Airway conductance (Gaw) and FEV 1 changes with aerosol bronchodilator and underlying mechanics

Airway conductance and FEV1 were measured in 25 patients before and after bronchodilator: Following bronchodilator, the correlation coefficient, r, between Gaw and FEV1 increased from 0.58 to 0.70 while there was almost negligible correlation (r = 0.1) between the respective Gaw and FEV1 changes. The lack of correlation is explained by the occurrence of saturated flow during a forced expiration, the saturated flow value also depending on the small airway resistance, the lung elastic recoil and the compressibility of the airway walls. It is concluded that the measurements are complementary but that the flow-alveolar pressure curve of a forced expiration or, better still, the measurement of the iso-volume alveolar pressure, flow curves, would contain the most information.