Impaired Pulmonary V˙O2 Kinetics in Cystic Fibrosis Depend on Exercise Intensity.
This study aimed to investigate the effects of mild-to-moderate cystic fibrosis (CF) on the pulmonary oxygen uptake (V˙O2) kinetics of seven pediatric patients (13.5 ± 2.8 yr) versus seven healthy matched controls (CON; 13.6 ± 2.4 yr). We hypothesized that CF would slow the V˙O2 kinetic response at the onset of moderate (MOD) and very heavy (VH) intensity cycling.



Changes in breath-by-breath V˙O2, near-infrared spectroscopy-derived muscle deoxygenation ([HHb]) at the vastus lateralis muscle and thoracic bioelectrical impedance-derived heart rate (HR), stroke volume index, and cardiac index were measured during repeat transitions to MOD (90% of the gas exchange threshold) and VH (Δ60%) intensity cycling exercise.



During MOD, the phase II V˙O2 τ (P = 0.84, effect size [ES] = 0.11) and the 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 (stroke volume index and cardiac index), and muscle [HHb] kinetics were unaltered in CF. However, the arteriovenous O2 content difference ((Equation is included in full-text article.)) 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, (Equation is included in full-text article.)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.



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.
1Children's Health and Exercise Research Centre, Sport and Health Sciences, University of Exeter, Exeter, Devon, UNITED KINGDOM; and 2Paediatric Unit, Royal Devon and Exeter NHS Foundation Trust, Exeter, Devon, UNITED KINGDOM.
Zoe Louise
ZL
Saynor
Alan Robert
AR
Barker
Patrick John
PJ
Oades
Craig Anthony
CA
Williams
D000293:Adolescent; D002302:Cardiac Output / Q000502:physiology; D016022:Case-Control Studies; D002648:Child; D003550:Cystic Fibrosis / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008168:Lung / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism / Q000502:physiology*; D010101:Oxygen Consumption / Q000502:physiology; D011659:Pulmonary Gas Exchange / Q000502:physiology; D013318:Stroke Volume / Q000502:physiology
D010100:Oxygen