Effects of End-Expiratory Lung Volume on Lung Mechanics in Normal and Edematous Lungs

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Abstract
This study determined the effects of end-expiratory pressures (EEP) and alterations in end-expiratory lung volume (EELV) on lung compliance (CL) and pulmonary resistance to gas flow (RP) in 20 cats with normal and edematous lungs. EELV was varied using EEP ranging from -8 to +10 cm H2O. Negative EEP was used to decrease EELV of the healthy lung causing CL to decrease and RP to increase. Positive EEP in the healthy lung also caused CL to decrease but did not significantly affect Rp. After inducing pulmonary edema using alloxan, functional residual capacity (FRC) decreased 38%, CL decreased 66% and RP increased 106% (p < 0.001). An EEP of 4 cm H2O returned EELV to normal FRC levels and produced maximum values for CL Increases in EEP to 4 cm H2O also caused decreases in RP in the edematous lungs but further increase did not cause significant changes in RP. These results show that (1) relatively low levels of EEP returned EELV to normal FRC levels in alloxan-induced pulmonary edema, and (2) optimal lung mechanics were obtained when EELV was equal to or slightly above normal FRC values in both healthy and edematous lungs.