Interaction of CBF Reactivity to Hypoxia and to Hypercapnia

Zachary M. Smith¹, Ethan Li¹, David J. Dubowitz¹

Cerebral blood flow (CBF) and pulmonary ventilation both increase with hypercapnia or hypoxia. We investigated 1) the CBF reactivity to isolated hypoxia and isolated hypercapnia, 2) reactivity to both stimuli in combination and 3) impact of prolonged hypoxic acclimatization on CBF response. Results were compared with ventilation reactivity. Following 7-days hypoxic acclimatization ventilatory reactivity to hypoxia increased, whereas CBF reactivity diminished. For combined hypoxic/hypercapnic stimuli, CBF shows an additive increase in sensitivity, whereas ventilation shows a multiplicative increase. However, after hypoxic acclimatization, the response in both CBF and ventilation is multiplicative. These differences in CBF and ventilatory sensitivity may provide insights into the mechanisms of hypoxic and CO₂ modulation of CBF.