PULMONARY VASOCONSTRICTION IN OLEIC-ACID INDUCED LUNG INJURY - A MORPHOMETRIC STUDY

Distribution and severity of active vasoconstriction of muscular pulmo nary arteries were morphometrically assessed in anaesthetized, paralys ed 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 9 6% alcohol, in multiple injections of 0.1 ml. Six pigs were used as co ntrols. After the oleic acid injections a stable hypoxaemia (PaO2 = 57 +/-8 mmHg, at an inspiratory oxygen fraction of 0.6) and pulmonary hyp ertension (mean Ppa=36+/-2 mmHg) were obtained for several hours. Elec tron microscopy revealed swelling of endothelial cells with signs of d egeneration. 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 vasoconstrictio n were lying in clusters. This pattern was the same in dependent and n on-dependent regions. We concluded that in oleic acid induced respirat ory distress active vasoconstriction of muscular pulmonary arteries is an important factor in the development of pulmonary hypertension. Bes ides vasoconstriction, endothelial swelling and intravascular clotting may contribute to the development of pulmonary hypertension.