Normal lung compliance is approximately how many milliliters per centimeter of water?

Normal lung compliance is approximately how many milliliters per centimeter of water?

• A. 50 mL/cm H2O
• B. 100 mL/cm H2O
• C. 200 mL/cm H2O
• D. 400 mL/cm H2O

Answer: (C)

Lung compliance tells you how much air volume you gain for every unit of pressure change during inflation. It’s the slope of the pressure–volume relationship and is expressed as ΔV/ΔP. In a healthy adult, static lung compliance is about 0.2 liters per centimeter of water, which is 200 mL per cm H2O. This means a 1 cm H2O increase in transpulmonary pressure yields roughly 200 mL of additional lung volume. For a typical breath around 500 mL, the pressure required is about 2.5 cm H2O, which matches normal breathing effort. If compliance were lower, the lungs would inflate less for the same pressure (stiffer lungs). If it were higher, the lungs would expand more easily for a given pressure, which is not typical of normal lung tissue. The value around 200 mL per cm H2O reflects normal lung mechanics.

Lung compliance tells you how much air volume you gain for every unit of pressure change during inflation. It’s the slope of the pressure–volume relationship and is expressed as ΔV/ΔP. In a healthy adult, static lung compliance is about 0.2 liters per centimeter of water, which is 200 mL per cm H2O. This means a 1 cm H2O increase in transpulmonary pressure yields roughly 200 mL of additional lung volume. For a typical breath around 500 mL, the pressure required is about 2.5 cm H2O, which matches normal breathing effort.

If compliance were lower, the lungs would inflate less for the same pressure (stiffer lungs). If it were higher, the lungs would expand more easily for a given pressure, which is not typical of normal lung tissue. The value around 200 mL per cm H2O reflects normal lung mechanics.