Are the small airways really quiet?

The results of recent epidemiological studies and of functional-pathological correlations suggest that morphologic alterations, specifically inflammatory lesions, of the peripheral airways (with an interval diameter of 2 mm or less) influences the values of FEV1, of the FEV1/VC ratio and of the maximal midexpiratory flow rate, also in the incipient stages of these lesions. Between the so-called tests of small airways obstruction and FEV1 there would only be a difference in sensitivity. This implies that the small airways are not as silent as postulated previously. This is corroborated by measurements of resistance of peripheral airways performed on excised human lungs, showing that with normal lungs as well as in cases of airways obstruction, the peripheral resistance constitutes 50 to 90% of the total resistance between the main bronchus and the pleura.