Surviving Without Oxygen: How Low Can the Human Brain Go?

Abstract

Bailey, Damian M., Christopher K. Willie, Ryan L. Hoiland, Anthony R. Bain, David B. MacLeod, Maria A. Santoro, Daniel K. DeMasi, Andrea Andrijanic, Tanja Mijacika, Otto F. Barak, Zeljko Dujic, and Philip N. Ainslie. Surviving without oxygen: how low can the human brain go? High Alt Med Biol 18:73-79, 2017.-Hypoxic cerebral vasodilation is a highly conserved physiological response coupling cerebral O delivery (CDO) to metabolic demand with increasingly important roles identified for the red blood cell (sensor) and nitric oxide (effector). In the current article, we reexamine previously published cerebral blood flow (CBF) and arterial blood gas data obtained in freedivers and mountaineers, extreme athletes in whom the lowest arterial partial pressures of O (19-23 mmHg) and greatest extremes of carbon dioxide (16-61 mmHg) were recorded during (acute) maximal static dry apnea or (chronic) exposure to terrestrial high altitude. Data highlight compensatory increases in CBF (+96% in freedivers to +209% in mountaineers relative to normoxic baseline controls) that were sufficient to sustain CDO (+24% in freedivers to +183% in mountaineers) even in the face of the most severe reductions in arterial O content (-61% in freedivers to -9% in mountaineers) reported in the literature, consistent with the conservation of mass principle. These unique findings highlight to what extent cerebral vasodilation likely contributes toward these athletes' extraordinary abilities to survive in such harsh environments characterized by physiological extremes of hypoxemia, alkalosis, and acidosis helping define the human brain's remarkable limits of tolerance.

Exaggerated systemic oxidative‐inflammatory‐nitrosative stress in chronic mountain sickness is associated with cognitive decline and depression

“…The human brain has evolved a much higher rate of obligatory oxygen (O 2 ) consumption because, unlike most other organs, its evolutionary 'drive for size' means that the brain is committed to a continually active state, demanding a disproportionate 20% of the body's basal O 2 budget in the resting state, more than 10 times that expected from its mass alone (Bailey et al 2017b). The requirement to process large amounts of O 2 over a relatively small tissue mass supports the high rate of ATP formation to fuel the maintenance of ionic equilibria and uptake of neurotransmitters for synaptic transmission (Alle et al 2009).…”

Competitive apnea and its effect on the human brain: focus on the redox regulation of blood‐brain barrier permeability and neuronal‐parenchymal integrity

“…The human brain functions almost entirely on oxidative metabolism and requires a disproportionately large, ~20%, of the basal O 2 budget (1, 2), despite occupying only 2‐3% of the body's mass. A burden of such high oxidative energy demands provides the potential for cerebral impairments when a person is deprived of O 2 .…”

Oxygen, evolution and redox signalling in the human brain; quantum in the quotidian

“…Furthermore, the concept of a two-step transition from a virtually anoxic environment to present day conditions has been challenged by the suggestion of a more gradual increase in O 2 levels, termed the Great Oxidation Transition (Lyons et al 2014). Likewise, though beyond the remit of the current review, other atmospheric gases have also helped shape life on Earth, notably carbon dioxide, to which the brain has evolved heightened sensitivity, buffering brain tissue pH for stabilisation of chemosensory and autonomic control at the level of the brainstem (Cummins et al 2014;Willie et al 2014;Bailey et al 2017b).…”