Brain strain: Blood flow and metabolism in environmental extremes

Area of Science:

• Environmental Physiology
• Neuroscience
• Human Physiology

Background:

• Environmental stressors significantly impact human physiological functions.
• Cerebrovascular functioning, including cerebral blood flow (CBF) and oxygen metabolism (CMRO2), is crucial for maintaining consciousness and cognitive function.
• Understanding the body's adaptive responses to stressors is vital for health and performance.

Purpose of the Study:

• To compare and contrast the effects of common environmental stressors on human cerebrovascular functioning.
• To review the regulation of CBF and CMRO2 under conditions such as high altitude, space, extreme apnea, heat, and cold stress.
• To consider the implications of these cerebrovascular changes for neuropsychological functioning.

Main Methods:

• This study is a narrative review of existing literature.
• It synthesizes findings on the impact of various environmental stressors on CBF and CMRO2.
• The review discusses physiological responses, including alterations in blood flow, oxygen delivery (CDO2), and metabolism.

Main Results:

• Hypoxia (low oxygen) generally maintains CMRO2 and CDO2 through CBF adjustments, though extreme apnea may reduce CMRO2.
• Heat and cold stress can lead to significant reductions in CBF and CDO2 due to hyperventilation-induced vasoconstriction.
• Spaceflight shows stable intracranial velocity despite altered CO2 levels, while cold exposure involves compensatory mechanisms like increased blood pressure.

Conclusions:

• Human cerebrovascular regulation demonstrates adaptive capacity to various environmental stressors, but extremes can challenge oxygen delivery and metabolism.
• Significant reductions in CBF and CDO2 can occur under heat stress, impacting CMRO2.
• Further research is needed, particularly on combined environmental exposures, to fully understand cerebrovascular adaptation and its neuropsychological consequences.