What does static lung compliance measure?

What does static lung compliance measure?

• A. The rate of gas exchange between alveoli and blood.
• B. The change in volume for any given applied pressure.
• C. The maximum inspiratory pressure generated during a breath.
• D. The time constant of lung filling.

Answer: (B)

Static lung compliance measures how much the lung volume changes for a given amount of applied pressure when there is no air flow. It is determined from the pressure–volume relationship during an inspiratory pause, so airway resistance doesn’t affect the reading. In formula terms, it’s ΔV/ΔP at zero flow, and the units are usually milliliters per centimeter of water (mL/cm H2O). Normal values in adults are on the order of about 50–100 mL/cm H2O, though ranges can vary. A higher compliance means the lungs and chest wall inflate more easily with less pressure. A lower compliance means the lungs are stiffer and require more pressure to achieve the same volume. For example, fibrosis lowers compliance, making inflation harder, whereas emphysema can increase compliance. This concept is distinct from dynamic compliance, which includes airway resistance and is measured during active airflow.

Static lung compliance measures how much the lung volume changes for a given amount of applied pressure when there is no air flow. It is determined from the pressure–volume relationship during an inspiratory pause, so airway resistance doesn’t affect the reading. In formula terms, it’s ΔV/ΔP at zero flow, and the units are usually milliliters per centimeter of water (mL/cm H2O). Normal values in adults are on the order of about 50–100 mL/cm H2O, though ranges can vary.

A higher compliance means the lungs and chest wall inflate more easily with less pressure. A lower compliance means the lungs are stiffer and require more pressure to achieve the same volume. For example, fibrosis lowers compliance, making inflation harder, whereas emphysema can increase compliance. This concept is distinct from dynamic compliance, which includes airway resistance and is measured during active airflow.