The Effect of Dietary Nitrate on Nocturnal Sleep-Disordered Breathing and Arterial Oxygen Desaturation at High Altitude.

Patrician, Alexander, Harald Engan, David Lundsten, Ludger Grote, Helena Vigetun-Haughey, and Erika Schagatay. The effect of dietary nitrate on nocturnal sleep-disordered breathing and arterial oxygen desaturation at high altitude. High Alt Med Biol 19:21-27, 2018.-Sleep-disordered breathing and fluctuations in arterial oxygen saturation (SaO2) are common during sleep among lowlanders ascending to high altitude. Dietary nitrate (NO3-) supplementation has been shown to lower the O2 consumption in various conditions. Our objective was to investigate whether dietary NO3- could reduce sleep-disordered breathing and SaO2 desaturation during sleep at altitude. Cardiorespiratory responses during sleep were measured in 10 healthy lowlanders at 330 m and then again in the Himalayas at 3700-4900 m. Each subject received two 70 mL shots of either beetroot juice (BR; ∼5.0 mmol NO3- per shot) or placebo (PL: ∼0.003 mmol NO3- per shot) in a single-blinded, weighted order over two consecutive nights at altitude. At 2.5-4.5 hours into sleep at altitude, BR increased the SaO2 desaturation drop (4.2 [0.1]% with PL vs. 5.3 [0.4]% with BR; p = 0.024) and decreased the SaO2 desaturation duration (14.1 [0.9] seconds with PL to 11.1 [0.9] seconds with BR; p = 0.0.041). There was a reduction in breaths with flow limitation (p = 0.025), but no changes in Apnea-Hypopnea Index (AHI), mean and minimum SaO2. The study suggests BR supplementation does not improve AHI or oxygenation, but may increase fluctuations in arterial O2 saturation during sleep at altitude in native lowlanders.

Voluntary apnea evokes diving responses in obstructive sleep apnea patients.

PURPOSE: Two potentially protective responses to apnea were studied in obstructive sleep apnea (OSA) patients; the diving response and the increase in Hb concentration [Hb] via spleen contraction. METHODS: Eight OSA patients and ten healthy controls performed apneas in air (A) and apneas with facial immersion in 15 °C water (FIA) after inspiration and without prior hyperventilation. In each condition, subjects performed three apneas of maximal voluntary duration spaced by 2 min of rest. Cardiorespiratory parameters were measured non-invasively, and venous blood samples for [Hb] analysis were drawn before and after apneas. RESULT: Mean (SD) apnea durations were similar between groups (NS). In controls, the heart rate (HR) reduction was 10 ± 10 % at apnea and 19 ± 10 % in FIA (P < 0.05). In OSA patients, however, the fall in HR was the same in both conditions, 13 ± 10 and 14 ± 8 % for A and FIA, respectively (NS). In controls, the [Hb] increase was the same in A and FIA (2.2 ± 2.9 and 2.1 ± 2.2 %), while in OSA the [Hb] increase was greater during FIA compared to A (3.3 ± 2.2 and 1.4 ± 0.9 %; P < 0.05). CONCLUSION: Apnea induces a diving response and [Hb] increase in both groups. OSA patients did not show the typical training effect of the diving response seen in apnea divers despite their frequent nocturnal apneas. However, they also deviated from normal controls in response pattern; face immersion enhanced the cardiovascular diving response in controls but not in OSA, while the hematological response was enhanced by face immersion only in OSA patients.