OBJECTIVE: To devise a new, practical and more accurate method for measuring bladder compliance, and to show that traditional estimates of compliance are impractical. MATERIALS AND METHODS: Childhood bladder capacity varies greatly with age while detrusor pressure in a normal bladder does not. Consequently, traditional bladder compliance (DeltaV/DeltaP) increases with age, i.e. maturation. Therefore we devised a standard method that includes normal values of pressures and volumes to calculate and report bladder compliance in children, and that also applies to adults. A dimensionless number (NWahl(-1)) was computed for standardizing bladder compliance, comparing the normalized capacity to normalized pressure by the ratio (DeltaV/V(cap,NL))/(DeltaP/P(cap,NL)), where DeltaP is the pressure at bladder capacity, DeltaV the volume at bladder capacity, V(cap,NL) the volume at mean expected bladder capacity and P(cap,NL) the pressure at mean expected bladder capacity. V(cap,NL) is obtained from nomograms of published data. RESULTS: The bladder compliance of patients undergoing urodynamic testing was calculated using NWahl(-1) and the traditional equation (DeltaV/DeltaP). NWahl(-1) provided a more accurate diagnosis and therefore was of more practical use. CONCLUSIONS: Bladder compliance depends on patient age, sex and size; the new estimate used to standardize bladder compliance is based on these factors and is a dimensionless number. This may help when comparing patients and assessing outcomes.
OBJECTIVE: To devise a new, practical and more accurate method for measuring bladder compliance, and to show that traditional estimates of compliance are impractical. MATERIALS AND METHODS: Childhood bladder capacity varies greatly with age while detrusor pressure in a normal bladder does not. Consequently, traditional bladder compliance (DeltaV/DeltaP) increases with age, i.e. maturation. Therefore we devised a standard method that includes normal values of pressures and volumes to calculate and report bladder compliance in children, and that also applies to adults. A dimensionless number (NWahl(-1)) was computed for standardizing bladder compliance, comparing the normalized capacity to normalized pressure by the ratio (DeltaV/V(cap,NL))/(DeltaP/P(cap,NL)), where DeltaP is the pressure at bladder capacity, DeltaV the volume at bladder capacity, V(cap,NL) the volume at mean expected bladder capacity and P(cap,NL) the pressure at mean expected bladder capacity. V(cap,NL) is obtained from nomograms of published data. RESULTS: The bladder compliance of patients undergoing urodynamic testing was calculated using NWahl(-1) and the traditional equation (DeltaV/DeltaP). NWahl(-1) provided a more accurate diagnosis and therefore was of more practical use. CONCLUSIONS: Bladder compliance depends on patient age, sex and size; the new estimate used to standardize bladder compliance is based on these factors and is a dimensionless number. This may help when comparing patients and assessing outcomes.