RECENT advances in cardiac surgery in infancy have made mandatory an increased knowledge of cardiac physiology in the newborn period. Smith1 in his book, "Physiology of the Newborn Infant," describes the known changes of circulation in newborn infants but states that additional knowledge would be gained if accurate circulation times were determined for the neonatal period. It would seem reasonable that definitive knowledge in this field may contribute to the understanding of neonatal physiology and to the diagnosis of some forms of congenital heart disease.
Circulation-time studies in newborn infants have utilized various methods and various segments of the cardiovascular system. The inherent technical difficulties are such that considerable discrepancy exists in the small amount of published data.
Feldman2 calculated that the circulation time equaled 27 times the heart rate. Assuming the average heart rate of a newborn infant to be about 134 beats per minute, he arrived