549 IN NEONATES, THE INCIDENCE OF APNEA DEPENDS ON A VARIETY OF FACTORS, SUCH AS BIRTH WEIGHT, 1 SEX, 2 GESTATIONAL AGE, 3 AND POSTNATAL AGE. 3,4 Central apnea is generally reported as occurring more frequently during active sleep than during quiet sleep. 2,3,[5][6][7] Many authors have pointed out that apnea incidence is also closely related to ambient temperature in both full-term [8][9][10] and preterm neonates 9,11,12 and that the rate of apneic events is increased by warm exposure (i.e., thermal drive). Although preterm neonates are more often exposed to cool stress than to warm stress, little is known about the influence of cool exposure on the incidence of apnea in the different sleep states. Bader et al 11 reported a lower rate of central apnea during transient decreases in incubator temperature from warm (29°C) to thermoneutral conditions (24°C) over 30 minutes, although this was only seen during quiet sleep for preterm infants and during active sleep for term infants.The mechanism linking thermal stress and apnea is unknown and thus warrants further investigation. On the basis of the above-cited studies, it can be supposed that suprapontine influences modify respiratory control, which must be considered as a multiple-interaction system. Abnormal functional interaction among the respiratory system, thermoregulatory system, and sleep processes may alter compensatory responses to autonomic cardiovascular or respiratory challenge and increase the likelihood of life-threatening events later in life. 13 The effect of thermal stress is usually assessed by monitoring the body's internal temperature (generally esophageal or rectal temperatures, which supposedly represent the core temperature) and/or mean skin temperature. 14 However, the central controller of the thermoregulatory system receives thermal inputs from thermosensitive structures distributed throughout the body. The regulated variable therefore results from a weighted sum of different body temperatures. 15 Hence, to fully understand the thermal influence on apnea incidence in cool environments, it is essential to quantify the magnitude of body cooling that is proportional to the radiant, convective, conductive, and evaporative heat losses (i.e., body heat loss) on the other. Any failure to maintain thermal balance stimulates the body's thermal control mechanisms and thus triggers regulatory adjustments. This approach may help clarify a hypothesis raised by Perlstein et al, 9 whereby apnea is not specifically induced by changes in air temperature but, rather, through processes controlling the overall body heat loss (BHL). Hence, in the present study, the role of thermal drive in the mechanisms underlying the genesis of central apnea in the sleeping neonate was assessed by taking into account BHL during mild warm and cool thermal exposures.Central apneic events were monitored in a group of 22 nearterm neonates. Indeed, there are few published studies on these infants, who are generally considered to be physiologically similar to term infants, even t...

The aim of the present study was to validate the measurement of metabolic heat production using partitional calorimetry (PC) in preterm neonates exposed to a near-thermoneutral environment in an incubator. In order to reduce experimental uncertainty (due to the different variables involved in the calculation of body heat exchanges between the infant and the environment), the mean radiant temperature and the heat transfer coefficients for convection, radiation and evaporation were measured using a multisegment, anthropometric thermal mannequin which represents a small-for-gestational-age neonate (body surface area: 0.150 m2; simulated birth weight: 1500 g). The metabolic heat production calculated by PC was compared with the results of indirect respiratory calorimetry, which is rarely done in clinical setting since this method interferes with the neonate's environment and requires a high degree of technical preparedness. The oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured in 20 preterm neonates exposed to thermoneutral (32.3 degrees C) and to slightly cool environments (30.2 degrees C). The mean skin temperature was measured by infrared thermography. The measurements were made during well-established periods of active and quiet sleep. Metabolic heat production was assessed by weighting each value of VO2 and VCO2 by the duration of the sleep stages. Our results showed that there was no significant difference between the two methods in terms of their estimation of metabolic activity at thermoneutrality (mean overall difference: 0.34 kJ h(-1) kg(-1)) and in the cool environment (0.26 kJ h(-1) kg(-1)). We observed significant interneonate variability. Partitional calorimetry enabled the prediction of body growth with a daily error of less than 5.3 g (2.38 kJ h(-1) kg(-1)) for all the neonates at thermoneutrality and for 85% of the subjects (3.03 kJ h(-1) kg(-1)) in the cool environment. Despite this limitation, we demonstrate here that PC provides reliable information for calculating the energy expenditure of individual preterm neonates on the basis of standard environmental input variables. We suggest that the technique can be advantageously used to assess the energy expenditure and normal growth of these infants.

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