The fetal and newborn lamb has been the subject of a great deal of experimental investigation, and the results obtained from these studies have been used to make analogies with human newborns where direct observations have been few.1,2 Many of the observations on lambs have been made under experimental conditions which undoubtedly have changed the normal resting physiological state, and the usual sequence of perinatal events may have, therefore, been interrupted or distorted.
Indicator-dilution techniques of studying the cardiovascular system can be performed in the intact, unanesthetized animal or man with minimal disturbance of the hemodynamics. These techniques were chosen for the study of the neonatal hemodynamic adjustments of normal unanesthetized lambs lying quietly either sleeping or sucking on a sugar nipple. These same techniques may be directly applicable to the study of human newborn infants with less risk than cineangiography.
Methods and Materials
Nine normal lambs were studied