Impaired dynamic cerebral autoregulation at extreme high altitude even after acclimatization

Ken Ichi Iwasaki, Rong Zhang, Julie H. Zuckerman, Yojiro Ogawa, Lærke H. Hansen, Benjamin David Levine

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


Cerebral blood flow (CBF) increases and dynamic cerebral autoregulation is impaired by acute hypoxia. We hypothesized that progressive hypocapnia with restoration of arterial oxygen content after altitude acclimatization would normalize CBF and dynamic cerebral autoregulation. To test this hypothesis, dynamic cerebral autoregulation was examined by spectral and transfer function analyses between arterial pressure and CBF velocity variabilities in 11 healthy members of the Danish High-Altitude Research Expedition during normoxia and acute hypoxia (10.5% O2) at sea level, and after acclimatization (for over 1 month at 5,260 m at Chacaltaya, Bolivia). Arterial pressure and CBF velocity in the middle cerebral artery (transcranial Doppler), were recorded on a beat-κBy-κBeat basis. Steady-state CBF velocity increased during acute hypoxia, but normalized after acclimatization with partial restoration of SaO2 (acute, 78%±2%; chronic, 89%±1%) and progression of hypocapnia (end-tidal carbon dioxide: acute, 342 mm Hg; chronic, 211 mm Hg). Coherence (0.40±0.05 Units at normoxia) and transfer function gain (0.77±0.13 cm/s per mm Hg at normoxia) increased, and phase (0.86±0.15 radians at normoxia) decreased significantly in the very-low-frequency range during acute hypoxia (gain, 141%±24%; coherence, 136%±29%; phase, 25%±22%), which persisted after acclimatization (gain, 136%±36%; coherence, 131%±50%; phase, 42%±13%), together indicating impaired dynamic cerebral autoregulation in this frequency range. The similarity between both acute and chronic conditions suggests that dynamic cerebral autoregulation is impaired by hypoxia even after successful acclimatization to an extreme high altitude.

Original languageEnglish (US)
Pages (from-to)283-292
Number of pages10
JournalJournal of Cerebral Blood Flow and Metabolism
Issue number1
StatePublished - Jan 2011


  • acclimatization
  • dynamic cerebral autoregulation
  • high altitude

ASJC Scopus subject areas

  • Neurology
  • Clinical Neurology
  • Cardiology and Cardiovascular Medicine


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