Correlations of maximum expiratory flow with small airway dimensions and pathology

Pressure-volume and maximum expiratory flow-volume curves with air and a He-O2 mixture were performed in 25 excised human lungs. Small airway dimensions were measured, and the degree of various small airway lesions and emphysema was graded. Correlations were then made between the maximum flow (Vmax) at a transpulmonary pressure (PL) of 5 cmH2O and these measurements and scores. Small airway dimensions correlated poorly with Vmax. However, significant correlations were obtained between Vmax and the inflammation score (P less than 0.05), fibrosis score (P less than 0.05), and emphysema grade (P less than 0.01) but not smooth muscle hyperplasia or pigmentation. Neither the increase in flow with He-O2 nor the volume of flow correlated significantly with any small airway measurement or score.