Thermal Balance of the Newborn Infant in a Heat-gaining Environment
| Autor: | L. S. Prod'hom, E. Jéquier, Endre Sulyok |
|---|---|
| Rok vydání: | 1973 |
| Předmět: |
Convection
Pediatrics medicine.medical_specialty Hot Temperature Time Factors Convective heat transfer Metabolic Clearance Rate Gestational Age Sweating Crying Calorimetry Environment Thermal energy storage Esophagus Thermal conductivity Animal science Weight loss Skin Physiological Phenomena Abdomen medicine Birth Weight Humans Relative humidity Full Term Foot Chemistry Respiration Infant Newborn Thermal Conductivity Hand Thigh Pediatrics Perinatology and Child Health Arm medicine.symptom Infant Premature Body Temperature Regulation |
| Zdroj: | Pediatric Research. 7:888-900 |
| ISSN: | 1530-0447 0031-3998 |
| DOI: | 10.1203/00006450-197311000-00005 |
| Popis: | Extract: The 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 infants were subjected to the same experimental conditions: ambient temperature 37°, relative 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 gesta-tional 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. In 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. Speculation: A 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 these data with the results obtained by indirect calorimetry. |
| Databáze: | OpenAIRE |
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