Effects of dietary inorganic nitrate on static and dynamic breath-holding in humans

Inorganic nitrate has been shown to reduce oxygen cost during exercise. Since the nitrate-nitrite-NO pathway is facilitated during hypoxia, we investigated the effects of dietary nitrate on oxygen consumption and cardiovascular responses during apnea. These variables were measured in two randomized, double-blind, placebo-controlled, crossover protocols at rest and ergometer exercise in competitive breath-hold divers. Subjects held their breath for predetermined times along with maximum effort apneas after two separate 3-day periods with supplementation of potassium nitrate/placebo.In contrast to our hypothesis, nitrate supplementation led to lower arterial oxygen saturation (SaO2, 77 ± 3%) compared to placebo (80 ± 2%) during static apnea, along with lower end-tidal fraction of oxygen (FETO2) after 4 min of apnea (nitrate 6.9 ± 0.4% vs. placebo 7.6 ± 0.4%). Maximum apnea duration was shorter after nitrate (329 ± 13 s) compared to placebo (344 ± 13 s). During cycle ergometry nitrate had no effect on SaO2, FETO2 or maximum apnea duration. The negative effects of inorganic nitrate during static apnea may be explained by an attenuated diving response.

► Oxygen consumption was evaluated during static and dynamic apneas after nitrate and placebo supplementation in breath-hold divers.
► Indications of higher oxygen consumption were observed during dry resting apnea.
► Attenuation of the diving response induced bradycardia and hypertension was evident during steady state cycling.
► NO-mediated microcirculatory vasodilation may be the explanation of the attenuated diving response.