Heterogeneity of left ventricular perfusion during pulmonary edema and microembolism treated with positive end-expiratory pressure and norepinephrine

RESUMO

Regional left ventricular myocardial blood flow was studied in an experimental model of pulmonary edema and microembolization (PEM) ventilated with positive end-expiratory pressure (PEEP). The analysis was based on a 3-dimensional extension of the autocorrelation function used to assess the spatial correlation (rspat) of myocardial perfusion. Experiments were performed on 8 premedicated, anesthetized and mechanically ventilated dogs. PEM was induced with oleic acid (0.01 mg/kg) and glass beads. Successive PEEP values of 10, 15 and 20 cm H2O (P20) were applied and norepinephrine (NE, 0.2-1.0 microgram min-1 kg-1) was administered after P20. Regional perfusion was measured with radioactive microspheres. The left ventricle (LV) was dissected into 256 samples. rspat was computed as the correlation of regional perfusions of samples p units apart in the apex-to-base, endo-epicardial and angular directions. Analysis was performed after anesthesia and instrumentation (control, C), P20 and NE. Control values of rspat were around 50 per cent in the apex-to-base and angular directions and the sign was inverted in the endo-epicardial direction. A reduction of rspat to values close to zero was observed in all directions for P20 and NE. This is the typical pattern of independent distribution. Thus, the results indicate that, under the experimental conditions used, there is some degree of neighborhood dependence of regional LV myocardial blood flow. This dependence is not observed under PEM, mechanical ventilation with PEEP and NE