Lung compliance is defined as the change in volume per change in transpulmonary pressure. Which ratio expresses this definition?

Lung compliance is defined as the change in volume per change in transpulmonary pressure. Which ratio expresses this definition?

• A. ΔV/ΔPL
• B. ΔPL/ΔV
• C. ΔP/ΔV
• D. ΔV/ΔP

Answer: (A)

Lung compliance describes how much the lung volume changes for a given change in pressure across the lung. That pressure is the transpulmonary pressure (the difference between alveolar pressure and pleural pressure). So the ratio that matches this definition is the change in volume divided by the change in transpulmonary pressure, ΔV/ΔPL. If the transpulmonary pressure increases by a certain amount and the volume increases by a given amount, that quotient tells you how “stretchy” the lung is. Higher compliance means a larger volume gain per unit of pressure, while lower compliance means the lung is stiffer and requires more pressure to achieve the same volume change. The inverse ratio, ΔPL/ΔV, would describe elastance (stiffness) rather than compliance.

Lung compliance describes how much the lung volume changes for a given change in pressure across the lung. That pressure is the transpulmonary pressure (the difference between alveolar pressure and pleural pressure). So the ratio that matches this definition is the change in volume divided by the change in transpulmonary pressure, ΔV/ΔPL.

If the transpulmonary pressure increases by a certain amount and the volume increases by a given amount, that quotient tells you how “stretchy” the lung is. Higher compliance means a larger volume gain per unit of pressure, while lower compliance means the lung is stiffer and requires more pressure to achieve the same volume change. The inverse ratio, ΔPL/ΔV, would describe elastance (stiffness) rather than compliance.