Alterations in regional myocardial blood flows during different levels of positive end-expiratory pressure

A decrease in myocardial blood flow (MBF) has been suggested recently as a contributing factor to the depression of cardiac function during application of PEEP. To test this hypothesis, 7 dogs were anesthetized and their chest wall and pericardium were removed. Hemodynamics, myocardial oxygenation status, and left and right ventricular MBF were measured during controlled ventilation without PEEP (IPPV), with 8 cm H2O of PEEP (CPPV8), 15 cm H2O of PEEP (CPPV15), and 25 cm H2O of PEEP (CPPV25). Compared to IPPV, CPPV8 significantly decreased left ventricular endocardial, epicardial, and septal blood flows. Right ventricular MBF and other measured variables were not affected. Compared to control, CPPV15 decreased left ventricular and septal MBFs in all regions, and right ventricular MBF in the endocardial region. CPPV15 also decreased cardiac index (CI) from 3.94 ± 0.57 L/min ± m during control to 2.78 ± 0.34 L/min ± m (p < .05). Compared to IPPV, CPPV25 further decreased MBF in all layers of both ventricles and septum. Compared to CPPV8, there were decreases in left ventricular midwall and septal (left ventricular side and midwall) blood flows during CPPV25. During application of CPPV25, compared to IPPV, mean arterial pressure (MAP) was reduced from 99 ± 5 to 85 ± 5 mm Hg, left ventricular stroke work index (LVSWI) decreased from 31.8 ± 5.4 to 13.8 ± 2.6 g±m/m, and CI decreased to 2.13 ± 0.38 L/min±m (p < .05). Dp/dtmax and dp/dt40 were both significantly decreased and pulmonary (PVRI) and systemic (SVRI) vascular resistance indices were increased significantly during CPPV25. The authors conclude that high levels of PEEP reduce cardiac output independent of venous return. The observed decrease in left ventricular MBF may cause depression of cardiac function seen with high levels of PEEP. We speculate that a decrease in regional MBF could be mediated reflexively by stimulation of lung receptors.