Study objectives: Orexin and orexin receptors are present in the CNS. The effects of orexin peptides have been uniformly reported as excitatory, and the posterior hypothalamus containing orexin neurons has been implicated in arousal state control. Therefore, it is probable that the orexin system may have a neuromodulatory effect on arousal states. The aim of the present study was to investigate the relationship between plasma orexin-A levels and arousals from sleep in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).
Design: An analysis was conducted in 30 male patients with OSAHS, which had been diagnosed by polysomnography by the presence of an apnea-hypopnea index (AHI) of > 5, and 20 male age-matched and body mass index (BMI)-matched control subjects.
Results: Plasma orexin-A levels were higher in patients with OSAHS compared with those in control subjects (p < 0.05). Plasma orexin-A levels correlated positively, but weakly, with the arousal index (r = 0.51; p < 0.05) and the AHI (r = 0.52; p < 0.05). However, plasma orexin-A levels did not relate to age, BMI, Epworth sleepiness scale, PaO(2), PaCO(2), minimum arterial oxygen saturation (SaO(2)) during sleep, or mean SaO(2) during sleep. Plasma orexin-A levels can be a measure of both AHI and arousal index.
Conclusion: These results suggested that the orexin system may be involved in arousal mechanisms in patients with OSAHS.