Abstract
It has already been established that the gradient of the flow-volume curve is determined by both airway resistance and lung compliance. Until recently however little attention has been paid to the relationship between these two factors in clinical terms. We designed this study to examine the relative contribution of airway resistance and lung compliance to the flow-volume curve in both normal subjects and patients with various lung diseases. Flow-volume curves, airway resistance and lung compliance were measured in 9 normal subjects, 10 patients with obstructive lung diseases, 13 patients with restrictive lung diseases and 8 patients with combined lung diseases.
There was a good correlation between the V50/V25 ratio and 1/(Raw×Cst)in all subjects(r=0.86). Therefore it was postulated that the V50/V25 ratio was a good index for expressing a time constant. In 13 patients with obstructive lung diseases, V50 and V25 correlated significantly with Gaw (r=0.93, r=0.83). In the same way, there was a good correlation between the V50/V25 ratio and 1/Cst in 13 patients with restrictive lung diseases (r=0.76).
In conclusion, we suggest that Raw affects V50 and V25 in obstructive lung diseases and lung compliance affects the V50/V25 ratio in restrictive lung diseases.
