A climber sleeping at 5000 m exhibits recurrent cycles of hyperpnea followed by apnea. The mechanism of this periodic breathing at altitude is best described as:

• A Pulmonary J receptor activation causing irregular breathing patterns
• B Failure of the central chemoreceptors to respond to hypoxia during sleep
• C Hypoxia driving ventilation until PaCO2 falls below the apneic threshold, removing the stimulus and allowing CO2 to rebuild ✓
• D Loss of the hypoxic ventilatory response due to carotid body fatigue

Explanation

At altitude, severe hypoxia strongly stimulates carotid bodies, producing hyperventilation that washes out CO2. When PaCO2 drops below the apneic threshold, central chemoreceptor drive ceases and breathing stops despite ongoing hypoxia. CO2 then accumulates and hypoxia worsens until ventilation restarts, creating the cycle. This instability arises because hypoxia and hypocapnia act as opposing drives; it is not caused by receptor failure or J receptor activation.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

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