INFLUENCE OF LUNG-VOLUME ON COLLATERAL RESISTANCE DURING METHACHOLINE-INDUCED BRONCHOSPASM

We tested the hypothesis that lung inflation in response to a bronchos pasm could be beneficial by maintaining the lung collateral channels o pen. Six mild asthmatics were studied on 2 separate days. The first da y we determined the methacholine dose response and measured collateral resistance (Rcoll) before and during the metacholine-induced bronchos pasm and the effects of decreasing lung volumes on Rcoll. The lung vol ume changes were induced by applying progressively increasing positive extrathoracic pressures (PEP). The second day we measured the changes in end-expiratory lung volume (EELV) resulting from the inhaled metha choline and from the applied positive extrathoracic pressure. With the inhalation of methacholine, the FEV(1) decrease ranged from 26-43% of the baseline values while Rcoll increased significantly in only three of the six subjects. EELV remained unchanged in one subject and incre ased by 1408, 990, 260, and 44 ml in four others. It was not measured in one subject. Decreasing EELV by PEP increased Rcoll in all subjects . By extrapolation of the lung volume-Rcoll relationship, we calculate d that Rcoll would have increased by 18 227%, 6843%, 994%, 140%, and 1 28% if EELV had not increased in the five subjects in whom Delta EELV was measured. We conclude that an increase in EELV in response to an i nduced bronchospasm helps maintain open and functional collateral path ways despite the bronchoconstriction.