An fMRI study of cerebrovascular reactivity and perfusion in obstructive sleep apnea patients before and after CPAP treatment

Abstract

Objective: Cerebrovascular reactivity is impaired in patients suffering from obstructive sleep apnea syndrome (OSAS) as demonstrated by transcranial Doppler studies. We use magnetic resonance imaging techniques to investigate the anatomical distribution of cerebrovascular reactivity changes in patients with OSAS, as well as their evolution after therapeutic and sham continuous positive airway pressure (CPAP) treatment.

Methods: Twenty-three men with moderate or severe obstructive sleep apnea were compared to a healthy control group (n=7) using a breath-holding functional magnetic resonance imaging task and the flow-sensitive alternating inversion recovery (FAIR) imaging before and after 2 months of therapeutic (active) or sub-therapeutic (sham) CPAP treatment.

Results: Significantly higher cerebrovascular reactivity was found in healthy controls as compared to patients in bilateral cortical and subcortical brain regions. Cerebrovascular reactivity increased with therapeutic CPAP in the thalamus and decreased with sham CPAP in medial frontal regions in OSAS patients. Duration of nocturnal hypoxemia and body mass index negatively correlated with cerebrovascular reactivity, particularly in the medial temporal lobe structures, suggesting a possible pathophysiological mechanism for hippocampal injury. There was no difference in perfusion between patients and control group, and no effect of CPAP or sham-CPAP treatment on perfusion in patients.

Conclusions: Observed cerebrovascular reactivity changes were neither homogeneous throughout the brain nor followed vascular territories, but rather corresponded to underlying neuronal networks, establishing a relationship between cerebrovascular reactivity and surrounding neuronal activity.

Keywords: CPAP; Cerebral perfusion; Cerebral vascular reactivity; Functional magnetic resonance imaging; Hypoxemia; OSAS; Obstructive sleep apnea; fMRI.