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

Abstract

Chronic heart failure (CHF) impairs skeletal muscle O 2 transport and utilization leading to restricted physical capacity. Dietary nitrate supplementation has been shown to improve vascular function, reduce the O 2 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 O 2 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 (VO 2 ) 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 O 2 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 O 2 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.