Characterizing the Dose Response of Hyperoxia with Brain Perfusion

Area of Science:

• Aerospace Medicine
• Neuroscience
• Physiology

Background:

• Tactical aviators use enhanced inspired oxygen (hyperoxia) to prevent hypoxia and decompression sickness.
• Hyperoxia can decrease cerebral blood flow (CBF), posing a potential risk.
• Understanding the relationship between inspired oxygen fraction (FIO₂) and CBF is vital for optimizing flight safety.

Purpose of the Study:

• To determine if a dose-response relationship exists between FIO₂ and CBF in healthy subjects.
• To identify the specific FIO₂ level at which CBF significantly decreases.

Main Methods:

• Twenty-six healthy subjects were randomized into two groups receiving incremental FIO₂ doses (30-100% or 60-100%).
• Cerebral blood flow (CBF) was measured using 3-Tesla MRI with pseudocontinuous arterial spin labeling (pCASL).
• Baseline CBF was established at 21% FIO₂, with subsequent measurements at increasing FIO₂ levels.

Main Results:

• No significant difference in baseline CBF between study arms.
• Inspired oxygen fractions up to 50% (FIO₂ ≤ 50%) did not impact CBF.
• FIO₂ levels of 60% and above (FIO₂ ≥ 60%) significantly reduced CBF.
• 100% FIO₂ exposure resulted in comparable CBF reductions in both arms.

Conclusions:

• The neurovascular system exhibits a dose-dependent response to inspired oxygen.
• Significant reductions in cerebral blood flow occur at FIO₂ levels of 60% or higher.
• Findings are critical for establishing safe oxygen administration protocols for aviators.