Distribution of parametric response mapping–determined small airway abnormality (PRMFSA, top) and emphysema (PRMEMPH, bottom) by age and presence of airflow obstruction. At any age, those without airflow obstruction (represented by group No) have significantly less small airway abnormality (y-axis, top) and emphysema (y-axis, bottom) than subjects of similar age with mild airflow obstruction (Yes).