AUTHOR=Luyken Matthias C. , Appenzeller Paula , Scheiwiller Philipp M. , Lichtblau Mona , Mademilov Maamed , Muratbekova Aybermet , Sheraliev Ulan , Abdraeva Ainura , Marazhapov Nuriddin , Sooronbaev Talant M. , Ulrich Silvia , Bloch Konrad E. , Furian Michael 

TITLE=Time course of cerebral oxygenation and cerebrovascular reactivity in Kyrgyz highlanders. A five-year prospective cohort study

JOURNAL=Frontiers in Physiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2023.1160050

DOI=10.3389/fphys.2023.1160050

ISSN=1664-042X

ABSTRACT=<p><bold>Introduction:</bold> This prospective cohort study assessed the effects of chronic hypoxaemia due to high-altitude residency on the cerebral tissue oxygenation (CTO) and cerebrovascular reactivity.</p><p><bold>Methods:</bold> Highlanders, born, raised, and currently living above 2,500 m, without cardiopulmonary disease, participated in a prospective cohort study from 2012 until 2017. The measurements were performed at 3,250 m. After 20 min of rest in supine position while breathing ambient air (FiO<sub>2</sub> 0.21) or oxygen (FiO<sub>2</sub> 1.0) in random order, guided hyperventilation followed under the corresponding gas mixture. Finger pulse oximetry (SpO<sub>2</sub>) and cerebral near-infrared spectroscopy assessing CTO and change in cerebral haemoglobin concentration (cHb), a surrogate of cerebral blood volume changes and cerebrovascular reactivity, were applied. Arterial blood gases were obtained during ambient air breathing.</p><p><bold>Results:</bold> Fifty three highlanders, aged 50 ± 2 years, participated in 2017 and 2012. While breathing air in 2017 vs. 2012, <italic>P</italic>aO<sub>2</sub> was reduced, mean ± SE, 7.40 ± 0.13 vs. 7.84 ± 0.13 kPa; heart rate was increased 77 ± 1 vs. 70 ± 1 bpm (<italic>p</italic> &lt; 0.05) but CTO remained unchanged, 67.2% ± 0.7% vs. 67.4% ± 0.7%. With oxygen, SpO<sub>2</sub> and CTO increased similarly in 2017 and 2012, by a mean (95% CI) of 8.3% (7.5–9.1) vs. 8.5% (7.7–9.3) in SpO<sub>2</sub>, and 5.5% (4.1–7.0) vs. 4.5% (3.0–6.0) in CTO, respectively. Hyperventilation resulted in less reduction of cHb in 2017 vs. 2012, mean difference (95% CI) in change with air 2.0 U/L (0.3–3.6); with oxygen, 2.1 U/L (0.5–3.7).</p><p><bold>Conclusion:</bold> Within 5 years, CTO in highlanders was preserved despite a decreased <italic>P</italic>aO<sub>2</sub>. As this was associated with a reduced response of cerebral blood volume to hypocapnia, adaptation of cerebrovascular reactivity might have occurred.</p>