Abstract
Using a gradient layer direct calorimeter, total heat losses were measured in 73 full term newborns in three different environments: ambient temperature (Ta) of 30, 32 or 34°. The relative humidity of the air was kept constant at 50%. Esophageal temperature (Ttnt) and mean skin temperature (T8) were continuously recorded. All experiments lasted at least 1 hr, and the data were obtained when the newborn was quiet. The mean total heat loss (± SEM) was at 30°: 41.85 ± 1.29 cal/kg/min; at 32°: 35.40 ± 0.71 cal/kg/min at 34°: 27.80 ± 0.85 cal/kg/min. Total heat loss was proportional to the difference between T8 andTa. Evaporative heat loss was very constant in these three conditions (even when Ttnt was higher than 37.0°), with a mean of 6.58 ± 0.13 cal/kg/min. This value is a measurement of insensible perspiration. The heat storage (ΔS) was calculated using the following formula: ΔS = weight (kg) × specific heat of body mass (0.84 kcal/g.C) × [(0.6 × variation of Ttnt) + (0.4 × variation of T8)]. ΔS was negative at Ta of 30° (body cooling), and positive at Ta of 34C (body warming). Regression analysis showed a mean heat loss of 36.26 cal/kg/min when the newborns were in thermal equilibrium (S = 0) this value corresponds to a calculated ṿ O2 of 7.52 ml O2/kg/min. The occurred in most babies at 32° (neutral enviroment). The skin thermal conductance [C = cutaneous heat loss/ (Ttnt - T8) × body surface], which is an index of cutaneous blood flow, increased sharply in most babies when T8 reached 35.8° and Ttnt 37.0°. These data indicate that the thermoregulatory mechanisms on the 1st of life are limited: at low Ta (30°), vasoconstriction and very likely that increase in metabolic rate are not large enough to prevent a fall of Ttnt. At high Ta (34°), vasodilatation occurs, but sweating is not elicited.
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Ryser, G., Jéquier, E. 40. Studies by direct calorimetry of thermal balance in the first day of life. Pediatr Res 5, 91 (1971). https://doi.org/10.1203/00006450-197102000-00045
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DOI: https://doi.org/10.1203/00006450-197102000-00045