Brain tissue oxygen concentration measurements.

Area of Science:

• Neuroscience
• Physiology
• Biomedical Engineering

Background:

• Brain function relies on oxygen for energy metabolism.
• Understanding brain oxygen levels is crucial for interpreting functional neuroimaging techniques like blood-oxygen-level-dependent functional magnetic resonance imaging (BOLD fMRI) and near-infrared spectroscopy (NIRS).

Purpose of the Study:

• To review historical and current understanding of brain tissue oxygen tension measurements.
• To clarify the spatial and temporal characteristics of brain oxygen distribution.
• To explain the physiological response of brain neurons to activation in terms of oxygenation.

Main Methods:

• Review of quantitative and qualitative techniques for measuring brain tissue oxygen tension over the past 50 years.
• Analysis of existing data on oxygen tension distribution in brain tissue.
• Discussion of the implications for interpreting functional neuroimaging data.

Main Results:

• Brain tissue oxygen tension is typically lower than venous partial pressure of oxygen (pO2).
• Oxygen tension is spatially and temporally heterogeneous at the microregional level.
• A characteristic or average brain tissue pO2 is not meaningful; an oxygen field with local gradients is a more accurate concept, best represented by a pO2 distribution curve.

Conclusions:

• Brain neurons normally operate in a hypoxic (low-oxygen) environment.
• Neuronal activation leads to increased local capillary blood flow, enhancing oxygen supply and improving tissue oxygenation.
• The heterogeneous nature of brain oxygenation necessitates nuanced interpretation of functional neuroimaging data.