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Cerebral blood flow (CBF) and its distribution are highly sensitive to changes in the partial pressure of arterial CO₂ (Pa_CO2). This physiological response, termed cerebrovascular CO₂ reactivity, is a vital homeostatic function that helps regulate and maintain central pH and, therefore, affects the respiratory central chemoreceptor stimulus. CBF increases with hypercapnia to wash out CO₂ from brain tissue, thereby attenuating the rise in central Pco₂, whereas hypocapnia causes cerebral vasoconstriction, which reduces CBF and attenuates the fall of brain tissue Pco₂. Cerebrovascular reactivity and ventilatory response to Pa_CO2 are therefore tightly linked, so that the regulation of CBF has an important role in stabilizing breathing during fluctuating levels of chemical stimuli. Indeed, recent reports indicate that cerebrovascular responsiveness to CO₂, primarily via its effects at the level of the central chemoreceptors, is …