Activity and Inactivity Cycles During the Sleep of Premature Infants Exposed to Neutral Temperatures

Abstract

Eight unclothed premature babies were observed during 20 test periods of 2-3.5 half hours duration in ambient neutral temperatures of 32[degree] to 34[degree]C. Oxygen consumption, rectal temperatures, skin blood flow and body movements were continuously recorded during the test periods. These premature infants demonstrated cycles of bodily inactivity (quiet sleep) and activity (active sleep) during sleep as described in older infants and adults. All but 2 of the infants had a total amount of quiet sleep of 55% or more of the observation time in all tests done in ambient neutral temperatures. Oxygen consumption was less during quiet sleep than in active sleep. This relationship of oxygen consumption to activity became more definite as the infants became older and larger. Two of the above infants were tested in ambient temperatures of 30[degree] and 31[degree]C, 2[degree] and 1[degree]C, respectively, below the lower limit of the neutral temperature range of 32[degree] to 34[degree]C. Their oxygen consumption during quiet and active phases of sleep increased. Their total amount of quiet sleep was reduced respectively to 31.8% and 46.0% of the test time. It was concluded in the preceding paper that ambient neutral temperatures may also be considered thermal comfort temperatures for the premature infant as they are in the adult. Since the premature infants used the least amount of oxygen and were less active but still retained activity cycles in ambient neutral temperatures, it may also be possible to consider the ambient neutral temperature as approximating the optimal ambient temperature. Slow, regular respirations are generally regarded as correlated with quiet sleep in older infants and adults. This was also true of our older and larger premature infants, but not of the smallest and youngest. This fact, along with our observation that oxygen consumption did not increase markedly with activity in the smallest and youngest premature infants, tends to confirm the observation of others that these infants do not have well defined sleeping and waking states, but seem to fluctuate in a twilight zone. Hunger appeared to be a less potent determinant of activity than cool ambient temperature.