Measurement of urinary flow rate using ultrasound in young boys and infants

Purpose: We present a technique for measuring urinary flow rates with ultra sound in male infants and children. Materials and Methods: Urinary flow rate was measured simultaneously by an ultrasound probe placed around the base of the penis and by a funnel with a rotating disk at the bottom in 30 boys with a mean age of 6.7 years (range 4.5 to 10.5), and by ultrasound in 8 infants with a mean age of 10 months (range 1 to 28). Voided volume was measured with a graded cylinder or calcu lated from the weight change of diapers in infants. Ultrasound and rotating disk maximum flow rates were calculated. The ultrasound signal was calibra ted by comparing the collected voided volume to the area under the curve fo r that void. The volume calculated from the rotating disk flow rate curve w as also compared with the collected volume. Results: Both methods yielded similar flow curves. However, ultrasound maxi mum flow rate significantly exceeded rotating disk maximum flow rate (13 +/ - 6 ml. per second, range 5 to 22 versus 10 4 ml. per second, range 4 to 21 , t test p < 0.001). The underestimation of the flow rate by the rotating d isk method may have been due to adherence of urine to the funnel wall. Rota ting disk maximum flow rate was lower and voided volume was underestimated by up to 50% (average 15 +/- 2%) in 21 cases. Ultrasound maximum flow rate averaged 6 +/- 3 ml. per second (range 3 to 11.6 [oldest infant]) in the 8 infants. Conclusions: Urinary flow rates can be measured accurately using ultrasound in boys who produce small volumes and/or who are not toilet trained and al so in infants. In future studies ultrasound will be applied to subsets of m ale infants with bladder dysfunction.