Objective: To evaluate changes in cerebral tissue oxygenation and blood volume during obstructive sleep apnea (OSA).
Methods: We studied eight men with moderate to severe OSA by near-infrared spectroscopy (NIRS) simultaneously with polysomnography during nocturnal sleep (five patients) and daytime naps (three).
Results: In all patients, a consistent decrease of oxyhemoglobin (OxyHb) and increases of deoxyhemoglobin and total hemoglobin (TotalHb) in the regional cerebral tissue were observed during the episode of OSA at every sleep stage. Changes in each hemoglobin and apnea duration were significantly (p<0.01) more remarkable during rapid eye movement (REM) sleep than non-REM (NREM) sleep. Significant correlations of changes in OxyHb and TotalHb during the apneic episode with apnea duration were found during both NREM and REM sleep (p<0.01).
Conclusions: Since TotalHb is used as an indicator of blood volume in the NIRS technique and the venous return is reported to increase during OSA, it is assumed that cerebral blood flow (CBF) increases during the episode of OSA. Because a decrease in OxyHb was observed and brain activity is reported to decrease during OSA, it is supposed that oxygen supply to the brain tissue decreases rather than oxygen consumption in the brain increases. The results of this study indicate that possibly increased CBF could not compensate for reduced arterial oxygen saturation and cerebral tissue hypoxia may occur during the episode of OSA.