Thermal Balance of the Newborn Infant in a Heat-gaining Environment

Abstract

ExtractThe thermal balance of 22 full term, 9 small for date, and 8 large premature infants was studied by gradient layer direct calorimetry on the 1st day of life. In addition, the influence of muscular activity on the ability to sweat of 8 full term infants was investigated. The same measurements were repeated in 20 infants on the 3rd day of life.All i nfants were subjected to the same experimental conditions: ambient temperature 37°, restive humidity 50%, and air flow 30 liters/min.It was demonstrated that the evaporation of water was the primary way to dissipate heat in a heat-gaining environment. Active thermoregulatory sweating was elicited at deep body temperatures of 37.45°, 37.8°, and 37.76° in the full term, small for date, and premature infants, respectively.The set-point temperature of sweating tended to be lower with increasing gestational and postnatal age, and with vigorous muscular activity. The physiologic weight loss of about 3%, and the intrauterine growth retardation resulted in significant increase in this threshold temperature.The maximal sweat rate of the premature infants (1.43 W/kg) was significantly lower than that of the full term (1.81 W/kg) and small for date infants (2.32 W/kg): P < 0.05 and 0.01, respectively.Heat loss by radiation and convection was directly related to the mean skin temperature; it was only when the latter reached the value of 37° that radiative plus convective heat loss became positive.There was a close inverse relation between the total heat loss and heat storage. After the beginning of sweating, the heat storage of full term and small for date infants sharply decreased and stabilized around 0, which showed that a new thermal steady state was reached. The premature infant was not able to reach this new equilibrium and the heat storage remained positive.The full term and small for date infants could keep the body temperature at a steady level of 37.66° and 37.98°, respectively, whereas the esophageal temperature of the premature infants kept on increasing.The cutaneous thermal conductance, an indicator of the heat-transferring blood flow, was at first negative, which showed that heat was transferred from the surface to the core. Later, before the evaporative heat loss, it increased and reached the maximal value at a body temperature of 37.6° in the normal, and of 37.9° in both the small for date and premature groups.The metabolic rate for the small for date and premature infants was significantly higher than that for the full term infants, and it directly related to the deep body temperature in each group. Neonatal thermal balance 889In the new thermal equilibrium, the metabolic rate of the full term infants was about 20% lower than that measured under neutral ambient conditions. We suggest that the term "neutral thermal environment" must be reconsidered. SpeculationA new method, gradient layer direct calorimetry, gave us the opportunity to measure directly the different heat losses of the neonate under well controlled experimental conditions, and to compare thes...

Relationship between Body Size, Thermal Balance and Thermal Insulation of Term Infants under Various Ambient Conditions

“…It can be seen that with increasing ambient temperature to 37 °C, the metabolic rate steadily decreases in each group of infants, as was found in our previous study (32). At temperatures of 28 and 32 °C there was a negative, statistically significant correlation, between body weight and metabolic rate per kilogramme.…”

“…Dry heat loss (convection + radiation) was measured with a gradient layer which covered the inner surface of the calorimeter, and evaporative heat loss was determined in a previously-described condenser (31,32).…”

Temperature variation in newborn babies: importance of physical contact with the mother

“…Information from the limited number of studies allowing quantification of dry heat loss from neonates from direct whole body calorimetry 15 or weighted direct calorimetry 7 14 in relation to the difference between core and foot skin temperature can be combined to illustrate heat loss over a range of core-foot skin temperature differences (fig 2). For all these references 7 14 15 values from diagrams of dry heat loss have to be combined with diagrams presenting core temperature and foot skin temperature.…”

Thermic Effects of Glucose, Amino Acid and Lipid in the Term Newborn

“…The ambient temperature of 32 °C can be considered as thermal neutrality for the normal term new-born (14). The direct calorimeter has been described previously (16) and measurements with new-born infants have been explained in detail (17).…”

“…In order to develop basic data on the ther mic effect of the primary food substrates in the normal term newborn within the first 5 days of life, metabolic rate and heat losses were mea sured by indirect and direct calorimetry in a whole body gradient layer calorimeter (16,17) following the ingestion of glucose, lipids or amino acids.…”