Clinical evaluation of patients with prostatic obstruction: correlation of flow rates with voided, residual or total...

Previous investigators reported that accurate estimation of average or maximum urinary flow rates required correlation with total bladder volume (voided plus residual volumes). To test this requirement we performed uroflowmetry studies on 124 patients before and 77 patients after prostatectomy. Of the patients 20 were tested on multiple preoperative and postoperative occasions to comprise paired observations. Observations were made on age, voided and residual volumes, voiding duration, and average, maximum and adjusted maximum flow rates. Prostatectomy resulted in significant increases in all flow rates and significant decreases in voiding duration. The procedure had significant effects on reducing residual volume but voided volumes increased and total volume decreased only slightly postoperatively. Preoperative average, maximum and adjusted peak urinary flow rates correlated negatively with residual volume (increasing residual volume correlates with decreasing flow rate). Maximum flow rates correlated positively with voided volume. Whether measured preoperatively or postoperatively no significant correlation was found among average, peak or adjusted flow rates and total bladder volume. The only consistent significant correlation found among voided, residual and total volumes, and other measurements was voiding duration, which increased as any of the aforementioned volumes increased. Comparison of the random total and paired populations revealed no significant difference. Use of voided rather than total volume seems preferred in correlations with maximum urinary flow rates. Determination of residual urine remains necessary as an estimation of emptying failure but it is not required information for determination of flow rates.