Static compliance is defined as?

Static compliance is defined as?

• A. correct VT / (Plateau pressure - PEEP)
• B. correct Vt / (PIP - PEEP)
• C. Tidal volume / Ti
• D. Te / Ti

Answer: (A)

Static compliance reflects the lung–thorax elastic properties when airway resistance is not contributing. It is measured with an inspiratory hold so there’s no air flow, and therefore the pressure you see is the plateau pressure. The driving pressure for elasticity is plateau pressure minus PEEP, and dividing the tidal volume by that driving pressure gives static compliance: Vt / (Pplat − PEEP). This tells you how much volume the lung opens per unit of elastic pressure. This differs from dynamic compliance, which uses peak inspiratory pressure minus PEEP (PIP − PEEP) and includes the resistance of the airways, making it lower and more variable with airflow. The timing terms Ti or Te are related to inspiratory and expiratory times, not to the pressure needed to expand the lungs, so they don’t define compliance.

Static compliance reflects the lung–thorax elastic properties when airway resistance is not contributing. It is measured with an inspiratory hold so there’s no air flow, and therefore the pressure you see is the plateau pressure. The driving pressure for elasticity is plateau pressure minus PEEP, and dividing the tidal volume by that driving pressure gives static compliance: Vt / (Pplat − PEEP). This tells you how much volume the lung opens per unit of elastic pressure.

This differs from dynamic compliance, which uses peak inspiratory pressure minus PEEP (PIP − PEEP) and includes the resistance of the airways, making it lower and more variable with airflow.

The timing terms Ti or Te are related to inspiratory and expiratory times, not to the pressure needed to expand the lungs, so they don’t define compliance.