Temporary loss of a metabolic response to cold stress in infants of low birthweight.

Though even very premature infants defend their body temperature by controlling skin blood flow and regulating heat production within hours of birth (Bruck and Bruck, 1960; Briick, 1961), small babies easily become hypothermic in the first few weeks of life. The tendency to hypo-thermia is generally attributed to lack of tissue insulation and to the high surface area to body weight ratio. Evidence has now accumulated to suggest that another factor may occasionally operate. We report here observations on 3 infants of low birthweight who were able to increase their heat production normally during the first few days of life when in cool surroundings, but who then lost this ability for a number of days. Subjects and Methods The observations reported here were obtained during studies on a group of 28 infants who weighed between 1 and 2 kg. at birth, and who were examined with the parents ' consent at regular intervals during the first 6 weeks of life. Measurements. Estimates of heat production at various environmental temperatures between 28 and 36 'C. were made by indirect calorimetry using a closed-circuit oxygen consumption apparatus (Hill and Rahimtulla, 1965). The babies were naked except for a thin napkin. Rectal temperature was between 36 and 37-8 'C. The metabolic response to cold stress was normally judged by measuring the O. consumption for 20 minutes while the infants were in an environment of 29 'C. In a few studies rectal temperature fell nearly a degree during this time; since the temperature of the infant influences mean air temperature in the chamber, a completely steady air temperature was not established in these circumstances, and the change in gas volume in the apparatus overestimated 02 consumption by up to 11 00. The results reported here have been corrected for this artefact (Hey, 1969). Heat production was calculated from oxygen consumption on the assump-tion that the metabolism of 1 litre 02 at s.t.p. (dry)