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UBC-Nepal expedition: dynamic cerebral autoregulation is attenuated in lowlanders upon ascent to 5050 m

Abstract

Purpose

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.

Methods

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.

Results

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.

Conclusion

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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Abbreviations

AMS:

Acute mountain sickness

CA:

Cerebral autoregulation

CBF:

Cerebral blood flow

CCA:

Common carotid artery

CVC:

Cerebrovascular conductance

HR:

Heart rate

ICA:

Internal carotid artery

KTM:

Kathmandu

MAP:

Mean arterial pressure

MCA:

Middle cerebral artery

NM:

Namche Bazaar

PETCO2 :

Partial pressure of end-tidal carbon dioxide

PYR:

Pyramid laboratory

RoR:

Rate of regulation

SL:

Sea level

SpO2 :

Peripheral oxygen saturation

TCD:

Transcranial Doppler ultrasound

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Acknowledgements

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.

Funding

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.

Author information

MMT and PNA conceived and designed the research study; all authors helped with data collection; MMT analyzed the data, prepared the figures, and drafted the manuscript; all authors interpreted the experiment results; all authors edited and approved the final version of manuscript.

Correspondence to Michael M. Tymko.

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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

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Keywords

  • High altitude
  • Hypoxia
  • Cerebral blood flow regulation