This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
[{'content': 'Earliest change in high altitude is \nSelect and explain. \nA. Hyperventilation, B. Decrease in work capacity, C. Drowsiness, D. Polycythemia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Immediate exposure to low PO2 stimulates the aerial chemoreceptors, and this stimulation increases alveolar ventilation to a maximum of about 1.65 times normal. Therefore, compensation occurs within seconds for the high altitude, and it alone allows the person to rise several thousand feet higher than would be possible without the increased ventilationGuyton 13 e pg: 563', 'role': 'assistant'}]