Brain functions in sleep apnea syndrome assessed by near-infrared spectroscopy

Objectives: Nocturnal respiratory disturbances and disrupted sleep architecture due to sleep apnea syndrome cause daytime sleepiness and cognitive deficits. The purpose of our study was to evaluate the functional brain imaging of sleep apnea syndrome patients with oral and cognitive tasks by multi-channel near-infrared spectroscopy. Methods: Ten Japanese patients with sleep apnea syndrome (mean age; 52.5 years, mean apnea-hypopnea index; 18.9) and ten normal subjects (mean age; 50.8 years) were examined in this study. The Hitachi ETG-4000 Optical Topography (Hitachi Medical, Tokyo, Japan) is able to estimate the changes of the concentration of oxyhemoglobin, deoxyhemoglobin and total hemoglobin simultaneously from 52 channels. We used this device to record the activity of the optical property of brain tissue in response to oral function tasks (mouth opening, clenching, gum chewing, tongue protrusion, phonation) and cognitive function task (word fluency task). In the word fluency task, the subjects were requested to generate words of which initial syllables were /a/, /ka/, or /sa/ as many as they could. 52 measurement points were placed on subjects' frontal and bilateral temporal regions. During measurements of the oral function tasks, the subjects repeated 30 s' rest and 10 s' tasks for 5 times. The cognitive activation consisted of a 30 s' pretask baseline, a 60 s' word fluency task, and a 60 s' posttask baseline. Results: In response to the oral function tasks, event-related increase in total hemoglobin was evident and all subjects showed significant (p<0.01) changes in total hemoglobin over the bilateral temporal cortex. No significant differences were observed between the two groups. During the word fluency task, clear oxyhemoglobin increases were observed in the lower frontal and anterior lower channels. The increases of hemoglobin in response to the word fluency task were significantly (p<0.05) reduced in sleep apnea patients than in normal controls. Conclusion: The results can be related to prefrontal lobe dysfunction in sleep apnea syndrome patients.