Control of upper airway function in response to hypoxia in patients with obstructive sleep apnea syndrome.

To clarify the characteristics of upper airway muscles under hypoxic condition in obstructive sleep apnea syndrome (OSAS), we performed the isocapnic progressive hypoxia test during wakefulness in 8 controls and 7 OSAS patients. Electromyographic activities were recorded from the genioglossal muscle (EMG(GG)) and diaphragm (EMG(DIA)) with ventilatory variables. Minute EMG (peak integrated EMG x respiratory rate) activity against P(ET)O2 was calculated by exponential equation, and its response slope represented the hypoxic sensitivity of each muscle, slope(GG) and slope(DIA). There was no significant difference between the slopes of OSAS and control. In contrast, the ratio of the two responses, slope(GG)/slope(DIA), was significantly higher in OSAS (1.61 +/- 0.49 SD) than in control (0.98 +/- 0.43). Moreover, the slope(GG)/slope(DIA) ratio was negatively correlated with the ratio of sleep time with SpO2 lower than 90% to total sleep time. We conclude that the neuromuscular compensatory mechanism of upper airway muscles is effectively developed and plays an important role in preventing nocturnal hypoxemia in OSAS.