Estimation of bladder contractility from intravesical pressure-volume measurements.

Aims: To describe parameters from urodynamic pressure recordings that describe urinary bladder contractility through the use of principles of muscle mechanics.

Methods: Subtracted detrusor pressure and voided flow were recorded from patients undergoing filling cystometry. The isovolumetric increase of detrusor pressure, P, of a voluntary bladder contraction before voiding was used to generate a plot of (dP/dt)/P versus P. Extrapolation of the plot to the y-axis and the x-axis generated a contractility parameter, v (the maximum rate of pressure development) and the maximum isovolumetric pressure, P , respectively. Similar curves were obtained in ex vivo pig bladders with different concentrations of the inotropic agent carbachol and shown in a supplement.

Results: Values of v , but not P , diminished with age in female subjects. v was most significantly associated with the 20-80% duration of isovolumetric contraction t ; and a weaker association with maximum flow rate and BCI in women. P was not associated with any urodynamic variable in women, but in men was with t and isovolumetric pressure indices.

Conclusions: The rate of isovolumetric subtracted detrusor pressure (t ) increase shows a very significant association with indices of bladder contractility as derived from a derived force-velocity curve. We propose that t is a detrusor contractility parameter (DCP). Neurourol. Urodynam. 36:1009-1014, 2017. © 2016 Wiley Periodicals, Inc.