Impaired pulmonary V˙O2 kinetics in cystic fibrosis depend on exercise intensity
Medicine and Science in Sports and Exercise
American College of Sports Medicine (ACSM)
Reason for embargo
PURPOSE: To investigate the effects of mild-to-moderate cystic fibrosis (CF) on the pulmonary oxygen uptake (V˙O2) kinetics of 7 pediatric patients (13.5 ± 2.8 y) versus 7 healthy matched controls (CON; 13.6 ± 2.4 y). We hypothesized that CF would slow the V˙O2 kinetic response at the onset of moderate (MOD) and very heavy (VH) intensity cycling. METHODS: Changes in breath-by-breath V˙O2, near-infrared spectroscopy-derived muscle deoxygenation ([HHb]) at the m. vastus lateralis and thoracic bioelectrical impedance-derived heart rate, stroke volume index (SVI) and cardiac index (CI) were measured during repeat transitions to MOD (90% of the gas exchange threshold) and VH (Δ60%) intensity cycling exercise. RESULTS: During MOD, the phase II V˙O2 τ (p=0.84; effect size (ES) = 0.11) and overall mean response time (MRT) (p=0.52; ES=0.11) were not significantly slower in CF versus CON. However, during VH exercise, the phase II V˙O2 τ (p=0.02, ES=1.28) and MRT (p=0.01, ES=1.40) were significantly slower in CF. Cardiac function, central O2 delivery (SVI and CI) and muscle [HHb] kinetics were unaltered in CF. However, the arterial-venous O2 content difference (C(a-V¯)O2) was reduced during VH at 30 s (p=0.03, ES=0.37), with a trend for reduced levels at 0 s (p=0.07, ES=0.25), 60 s (p=0.05, ES=0.28) and 120 s (p=0.07, ES=0.25) in CF. Furthermore, [INCREMENT]C(a-V¯)O2 significantly correlated with the VH phase II V˙O2 τ (r= -0.85; p=0.02) and MRT (r = -0.79; p=0.03) in CF only. CONCLUSION: Impairments in muscle oxidative metabolism during constant work rate exercise are intensity-dependent in young people with mild-to-moderate CF. Specifically, V˙O2 kinetics are slowed during VH but not MOD cycling and appear to be mechanistically linked to impaired muscle O2 extraction and utilization.
Funding was provided by the Royal Devon and Exeter NHS Foundation Trust, Exeter.
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.
Published online 9th June 2016