Vascular responses of hypercapnia challenge in mice

Hypercapnia challenge with a few percent of carbon dioxide is popularly used in physiological studies to investigate the dynamic vascular properties. A typical hypercapnia experiment can be divided into four phases: baseline (regular air), transition (CO2 enriched), hypercapnia (CO2 enriched), and recovery (regular air). Cerebrovascular reactivity (CVR), denoting the percentage of functional changes between baseline and hypercapnia phases, can be measured to assess vascular health. In this study, we focus on the transition and recovery phases to track the built-up of cerebral blood flow (CBF) increase induced by CO2-enriched gas and recovery of CBF after returning to regular air. Dynamic features were compared with those of another potent vasodilatory agent, acetazolamide. Our results reveal that 5 min is sufficiently long to ensure 95% built-up of CBF increase under 5% CO2, but it takes much longer to recover to baseline.