Abstract
BACKGROUND: Skeletal muscle atrophy contributes to increased afferent feedback (group III and IV) and may influence ventilatory control (high VE/VCO2 slope) in heart failure (HF). OBJECTIVE: This study examined the influence of muscle mass on the change in VE/VCO2 with afferent neural block during exercise in HF. METHODS: 17 participants [9 HF (60±6 yrs) and 8 controls (CTL) (63±7 yrs, mean±SD)] completed 3 sessions. Session 1: dual energy x-ray absorptiometry and graded cycle exercise to volitional fatigue. Sessions 2 and 3: 5 min of constant-work cycle exercise (65% of peak power) randomized to lumbar intrathecal injection of fentanyl (afferent blockade) or placebo. Ventilation (VE) and gas exchange (oxygen consumption, VO2; carbon dioxide production, VCO2) were measured. RESULTS: Peak work and VO2 were lower in HF (p<0.05). Leg fat was greater in HF (34.4±3.0 and 26.3±1.8%) and leg muscle mass was lower in HF (63.0±2.8 and 70.4±1.8%, respectively, p<0.05). VE/VCO2 slope was reduced in HF during afferent blockade compared with CTL (-18.8±2.7 and -1.4±2.0%, respectively, p=0.02) and was positively associated with leg muscle mass (r2=0.58, p<0.01) and negatively associated with leg fat mass (r2=0.73, p<0.01) in HF only. CONCLUSIONS: HF patients with the highest fat mass and the least leg muscle mass had the greatest improvement in VE/VCO2 with afferent blockade with leg fat mass being the only predictor for the improvement in VE/VCO2 slope. Both leg muscle mass and fat mass are important contributors to ventilatory abnormalities and strongly associated to improvements in VE/VCO2 slope with locomotor afferent inhibition in HF.