Acute dietary nitrate supplementation improves dry static apnea performance

Acute dietary nitrate (NO??) supplementation has been reported to lower resting blood pressure, reduce the oxygen (O?) cost of sub-maximal exercise, and improve exercise tolerance. Given the proposed effects of NO?? on tissue oxygenation and metabolic rate, it is possible that NO?? 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 NO?? supplementation on pre-apnea blood pressure, apneic duration, and the heart rate (HR) and arterial O? saturation (SaO?) 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 SaO? 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 SaO? were greater than in PL (P ≤ 0.05). The results suggest that acute dietary NO?? supplementation may increase apneic duration by reducing metabolic costs.