The regional distribution and determinants of myocardial blood flow during asphyxia in the fetal lamb.

The syndrome of hypoxemia-related myocardial dysfunction in the newborn is generally associated with severe intrapartum asphyxia. We investigated the changes in total and regional distribution of myocardial blood flow (MBF) that occur during asphyxia and the factors that regulate MBF, in the chronically prepared, near term, fetal lamb. Studies were done in the awake, physiologically stable state 36-72 h after surgical preparation. In utero asphyxia was produced by partial cord occlusion and blood flow to fetal organs was measured by the radioactive microsphere technique. A complete set of control measurements was made, and then an occlusion loop was inflated to partially occlude the umbilical vessels. After 30-60 min of partial occlusion, all measurements were repeated. The third set of measurements was made after release of the occlusion loop. Six animals were studied and 17 sets of measurements obtained. Partial umbilical cord constriction produced a progressive asphyxia and acidosis. Cardiac output was severely depressed, although the increase in percentage of cardiac output directed to the myocardium (%F) was very significant. Release resulted in improved cardiac output and O2 and CO2 exchange, although the metabolic acidosis was worse. No change occurred in the intramyocardial distribution of MBF during asphyxia or recovery. Total MBF was not significantly increased during asphyxia. Multiple linear regression analysis indicated that arterial oxygen saturation (SaO2) and heart rate were statistically significant predictor variables for absolute MBF, accounting for about 45% of the variation in MBF.(ABSTRACT TRUNCATED AT 250 WORDS)