Reduced Oxygen Extraction Fraction as a Biomarker for Cognitive Deficits in Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is characterized by disruptive breathing, resulting in a decline in cognitive performance. This study investigates the role of oxygen extraction fraction (OEF) and quantitative susceptibility mapping (QSM) in OSA-related cognitive impairment.

The study recruited 15 patients with confirmed OSA and 16 healthy controls, who underwent overnight polysomnography and brain MRI using a 3 Tesla machine and 64-channel head coil. A two-step MRI analysis was employed to measure OEF. QSM was first created by processing separate phase and magnitude images. OEF maps were then generated by identifying veins based on their susceptibility. Volumetric analysis was performed using the FreeSurfer. Neuropsychological tests were administered to evaluate cognition.

The analysis of OEF revealed significantly lower values in various cerebral cortical regions of OSA patients than in controls. Notably, OEF in the cerebral cortex and frontal, temporal, and occipital regions showed negative correlations with the duration of stage N2 sleep (highest correlation between N2 and right temporal OEF: p = 0.005, r = -0.681). Furthermore, poorer performance on neuropsychological tests, such as the backward digit span test, was significantly correlated with reduced OEF in the left hemisphere (p = 0.016), left cerebral cortex (p = 0.019), right frontal (p = 0.034), left frontal (p = 0.014), left parietal (p = 0.008), left temporal (p = 0.048), and left occipital lobes (p = 0.015). No significant differences in QSM or brain volume were observed.

Decreased OEF emerges as a potential biomarker for cognitive deficits in OSA, suggesting disturbances in cerebral oxygen metabolism may underlie cognitive impairments. These findings underscore the importance of investigating physiological markers in understanding OSA-related cognitive dysfunction.