REDUCTIONS IN CARDIAC-OUTPUT IN HYPOXIC YOUNG-PIGS - SYSTEMIC AND REGIONAL PERFUSION AND OXYGEN-METABOLISM

We tested the hypotheses that, in hypoxic young pigs, reductions in ca rdiac output restrict systemic oxygen transport to a greater extent th an does hypoxia alone and that compensatory responses to this restrict ion are more effective in higher than in lower priority vasculatures. To study this, 10- to 14-day-old instrumented awake hypoxic (arterial oxygen tension = 39 Torr) pigs were exposed to reduced venous return b y inflation of a right atrial balloon-tipped catheter. Blood flow was measured with radionuclide-labeled microspheres, and oxygen metabolism was determined with arterial and venous oxygen contents from appropri ate vessels. Hypoxia resulted in a reduction in oxygen tension; increa ses in cardiac output and perfusion to brain (72% over baseline), hear t, adrenal glands, and liver without reductions to other organs except for the spleen; reductions in systemic and intestinal oxygen delivery ; and increases in systemic and intestinal oxygen extraction without c hanges in systemic, cerebral, or intestinal oxygen uptake. During hypo xia, decreasing venous return was associated with increases in arteria l lactic acid concentration and central venous pressure; attenuation o f the hypoxia-related increase in cardiac output; sustained increases in brain (72% over baseline) and heart perfusion; reductions in lung ( bronchial artery), pancreatic, renal, splenic, and intestinal (-50% be low baseline) perfusion; decreases in systemic and gastrointestinal ox ygen delivery; sustained increases in systemic and intestinal oxygen e xtraction; and decreases in intestinal oxygen uptake, without changes in cerebral oxygen metabolism. We conclude that when venous return to the heart is reduced in hypoxic young pigs, the hypoxia-related increa se in cardiac output was attenuated and the relative reduction in card iac output was associated with preserved cerebral oxygen uptake and co mpromised intestinal oxygen uptake. Regional responses to hypoxia comb ined with relative reductions in cardiac output differ from that of hy poxia alone, with the greatest effects on lower priority organs such a s the gastrointestinal tract.