Effects of intermittent hypoxia on the cerebrovascular responses to submaximal exercise in humans

Abstract

Intermittent hypoxia (IH) has been shown to alter the ventilatory and cardiovascular responses to submaximal exercise; however, the effect of IH on the cerebral blood flow (CBF) response to submaximal exercise has not been determined. This study tested the hypothesis that IH would blunt the CBF response during eucapnic and hypercapnic exercise. Nine healthy males underwent 10 consecutive days of isocapnic IH (oxyhaemoglobin saturation = 80%, 1 h day⁻¹). Ventilatory, cardiovascular, and cerebrovascular responses to cycle exercise (50, 100, and 150 W) were measured before and after IH. Carbon dioxide (5% CO₂), a mediator of CBF during exercise, was administered for 2 min of each exercise stage. Over the 10 days of IH, there was an increase in minute ventilation $\left( {\dot{V}_{\text{E}} } \right)$ during the IH exposures (P < 0.05). Although exercise produced increases in $\dot{V}_{\text{E}} ,$ middle cerebral artery mean velocity (MCA V _mean), and mean arterial pressure (P < 0.05), there was no effect of IH. Similarly, hypercapnic exercise increased $\dot{V}_{\text{E}}$ and MCA V _mean (P < 0.05); however, the magnitude of the response was unchanged following IH. Our findings indicate that ten daily hypoxia exposures does not alter the CBF response to submaximal exercise.