Characterizing the Dose Response of Hyperoxia with Brain Perfusion.

BACKGROUND

Tactical aviators require administration of enhanced inspired oxygen concentrations (hyperoxia) to reduce risk of hypobaric hypoxia and decompression injuries. Hyperoxia is not without consequence; it reduces cerebral perfusion (CBF). Characterizing the relationship between FIO₂ and CBF is necessary to establish FIO₂ levels that do not reduce CBF yet are sufficient to mitigate risk of in-flight physiological stressors. To achieve that goal, this study's objective was to determine whether a dose-response relationship exists between FIO₂ and CBF and, if so, the FIO₂ at which CBF significantly declines.

METHODS

Healthy male and female subjects (N = 26) were randomized to receive either low dose FIO₂ of 30%, 40%, 50%, and 100% (Arm 1) or high dose FIO₂ of 60%, 70%, 80%, and 100% (Arm 2), followed by a return to 21% for both groups. Subjects were placed within a 3-Tesla MRI scanner equipped with pseudocontinuous arterial spin labeling software (pCASL) to measure CBF. Baseline CBF measurements were obtained during exposure to 21% FIO₂, with subsequent CBF measurements obtained at each predetermined FIO₂ level.

RESULTS

Baseline CBF did not differ between subjects in Arm 1 and Arm 2. Low dose FIO₂ ≤ 50% did not affect CBF. In contrast, high dose FIO₂ ≥ 60% significantly reduced CBF. Exposure to 100% FIO₂ led to similar reductions of CBF for subjects in both Arm 1 and Arm 2.DISCUSSION: The neurovascular system appears to respond to increasing FIO₂ levels in a dose dependent manner, with significant reductions in CBF with FIO₂ exposures ≥ 60%.Damato EG, Fillioe SJ, Vannix IS, Norton LK, Margevicius SP, Beebe JL, Decker MJ. Characterizing the dose response of hyperoxia with brain perfusion. Aerosp Med Hum Perform. 2022; 93(6):493-498.