Static Compliance,Static Effective Compliance,and Dynamic Effective Compliance as Indicators of Elastic Recoil in the Presence of Lung Disease

Abstract

The measurement of compliance is important in the management of ventilator patients. Three methods commonly used to measure compliance were studied and were found to be neither equivalent nor interchangeable in the presence of simulated disease. The three methods are: 1) dynamic effective compliance (DEC) = V_T/peak inflation pressure; 2) static effective compliance (SEC) = V_T/end-inspiratory pressure; 3) static compliance (SC) = V_T/true plateau pressure. DEC and SEC are not truly compliance values, as flow within and/or between the lungs (pendelluft) may still be present. Additional time must be permitted for static conditions to be reached and true plateau pressure recorded for SC to be measured. By comparison of the three methods, it was noted that as the severity of disease increased, the variation between DEC or SEC and SC increased. Therefore, static compliance is the test of choice in determining elastic recoil in the presence of lung disease.