Dependence of male voiding efficiency on age, bladder contractility and urethral resistance: development of a voiding efficiency nomogram

The influence of age, urethral resistance and bladder contractility on voiding efficiency was evaluated by pressure-flow studies in 138 men of a mean age of 60 years (range 18 to 86). From these studies the urethral resistance parameter was calculated and the maximum bladder contraction strength was determined. Premature fading of the bladder contraction was quantified by a bladder contraction strength decay factor. Voiding efficiency was expressed by the parameter of post-void residual urine volume as a percentage of the initial bladder volume. Multiple regression analysis showed that voiding efficiency depended significantly in descending order of importance on urethral resistance, maximum bladder contraction strength and bladder contraction strength decay factor. Patient age was not an independent factor. Maximum bladder contraction strength and bladder contraction strength decay factor were not correlated, suggesting that maximum bladder contraction strength and its decay constitute different properties of bladder contractile function. A voiding efficiency nomogram is proposed, making use of the values for maximum bladder contraction strength and urethral resistance in individual patients. Such a nomogram may have predictive value for the occurrence of acute retention but it must be tested prospectively.