Ventricular function in the newborn lamb

¹ Departments of Pathology and Pediatrics, Yale University School of Medicine, New Haven, Connecticut

The present study was initiated with the objective of evaluating in the newborn those aspects of ventricular mechanics which form the basis of the Frank-Starling relation, and which permit a determination of changes in the inotropic state of the heart. Left ventricular function was studied in lambs, 12 hr to 5 days old, utilizing a preparation designed to permit control and measurement of systemic arterial pressure (AP), cardiac output, heart rate (HR), and temperature. Continuous measurements of arterial Po₂ and pH were made. These data permitted the construction of ventricular function curves relating stroke volume, mean ejection rate, and stroke work and power to left ventricular end-diastolic pressure, at constant AP and HR. In all preparations the Frank-Starling relation was found to be operative. Norepinephrine infusion, 1–2 µg/kg per min, resulted in a substantial increment of both force and speed parameters, thereby demonstrating the ability of the newborn heart to alter its inotropic state. Severe metabolic acidosis did not inhibit the response of the myocardium to norepinephrine.

Key Words: Frank-Starling law of the heart • pressure load and ventricular performance • flow load and ventricular performance • afterload in the newborn heart • ventricular contractility • catecholamines and contractility in the newborn heart • metabolic acidosis • myocardial responsiveness to catecholamines in metabolic acidosis

Submitted on September 21, 1964

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