Skeletal muscle metabolic recovery following submaximal exercise in chronic heart failure is limited more by O2 delivery than O2 utilization
Résumé
Chronic heart failure (CHF) is associated with a prolonged recovery of skeletal muscle energy stores following submaximal exercise, limiting the ability to perform repetitive daily activities. The pathophysiological background of this impairment is not well established. The aim of this study was to investigate whether muscle metabolic recovery following submaximal exercise in patients with CHF is limited by O2 delivery or O2 utilization. Thirteen stable CHF patients (New York Heart Association class II-III) and 8 healthy subjects, matched for age and BMI were included. All subjects performed repetitive submaximal dynamic single-leg extensions in the supine position. Post-exercise phosphocreatine (PCr) resynthesis was assessed by 31P magnetic resonance spectroscopy. Near-infrared spectroscopy was applied simultaneously, using the rate of decrease in deoxygenated hemoglobin (HHb) as an index of post-exercise muscle re-oxygenation. As expected, PCr recovery was slower in CHF patients than in control subjects (time constant: 47±10 sec versus 35±12 sec, P=0.04). HHb recovery kinetics were also prolonged in CHF patients (mean response time: 74±41 sec versus 44±17 sec, P=0.04). In the patient group, HHb recovery kinetics were slower than PCr recovery kinetics (P=0.02), while no difference existed in the control group (P=0.32). In conclusion, prolonged metabolic recovery in CHF patients is associated with an even slower muscle tissue re-oxygenation, indicating a lower O2 delivery relative to metabolic demands. Therefore, we postulate that the impaired ability to perform repetitive daily activities in these patients depends more on a reduced muscle blood flow than on limitations in O2 utilization.
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