Abstract

Because isometric detrusor contraction pressure (P_iso) increases with outlet obstruction and maximum urinary flow rate (Qmax) tends to decrease with obstruction, we hypothesize that specific criteria consisting of a combination of high P_iso and low Qmax may be able to differentiate obstructive from nonobstructive voiding dysfunction better than either parameter alone.

Two hundred five men with lower urinary tract symptoms underwent uroflowmetry and videourodynamics, including cystometry, continuous outlet occlusion test, and micturitional urethral pressure profilometry. Combined threshold values of Qmax of less than 12 mL/s and P_iso of 100 cm H₂O or greater were used to predict obstruction, whereas threshold values of Qmax of at least 12 mL/s and P_iso less than 100 cm H₂O were used to predict nonobstruction.

Of the 205 patients, 103 (50%) were significantly obstructed and 102 (50%) were only mildly obstructed or nonobstructed. Of the total population, 151 patients (74%) were categorized by the combined flow and contractility criteria. Of the categorized patients, 141 (93%) were correctly diagnosed with regard to infravesical obstruction (sensitivity 89%, specificity 97%, positive predictive value 97%, and negative predictive value 91%).

A combination of Qmax and P_iso criteria can predict obstructive and nonobstructive voiding dysfunctions with high positive and negative predictive values in most patients with lower urinary tract symptoms. Combining the results of uroflowmetry and isometric tests may help to guide treatment strategies that may improve the outcome of selected therapeutic options compared with strategies based on symptoms or uroflowmetry alone. Furthermore, this approach forms a basis for interpreting various noninvasive methods that have recently been introduced for the purpose of diagnosing bladder outlet obstruction.