Hypoxia and Cold Stress on Pulmonary Venous Obstruction

Hemodynamic changes induced by hypoxia and cold stress were examined on the model of pulmonary venous obstruction (PVO) to investigate the mechanism of pulmonary hypertensive crisis. Bilateral pulmonary venous stenosis was surgically created in 7 newborn piglets of the PVO group. Sham operations were performed on 6 piglets of the control group. Following the baseline hemodynamic measurement (FiO₂= 0.3) at 8 weeks after the operation, the piglets were exposed to hypoxia (FiO₂= 0.14) for 10 minutes, and were also exposed to cold stress for 20 minutes. Hypoxia significantly increased mean pulmonary arterial pressure in the PVO group. Hypoxia increased not only pulmonary arterial resistance, but also pulmonary venous resistance in the PVO group. Cold stress did not change pulmonary arterial resistance or pulmonary venous resistance in each group. In the lungs of the PVO group, the medial muscular layer of the pulmonary arteries and pulmonary veins were thickened. This probably accelerates hypoxia-induced vasoconstriction, which in turn increases pulmonary arterial and venous resistances.