[Density of rapid eye movements during active sleep in preterm newborn infants].

Rapid eye movement (REM) density has been helpful as a reliable index of phasic eye movements activity during REM (active) sleep in adults. We evaluated this index in 28 newborns, at 34 to 39 weeks of conceptional age (CA). The 5 hours polysomnographic recording during sleep included electroencephalogram, electrooculogram, electrocardiogram, pneumogram, nasal thermistor for detecting airflow, and continuous oxygen saturation (tcPO2) monitoring. REM density was measured by two distinct criteria: REM density as the duration of phasic eye movements in relation to REM periods (REMP). Such index varied from 10.6 to 14.1% and was higher in the 36-37 weeks CA group. REM density was calculated as a percentage of 10-second epochs of REM sleep in which phasic eye movements occurred. This criterion confirmed the narrow range of such index in this age bracket (39.9-44.6%), was higher in the first REMP and in the 36-37 weeks CA group. Our data suggest that REM density is a consistent phasic REM sleep feature in preterm newborns with levels close to the adult population, in spite of the gradual decrease of REM sleep duration with age. Higher indices were also found in the first REMP and in the 36-37 weeks CA group by both methods.