Cerebral blood flow at high altitude

Area of Science:

• Physiology
• Altitude Medicine
• Neuroscience

Background:

• Human exposure to high altitude triggers physiological changes, notably in cerebral blood flow (CBF).
• Early research in 1964 using the Kety-Schmidt technique documented initial increases in CBF at high altitude.
• CBF regulation at altitude is complex, influenced by oxygen and carbon dioxide levels, pH, and hematocrit.

Purpose of the Study:

• To review 50 years of research on human cerebral blood flow (CBF) at high altitude.
• To summarize the integrated reflexes governing CBF regulation under hypoxic conditions.
• To explore potential cerebrovascular adaptations and the role of CBF in acute mountain sickness (AMS).

Main Methods:

• Historical review of studies on CBF in humans at high altitude over the past 50 years.
• Analysis of factors influencing CBF, including arterial blood gases and hematological parameters.
• Examination of integrated physiological reflexes: hypoxic cerebral vasodilatation, hypocapnic cerebral vasoconstriction, and ventilatory responses.

Main Results:

• CBF increases within 12 hours of high-altitude exposure and returns to near sea-level values after 3-5 days of acclimatization.
• Four key reflexes (hypoxic/hypocapnic vasodilation/vasoconstriction and ventilatory responses) are central to CBF regulation at altitude.
• The integrated CBF response appears sufficient to meet the brain's oxygen demand, even in chronic hypoxia.

Conclusions:

• Understanding the interplay of these reflexes is crucial for comprehending global and regional CBF regulation.
• It remains unknown whether high-altitude populations have specific cerebrovascular adaptations or if CBF changes relate to AMS.
• Future research should focus on these unknowns to advance knowledge of altitude physiology and AMS pathophysiology.