[Skeletal muscle efficiency in heart failure]

Heart failure is associated with modifications of skeletal muscle cells, which could participate in the exercise limitation of the patients. However, the mechanical efficiency of the skeletal muscle has not been fully evaluated in these patients. We therefore measured VO2 during prolonged exercise (15 min) at constant load to obtain stable conditions. Load was chosen after maximal stress test as 35% and 65% of load at anaerobic threshold. VO2 during assisted cycling was subtracted from that during constant load to evaluate the relationship between VO2 and Watt. Twenty CHF patients (peak VO2 17.6 ml/kg/min, LVEF <35%) have been compared to 11 controls (peak VO2 40.2 ml/ml/kg). VO2 was similar in the two groups at rest and during assisted cycling. Ventilation on contrary was higher in CHF patients. The relationship between VO2 and Watt was similar in the two populations, indicating that skeletal muscle mechanical efficiency was not altered in CHF patients. In conclusion, histological modifications present in skeletal muscle of CHF patients do not translate into altered skeletal muscle efficiency.