Objectives. Previously we had developed a new method of noninvasive urodynamics using color Doppler ultrasound. Using this technique, we attempted to identify parameters that would diagnose bladder outlet obstruction (BOO).

Methods. Twenty-two men who underwent pressure-flow urodynamic studies were included. Color scale transperineal ultrasound and uroflowmetry data were analyzed by custom-made software. The maximum flow velocities in the entire prostatic urethra (V₀), in the distal prostatic urethra just proximal to the external urethral sphincter (V₁), and in the membranous urethra (V₂) were obtained. Corresponding functional cross-sectional areas of the urethra at these three sites (A₀, A₁, and A₂) were calculated as Qmax/V. The velocity ratio (VR), which was equal to V₁/V₂, was also calculated as a parameter. All these parameters obtained by the velocity-flow urodynamics were compared with the Abrams-Griffiths number (AG).

Results. From the x-y plots obtained, VR correlated best with AG, with Spearman’s ρ of 0.728. A₀ and A₁ had ρ values of −0.461 and −0.708 against AG, respectively. All men with VR exceeding 1.6 had obstruction, whereas those with VR less than 1.1 did not.

Conclusions. The VR was found to be the best parameter for diagnosing BOO. When prostatic urethral obstruction was present, the velocity in the prostatic urethra would be high but the velocity slows down to 62.5% or greater immediately below the sphincter. We believe that noninvasive pressure-flow-like urodynamic evaluation based on Doppler ultrasound has clear potential for diagnosing BOO.