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Background: Understanding the regulation of resting cerebral blood flow (CBF) is crucial in the realm of brain health as previous studies indicate reduced CBF is associated with an increased risk of several neurological and cerebrovascular conditions. Concurrently, cerebrovascular reactivity (CVR), which assesses the ability of blood vessels to respond to stimuli, is a valuable indicator of cerebrovascular health, as reduced CVR to increased CO 2 is associated with increased stroke, cognitive decline, and mortality risk. Thus, evaluating CVR may serve as a useful tool to understand pathologic brain conditions. In this study, we sought to address these intricacies by examining how the brain responds to different physiological stressors, such as hypercapnia, hyperoxia, and hypoxia. We tested the hypothesis that a) lower resting CBF is associated with reduced CVR-CO 2 , b) lower resting CBF is associated with reduced CVR-hyperoxia c) lower resting CBF is associated with reduced CVR-hypoxia. Methods: 51 young, healthy adults (19F) were included (23±4 yr). Females were not taking hormonal birth control and studied on days 1-7 of the menstrual cycle. Participants completed a magnetic resonance imaging (MRI) scan and CBF was quantified using arterial spin labeling (ASL). CVR was evaluated using a resting normoxia compared to: hypercapnia (5% CO 2 ; 32M/19F), isocapnic-hyperoxia (100% O 2 ; 8M/7F) and isocapnic hypoxia (80-85±1% oxygen saturation (SpO 2 ); 12M/2F). Relative CVR was calculated by the ratio of %ΔCBF/ΔEnd tidal CO 2 (ETCO 2 ) for hypercapnia, %ΔCBF/ΔSpO 2 for hypoxia, and hyperoxic reactivity was analyzed as relative CBF change (%Δ). Data were analyzed using correlation with significance set at p0.05 for both). SpO 2 decreased from 98±1% to 84±2 % during hypoxia (p<0.05). There was no significant correlation between resting CBF and CVR-CO 2 (r 2 =0.02, p=0.23), as well as CVR-hyperoxia (r 2 =0.07, p=0.3). However, lower CVR-hypoxia was significantly correlated with lower resting CBF (r 2 =0.27; p=0.05). Conclusion: These findings suggest there is an association between resting CBF and hypoxic reactivity, but not hypercapnic or hyperoxic reactivity indicating a single measure of vascular health may not be suffcient to understand cerebrovascular function in health. Further studies with larger and more diverse populations may provide deeper insights into these intricate interactions. Funding NIH R01 HL 150361. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
Motlagh et al. (Wed,) studied this question.