Flow rate nomograms in 7- to 16-year-old healthy children.

To construct flow rate nomograms for children, 180 healthy boys and girls aged 7-16 years were examined with a new kind of flowmeter. Each child presented at least two registrations. The flow rate was significantly higher at the second examination and these micturitions were used to construct the nomograms. The relation between flow rate and volume may be described by the function flow = b volume(c), where b and c describe the slope and curvature, respectively. The advantages of using this relation are that non-parametric statistics can be employed, the variation around the median increases with increasing volume, and it is easy to calculate volume corrected flow rates. The exponent 0.5, often used earlier, was found to overestimate flow rates obtained at low volumes. In the constructed nomograms, the exponent varied between 0.29 and 0.42. The volume corrected maximum flow rate was about 2 ml/s higher in girls than in boys. This difference was significant. The difference of about 1.5 ml/s in average flow rate was not significant. The flow rate increased significantly with age. For volume corrected flow rates, there was, however, no significant change with age. Thus, the increase in flow rate with age is secondary to an increase in voided volume. As a result of these analyses, four nomograms were constructed showing the maximum and average flow rates for boys and girls separately. The flow rates of the new nomograms are on a level with or somewhat higher than the flow rates in previously presented nomograms for both children and young adults.