We examined the effects of hypoxaemia on dynamic cerebral autoregulation (dCA) in lowlanders and Sherpa highlanders. We hypothesized that dCA in lowlanders would be reduced to a greater extent in the common carotid artery (CCA) compared to the internal carotid artery (ICA) during acute hypoxia at sea level and at high altitude, whereas Sherpa highlanders would have preserved dCA upon ascent to high altitude.
dCA was calculated as the change in cerebrovascular conductance during transient hypotension induced via dual thigh-cuff release. Data were collected in 13 healthy lowlanders in normobaric normoxia and hypoxia (FIO2 = 0.11) at sea-level (344 m), and the day after arrival at 3440 m and 5050 m. In addition, 10 healthy Sherpa highlanders were tested at Kathmandu (~ 1400 m), and the day after arrival at 3440 m and 5050 m.
The main findings were that: (1) in lowlanders, dCA in the CCA and ICA were both reduced by ~ 35% during normobaric hypoxia exposure at sea-level (P = 0.06 and P = 0.04, respectively); (2) CCA and ICA dCA were both similarly attenuated by ~ 40% at 5050 m in lowlanders, but not 3440 m, compared to sea-level (both P = 0.04); and (3) in Sherpa, high altitude had no impact on CCA dCA (P = 0.275), indicating intact cerebral autoregulation.
Herein, we provide novel evidence that dCA, assessed via Duplex ultrasound, was attenuated in lowlanders with exposure to normobaric and hypobaric hypoxia, whereas it is potentially preserved in the Sherpa. The clinical implications of attenuated dCA in lowlanders, and the adaptive significance of this response in the Sherpa highlanders, remains to be elucidated.
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Acute mountain sickness
Cerebral blood flow
Common carotid artery
Internal carotid artery
Mean arterial pressure
Middle cerebral artery
- PETCO2 :
Partial pressure of end-tidal carbon dioxide
Rate of regulation
- SpO2 :
Peripheral oxygen saturation
Transcranial Doppler ultrasound
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This study was performed within the framework of the UBC International Research Expedition to Nepal. We thank the research station staff for friendly accommodation. We are grateful to the members of the UBC International Research expedition to the Ev-K2 CNR pyramid laboratory for invaluable help with organization and implementation of this research study.
This study was supported by the Natural Sciences and Engineering Research Council of Canada (P.N.A.), the Canadian Foundation for Innovation and a Canada Research Chair (P.N.A.). M.M.T. was supported by a Natural Sciences and Engineering Research Council of Canada Doctoral CGS award.
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Communicated by Guido Ferretti.
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Tymko, M.M., Hansen, A.B., Tremblay, J.C. et al. UBC-Nepal expedition: dynamic cerebral autoregulation is attenuated in lowlanders upon ascent to 5050 m. Eur J Appl Physiol (2020). https://doi.org/10.1007/s00421-020-04307-7
- High altitude
- Cerebral blood flow regulation