Skeletal Muscle Afferent Inhibition Improves Exercise Tolerance in Heart Failure

Abstract

BACKGROUNDIncreased activation of Group III/IV skeletal muscle afferents is suggested to play a role in exercise intolerance in heart failure (HF).PURPOSEThe purpose of this study was to examine if skeletal muscle afferent feedback inhibition improves exercise tolerance in HF.METHODS8 HF patients [59±8 yr, mean±SD] participated in two randomized incremental recumbent cycling exercise sessions to peak capacity (peak oxygen consumption, VO2). Session 1: The synthetic opioid fentanyl (50 mcg), known to block afferent feedback, was injected intrathecally (INJ) in the lumbar spine (L3‐L4 intervertebral space) prior to exercise. Session 2: Participants were prepared similarly with a sham injection (placebo, PLA). Gas exchange, dyspnea and RPE were measured.RESULTSHF patients exercised for a longer duration (Δ3±3 min, p=0.02) and reached a higher power output (PLA:109±30 vs. INJ:128±34 W, p=0.02) with locomotor afferent inhibition. Additionally, peak VO2 was non‐significantly greater (PLA:18.7±3.3 vs. INJ:21.8±4.4 ml/kg/min, p=0.10). With INJ workload matched to peak PLA workload, RPE was reduced (PLA:18±2 vs. INJ:15±2, respectively, p=0.005) and dyspnea was lower (PLA:7.5±2 vs. INJ:4.2±1, p=0.003) with no difference in VO2 (p>0.05).CONCLUSIONInhibition of group III/IV locomotor muscle afferent feedback contributes to improved exercise tolerance and exertional symptoms in HF patients.