To investigate whether the maximum Watts factor (WF) is 1 parameter of describing detrusor contraction in male patients with lower urinary tract symptoms (LUTS). Researchers retrospectively reviewed urodynamic data of male subjects with LUTS.

Data on age, maximum flow rate (Qmax), post-void residual (PVR), detrusor pressure at a maximum flow rate (PdetQmax), maximum Watts factor (WFmax), and Schafer contractility grades were collected.

First, all patients were divided into 6 groups according to Schafer contractility grade. The urodynamic parameters include WFmax and bladder contractility index (BCI) were compared and analyzed among the 6 groups by using the Kruskal–Wallis test statistically. The box plot of Schafer contractility grade with WFmax or BCI were plotted and analyzed.

Second, the correlation scatters diagram between WFmax and BCI was plotted and analyzed. Spearman's correlation test was performed. Third, we drew the Receiver Operating Characteristic (ROC) curve and confirmed the area under the curve, the Optimal Operating Point (OOP) and corresponding sensitivity and specificity for WFmax by the reference standard of Schafer contractility grade and BCI respectively. 

Kruskal-Wallis test 

A total of 455 men were included. The mean age of patients was 57 ± 17.9 years, ranging from 18 to 87 years. Median of WFmax increased from 5.8 W/m2 in every week (VW) group to 19.5 W/m2 in strong (ST) group, while BCI rose from 70 to 170. The box plot of Schafer contractility grade with WFmax or BCI showed that both WFmax and BCI were positively correlated with Schafer contractility grade. Kruskal-Wallis test among the 6 groups showed a statistically significant difference (P <.001).

The correlation scatter diagram showed that WFmax increased significantly with BCI (Fig. 3), the linear regression equation being Y = 3.33 + 0.07X, R2 = 0.298. Spearman's correlation test revealed that WFmax and BCI were positively correlated, with the correlation coefficient being 0.616 (P <.001).

The WFmax area under ROC curve by Schafer contractility grade was 0.894 and WFmax OOP was interpreted at 11.1 W/m2. In addition, the area under ROC curve by BCI was 0.802 and WFmax OOP was interpreted at 9.8 W/m2.

Our findings suggest that WFmax was a good parameter of evaluating detrusor contraction as well as Schafer contractility grade and BCI, which should be widely used in clinical.