Oxygen consumption and neonatal sleep states

1. In thirty full‐term infants in the first week of life, nursed in a constant volume, closed‐circuit metabolism chamber in a neutral thermal environment (31·5‐33·5 °C), measurements were made of oxygen consumption ( V̇ O 2 ) during periods of rapid eye movement (REM) sleep and non‐rapid eye movement (NREM) sleep. 2. The mean V̇ O 2 during REM sleep was 5·97 ml. kg −1 . min −1 . In NREM sleep the mean V̇ O 2 was 5·72 ml. kg −1 . min −1 . This difference was significant (paired t test P < 0·05). 3. When the direction of sleep state change was taken into account the difference in V̇ O 2 between the two states was much less when REM sleep preceded NREM than when the change was in the opposite direction. In nineteen infants in whom the change was from REM to NREM the difference in V̇ O 2 (6·18 and 6·03 ml. kg −1 . min −1 ) was not significant ( P > 0·05). The mean difference when the sleep state change was from NREM to REM was significant ( P < 0·01), the values being 5·54 and 5·81 ml. kg −1 . min −1 respectively. 4. In the NREM state, a gradual diminution of V̇ O 2 with time was consistently found. This was not the case in REM sleep. 5. In twelve infants studied in a cool environment (29 ± 0·5 °C) V̇ O 2 during REM sleep was 7·77, and during NREM sleep it was 6·58 ml. kg −1 . min −1 , ( P < 0·001). Thus even the maximum difference found in a neutral thermal environment of 6·6% was significantly increased to 14·9% ( P < 0·01) with mild thermal stress. 6. No consistent changes in V̇ O 2 with time were found in either REM or NREM sleep in twelve infants studied in a cool environment, in contrast to the findings in thermal neutrality