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INTRODUCTION: During urodynamics, pressure generally increases little during filling. Furthermore, afferent nerve signaling reflects detrusor wall tension rather than pressure. Thus, there is a pressing need for methods that evaluate detrusor wall tension. We describe a novel method to determine detrusor wall tension during urodynamics by incorporating real-time ultrasound.
MATERIALS AND METHODS: As part of an IRB−approved extended urodynamics protocol individuals with OAB defined as ICIq−OAB question 5a≥3 had real-time ultrasound during filling. Fill rate was set at 10% cystometric capacity (C_cap). Ultrasound images were obtained by an ultrasound technologist, holding the probe in a constant position throughout filling to capture mid−sagittal and maximum transverse images every 60 seconds. Images were time-linked to bladder pressure (P_ves) data.
RESULTS: Using acquired ultrasound image and P_ves data, we developed an objective technique to calculate detrusor wall tension, wall stress, and wall compliance as follows: From acquired cross−sectional images, we measured wall and luminal areas as well as inner and outer perimeters. Wall tension was calculated as P_ves*luminal area and wall stress as wall tension/wall area. While P_ves remained relatively constant during filling, wall stress increased exponentially. Strain was calculated as the change in inner perimeter/inner perimeter at 10%C_cap, and compliance as strain/stress.
CONCLUSIONS: Detrusor wall tension, wall stress, and wall compliance can be calculated by adding real-time ultrasound to standard urodynamics. Furthermore, P_ves measurements do not reflect the underlying state of detrusor wall tension. This technique may be useful in the diagnosis and treatment of OAB and other disorders of voiding dysfunction.