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 bowel bladders is presented. The results are compared with clinical findings following bladder substitution with the tubular ileocaecal and the detubularised urethral Kock reservoir. The theoretical results are consistent with clinical observations showing that detubularisation increases reservoir capacity substantially, delays the onset and reduces the amplitude of the pressure rise produced by contractions. These findings account for the markedly improved nocturnal continence (80 versus 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 year) with detubularised bladder substitution. A simple equation is derived to calculate the capacities of both near-spherical and cylindrical reservoirs. The capacity of the U pouch is calculated to be less than that of the W-shaped, S-shaped and Kock reservoirs. Altering the shape of a reservoir from spherical to ellipsoid is calculated to have only a slight effect on its mechanical characteristics. Consequently the essence of detubularisation is to create a reservoir with high capacity, while shape is of secondary importance.