Maximal expiratory flows at functional residual capacity: a test of lung function for young children.

Maximal expiratory flows at functional residual capacity were measured noninvasively from partial expiratory flow-volume curves in 65 awake, healthy children, 4 to 6 years of age. The variabilities within and between subjects were nearly identical to those reported for flows low in the vital capacity obtained from older subjects. This test of maximal expiratory flow at functional residual capacity has the advantage that the subject does not have to inspire to total lung capacity, exhale to residual volume, or make a maximal effort, and it is therefore applicable to the testing of young children who cannot perform a vital capacity maneuver. Measurement of this flow rate in 20 patients of the same age with lung disorders of varying severity revealed abnormal flow rates in more than 50 per cent of patients. Functional residual capacity was measured by the closed-circuit helium-equilibration method. When flow rates in liters per sec were compensated for lung size, girls had significantly larger flow rates than did boys. This suggests that the lungs of young children may grow differently according to genetic determinants related to sex.