preterm and full-term newborn lambs

We studied left ventricular performance and contractility after volume loading in lambs at 122 days (group I, n = 9) and 139 days gestational age (group IL, n = 9) and in 8-day-old full-term lambs (group III, n = 7). All were mechanically ventilated; each preterm lamb was treated with surfactant to stabilize pulmonary function and the ductus arteriosus was occluded with an inflated catheter balloon. Cineangiograms, left ventricular and vascular pressures, and the isovolumetric index of contractility, first derivative of left ventricular pressure (dP/dt), were recorded before and after three successive whole blood volume infusions of 10 ml/kg (total 30 ml/kg). The left ventricular enddiastolic volume per kilogram and stroke volume per kilogram increased significantly in all groups after volume infusion; these measurements and heart rate and systemic vascular resistance did not differ significantly between the groups either before or after the infusions. The left ventricular peak dP/dt did not change significantly within the groups during the volume infusions. The left ventricular stroke work was greatest in full-term animals and increased significantly in all groups after volume infusion. Thus, the left ventricles of the preterm and full-term lambs had quantitatively similar Frank-Starling responses and there was no increase in contractility during the infusions of whole blood. However, the left ventricle of the full-term lamb is capable of generating greater stroke work than that of the preterm lamb. These findings may contribute to the understanding of developmental aspects of postnatal circulatory adaptation. Circulation 73, No. 5, 1042-1049, 1986. IT HAS BEEN suggested that the left ventricle of the premature infant may be less capable than the mature left ventricle of adjusting to transitional circulatory changes required postnatally, such as increasing volume and resistance work.' 2 These conclusions followed from ultrastructural observations and from developmental studies of myocardial contraction in isolated muscle preparations, and from comparative studies of left ventricular performance in the intact fetus and full-term newborn lamb.'-' Until recently developmental studies of postnatal left ventricular performance were not possible in newly born preterm animals, because prematurity was associated with a From the University of California, Los Angeles, School of Medicine, and Harbor-UCLA Medical Center, Department of Pediatrics, Torrance, CA. Supported by grants 590 GLO3 and 676 IG from the American Heart Association, Greater Los Angeles Affiliate, NIH grant HD 12714, and a grant from the Upjohn Corporation, Kalamazoo, MI. Address for correspondence: Barry G. Baylen, M.D., Division of Pediatric Cardiology, Harbor-UCLA Medical Center, 1000 West Carson St., Torrance, CA 90509. Received July 9, 1985; revision accepted Feb. 13, 1986. 1042 rapid deterioration of pulmonary function and metabolic status.9 10 Now, however, acceptable pulmonary function can be maintained with the combined use of surfactant treatment and mechanical ventilation. 10 The purpose of this study was to characterize developmental aspects of left ventricle pump performance and contractility in surfactant-treated preterm lambs and in full-term lambs under conditions simulating those encountered in the neonatal intensive care setting. Material and methods We studied the hemodynamic responses to volume infusions in three groups ofpreterm and full-term lambs. Group I lambs (n 9) were 122 ± 2 (SD) days gestational age, group II lambs (n = 9) were 139 + 2 days gestational age, and group III (n = 7) consisted of 8 + 3 day old spontaneously delivered full-term lambs. The preterm lambs were delivered by cesarean section of date-bred Western mixed-breed ewes. The ewes (groups I and II) were premedicated with intramuscular injections of ketamine (800 mg) and atropine sulfate (3 mg), and surgery was performed under spinal anesthesia. The head and neck of each lamb were exposed through an anterior midline abdominal incision, and an appropriately sized endotracheal tube was secured in the