Relationship between swallowing function and gas exchange during day and night in patients with obstructive sleep apnea syndrome.

Patients with obstructive sleep apnea syndrome (OSAS) are likely to exhibit an impaired swallowing reflex. However, mechanisms of disturbed swallowing reflex have not been determined. Because the upper-airway function is inhibited by hypoxia and hypercapnia, we examined the relationship between the swallowing function and gas exchange during day and night in patients with OSAS. Twenty-four patients with OSAS and 24 age-matched controls were studied. OSAS was diagnosed from overnight polysomnography. The swallowing reflex was judged by the latent time (LT) for swallowing following bolus injection of distilled water at the suprapharynx, the inspiratory suppression time (IST) from swallowing termination to the next onset of inspiration, and the threshold for evoking the swallowing response in terms of a volume of water (TV). Whereas the LT values are positively correlated with PaCO2 but not with PaO2 during the day, the values of IST and TV were not associated with daytime PaCO2 or PaO2. Nocturnal nadir SaO2 was correlated with LT, IST, and TV. These results indicate that oxyhemoglobin desaturation and hypercapnia may be associated with one of the mechanisms of the impaired swallowing function in patients with OSAS.