Hippocampal area metabolites relate to severity and cognitive function in obstructive sleep apnea

Obstructive sleep apnea (OSA) is associated with intermittent hypoxia and cognitive decrements. As the hippocampus is particularly susceptible to hypoxia, we hypothesized that it may show biochemical abnormalities, and they may relate to apnea severity.

Eight males with OSA and five age-matched controls underwent neurocognitive testing before and after polysomnography and proton magnetic resonance spectra were obtained from the left hippocampal area of all subjects.

In the left hippocampal area, N-acetyl-containing/creatine-containing compounds was significantly increased in OSA (P=0.04). Inspection of these compounds with respect to the water resonance indicated that this was most likely due to a decrease in creatine-containing compounds rather than any change in N-acetyl-containing compounds. Lower levels of hippocampal creatine-containing compounds were correlated with worse OSA severity and neurocognitive performance.

We suggest the changes in creatine levels in the hippocampal area represent adjustments to brain bioenergetics, similar to those seen in ischemic preconditioning, and may reflect the different susceptibility of these tissues to hypoxic damage in OSA.