Hyperoxic cerebral vasoconstriction in healthy humans: global, lobe and regions of interest

Hyperoxia is used for hypoxia/ischemia-related conditions, but is associated with poorer clinical outcomes, potentially related to reductions in cerebral blood flow (CBF). Global CBF hyperoxia responses are variable; limited evidence suggests heightened sensitivity in anterior brain regions, leaving important gaps in understanding spatial resolution. Using 3-Tesla magnetic resonance imaging (MRI), we tested the hypotheses that 1) isocapnic hyperoxia would reduce CBF at whole brain, grey matter (GM), and white matter (WM), and 2) This reduction would differ across all lobes. CBF was quantified using pseudo-continuous arterial spin labeling (pcASL) in 15 young adults (7 females) during normoxia followed by hyperoxia (~80% O₂). Data presented as mean ± SD. End-tidal CO₂ remained unchanged between conditions (p=0.127) and blood pressure increased by 5±6 mmHg (p=0.013). Hyperoxia did not significantly reduce CBF at whole brain, lobar, or any of 65 brain regions of interest (ROIs) (all p>0.05). In contrast, whole brain cerebrovascular conductance (CVC) decreased by 12±15%, (75±20 to 66±21 mL/100 g/min/100mmHg; p=0.011), with similar relative reductions in GM (13±18%, 90±24 to 78±27 mL/100 g/min/100mmHg; p=0.021) and WM (8±11%, 53±14 to 49±14 mL/100 g/min/100mmHg; p=0.013). CVC decreased across all lobes (9-12%; all p<0.05), with no inter-lobar differences (p=0.866). Exploratory analyses showed reduced CVC in all 65 ROIs (3-35%; all p<0.026), but no regional heterogeneity were found within a given lobe (all p>0.401). These new findings demonstrate widespread cerebral vasoconstriction without lobe- or region-specific effects during acute hyperoxia, providing a foundation for future studies involving greater hyperoxic exposure and clinically relevant populations.