Muscle oxygen utilization and ventilatory parameters during exercise in people with cystic fibrosis: Role of HbA(1c)

INTRODUCTION: Glycated hemoglobin can interfere with oxygen delivery and CO(2) removal during exercise. Additionally, pancreatic insufficiency increases oxidative stress and exacerbates exercise intolerance in people with cystic fibrosis (PwCF). This investigation sought to test the hypotheses that elevated Hemoglobin A(1c) (HbA(1c)) can negatively affect exercise parameters in PwCF and that reductions in oxidative stress can improve tissue oxygenation in individuals with elevated HbA(1c). METHODS: Twenty four PwCF were divided into two groups; normal HbA1c <5.7% (N-HbA(1c)) and elevated HbA(1c) >5.7% (E-HbA(1c)). A maximal exercise test was conducted to obtain peak oxygen uptake (VO(2)peak), VO(2) at ventilatory threshold (VT), ventilatory parameters (V(E)/VCO(2) slope and end-tidal CO(2) (petCO(2))). Near-Infrared Spectroscopy (NIRS) was used to assess muscle oxygenated/deoxygenated hemoglobin during exercise. A subset of individuals with E-HbA(1c)were given an antioxidant cocktail (AOC) for 4 weeks to determine the effects on tissue oxygenation during exercise. RESULTS: A negative relationship between HbA(1c) and VO(2)peak at VT was observed (r = −0.511; p = 0.018). In addition, a positive relationship between HbA(1c) and V(E)/VCO(2) slope (r = 0.587;p = 0.005) and a negative relationship between HbA(1c) and petCO(2) at maximal exercise (r = −0.472;p = 0.031) was observed. N-HbA(1c) had greater VO(2)peak (p = 0.021), VO(2) at VT (p = 0.004), petCO(2) (p = 0.002), and lower V(E)/VCO(2) slope (p = 0.004) compared with E-HbA(1c). Muscle deoxygenated hemoglobin at VT was higher in N-HbA(1c) vs. E-HbA(1c) and 4 weeks of AOC improved skeletal muscle utilization of oxygen. CONCLUSION: Findings demonstrate that glycated hemoglobin may lead to tissue oxygenation impairment and ventilation inefficiency during exercise in PwCF. In addition, antioxidant supplementation may lead to improved tissue oxygenation during exercise.