Proposed urodynamic pressure-flow nomogram to diagnose female bladder outlet obstruction.

OBJECTIVE: To investigate female bladder outlet obstruction by urodynamics and create a nomogram to propose in clinical applications. PATIENTS AND METHODS: We investigated by urodynamic studies 200 women referred for lower urinary tract symptoms. A total of 179 patients were available for analysis: 136 served as control and 43 as obstructed. The following urodynamic variables were studied and compared in both groups: Free peak urinary flow (Free Qmax), intubated peak urinary flow (Qmax P/F), Free voiding time, pressure-flow voiding time, Detrusor pressure at peak flow rate (PdetQmax), Maximum detrusor pressure (PdetMax), Free postvoiding residual, Pressure-flow postvoiding residual. All data are presented according to descriptive statistics as mean and standard deviation (SD). Comparisons between the control and between the obstructed group were performed by means of Student's t test for equality of means, p<0.01 were considered significant. By creating ROC curves we calculated sensitivity, specificity, and positive and negative predictive values in all the patients data to derive the optimal combination of Maximum flow together with detrusor pressure at maxflow, and Maximum flow together with Maximum detrusor pressure.
RESULTS: Free peak urinary flow (Free Qmax) was 26.6+/-11 ml/seconds for the control and 10.9+/-3.6 ml/seconds for the obstructed group (p<0.001). Qmax P/F were 22+/-8.7 cm water in the control group and 10+/-3.9 cm water in the obstructed group (p<0.001). Free voiding time were in both 28.2+/-15 seconds and 48+/-24 seconds (p<0.001) respectively; P/F voiding time were 41.4+/-21 seconds and 78.2+/-52 seconds (p<0.001) respectively. PdetQmax in control and obstructed group were 17.2+/-11.3 and 27.6+/-12.5 cm water (p<0.001) respectively. PdetMax were 25.2+/-14.0 and 39.4+/-18.9 cm water (p<0.001) respectively. Free postvoiding residual 25.1+/-37.4 and 74.6+/-79.3 cc (P<0.001). P/F postvoiding residual were respectively 24.9+/-44.7 and 96.0+/-102.6 cc (p<0.001). All the differences among the variables investigated in both groups were statistically significant. We calculated sensitivity, specificity, and positive and negative predictive values. According to receiver operating characteristics (ROC) curve analysis, the overall combining values of free max flow rate of 13 ml/sec or less and detrusor pressure at max flow rate of 22 cm water or greater we obtained a sensitivity of 55.8%, a specificity of 96.3%, a positive predictive value of 82.8% and a negative predictive value of 87.3%. Moreover we combined Max flow rate of 13 ml/sec and Maximum detrusor pressure of 38 cm water to obtain a sensibility of 48.8%, a specificity of 99.3%, a positive predictive value of 95.5% and a negative predictive values of 86%.
CONCLUSIONS: Diagnosing female BOO is a challenge condition and an accepted pressure-flow nomograms are still missing. We propose our nomogram as a valid and reliable tool to investigate female bladder outlet obstruction.