DYNAMIC CHANGES IN AROUSAL THRESHOLD DURING SLEEP IN THE HUMAN INFANT

Failure to arouse from sleep is a possible mechanism leading to sudden infant death. Using a controlled pulsatile air jet applied alternatel y to the nostrils we have made multiple measures of arousal threshold both between and within sleep states. Infants (n = 22) born at term we re studied at 2-3 wk postterm (mean age 13 d, range 9-17 d, study 1) a nd again at 2-3 mo postterm (mean age 78 d, range 56-98 d, study 2). A rousal threshold (stimulus driving pressure, cm H2O) was determined in both active sleep (AS) and quiet sleep (QS). At both ages arousal thr eshold in QS was significantly higher (251 +/- 24 and 298 +/- 35) than in AS (163 +/- 19 and 144 +/- 29) (p < 0.001). In a morning sleep per iod, the first and second QS epochs were compared in each baby. In bot h study 1 and study 2, respectively, arousal thresholds were significa ntly higher in the second QS epoch (270 +/- 34 and 497 +/- 100) than i n the first QS epoch (198 +/- 29 and 252 +/- 69) (p < 0.05 and p < 0.0 2). There was a significant correlation in individual infants between arousal thresholds in the two states at both ages (p < 0.005 and p < 0 .007, respectively). Regression analysis showed no correlation between the length of time the infant had been in a particular sleep state an d the arousal threshold in either state in study 1 or in AS in study 2 ; however, arousal threshold increased significantly (p < 0.01) with t ime in QS in study 2. This study has expanded on previous findings tha t arousability is sleep state-dependent by demonstrating that arousabi lity in QS is also altered by the length of time that the infant has b een asleep.