Abstract
Cerebral autoregulation (CA) is impaired during acute high-altitude (HA) exposure, however, effects of temporarily living high and working higher on CA require further investigation. In 18 healthy lowlanders (11 women), we hypothesized that the cerebral autoregulation index (ARI) assessed by the percentage change in middle cerebral artery peak blood velocity (Δ%MCAv)/percentage change in mean arterial blood pressure (Δ%MAP) induced by a sit-to-stand maneuver, is (i) reduced on Day1 at 5050 m compared to 520 m, (ii) is improved after 6 days at 5050 m, and (iii) is less impaired during re-exposure to 5050 m after 7 days at 520 m compared to Cycle1. Participants spent 4-8 h/day at 5050 m and slept at 2900 m similar to real-life working shifts. High/low ARI indicate impaired/intact CA, respectively. With the sit-to-stand at 520 m, mean (95% CI) in ΔMAP and ΔMCAv were − 26% (− 41 to − 10) and − 13% (− 19 to − 7), P < 0.001 both comparisons; mean ± SD in ARI was 0.58 ± 2.44Δ%/Δ%, respectively. On Day1 at 5050 m, ARI worsened compared to 520 m (3.29 ± 2.42Δ%/Δ%), P = 0.006 but improved with acclimatization (1.44 ± 2.43Δ%/Δ%, P = 0.039). ARI was less affected during re-exposure to 5050 m (1.22 ± 2.52Δ%/Δ%, P = 0.027 altitude-induced change between sojourns). This study showed that CA (i) is impaired during acute HA exposure, (ii) improves with living high, working higher and (iii) is ameliorated during re-exposure to HA.
Highlights
Cerebral autoregulation (CA) is impaired during acute high-altitude (HA) exposure, effects of temporarily living high and working higher on CA require further investigation
Abbreviations ALMA Atacama Large Millimeter/Submillimeter Array ALMA ASF ALMA Operation Support Facility, 2900 m ALMA AOS ALMA Operation Site, 5050 m acute mountain sickness (AMS) Acute mountain sickness as the environmental symptoms questionnaire cerebral score (AMSc) Environmental symptom questionnaire, cerebral score ARI Cerebral autoregulation index CA Cerebral autoregulation CVCi Cerebrovascular conductance index CVRi Cerebrovascular resistance index mean artery blood pressure (MAP) Mean arterial blood pressure MCA Middle cerebral artery MCAv Middle cerebral artery peak blood velocity PETCO2 End-tidal partial pressure of carbon dioxide SpO2 Arterial oxygen saturation measured by pulse oximetry
With acute exposure to 5050 m, participants had lower values in S pO2, mean ± SD, 77.6 ± 3.4% vs. 96.5 ± 3.4%, lower values in P ETCO2, 24.5 ± 3.0 mmHg vs. 33.9 ± 2.5 mmHg and higher heart rates, 93 ± 13 bpm vs. 70 ± 13 bpm and more symptoms of AMS assessed by the AMSc score, 0.94 ± 0.38 vs. 0.12 ± 0.38 compared to 520 m (P < 0.001 all comparisons)
Summary
Cerebral autoregulation (CA) is impaired during acute high-altitude (HA) exposure, effects of temporarily living high and working higher on CA require further investigation. At the Atacama Large Millimeter/Submillimeter Array (ALMA), the largest ground-based telescope station worldwide, employees sleep at 2900 m and work at 5050 m for 7 days, and recover for 7 days at their permanent residence, normally near sea level These repeated live high, work higher periods may have adverse effects on health, performance and safety of workers[1,2,3]. Real-life working shifts as implied in ALMA require workers to sleep at 2900 m and work at 5050 m This pattern of exposure to high altitude (living high, working higher) induces an intermittent hypobaric hypoxic exposure, which might have beneficial effects on the CA functionality as suggested for intermittent hypoxic training in patients with Alzheimer diseases[9]. This study assessed whether altitude exposure has sustained effects on CA functionality after descending to low altitude
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