Dietary nitrate supplementation and exercise tolerance in chronic heart failure: A double-blind, randomized, placebo-controlled, crossover trial

Chronic heart failure (CHF) impairs skeletal muscle O2 transport and utilization leading to restricted physical capacity. Dietary nitrate supplementation has been shown to improve vascular function, reduce the O2 cost of muscle contraction and enhance exercise tolerance (Tlim) in both healthy and clinical populations (e.g., COPD). We tested the hypothesis that dietary nitrate would improve locomotor muscle O2 delivery-utilization matching and Tlim in CHF patients. Methods: Nine males with CHF (ejection fraction=33±6%) consumed either nitrate-rich (∼12 mmol nitrate; beetroot juice) or nitrate-depleted beetroot juice (placebo) for 8 days. Mean arterial pressure (MAP), central hemodynamics by impedance cardiography (stroke volume, heart rate and cardiac output), pulmonary oxygen uptake (VO2) and muscle oxygenation by near-infrared spectroscopy were determined at rest and during low- and high-intensity “step” exercise tests. Results: No differences were observed between placebo vs. beetroot juice for resting and exercising MAP, central hemodynamics or muscle oxygenation (p>0.05). The O2 cost of exercise during both low- (placebo: 0.88±0.19 vs. beetroot juice: 0.94±0.24 l/min) and high-intensity (1.33±0.30 vs. 1.36±0.31 l/min) cycling and Tlim (489±194 vs. 485±173 s) were also unaffected by beetroot juice (p>0.05). Conclusions: Contrary to the hypothesis, 8 days of dietary nitrate supplementation did not enhance skeletal muscle O2 delivery-utilization matching or exercise tolerance in CHF patients. Whether longer treatment duration and/or higher doses are therapeutically effective in this patient population remains to be determined.