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: Gynaecology & Obstetrics
[{'content': 'Changes in the respiratory system in pregnancy: \nSelect and explain. \nA. Vital capacity is increased, B. Subcostal angle remains unchanged, C. Tidal volume remains unaltered, D. Residual volume is decreased', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Changes in respiratory system during pregnancy:\n\nWith the enlargement of the uterus, specially in the later months, there is elevation of the diaphragm by 4 cm.\nTotal lung capacity is reduced by 5% due to this elevation.\nBreathing becomes diaphragmatic. Total pulmonary resistance is reduced due to progesterone effect.\nThe subcostal angle increases from 68° to 103°, the transverse diameter of the chest expands by 2 cm and the chest circumference increases by 5–7 cm.\n\xa0A state of hyperventilation occurs during pregnancy leading to increase in tidal volume and therefore respiratory minute volume by 40%.', 'role': 'assistant'}]