RIGHT-VENTRICULAR FUNCTION IN CHRONICALLY ANEMIC FETAL LAMBS

OBJECTIVE: Our purpose was to determine whether the increase in extrav ascular fluid in chronic fetal anemia occurs either because of heart f ailure or despite successful cardiac adaptation. STUDY DESIGN: Right v entricular function curves were obtained in Rye ovine fetuses at the s tart, midpoint, and end of 5 to 8 days of anemia induced by isovolemic daily hemorrhage. Least-squares fit of the ascending and plateau line s of stroke volume versus right atrial pressure were used to establish breakpoints (intersection of the ascending and plateau lines), which were compared by analysis of variance for repeated measures. Myocardia l blood flow was measured by microspheres. RESULTS: Carotid arterial o xygen content was reduced from 7.0 +/- 0.3 to 2.1 +/- 0.1 ml/dl and th e hematocrit from 29% +/- 1.8% to 13% +/- 0.6%. Breakpoint analysis of function curves showed that although right atrial pressure remained u nchanged (3.4 +/- 0.7 and 3.6 +/- 0.6 mm Hg) stroke volume increased f rom 1.03 +/- 0.14 to 1.62 +/- 0.25 ml/kg. Both right and left ventricu lar coronary blood flow were increased, 1351 +/- 313 and 1166 +/- 264 ml/min per 100 gm. Excess fluid was present in the abdomen and chest o f most animals at autopsy. CONCLUSION: Tissue edema during severe anem ia occurs despite normal right atrial pressure, increased stroke volum e, and markedly increased coronary blood flow, markers of successful c ardiac adaptation.