Mechanism of reduced maximal expiratory flow with aging

To investigate the determinants of maximal expiratory flow (MEF) with aging , 17 younger (7 men and 10 women, 39 +/- 4 yr, mean +/- SD) and 19 older (1 1 men and 8 women, 69 +/- 3 yr) subjects with normal pulmonary function wer e studied. For further comparison, we also studied 10 middle-aged men with normal lung function (54 +/- 6 yr) and 15 middle-aged men (54 +/- 7 yr) wit h mild chronic airflow limitation (CAL; i.e., forced expiratory volume in 1 s/forced vital capacity = 63 +/- 8%). MEF, static lung elastic recoil pres sure (Pst), and the minimal pressure for maximal flow (Pcrit) were determin ed in a pressure-compensated, volume-displacement body plethysmograph. Valu es were compared at 60, 70, and 80% of total lung capacity. In the older su bjects, decreases in MEF (P < 0.01) and Pcrit (P < 0.05), compared with the younger subjects, were explained mainly by loss of Pst (P < 0.05). In the CAL subjects, MEF and Pcrit were lower (P < 0.05) than in the older subject s, but Pst was similar. Thus decreases in MEF and Pcrit were greater than c ould be explained by the loss of Pst and appeared to be related to increase d upstream resistance. These data indicate that the loss of lung recoil exp lains the decrease in MEF with aging subjects, but not in the mild CAL pati ents that we studied.