EFFECT OF AGE ON CHANGES IN FLOW-RATES AND AIRWAY CONDUCTANCE AFTER A DEEP BREATH

The effects of aging on changes in maximal expiratory flow rates and specific airway conductance after a deep breath were evaluated in 64 normal subjects. Flow rates (V̇p) on partial expiratory flow-volume curves (PEFV), initiated from 60-70% of the vital capacity (VC), were compared with those (V̇c) on maximal flow-volume curves (MEFV), initiated from total lung capacity (TLC), at a lung volume corresponding to 25% of VC on the MEFV curves. Specific airway conductance was measured before (sGaw) and after a deep inspiration (sGawDI). Bronchodilation after inspiration to TLC was inferred by V̇p/V̇c < 1 and sGaw/sGawDI < 1. The mean V̇p was less than V̇c. However, the ratio V̇p/V̇c increased significantly with age (r = 0.75, P < 0.001). Specific conductance also increased after a deep inspiration (sGaw < sGawDI). The ratio sGaw/sGawDI increased slightly but significantly with age (r = 0.28, P < 0.02). Measurement of lung elastic recoil pressures before and after a deep breath in a subgroup of patients (n = 14) suggested that the age-related increase in V̇p/V̇c was secondary to a decrement in the ability of a deep breath to decrease the upstream airway resistance. These findings suggest that even though changes in airway size after a deep breath as measured by sGaw/sGawDI have minimal age dependence, aging diminishes expiratory flow rates of MEFV curves relative to PEFV curves because of a decrease in the ability of a deep breath to increase the size of the peripheral airways.