observations showing that detubularisation in creases reservoir capacity substantially, delays the onset and reduces the amplitude of the pressure rise produced by contractions. These fi ndings account for the markedly improved nocturnal continence (80 vers us 17% at 2 years), the longer voiding intervals (4 versus 2.5 h at 1 year) and the predisposition to urinary retention (25 versus 0% at 1 y ear) with detubularised bladder substitution. A simple equation is der ived to calculate the capacities of both near-spherical and cylindrica l reservoirs. The capacity of the U pouch is calculated to be less tha n that of the W-shaped, S-shaped and Kock reservoirs. Altering the sha pe of a reservoir from spherical to ellipsoid is calculated to have on ly a slight effect on its mechanical characteristics. Consequently the essence of detubularisation is to create a reservoir with high capaci ty, while shape is of secondary importance.