Bladder compliance describes the relationship between bladder volume and detrusor pressure and is defined as the change in detrusor pressure during the filling phase of urodynamics. The first problem is determining what is normal and how best to measure it.
The calculation is simple: change in pressure divided by change in volume. However, this assumes a linear curve and ignores the shape of the curve between the beginning and end of filling. The classic study by Ed McGuire defined a limit of 40 cm H₂O as the point above which upper tract deterioration occurred.2 However, this was in a group of children with myelomeningocele. Whether the same threshold applies to other populations remains uncertain.
Other investigators have defined a normal threshold as 10–40 mL/cm H₂O. Rovner and colleagues discussed whether it might be better to calculate the area under the urodynamic filling pressure curve and establish values based on that approach.
The authors further cite the important fact that grossly unphysiological filling rates — normal rates are 1–2 mL/min — create a problem for all urodynamic parameters using current methodologies. If intravesical pressure measurements obtained by totally bladder-contained pressure sensors become popular, a new set of standards will need to be established, not only for compliance and “high-risk bladders,” but likely for other urodynamic parameters as well.
The authors further expand our knowledge regarding the measurement of bladder compliance by pointing out additional precepts from their own experience and from the experience of others. The bibliography is excellent. These points include:
- Compliance assessment should not continue beyond the first episode of incontinence during filling.
- Fluid escaping from the bladder distorts accurate assessment of pressure and volume. Examples include bladder diverticulum, vesicoureteral reflux, and fistula.
- Different parts of the bladder may respond differently to sustained elevations in pressure, raising the question of whether this could affect compliance measurement.
- Less invasive measurement techniques
- Ultrasound bladder vibrometry and shear wave elastography
- Patterns of abnormal bladder shape and the presence of trabeculations
- Measurement of effective renal plasma flow with MAG3 renal scintigraphy
- Potential biomarkers for poor bladder compliance, including urinary nerve growth factor (NGF), transforming growth factor beta 1 (TGF-β1), tissue inhibitor of metalloproteinases 2 (TIMP-2), and bladder wall thickness
- Urodynamic parameters: compliance, with a separate table listing confounders; detrusor overactivity; bladder outlet obstruction; capacity; sensation; and post-void residual
- Etiology of lower urinary tract dysfunction: bladder outlet obstruction, neurogenic disease, infection, radiotherapy, and chemical cystitis
- Bladder morphology: diverticula and trabeculation
- Ureteral morphology: vesicoureteral reflux
- Age
- Gender
Written by: Alan Wein, MD, PhD, FACS, Professor of Clinical Urology, Department of Urology, Desai Sethi Urology Institute (DSUI), University of Miami Miller School of Medicine, University of Miami Health Systems, Miami, FL
References:
- Rovner E, et al. What are the limitations of measuring bladder compliance as the sole indicator of future risk to the upper urinary tract and renal function? ICI-RS 2025. Neurourology and Urodynamics. 2026;1-8. doi:10.1002/nau.70236.
- McGuire E, et al. Prognostic value of urodynamic testing in myelodysplastic patients. Journal of Urology. 2002;167:1049-1053.
- Wyndaele J, et al. Bladder compliance: what does it represent; can we measure it, and is it clinically relevant? Neurourology and Urodynamics. 2011;30:714-722.