ExtractIt seemed desirable and interesting to study the total energy expended during a period of several hours under conditions most commonly encountered under different infant care practices.The investigations were carried out on a total of 23 premature infants with a birth weight ranging from 1100 to 2120 g and aged from 2 to 31 days. Oxygen consumption was measured by an open circuit method using the Kipp diaferometer. Using three thermal conditions, measurements were started when four hours had elapsed after the last feed. Physical activity was observed and recorded continuously by an arbitrary method. The basal metabolic rate and the metabolic response to cold subtracted from the total metabolism measured under different experimental conditions gave the combined number of calories produced by specific dynamic action and physical activity. The information obtained from a previous study on specific dynamic action made it possible to approximate the calorigenic effect of food in the four series of examinations reported.Details of the studies carried out on premature infants while receiving human milk and kept in incubators with temperature maintained between 33-36° are shown in table I. In addition to the basal metabolic rate, total heat production observed throughout the observational period, calculated total daily heat production, and the percentage distribution of times spent in sleep and in physical activity with various intensity are also listed.. The average total heat production observed exceeds the minimal metabolic rate by 9.8 kcal/kg/24 h per subject. If allowance is made for the specific dynamic action expected from the average daily intake of human milk (1.1 g protein/ml) 3.0 kcal/kg/24 h can be attributed to muscular activity. The magnitude of this component of the total energy expenditure is consistent with the markedly reduced physical activity exhibited by premature infants maintained in a thermally neutral environment.The results obtained on premature infants receiving an artificial formula containing 3.43 % protein are listed in table II and shown diagrammatically in figure 1. The total daily caloric output averages 55.0 kcal/kg/24 h, a value roughly 39% above the basal rate, in contrast to the average increase of 25 % observed in breast milk-fed infants. This difference in the combined quota of specific dynamic action and physical activity (8.8 and 15.3 kcal/kg/24 h, respectively) is due partly to the higher protein and caloric intake, and partly to the lesser proportion of time spent in deep sleep. Table III summarizes the results of studies of the energy exchange of five swaddled premature infants kept at a room temperature of 20-22°. It can be seen that the total daily heat production averages 58.3 kcal/kg/24 h, which is not appreciably greater than that observed in Adapta-fed infants maintained at neutral temperature. The extra calories above the basal amount to 18.6 kcal/kg/24 h, II Pediat. Res., Vol. 2, No. 3 (1968) 162 MESTYAN, JARAI, FEKETE representing a 47 % rise above the minim...

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4. The small intestine of new-born rabbits received 24 % of the cardiac output while renal flow was only 8 %. There were large changes in the proportions of body weight and in the distribution of cardiac output with age from 1 to 6 days from birth.5. The results support the contention that brown adipose tissue is the principal site of additional thermogenesis in anaesthetized new-born rabbits exposed to cold.

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The calorigenic effect of an artificial formula, Adapta, was examined in premature infants kept a t and below the neutral temperature. After a preliminary period of 15-30 minutes, a feeding (40-60 ml) was offered or given by gavage. The test feeding was followed by an experimental period of four hours, during which time oxygen consumption and CO, production were continuously recorded by an open circuit method using the Kipp diaferometer.The results of investigations carried out in the zone of thermoneutrality are summarized in table I. The amount of oxygen consumed 30 minutes after ingestion of the formula was already appreciably larger than that corresponding to the basal metabolic rate. At 90 or 120 minutes, the average oxygen consumption was 30 % higher than that a t the preliminary level. Oxygen consumption then fell and had approached the fasting level by the end of the period of observation.I n order to obtain the cumulative effect of thermogenesis, total and basal heat production were calculated for a period of four hours. The average amount of total extra calories was 1.7 kcallkg which, in relation to basal heat production during the same period of time and to the ingested calories, represented an increase of 26.4 and 9.2%, respectively (table VI).The changes in oxygen consumption a t different levels of thermoregulatory heat production in totally and partially swaddled premature infants maintained at 20-22' are shown in tables 11, I11 and IV. The responses are also diagrammatically compared (fig. 4). I t can be seen that the magnitude of specific dynamic action is the same for babies in a thermoneutral and colder environment, despite the difference in the preingestion levels of oxygen consumption. Control experiments in nonfed premature infants revealed that the specific dynamic action of food in a heat-losing environment is not due to muscular activity, but appears in an additive manner and independently of the metabolic increase induced by the cold environment (table V).The summation of the metabolic response to cold and to food was also reflected by the behavior of body temperature. The ingestion of 50 ml of formula stopped the fall in body temperature and even caused a small transient rise during the period of maximum increase in heat production.