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 term infants do not include simultaneous measurements of basal and sleeping metabolic rates (BMR and SMR) or a measure of physical activity (PA). Furthermore, prediction equations for calculating EE are not appropriate for use in infants with metabolic disorders. Objective: To develop and utilize a new infant respiratory chamber for simultaneous 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 allowing 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. Six of these infants were healthy, seven had thyroid dysfunction, five were HIV-exposed, one had AIDS, one had intrauterine and postnatal growth retardation 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 obtained with the infant respiratory chamber was compared to BMR that was calculated using the appropriate World Health Organization (WHO) equations. Results: In all infants both extrapolated 24-hour EE and BMR correlated with fat-free mass (r = 0.89, p < 0.01 and r = 0.88, p < 0.01 respectively). Twenty-four hour EE also correlated with PA (r = 0.52, p < 0.05). The HIV-exposed infants had higher BMR (p < 0.05) than that calculated by the appropriate WHO equation. We found that the caloric requirements for the infant with growth retardation were underestimated based on the infant's weight and age. Conclusions: The infant respiratory chamber can measure all of the main components of EE. Some of the results obtained differed significantly from those obtained by the WHO equations; therefore, the new infant respiratory chamber is necessary for estimating EE in infants with metabolic and growth disorders.