Challenging the maximum flow rate: a new index of voiding dysfunction in men with benign prostatic enlargement

To present the theoretical development and clinical relevance of a new index of voiding dysfunction (D) based purely on free uroflow (FF), to assist in the management of patients with benign prostatic enlargement (BPE), and to compare its merits against the maximum flow rate (Q(max)).

In the Valentini-Besson-Nelson (VBN) micturition model for men, two variables characterize urethral obstruction, i.e. the prostatic urethral counter-pressure pucp and the detrusor force coefficient k. D can be obtained from a FF assuming a normal detrusor (k = 1). Clinically, multiple FF from patients entered in a double-blind pharmacological trial provided variations of D over time. D values were also compared before and after transurethral resection of the prostate (TURP).

In 137 patients with BPE from several institutions, D was more precise than Q(max) because D is independent of volume and of perturbations of short duration during the flow. The change in D was proportionate to the invasiveness of treatment; the mean (SD) decrease after TURP was 14.6 (8.7) cmH(2)O, vs 8.1 (5.4) cmH(2)O after 90 days of alpha-blocker intake. Retrospectively, the range of D fitted with the clinician's decision, i.e. pharmacological trial (16-31 cmH(2)O) vs TURP (27-46 cmH(2)O; P < 0.001).

The new index (D), deduced from the VBN analysis of only FF, is responsive to treatment. This simple calculation offers an insight into the voiding status of a patient with BPE beyond that obtained by Q(max) alone.