Micturition Studies in Infants and Children: Intravesical Pressure, Urinary Flow and Urethral Resistance in Boys without Infravesical Obstruction

Abstract

Simultaneous measurement of intravesical pressure and urinary flow was carried out on 16 boys (including 5 infants) without intravesical obstruction. the maximum exit velocity of the urine and the urethral energy losses were calculated in 6 cases. the mean values and standard deviation of different pressure variables are shown. Infants (who were examined in a lying position) showed a tendency to lower pressure values than older children. A significant difference, however, could be demonstrated only for peak-flow pressure. Otherwise, age and micturition volume apparently had little effect on intravesical pressure. Values for various time intervals in the micturition process are reported. Values for various pressure variables in boys were somewhat below those in men, most likely because the superimposed intra-abdominal pressure in children was lower. Opening pressure deviated more than other values, probably because flow initiation occurs more readily in boys who have less rigid tissues and a less developed prostate ring than men. the maximum voiding velocity of the urine averaged 209 cm/sec. the urethral energy losses averaged 65%. the character of urinary flow is discussed. Most factors indicate that flow in children without intravesical obstruction, including infants, is mainly turbulent. the problems of determining urethral resistance are discussed. in the present study, resistance (R_min) was defined as peak-flow pressure/(maximum flow)² and was related to micturition volume. R_min decreased with increasing volume. An estimation of the upper normal limit of the relationship R_min/micturition volume was made for various age groups, and although the urethral resistance thus calculated is inaccurate in terms of absolute resistance it provides a simple means of obtaining a coherent picture of the pressure-flow situation.