Cerebrovascular Response to CO2 Following 10 Days of Intermittent Hypoxia in Humans

It has been demonstrated that the cerebrovascular response to hypoxia is blunted following 10 days of intermittent hypoxia (IH) in healthy humans. The purpose of this study was to test the hypothesis that IH reduces the cerebrovascular response to CO2. Healthy male subjects (N = 8; 25 ± 2 yr) were exposed to 10 consecutive days of IH (12% O2 for 5 min followed by 5 min of normoxia for 1 h/d). The cerebrovascular response to CO2 was assessed prior to (PRE-IH) and following (POST-IH) the IH paradigm with transcranial Doppler ultrasound. There was no change in eupnic measures during or following the IH paradigm; however, the ventilatory response to IH increased by the last exposure (3.0 ± 2.8 L · min−1). Cerebral blood flow velocity decreased and increased with hypocapnia and hypercapnia, respectively, but cerebrovascular sensitivity to CO2 remained unchanged with IH (PRE-IH: 2.58 ± 0.50%/mmHg; POST-IH: 2.59 ± 0.74%/mmHg). The authors’ data indicates that 10 days of IH in healthy humans does not alter the cerebrovascular response to CO2. Redundancy of cerebrovascular regulation mechanisms to CO2 may work to counteract IH-induced dysregulation and protect cerebral tissue..