Cerebrovascular autoregulation in hypoxia: quantitative insights from arterial spin labeling.

Hypoxia, defined as an insufficient oxygen supply relative to metabolic demand, induces a cascade of cerebrovascular and metabolic responses aimed at preserving cerebral homeostasis. These responses vary depending on the temporal profile of exposure, with acute (e.g., hypoxic-ischemic encephalopathy, acute high-altitude exposure) versus chronic (e.g., obstructive sleep apnea, long-term altitude residence) conditions, and may range from compensatory vasodilation to long-term maladaptive remodeling. Arterial Spin Labeling (ASL) MRI offers a quantitative, non-invasive, and contrast-free method to assess cerebral perfusion, making it well-suited to characterize the spatial and temporal dynamics of these responses. This narrative review critically examines the application of ASL to quantify key hemodynamic parameters, including cerebral blood flow (CBF), arterial transit time (ATT), cerebrovascular reactivity (CVR), and, when integrated with complementary models, cerebral metabolic rate of oxygen consumption (CMRO₂), in the context of hypoxia. By synthesizing evidence from both environmental and pathological models induced by hypoxia, we highlight how ASL captures early signatures of cerebrovascular adaptation, impaired autoregulation, and emerging neurovascular dysfunction. Particular emphasis is placed on the potential of ASL-derived metrics to serve as early biomarkers for hypoxia-induced risk, enabling non-invasive longitudinal tracking of vascular integrity in both clinical and subclinical populations. Overall, ASL emerges as a powerful modality for elucidating the mechanisms of neurovascular adaptation to hypoxia and for supporting precision diagnostics in disorders where oxygen insufficiency constitutes a key pathophysiological driver.