What is the formula for static respiratory system compliance Crs?

What is the formula for static respiratory system compliance Crs?

• A. ΔV / ΔP
• B. VT /(Pplat - PEEP)
• C. ΔV / (Pplat - PEEP)
• D. ΔP / ΔV

Answer: (C)

Static compliance measures how much volume the respiratory system gains for a given distending pressure when there is no airflow. To obtain it, an inspiratory pause is used so that plateau pressure reflects alveolar pressure without airway resistance. The pressure that actually distends the system is the plateau pressure minus the positive end-expiratory pressure (Pplat − PEEP). The amount of air moved in that breath is the change in volume, typically the tidal volume. Therefore, the static compliance is the volume change divided by the distending pressure: Crs = ΔV / (Pplat − PEEP). In clinical terms, this is often written as Crs = VT / (Pplat − PEEP). Since ΔV and VT refer to the same breath, they yield the same value. This differs from dynamic compliance, which uses the peak inspiratory pressure and includes resistive pressure, not just the static distending pressure.

Static compliance measures how much volume the respiratory system gains for a given distending pressure when there is no airflow. To obtain it, an inspiratory pause is used so that plateau pressure reflects alveolar pressure without airway resistance. The pressure that actually distends the system is the plateau pressure minus the positive end-expiratory pressure (Pplat − PEEP). The amount of air moved in that breath is the change in volume, typically the tidal volume. Therefore, the static compliance is the volume change divided by the distending pressure: Crs = ΔV / (Pplat − PEEP). In clinical terms, this is often written as Crs = VT / (Pplat − PEEP). Since ΔV and VT refer to the same breath, they yield the same value. This differs from dynamic compliance, which uses the peak inspiratory pressure and includes resistive pressure, not just the static distending pressure.