This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
Normal respiratory compliance is ? 
Select and explain. 
A. 200 ml/cm water, B. 50 ml/cm water, C. 100 ml/cm water, D. 150 ml/cm water
A: 200 ml/cm water
Answer: A: 200 ml/cm water 
Explanation: The lungs and thoracic cage are both elastic structures. Hence they display a constant relationship between distending pressure and change in volume. The change in volume per unit change in pressure is called "compliance". The total compliance of both lungs together in the normal adult human being is about 0.2 L/cm water. That is, every time the transpulmonary pressure increases by 1 centimeter of water, the lung volume will expand 0.2 L (200 ml). Compliance is a measure of distensibility. Ref: Guyton 12th Ed.