Normal hypercapnic cerebrovascular conductance in obstructive sleep apnea

• Conductance CVR was unchanged overnight in both healthy control subjects and in treatment naïve subjects with OSA.
• Conductance CVR was not impaired in subjects with OSA.
• Conductance CVR was higher during hypoxia compared with hyperoxia in both control and OSA subjects.

Both obstructive sleep apnoea (OSA) and impaired cerebrovascular reactivity (CVR) are associated with an increased risk of stroke. We therefore hypothesized that CVR would be decreased in OSA patients. Since OSA is associated with altered endothelial function and this dysfunction may in turn lead to impaired CVR, we further hypothesized that a CVR decrease could be the responsible mechanism for stroke. Middle cerebral artery blood flow velocity (MCAv) and mean arterial blood pressure (MAP) responses to hypercapnia were measured to determine cerebrovascular conductance (MCAv/MAP). Overnight changes in conductance CVR were assessed in treatment naïve, otherwise healthy OSA (n = 13) and non-OSA (n = 9) subjects at two isoxic tensions (150 and 50 mmHg). We found no significant overnight changes in CVR for either group. There were no differences in CVR between OSA and non-OSA subjects for either isoxic tension, although CVR was increased in hypoxia.