Maximal and partial expiratory flow rates in a population sample of 10-to 11-yr-old schoolchildren - Effect of volume history and relation to asthma and maternal smoking

The effect of volume history on forced expiratory flow rates has been repor ted to differ between patients with asthma and healthy persons, and it has been hypothesized that the peripheral airway inflammation of patients with asthma may underlie this difference. There are no published data, however, on the distribution of such volume history effects or the relation of these effects to airways disease in children. We obtained combined partial and m aximal forced expiratory flow-volume curves on 1,834 children, age 10-11 yr , in eight communities in the United States and Canada. The effect of a dee p inhalation on forced expiratory flow rates at low lung volumes was quanti tated by the ratio of V-30 during a maximal expiratory maneuver (V-30M) to V-30 during a partial expiratory maneuver (V-30P). The V-30M/V-30P ratio wa s slightly higher among girls than boys (1.26 versus 1.18, p = 0.0001) indi cating that a deep inhalation increased V-30 slightly more among girls than among boys. The V-30M/V-30P ratio was related to neither history of asthma nor to maternal smoking. In contrast, most spirometric indices from either the maximal or the partial expiratory flow-volume curve were lower in asso ciation with a history of asthma or a report of maternal smoking. The ratio of FEF25-75/FVC was particularly consistent as a measurement that discrimi nated both of these effects in boys and girls. These results suggest that t he measurement of volume history effects offers no benefits for epidemiolog ical studies of childhood respiratory disease whereas spirometric indices s uch as the FEF25-75/FVC ratio are quite sensitive to the effects of asthma and environmental tobacco smoke exposure on the airways.