Comparison of passive urethral resistance relation and urethral resistance factor in analysis of bladder outlet obstruction in patients with benign prostatic enlargement.

Analysis of the pressure/flow relation renders objective and detailed information on bladder outlet obstruction. The benefit of pressure/flow analysis for clinical and fundamental research questions, however, cannot be acknowledged without comparison of the different methods that exist. We compared one parameter analysis (URA) with two parameter (PURR) analysis in 99 consecutive patients with benign prostatic enlargement. The normal (instantaneous intrapatient) variability of both the PURR parameter Pvoidmin (minimal pressure during voiding) and the URA is approximately 10-15 cm H2O. Within these limits agreement between the two methods of analysis in the quantification of (minimal) outlet obstruction was observed in about 50% of the cases. However, when Qmax is less than 6 ml/s (in 49.5% of the patients) the URA number exceeds the value Pvoidmin in 96% of the cases. Predominantly this is caused by the fact that in the majority of these cases the type of bladder outlet obstruction is more constrictive than the URA curve, based on Pdet at Qmax indicated. In patients with a low flow rate and/or a constrictive type of obstruction, the Pvoidmin resulting from PURR analysis indicates a lower minimal pressure during voiding compared to URA.