Acute dietary nitrate supplementation improves dry static apnea performance

Abstract

Acute dietary nitrate (NO₃⁻) supplementation has been reported to lower resting blood pressure, reduce the oxygen (O₂) cost of sub-maximal exercise, and improve exercise tolerance. Given the proposed effects of NO₃⁻ on tissue oxygenation and metabolic rate, it is possible that NO₃⁻ supplementation might enhance the duration of resting apnea. If so, this might have important applications both in medicine and sport. We investigated the effects of acute NO₃⁻ supplementation on pre-apnea blood pressure, apneic duration, and the heart rate (HR) and arterial O₂ saturation (SaO₂) responses to sub-maximal and maximal apneas in twelve well-trained apnea divers. Subjects were assigned in a randomized, double blind, crossover design to receive 70 ml of beetroot juice (BR; containing ∼5.0 mmol of nitrate) and placebo juice (PL; ∼0.003 mmol of nitrate) treatments. At 2.5 h post-ingestion, the subjects completed a series of two 2-min (sub-maximal) static apneas separated by 3 min of rest, followed by a maximal effort apnea. Relative to PL, BR reduced resting mean arterial pressure by 2% (PL: 86±7 vs. BR: 84 ± 6 mmHg; P=0.04). The mean nadir for SaO₂ after the two sub-maximal apneas was 97.2±1.6% in PL and 98.5±0.9% in BR (P=0.03) while the reduction in HR from baseline was not significantly different between PL and BR. Importantly, BR increased maximal apneic duration by 11% (PL: 250 ± 58 vs. BR: 278±64s; P=0.04). In the longer maximal apneas in BR, the magnitude of the reductions in HR and SaO₂ were greater than in PL (P ≤ 0.05). The results suggest that acute dietary NO₃⁻ supplementation may increase apneic duration by reducing metabolic costs.