Prolonged Oxygen Kinetics During Constant Workload Submaximal Exercise Is Associated With Disease Severity in Adult Subjects With Cystic Fibrosis

BACKGROUND: The goal of this study was to explore the relation between oxygen kinetics during constant work load submaximal cardiopulmonary exercise test (CPET) and disease severity in adult subjects with cystic fibrosis. METHODS: Fourteen adult subjects with cystic fibrosis (CF; 8 males, 22 ± 4 y old) and a mean Schwachman score of 73 ± 11 and 10 healthy individuals (5 males, 29 ± 4 y old) underwent pulmonary function tests at rest, maximal and constant work load submaximal CPET on a cycloergometer. Breath-by-breath analysis was used for measuring oxygen kinetic parameters and the time constant (tau), expressing phase 2 of submaximal CPET. RESULTS: Subjects with CF had a significantly prolonged tau compared with healthy subjects (42.3 ± 21.5 vs 29.3 ± 6.4, s, P < .05). The tau during phase 2 was inversely correlated with FEV1(% pred) (r = −0.77, P = .001), breathing reserve (r = −0.74, P = .003), VO2peak (r = −0.53, P = .049), VO2/t slope (r = −0.58, P = .03), and Schwachman score (r = −0.80, P = .001). In a multivariate regression model including all the above variables, the Schwachman score (β = −0.697, P = .002) emerged as independent predictor of tau (R2 = 0.719, P = .001). CONCLUSIONS: We conclude that adult subjects with CF present significant prolonged oxygen kinetics during constant work load submaximal exercise in relation to disease severity. Thus, submaximal exercise should be considered the preferable CPET choice in adult patients with severe CF.