Quantitation of cardiac output components in the presence of bidirectional shunts

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Abstract
A right-to-left shunt across the foramen ovale and the potential for shunts in either or both directions through the ductus arteriosus play an important pathophysiological role in hyaline membrane disease (HMD), both in the human infant and the experimental lamb model. Using radioactive microspheres as a nonrecirculating indicator, a technique was devised to quantify right and left ventricular outputs, ductus flow in both directions, pulmonary flow and systemic flow simultaneously in newborn lambs. This technique was validated in 4 healthy full-term lambs 3-7 days old whose fetal shunts had closed. The components of cardiac output were measured by this technique in 10 premature lambs with HMD and 4 premature lambs with respiratory distress but not HMD. In all but 1 HMD lamb, left ventricular output (LVO) was greater than right ventricular output, a result expected in the presence of a right-to-left foramen ovale shunt and a left-to-right ductus shunt. Left-to-right ductus shunts were present in all but 1 HMD lambs and 6 of 10 had greater than 30% of LVO shunted through the ductus. The relationship among component flows in the 4 premature lambs without HMD was simialar to that in lambs with HMD, but the flow values tended to be less, particularly for LVO.

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