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Arousal is believed to be needed for upper airway opening in obstructive hypopneas-apneas, without compelling evidence to support this notion. The association may be incidental. I studied the temporal relation between arousal and opening and impact of arousal on flow response at opening in 82 patients (apnea-hypopnea index, 46 +/- 35/hour). Obstructive apneas-hypopneas were induced by dial-down of continuous positive airway pressure. Obstructions and hypopneas occurred in 44 and 56% of dial-downs, respectively. When arousal occurred (83% of dial-downs), the temporal relation between arousal and opening was inconsistent between and within patients. Frequency of opening without or before arousal increased with milder obstructions (p < 10(-9)) and with delta power of EEG (p < 10(-6)). Time of opening was unaffected by whether arousal occurred before or after opening (18.0 +/- 9.8 vs. 18.1 +/- 10.5 seconds). Flow response was already excessive when opening occurred without or before arousal (180 +/- 148% of initial flow decline) and was considerably higher when arousal occurred (267 +/- 154%, p < 10(-10)). Flow undershoot after first ventilatory response was greater if arousal occurred (p < 0.01). It is concluded that arousals are incidental events that occur when thresholds for arousal and for arousal-independent opening are close. They are not needed to initiate opening or to obtain adequate flow and they likely increase the severity of the disorder by promoting greater ventilatory instability.
Magdy Younes (Mon,) studied this question.