82 REGIONAL BLOOD FLOW DISTRIBUTION AND OXYGEN DELIVERY IN CHRONICALLY HYPOXEMIC NEWBORN LAMBS

Abstract

Redistribution of blood flow is an important response to acute hypoxemia(AH); myocardial and cerebral flows increase but GI, renal, musculoskeletal and skin flows decrease. It is not known if these changes persist during chronic hypoxemia(CH). We produced CH in 7 newborn lambs by placing a balloon occluder around the pulmonary artery and performing a balloon atrial septostomy. The occluder was inflated to produce atrial R-L shunting and aortic O2 sat. was maintained at 60-70% of control for 2 weeks. Cardiac output(CO) was measured by electromagnetic flowmeter and flow distribution with radionuclide-labelled microspheres. Compared to 9 control lambs, CH did not alter CO. As with AH, myocardial blood flow increased. Unlike AH, cerebral flow was unchanged from control. Renal, GI tract, musculoskeletal and skin flows decreased, with the percent decreases in flow to the gut and carcass greater during CH than during AH. Hemoglobin increased so that systemic O2 delivery was normal. However, O2 delivery to all individual organs was decreased, except to the heart, which showed an increase. Total systemic vascular resistance was unchanged while resistances across each vascular bed changed inversely related to the changes in flow. Thus regional blood flows are similar during CH and AH, except for cerebral flow which failed to maintain the increase seen acutely. Although total CO and O2 delivery may remain normal, decreases in regional O2 delivery may be responsible for. alterations of metabolism and growth in the newborn with cyanotic heart disease.