Central shunt flows and pressures in the mature fetal lamb

Abstract

Two to eight days after surgery, we determined biventricular cardiac output with the microsphere-dilution method and individual ventricular output with an electromagnetic flow sensor in 12 fetal lambs. Mean biventricular output was 462 ml.min-1.kg-1. Right ventricular output was 60%, pulmonary blood flow was 6%, blood flow in the ductus arteriosus was 54%, flow through the foramen ovale was 34%, and flow in the descending thoracic aorta above the ductus arteriosus was 12% of the biventricular cardiac output. Foramen ovale flow did not correlate with the pressure difference between the atria. The flow though the foramen ovale correlated positively with the flow in the inferior caval vein. It was concluded the shunt flow through the foramen ovale is mainly determined by the kinetic energy of the blood in the "lower atrial inflow tract." Fetal systemic somatic blood flow showed a reliable negative correlation with the oxygen tension in the fetal arterial blood. This was taken as presumptive evidence for long-term autoregulation of flow in the peripheral tissues.

Cardiac Output and Central Distribution of Blood Flow in the Human Fetus

“…24,26 In the present study, median left cardiac output per 1 kg fetal weight was estimated to be 179 mL · min Ϫ1 · kg…”

“…1 About 60% to 65% of cardiac output is ejected by the right ventricle and 35% to 40% by the left ventricle, corresponding to a ratio of right to left cardiac output of 1.5 to 1.85. 1,23,24 In fetal lambs, pulmonary blood flow is 6% to 8% of combined cardiac output and Ϸ10% of right cardiac output; ductus arteriosus blood flow is 54% to 57% of combined cardiac output and Ϸ90% of right cardiac output. 1,[23][24][25] Lamb experiments 26 (nϭ44) have suggested an increase in pulmonary blood flow from 3.7% of combined cardiac output in 80-g to 450-g fetuses (nϭ7) to 7% of combined cardiac output in near-term fetuses (nϭ10).…”

“…1,23,24 In fetal lambs, pulmonary blood flow is 6% to 8% of combined cardiac output and Ϸ10% of right cardiac output; ductus arteriosus blood flow is 54% to 57% of combined cardiac output and Ϸ90% of right cardiac output. 1,[23][24][25] Lamb experiments 26 (nϭ44) have suggested an increase in pulmonary blood flow from 3.7% of combined cardiac output in 80-g to 450-g fetuses (nϭ7) to 7% of combined cardiac output in near-term fetuses (nϭ10). In fetal lambs in the third trimester of pregnancy, pulmonary blood flow did not change relative to lung weight and right ventricular output at the normal low oxygen tension of the fetus despite an increase in pulmonary vessel density.…”

“…In fetal lamb studies, foramen ovale flow was 34% of combined cardiac output. 24 Although animal experiments have demonstrated that the echocardiographic Doppler method can accurately quantify volumetric flow through the aortic and pulmonary valve, 8 methodological problems have to be considered. Errors in volumetric measurements arise from inaccuracies in vessel diameter and Doppler recordings.…”

In Utero Ventilation Augments the Left Ventricular Response to Isoproterenol and Volume Loading in Fetal Sheep

“…(Pediatr Res 29: 466-472, 1991) The fetal left ventricle functions in an environment of low oxygen demand and in parallel with a dominant right ventricle. Consequently, its output need not be as high as that of the newborn left ventricle (1)(2)(3)(4). At birth, when oxygen demand increases dramatically and the systemic and pulmonary circulations separate, left ventricular output increases threefold (5)(6)(7)(8)(9)(10)(11)(12).…”