Bladder outlet resistance

We developed a method to objectively compare methods for the quantification of bladder outlet resistance.

We studied unselected voiding cystometries from 131 male patients. Several models proposed for bladder outlet resistance were fitted to the lowest monotonically increasing part (bottom) of the pressure flow plots. In conjunction with a parameter for bladder contractility, the model parameters were used as predictors of post-void residual greater than 20% of filled volume.

The pressure decrease in relaxed bladder outlet was best described by a linear function of the flow rate. The flow rate independent and dependent parts of that function were statistically significant predictors for residual. However, they could be combined into 1 index that was as efficient as the 2 numbers separately in predicting residual. This index is the average pressure of the bottom of the pressure flow plot.

We describe how different models for the quantification of bladder outlet resistance can be compared objectively on the basis of their ability to predict a significant post-void residual. Using this criterion in an unselected group of measurements, the average pressure of the bottom of the pressure flow plot performed best as an index for bladder outlet resistance quantification. It combines (or weights) 2 components (dependent and independent flow rates) without losing its power to predict post-void residual.