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# LUNG COMPLIANCE Lung compliance is the degree of lung expansion per unit pressure change. It's calculated as \(C = \Delta V / \Delta P\), where C = compliance, \(\Delta V\) = volume change, and \(\Delta P\) = pressure change. **Compliance Measurement** Abnormally low or high lung compliance ca...

# LUNG COMPLIANCE Lung compliance is the degree of lung expansion per unit pressure change. It's calculated as \(C = \Delta V / \Delta P\), where C = compliance, \(\Delta V\) = volume change, and \(\Delta P\) = pressure change. **Compliance Measurement** Abnormally low or high lung compliance can impair gas exchange and often contributes to the need for mechanical ventilation. * **Low Compliance:** Low compliance (high elastance) means small volume change per unit pressure change. Lungs are stiff, making breathing work harder. This can be associated with conditions like acute respiratory distress syndrome (ARDS). * **High Compliance:** High compliance indicates large volume change per unit pressure change. This can lead to incomplete exhalation with air trapping, making CO2 elimination difficult. **Methods to Measure Lung Compliance** Table 1-2 outlines methods for measuring both static and dynamic compliance: **Table 1-2: Method to Measure Static and Dynamic Compliance** | Step | Procedure | |---|---| | 1 | Obtain corrected expired tidal volume | | 2 | Apply inspiratory hold or occlude exhalation port to obtain plateau pressure at end-inspiration | | 3 | Obtain peak inspiratory pressure | | 4 | Obtain positive end-expiratory pressure (PEEP), if applicable | **Calculations** * **Static Compliance:** \( = \frac{\text{Corrected Tidal Volume}}{(\text{Plateau Pressure - PEEP})}\) * **Dynamic Compliance:** \( = \frac{\text{Corrected Tidal Volume}}{(\text{Peak Inspiratory Pressure - PEEP})}\)