Reliability of flow-volume measurements in children

Flow-volume curves were measured in a group of 43 healthy children breathing air and a helium-oxygen gas mixture. Analysis of maximal flow at 25, 50 and 75% of forced vital capacity and at 50, 60 und 70% of total lung capacity (TLC) was performed. There is a correlation between maximal flow rates and height; however, the standard deviations are considerable. Maximal flow rates at different lung volumes expressed in units of TLC/s are independent of height. There is a significant correlation between maximal flow rates and airway resistance expressed as percent of predicted values. Flow increment while breathing a helium-oxygen gas mixture is significant at all lung volumes, but the standard deviation is considerable. Technical problems of measuring flow-volume curves are discussed. Results are compared with those published in the literature. The practical value of these lung function parameters in early detection of small-airway obstruction is doubted.