LUNG VASCULAR-RESPONSES AND V-A Q MATCHING AFTER CHRONIC HYPOXIA IN NEONATAL PIGLETS/

We hypothesized that exposure of neonatal swine to chronic alveolar hy poxia (CH) would cause increased PVR, blunt acute hypoxic vasoconstric tion, and increase V-A/Q mismatch. After exposure to either normobaric alveolar hypoxia (FIO2=0.10) or room air for 2 weeks, animals were an esthetized and ventilated first with room air and then with hypoxic ga s (FIO2=0.12). PVR, and pressure-flow (P/Q) relations were measured be tween 15-100% of baseline cardiac output. V-A/Q matching was measured by the multiple inert gas elimination technique. During room air breat hing, the mean PVR and P/Q slope in the CH animals was significantly g reater than in the control (C) animals. P/Q intercepts were similar an d near the origin for both groups. The absolute PVR and P/Q slope were greater for CH compared to C animals during acute alveolar hypoxia. T he fractional increase in PVR and P/Q slope in the response to acute h ypoxia was similar for both groups. PaO2, intrapulmonary shunt, and SD Qp (an index of V-A/Q heterogeneity) were similar for both groups. We conclude that CH in neonatal swine causes pulmonary hypertension, but does not attenuate acute hypoxic pulmonary vasoconstriction, nor V-A/Q matching.