Cardiovascular and cerebrovascular responses to acute hypoxia following exposure to intermittent hypoxia in healthy humans

Intermittent hypoxia (IH) is thought to be responsible for many of the long-term cardiovascular consequences associated with obstructive sleep apnoea (OSA). Experimental human models of IH can aid in investigating the pathophysiology of these cardiovascular complications. The purpose of this study was to determine the effects of IH on the cardiovascular and cerebrovascular response to acute hypoxia and hypercapnia in an experimental human model that simulates the hypoxaemia experienced by OSA patients. We exposed 10 healthy, male subjects to IH for 4 consecutive days. The IH profile involved 2 min of hypoxia (nadir PET,02 = 45.0 mmHg) alternating with 2 min of normoxia (peak PET,02= 88.0 mmHg) for 6 h. The cerebral blood flow response and the pressor responses to hypoxia and hypercapnia were assessed after 2 days of sham exposure, after each day of IH, and 4 days following the discontinuation of IH. Nitric oxide derivatives were measured at baseline and following the last exposure to IH. After 4 days of IH, mean arterial pressure increased by 4 mmHg (P < 0.01), nitric oxide derivatives were reduced by 55% (P < 0.05), the pressor response to acute hypoxia increased (P < 0.01), and the cerebral vascular resistance response to hypoxia increased (P < 0.01). IH alters blood pressure and cerebrovascular regulation, which is likely to contribute to the pathogenesis of cardiovascular and cerebrovascular disease in patients with OSA.