Pulmonary vasoconstriction in oleic acid induced lung injury. A morphometric study.

Distribution and severity of active vasoconstriction of muscular pulmonary arteries were morphometrically assessed in anaesthetized, paralysed and mechanically ventilated pigs with respiratory distress, induced by oleic acid. Vasoconstriction was deduced from the medial thickness which was measured and expressed as a percentage of external diameter. Six pigs received oleic acid (0.12 +/- 0.07 ml/kg), dissolved 1:1 in 96% alcohol, in multiple injections of 0.1 ml. Six pigs were used as controls. After the oleic acid injections a stable hypoxaemia (PaO2 = 57 +/- 8 mmHg, at an inspiratory oxygen fraction of 0.6) and pulmonary hypertension (mean Ppa = 36 +/- 2 mmHg) were obtained for several hours. Electron microscopy revealed swelling of endothelial cells with signs of degeneration. Medial thickness was far greater in the oleic acid group than in the control group; overall mean values were 8.1 +/- 3.2 and 3.8 +/- 1.7% respectively (P < 0.001). Arteries with prominent vasoconstriction were lying in clusters. This pattern was the same in dependent and non-dependent regions. We concluded that in oleic acid induced respiratory distress active vasoconstriction of muscular pulmonary arteries is an important factor in the development of pulmonary hypertension. Besides vasoconstriction, endothelial swelling and intravascular clotting may contribute to the development of pulmonary hypertension.