Large airway size, lung size, and maximal expiratory flow in healthy nonsmokers

It has been postulated that airway size and lung size may be dissociated because of developmental differences between the tracheobronchial tree and the pulmonary parenchyma (dysanapsis). To test this hypothesis, we compared measurements of airway size (diameters, cross-sectional area, length and volume of the trachea, diameter and cross-sectional area of the mainstem bronchi) and lung size (total lung capacity, thoracic diameters, lung length), as determined from plain chest radiographs in 79 male and 86 female healthy nonsmokers. In both groups of subjects, the correlation between indexes of airway size and lung size was low. Airway size was not significantly different between men and women, when standardized for lung size. Tracheal diameter and length tended to increase with age. To assess the value of airway size measurements in the prediction of maximal expiratory flow, we compared tracheal and bronchial size with FVC, FEV 0.5, FEV1, and mean forced expiratory flow during the middle half of VC. The correlation between airway size and spirometric indexes was very low. Multiple regression analysis showed that the use of airway size variables in addition to the age and height variables did not substantially improve the prediction of maximal expiratory flow. Our results are consistent with the dysanapsis hypothesis, but they suggest that the introduction of radiologic estimates of large airway size in the prediction equations relating maximal expiratory flow to age and height is not justified, at least in the general population.