Categorization of Obstruction Using Noninvasive Pressure Flow Measurements: Sensitivity to Change Following Prostatectomy

Abstract

We determined whether categorizing men with lower urinary tract symptoms using a noninvasive pressure flow nomogram is sensitive to change following the removal of obstruction. A prospective cohort of men undergoing transurethral prostate resection was recruited, of whom 143 (69%) underwent noninvasive pressure flow study using the penile cuff technique before and 4 months following surgery. Cuff pressure required to interrupt voiding, estimated isovolumetric bladder pressure and maximum flow rate were recorded during a single void. Values were plotted on a nomogram categorizing cases as obstructed (upper left quadrant), not obstructed (lower right quadrant) or diagnosis uncertain (upper right and lower left quadrants). Changes in maximum flow rate, cuff pressure required to interrupt voiding and nomogram position following transurethral prostate resection were then analyzed. Transurethral prostate resection resulted in an improved flow rate for all diagnostic groups, which was highest for obstructed cases with a mean +/- SD increase of 11 +/- 6 ml second(-1) (p <0.01). Men categorized with obstruction and those placed in the upper right quadrant showed significant decreases in cuff pressure required to interrupt voiding following transurethral prostate resection with a mean decrease of -45 +/- 35 and -48 +/- 32 cm H(2)O, respectively (p <0.01). The number of cases classified as not obstructed increased from 28 (19%) preoperatively to 114 (80%) after transurethral prostate resection. Sensitivity to change following the removal of obstruction further validates the usefulness of noninvasive measurement of bladder pressure by the penile cuff test and the categorization of obstruction by the noninvasive nomogram. Decreased isovolumetric bladder pressure following transurethral prostate resection may reflect a return to normal detrusor contraction strength.