V. FORCED FLOW RATES

Abstract

1. Data from normal subjects on the peak expiratory flow rate, the peak inspiratory flow rate, and the flow rate at the point where half the vital capacity has been expired (E50), have been obtained as part of a longitudinal study of the growth of lung function in school children. 2. The peak flow rates grow in a manner similar to that of the lung volumes. 3. The E50, in contradistinction, grows in a manner similar to airway conductance (the reciprocal of airway resistance). 4. Longitudinal studies of the peak flow rates indicate that individuals tend to maintain their positions in relation to the group. 5. A theoretical postulation of the forced flow-volume relationship has been suggested. According to this postulation the lungs of the normal subject empty as a unit or nearly so. The flow (after the initial acceleration) at any point in time is dependent on his vital capacity and an emptying factor. This emptying factor decreases somewhat with increasing body size. This is more evident in the girls. 6. In the patient with airway obstructive disease (as asthma) the lung can be thought of as composed of multiple units in parallel with varying amounts of reduction in their emptying factor. 7. The theoretical advantages of clinical tests based upon flow in the mid or later portions of the forced expiration have been given.