Morphologic basis of pulmonary resistance in the human lung and effects of aging

Airflow resistive properties of 26 postmortem lungs from persons 10-82 yr in age have been compared with morphological measurements in these same lungs. Morphological measurements were made of bronchiolar diameter, bronchiolar density, segmental bronchial diameter, the proportion of bronchial mucous glands, and the extent of mucous plugging in small airways. Contrary to currently accepted ideas, the major determinant of pulmonary resistance in this population of normal and minimally diseased lungs was found to be mean bronchiolar diameter. The correlation of other morphological parameters with flow resistive measurements was weak or nonexistent. Evidence is presented which suggests that the resistance of peripheral airways in adult human lungs is highly variable and is much greater in lungs from older persons compared to young adults. The physiological and morphological observations in this study are consistent with theoretical analyses of airflow in the bronchial tree.