This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Which of the following statement is true about physiological dead space? \nSelect and explain. \nA. It is sometimes measured using the aerial PO2, B. It is generally smaller than the anatomic dead space, C. It is often increased in lung disease, D. It is determined primarily by the geometry of the branching airways', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The PCO2 is used for measuring physiological dead space and not the PO2. Second choice is incorrect because the physiological dead space contains the anatomic dead space, and may be substantially larger if there is inequality of ventilation and blood flow within the lung. This is the reason why the physiological dead space is frequently increased in lung disease. Ref: Levitzky M.G. (2007). Chapter 5. Ventilation-Perfusion Relationships. In M.G. Levitzky (Ed), Pulmonary Physiology, 7e.', 'role': 'assistant'}]