Levels of neuroglobin in serum and neurocognitive impairments in Chinese patients with obstructive sleep apnea.

PURPOSE

The impact of different severities of obstructive sleep apnea (OSA) on cognition has not well been documented. Neuroglobin, a recently discovered vertebrate protein, shows a neuroprotective function to modulate hypoxic-ischemic brain injury. This study investigated the cognitive function of patients with varying OSA severities and intended to explore the relationship between levels of neuroglobin in serum and cognitive deficits of OSA.

METHODS

Sixty Chinese adults aged 18-59 years old were enrolled and categorized into four groups based on apnea-hypopnea index (AHI): primary snoring (n = 7), mild (n = 13), moderate (n = 20), and severe (n = 20) OSA groups. Computer-based neurocognitive tests (including calculation, memory, and attention) and Epworth sleepiness scale were administered before polysomnographic monitoring, and blood sample was taken the next morning. Concentrations of serum neuroglobin were measured using ELISA.

RESULTS

No significant difference was observed in cognitive function regardless of OSA severities, but patients with moderate and severe OSA presented significantly more sleepiness than patients with primary snoring and mild OSA. Memory significantly correlated with time spent with oxygen saturation below 90 % during nighttime (T < 90 %), as well as oxygen desaturation index, AHI, or NREM sleep. Calculation correlated significantly with sleepiness and respiratory arousal index. Levels of neuroglobin in serum of patients with varying OSA severities were significant elevated than that of patients with primary snoring. No relationship was found between the neurobehavioral ability index of neurocognitive tests and serum neuroglobin concentrations after controlling for gender, age, and BMI, whereas the unique association between levels of neuroglobin in serum and the scores of auditory digit span test was noted.

CONCLUSIONS

Our findings suggest that different neurocognitive domains might specifically correlate to either sleepiness or hypoxemia. Changes of concentrations of neuroglobin in serum may possibly be used as an indicator to monitor the brain damage of OSA. Further investigations are needed to explore the relationship between regulation of neuroglobin in serum and severity of brain damage in OSA.