Energy Intake, Norepinephrine Excretion, and Oxygen Consumption in Low Birthweight Infants

Abstract

Summary:Eleven healthy, appropriately grown low birthweight infants, ages 3–15 days and 28–33 weeks gestation, were the subjects of this study. Energy intake, urinary norepinephrine excretion, and metabolic rate as reflected in VO2 were examined concurrently. Energy intakes were recorded. Simultaneous collection of a timed urine for norepinephrine excretion and measurement of VO2 using indirect calorimetry were performed. A servo control device was used to maintain an abdominal skin temperature of 36.5°C. The results demonstrated increases in energy intake, urinary norepinephrine, and VO2 with advancing postnatal age. Simple linear regression analysis revealed significant positive correlations between energy intake and VO2 (p < 0.003), norepinephrine excretion and VO2 (p < 0.003), postnatal age and VO2 (p < 0.01), and postnatal age and energy intake (p < 0.001). Multiple regression analysis revealed a strong positive correlation between urinary norepinephrine excretion and VO2, and energy intake and VO2. When postnatal age was added to the multiple linear regression analysis as a variable, energy intake was no longer strongly correlated with VO2. This implies postnatal age and energy intake are closely linked in this study, and further studies are needed to better define these relationships.