Ventilatory inhomogeneity associated with acute bronchoconstriction in asthmatic patients

Ventilation inhomogeneity was assessed in asthmatic subjects before and after antigen-induced bronchoconstriction and bronchodilator administration. As an index of inhomogeneous distribution of inspired air, the mean dilution number (the ratio of the first to zero moments) was calculated from each multibreath nitrogen washout during spontaneous breathing. This index was compared to plethysmographic, spirometric, and lung volume indices. In the baseline state, a weak relationship existed between the mean dilution number (MDN) and indices of mechanical abnormality, FEV1/FVC and SRAW. Antigen-induced bronchoconstriction led to increases in the MDN, SRAW, and RV/TLC, and a decrease in FEV1/FVC. The reverse effects were found by administering bronchodilators. No statistically significant correlations were found between changes in MDN and changes in the other indices of pulmonary function. Thus, the maldistribution of inspired air resulting from acute bronchoconstriction cannot be quantified from common indices of pulmonary function.