6 - The Unstable Bladder

Abstract

Overactive bladder is often characterized by biomechanical changes in the bladder wall, but there is no established method to measure these changes in vivo. The goal of this study was to develop a novel method to determine detrusor wall biomechanical parameters during urodynamics through the incorporation of transabdominal ultrasound imaging. Individuals with overactive bladder (OAB) underwent ultrasound imaging during filling. The fill rate was 10% of the cystometric capacity per minute as determined by an initial fill. Transabdominal ultrasound images were captured in the midsagittal and transverse planes at 1 min intervals. Using image data and Pves, detrusor wall tension, stress, and compliance were calculated. From each cross − sectional image, luminal and wall areas along with inner perimeters were measured. In the sagittal and transverse planes, wall tension was calculated as Pves ∗ luminal area, wall stress as tension/wall area, and strain as the change in perimeter normalized to the perimeter at 10% capacity. Elastic modulus was calculated as stress/strain in the medial–lateral and cranial-caudal directions. Patient-reported fullness sensation was continuously recorded. Data from five individuals with OAB showed that detrusor wall tension, volume, and strain had the highest correlations to continuous bladder sensation of all quantities measured. This study demonstrates how detrusor wall tension, stress, strain, and elastic modulus can be quantified by adding ultrasound imaging to standard urodynamics. This technique may be useful in diagnosing and better understanding the biomechanics involved in OAB and other bladder disorders.