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

Abstract

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 FEV 1 (% pred) (r ‫؍‬ ؊0.77, P ‫؍‬ .001), breathing reserve (r ‫؍‬ ؊0.74, P ‫؍‬ .003), V O2peak (r ‫؍‬ ؊0.53, P ‫؍‬ .049), V O2 /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 (␤ ‫؍‬ ؊0.697, P ‫؍‬ .002) emerged as independent predictor of tau (R 2 ‫؍‬ 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.

High-intensity interval training accelerates oxygen uptake kinetics and improves exercise tolerance for individuals with cystic fibrosis

“…It is well established that individuals with CF possess slower V O 2 kinetics compared to healthy counterparts [13,18,26]. Generally speaking, V O 2 kinetics can be rate limited by an upstream O 2 -transport limitation or a 'metabolic inertia' within the active muscle mitochondria [14] (i.e., a central or peripheral limitation, respectively).…”

“…This has resonance for individuals with CF who typically demonstrate low tolerance for physical activity [15][16][17]. It is, therefore, not surprising that a strong correlation exists between the V O 2 time constant (a parameter that quantifies the rapidity of the V O 2 response) and disease severity in subjects with CF [18]. With this in mind, it stands to reason that a training program that improves the capacity to rapidly adjust V O 2 in response to lower-intensity energetic transitions like those encountered on a daily basis would likely have clinical implications [13].…”

“…With respect to oxidative capacity, limiting factors can include an impaired ability to deliver O 2 to skeletal muscle due to a disease-related decline in pulmonary [20][21][22] and/or cardiac [23] function (central limitation) and/or a reduced capacity for skeletal-muscle mitochondria to extract/use O 2 that is delivered (peripheral limitation) [13,24,25]. A slower V O 2 response has been observed for CF subjects [13,18,25,26] with the decrement found to be mechanistically linked to impaired muscle extraction and utilization [13]. If an O 2 -utilization limitation to V O 2 kinetics is responsible for the reduced tolerance to exercise displayed by individuals with CF, exercise training to improve mitochondrial function might be particularly important for these individuals.…”