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Impaired Pulmonary V˙O2 Kinetics in Cystic Fibrosis Depend on Exercise Intensity
Zoe Louise Saynor1, Alan Robert Barker, Patrick John Oades
11Children'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.
Insights
Children with cystic fibrosis (CF) show slower pulmonary oxygen uptake (V˙O2) kinetics during very heavy exercise, indicating intensity-dependent impairments in muscle oxygen use. This impacts their ability to utilize oxygen efficiently during strenuous physical activity.
Area of Science:
- Exercise Physiology
- Pediatric Pulmonology
- Cardiorespiratory Fitness
Background:
- Cystic Fibrosis (CF) affects multiple organs, including the lungs, potentially impacting exercise capacity.
- Understanding the kinetics of pulmonary oxygen uptake (V˙O2) is crucial for assessing cardiorespiratory function during exercise.
- Pediatric patients with mild-to-moderate CF may exhibit subtle impairments in oxygen utilization during physical exertion.
Purpose of the Study:
- To investigate the effects of mild-to-moderate cystic fibrosis (CF) on pulmonary oxygen uptake (V˙O2) kinetics in pediatric patients.
- To compare V˙O2 kinetics during moderate (MOD) and very heavy (VH) intensity cycling exercise between CF patients and healthy controls.
- To determine if CF-related impairments in V˙O2 kinetics are intensity-dependent and linked to central or peripheral factors.
Main Methods:
- Seven pediatric patients with mild-to-moderate CF and seven healthy matched controls performed repeat transitions to MOD and VH intensity cycling.
- Breath-by-breath V˙O2, vastus lateralis muscle deoxygenation ([HHb]) via near-infrared spectroscopy, and cardiac function (HR, SV index, CI) were measured.
- Phase II V˙O2 time constant (τ) and mean response time (MRT) were calculated to assess V˙O2 kinetics.
Main Results:
- During MOD exercise, V˙O2 kinetics (phase II τ and MRT) were not significantly different between CF patients and controls.
- During VH exercise, V˙O2 kinetics (phase II τ and MRT) were significantly slower in CF patients compared to controls.
- Reduced arteriovenous O2 content difference was observed in CF patients during VH exercise, correlating with slower V˙O2 kinetics.
Conclusions:
- Impaired muscle oxidative metabolism during constant work rate exercise is intensity-dependent in young individuals with mild-to-moderate CF.
- Pulmonary V˙O2 kinetics are slowed during VH but not MOD cycling in pediatric CF patients.
- The observed slowing of V˙O2 kinetics during VH exercise in CF appears mechanistically linked to impaired muscle O2 extraction and utilization.
Purpose:
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.
Methods:
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.
Results:
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.
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.
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