Lung function in North American Indian children: Reference standards for spirometry, maximal expiratory flow volume curves, and peak expiratory flow

Reference standards of lung function were determined in 176 healthy North American Indian children (94 girls, 82 boys) 7 to 18 yr of age. Spirometry, maximal expiratory flow volume curves, and peak expiratory flow rate were measured using techniques and equipment recommended by the American Thoracic Society. Standing height was found to be an accurate predictor of lung function, and prediction equations for each lung function variable are presented using standard heights as the independent variable. Lung volumes and expiratory flow rates in North American Indian children were similar to those previously reported for white and Mexican-American children but were greater than those in black children. In both boys and girls, lung function increased in a curvilinear fashion. Volume-adjusted maximal expiratory flow rates after expiring 50 or 75% of FVC tended to decrease in both sexes as age and height increased. Our maximal expiratory flow volume curve data suggest that as North American Indian children grow, lung volume increases at a significantly faster rate than airway size does.