PEEP only partly restores disturbed distribution of regional pulmonary blood flow in lung injury.

The effects of lung injury, positive end-expiratory pressure (PEEP), and norepinephrine on heterogeneity of regional pulmonary blood flow (rPBF, radioactive microspheres) were investigated. We hypothesized that lung injury increases heterogeneity of rPBF and that PEEP ventilation reduces these effects. Heterogeneity of rPBF is scale dependent and was therefore assessed in detail. Local correlation (ρ), relative dispersion (RD), fractal dimension (D), perfusion gradients, and histograms of rPBF each measures a different aspect of heterogeneity. In eight anesthetized dogs, lung injury was induced with oleic acid and glass bead injection. Afterward, PEEP of 10-20 cmH2O was instituted. Norepinephrine was infused at 20 cmH2O PEEP. Heterogeneity increased upon lung injury (ρ, 0.44 ± 0.09 vs. 0.24 ± 0.09; RD, 0.36 ± 0.06 vs. 0.64 ± 0.12; both P ≤ 0.05), but fractal dimension remained constant. PEEP did not change ρ, RD, or D. Perfusion gradients were reversed after lung injury (right, -27 ± 18 vs. 196 ± 115%; left, -24 ± 18 vs. 282 ± 184%; P ≤ 0.05). PEEP (10 cmH2O) reduced gradients (116 ± 73 and 143 ± 62%, respectively; P ≤ 0.05). Norepinephrine, in part, further reduced gradients (right, 50 ± 58%; P ≤ 0.05; left, 102 ± 94%; P = NS). We conclude that oleic acid- and glass bead-induced lung injury produces abnormal distribution of rPBF. Of these changes, application of PEEP only reverses perfusion gradients.