Longitudinal measurements of oxygen consumption in growing infants during the first weeks after birth: old data revisited.
BACKGROUND
In a study conducted in 1966-1969, longitudinal measurements were made of the metabolic rate in growing infants. Statistical methods for analyzing longitudinal data weren't readily accessible at that time.


OBJECTIVE
To measure minimal rates of oxygen consumption (V·O2, ml/min) in growing infants during the first postnatal weeks and to determine the relationships between postnatal increases in V·O2, body size and postnatal age.


METHODS
We studied 61 infants of any birth weight or gestational age, including 19 of very low birth weight. The infants, nursed in incubators, were clinically well and without need of oxygen supplementation or respiratory assistance. Serial measures of V·O2 using a closed-circuit method were obtained at approximately weekly intervals. V·O2 was measured under thermoneutral conditions with the infant asleep or resting quietly. Data were analyzed using mixed-effects models.


RESULTS
During early postnatal growth, V·O2 rises as surface area (m(2))(1.94) (standard error, SE 0.054) or body weight (kg)(1.24) (SE 0.033). Multivariate analyses show statistically significant effects of both size and age. Reference intervals (RIs) for V·O2 for fixed values of body weight and postnatal age are presented. As V·O2 rises with increasing size and age, there is an increase in the skin-operative environmental temperature gradient (T skin-op) required for heat loss. Required T skin-op can be predicted from surface area and heat loss (heat production minus heat storage).


CONCLUSIONS
Generation of RIs for minimal rates of V·O2 in growing infants from the 1960s was enabled by application of mixed-effects statistical models for analyses of longitudinal data. Results apply to the precaffeine era of neonatal care.
Department of Pediatrics, McMaster University, Hamilton, Ont., Canada. sinclair@mcmaster.ca
J C
JC
Sinclair
K
K
Thorlund
S D
SD
Walter
D000367:Age Factors; D001724:Birth Weight; D049628:Body Size; D001830:Body Surface Area; D001833:Body Temperature Regulation; D002657:Child Development; D004734:Energy Metabolism; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D019102:Infant, Very Low Birth Weight; D008137:Longitudinal Studies; D015999:Multivariate Analysis; D010101:Oxygen Consumption; D012881:Skin Temperature