A 45-year-old man ascends rapidly to an altitude of 3,000 meters and develops progressive dyspnea at rest. An arterial blood gas drawn at sea level shows: PaO2 90 mmHg, PaCO2 40 mmHg, pH 7.40, HCO3– 24 mEq/L. After ascending, his ABG shows: PaO2 55 mmHg, PaCO2 36 mmHg, pH 7.40, HCO3– 24 mEq/L. Which of the following changes is the most important stimulus for increased ventilation mediated by peripheral chemoreceptors in this patient?
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