The aim of this study was to establish the characteristics and to investigate the interactions between prostate volume, degree of obstruction, bladder contractility, the prevalence of residual volume, bladder compliance, bladder capacities, and the prevalence of instability in a large, well-defined group of men with lower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH). The 565 consecutive men included in this study met the criteria of the International Consensus Committee on BPH and voided more than 150 mL during uroflowmetry. Their residual urine volume and prostate size were estimated, and filling cystometry and pressure-flow studies were performed. Fifty-three percent of the men appeared to have obstruction. We found a positive correlation between prostate volume and Schafer's obstruction grade, except that mean prostate volume decreased at Schafer's grades 5 and 6. Significant negative correlations existed between Schafer's grade and cystometric bladder capacity and effective capacity. Bladder outlet obstruction results in incomplete emptying. Of all men, 26% had a significant residual volume (> 20% of cystometric capacity). Thirty-nine percent did not have residual volume. Of the 565 men, 46% had an unstable bladder. In particular, patients with an unstable bladder in the sitting and lying positions have a significantly higher Schafer's grade and contractility grade and a significantly lower cystometric and effective bladder capacity compared with patients without instability. Patients with a residual volume or instability were significantly older. We conclude that in men with LUTS suggestive of BPH, abnormalities of bladder and bladder outlet function vary greatly and have complex mutual interactions. (C) 2001 Wiley-Liss, Inc.
