Comprehensive assessment of the components of energy expenditure in infants using a new infant respiratory chamber

Background: Current methods for energy expenditure (EE) measurements in ter m infants do not include simultaneous measurements of basal and sleeping me tabolic rates (BMR and SMR) or a measure of physical activity (PA). Further more, prediction equations for calculating EE are not appropriate for use i n infants with metabolic disorders. Objective: To develop and utilize a new infant respiratory chamber for simu ltaneous measurements of EE (kJ/d), preprandial BMR (kJ/d), SMR (kJ/d) and an index of PA (oscillations/min/kg body weight) in infants with a variety of metabolic disorders, for up to four hours in a hospital setting, while a llowing parental interaction in a comfortable environment. Methods: We obtained simultaneous measurements of EE, BMR, SMR and PA in 21 infants (66 +/- 73 days of age, 4.5 +/- 1.7 kg body weight, 55 +/- 8 cm in length and 16 +/- 7% body fat) using our new infant respiratory chamber. S ix of these infants were healthy, seven had thyroid dysfunction, five were HIV-exposed, one had AIDS, one had intrauterine and postnatal growth retard ation and one was a hypothermic preterm infant. Energy expenditure, BMR and SMR were extrapolated for 24 hours. Body composition was estimated by skin -fold thickness, using age-appropriate formulae. Basal metabolic rate obtai ned with the infant respiratory chamber was compared to BMR that was calcul ated using the appropriate World Health Organization (WHO) equations. Results: In all infants both extrapolated 24-hour EE and BMR correlated wit h fat-free mass (r = 0.89, p < 0.01 and r = 0.88, p < 0.01 respectively). T wenty-four hour EE also correlated with PA (r = 0.52, p < 0.05). The HIV-ex posed infants had higher BMR (p < 0.05) than that calculated by the appropr iate WHO equation. We found that the caloric requirements for the infant wi th growth retardation were underestimated based on the infant's weight and age. Conclusions: The infant respiratory chamber can measure all of the main com ponents of EE. Some of the results obtained differed significantly from tho se obtained by the WHO equations; therefore, the new infant respiratory cha mber is necessary for estimating EE in infants with metabolic and growth di sorders.