A patient with obstructive sleep apnea (OSA) undergoes overnight polysomnography showing repetitive apneas of 25–35 seconds with O2 desaturations to 82%. What is the primary mechanism of arousal that terminates each apneic episode?
- A Hypoxia and hypercapnia progressively stimulate peripheral (carotid body) and central chemoreceptors, raising ventilatory drive until arousal occurs ✓
- B The cortex detects the apnea and voluntarily initiates breathing
- C The hypoglossal nerve is activated by cardiac baroreceptors when blood pressure falls during apnea
- D Gastroesophageal reflux triggers the laryngeal chemoreflex, causing arousal
Explanation
During obstructive apnea, upper airway occlusion prevents airflow despite respiratory effort. Progressive hypoxemia and hypercapnia stimulate carotid body peripheral chemoreceptors (responding rapidly to PaO2 fall) and central chemoreceptors in the medulla (responding to rising PaCO2/H+). The combined chemoreceptor drive eventually overcomes the arousal threshold — the patient partially awakens, restoring upper airway tone (genioglossus activation) and ventilation. This arousal→sleep cycle repeats hundreds of times per night, causing sleep fragmentation and daytime somnolence.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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