Nonhomogeneous Lung Emptying in Cystic Fibrosis Patients: Volume History and Bronchodilator Effects

Abstract

In spontaneous asthma after a deep inhalation (DI) obstruction occurs in direct proportion to disease severity. Since this has been associated with peripheral inflammation, which is present in cystic fibrosis (CF), we tested whether worsening obstruction after DI also occurs in CF in 12 patients. We assessed volume history effects by comparing isovolumic expiratory flows (Vmax) during forced exhalation begun at the end of tidal inspiration (partial P) with those begun at TLC (maximal M) to obtain M/P. As in asthma there was a correlation between M/P and FEV1 (% predicted; r = 0.64, p less than or equal to 0.03, n = 12). To control for a time dependency effect due to preferential emptying of fast compartments early in both the P and M maneuvers, we compared Vmax obtained from a first partial (P1) with a second (P2) obtained after inspiration to TLC and slow exhalation to the same starting volume as P1 (P2/P1). In contrast to asthma the P2/P1 was greater than the M/P and not related to disease severity. A further index of nonhomogeneous lung emptying was the relationship between M/P and the slope ratio at 70% TLC (r = -0.67, p less than or equal to 0.03). After isoetharine inhalation the M/P decreased (-0.12 +/- 0.12, p less than or equal to 0.01) but no change was apparent in P2/P1, indicating further increases in the degree of nonhomogeneity. We conclude that although volume history effects on M/P are similar in asthma and CF, this is due to a predominance of parenchymal hysteresis in the former and nonhomogeneity in the latter, which worsens with bronchodilator use.