ATRIAL MYOCARDIAL BLOOD-FLOW DURING ACUTE RIGHT-VENTRICULAR PRESSURE LOAD AND ADENOSINE INFUSION IN LATE-GESTATION FETAL SHEEP

The purpose of this study was to investigate atrial myocardial blood f low in the fetus under conditions of acute right ventricular pressure load and adenosine infusion. Late gestation fetal sheep were instrumen ted for acute right ventricular pressure loading or adenosine infusion , and regional myocardial blood flow was measured at rest and under ex perimental conditions with radiolabeled microspheres and standard refe rence sample technique, Resting myocardial blood flow to the atria was less than half of ventricular flow per gram tissue. During the maximu m tolerated pulmonary artery pressure load, right atrial peak systolic pressure rose significantly, and atrial blood flow increased 3-fold. The percentage of total myocardial blood flow received by the right at rium during maximal pressure loading increased from 4.3 +/- 1.4% to 5. 9 +/- 1.6%, p < 0.05. Adenosine infusion was associated with a 4-fold increase in atrial myocardial blood flow and a 3-fold increase in vent ricular and septal blood flow. The percentage of total myocardial bloo d flow to both atria also increased with adenosine infusion (right atr ium, 3.8 +/- 0.4% to 5.4 +/- 1.3%, and left atrium, 4.2 +/- 0.8% to 6. 9 +/- 2.0%, p < 0.05). We conclude the following: I)at rest, fetal atr ial myocardial blood flow is less than one half of ventricular myocard ial blood flow per gram tissue; 2)fetal atrial blood flow increases mo re than ventricular blood flow with acute right ventricular pressure l oad or adenosine infusion; and 3) these data suggest that fetal atrial blood flow is regulated independently from ventricular blood flow and may be influenced by atrial work.