Thermal balance and sleep state in the newborn.

The thermal balance of 35 healthy newborn term infants was measured during active (AS) and quiet sleep (QS) in thermoneutral and cool environments. As conductive heat loss was found to be small, some 3% of the total, only the effective surface area involved in insensible heat loss was used in calculating insulation values. This area varied with posture, being 84% of the total when supine and 70% in the prone, crouched position. In thermoneutrality oxygen consumption rose significantly when the change was from QS to AS, but the associated fall in insulation did not reach significance. In a cool environment the differences were in the same direction but of greater magnitude, and the decrease in insulation of 17% found in AS was significant.