Static Compliance , Dynamic Compliance & Plateau Pressure

🔵 Compliance is a measurement of the distensibility of the lung

🔵 Compliance of both the chest wall and the lung tissue is known as Total Lung Compliance

🔵 Total Lung Compliance = Change in volume / Change in pressure 

🔵 Static Compliance is the truest measure of the compliance of the lung tissue

🔵 It is measured when there are no gases flowing into or out of the lungs

🔵 Static Compliance = Exhaled Tidal Volume /  (Plateau Pressure-PEEP)

🔵 The Plateau Pressure is obtained by instituiting a 2 second inspiratory pause at the peak of inspiration. This pause creates the condition of no gases flowing into the lungs.

🔵 This reflects the pressure due to the elastic recoil forces of the lung tissue alone . No pressure resulting from the flow of gases is measured. 

🔵 Normal value for Static Compliance is 70-100 mL/cm H2O. This means that for every 1 cm H2O pressure change in the lungs , there is a change in volume of 70-100 mL of gas

🔵 As Dynamic Compliance is a measurement taken while gases are moving in the lungs , it measures both the Compliance of the lung tissue and the resistance to air flow

🔵 It is easier to obtain as it doesn't require the inspiratory hold maneuver

🔵 Dynamic Compliance = Exhaled Tidal Volume / (Peak Inspiratory Pressure-PEEP)

🔵 The normal value for Dynamic Compliance is 50-80 mL/cm H2O

🔵 Dynamic Compliance measures are always always smaller than Static Compliance because Peak Airway Pressure is always greater than Plateau Pressure 

🔵 A decrease in Dynamic Compliance may indicate a decrease in lung compliance or an increase in airway resistance.