Discordance of airflow limitation and ventilatory inhomogeneity in asthma and cystic fibrosis.

Although it is known that both airflow rates and gas distribution are impaired in asthma and cystic fibrosis (CF), the concordance of the change in these defects between two points in time has not been studied. On two separate occasions, the FEV1, FVC and slope of Phase III (SBN2/L%) of the single breath nitrogen test were determined, as well as the concordance between the change in these indices in 14 healthy subjects, 14 subjects with asthma, and seven subjects with CF. The coefficient of variation within a test session averaged less than 5% for the FEV1 and less than 10% for the SBN2/L% within each group. The change in FEV1 correlated with the change in FVC in all three groups, but did not correlate with the change in SBN2/L% in any group. In seven of the 14 cases of asthma and six of the seven cases of CF (outliers), the differences in the indices (expressed as the change in percent predicted) were greater than the differences observed in the control group. In three of the asthmatic and four of the CF outliers, the changes were as predicted, that is, both tests returned toward normal, or both became more abnormal. In two of the asthmatic and CF outliers both the FEV1 and SBN2/L% increased, while both decreased in the other two asthmatic outliers. Although some of the same factors will affect both indices, a worsening of ventilation inhomogeneity, which will affect the SBN2/L%, could occur with an improvement in ventilatory flow rate. Alternatively, airflow limitation could worsen but be accompanied by an improvement in ventilation homogeneity.(ABSTRACT TRUNCATED AT 250 WORDS)