811 ments during sleep identified differ- ences in sleep characteristics in infants who subsequently died from SIDS compared with control subjects. 4 See editorial, p 793. The prone sleeping position has been identified as the major risk factor for SIDS. 5-10 Prone sleeping has also been shown to increase the amount of time spent in quiet sleep. 11-13 In previous studies we demonstrated that infant arousal thresholds are elevated in QS compared with active sleep and that thresholds increase with time spent in QS at 2 to 3 months of age when SIDS incidence is highest. 14 Previous studies of arousability to an external stimulus in the prone position have, however, been confined to AS, 15 and no longitu- dinal studies have been carried out. Various mechanisms have been pro- posed to explain the increased risk of SIDS associated with prone sleeping, including rebreathing of expired gases, 16,17 overheating, 18,19 and impair- ment of autonomic function. 20,21 We in- vestigated the effects of sleeping posi- tion longitudinally on arousal from both AS and QS together with cardiorespi- ratory variables and temperature in healthy term infants. Our hypothesis was that arousability would be im- paired when infants slept prone in both sleep states. Our study design also al- Despite the dramatic decline in the in- cidence of sudden infant death syn- drome following world-wide education programs, SIDS remains the major cause of death in infants between 1 The prone sleeping position impairs arousability in term infants Rosemary S. C. Horne, BSc, MSc, PhD, BLitt, Dorota Ferens, BSc, Anne-Maree Watts, BSc, Jessica Vitkovic, BSc, Brendan Lacey, BSc, Sarah Andrew, BSc, BA, Susan M. Cranage, Bonnie Chau, BAppl Sc, and T. Michael Adamson, MBBS, MRACP, FRACP month and 1 year of age. 1,2 Arousal from sleep is believed to be an impor- tant survival mechanism, which may be impaired in victims of SIDS. 3 In a prospective study, fewer body move- From the Department of Paediatrics and Ritchie Centre for Baby Health Research, Monash University, Clayton, Victoria, Australia. Supported by SIDSaustralia. Submitted for publication Aug 23, 2000; revision received Dec 5, 2000; accepted Jan 17, 2001. Reprints not available from author. Correspondence: Rosemary S. C. Horne, PhD, Department of Paediatrics, Monash Medical Centre, 246 Clayton Rd, Clayton, Victoria, Australia 3168. Copyright © 2001 by Mosby, Inc. 0022-3476/2001/$35.00 + 0 9/21/114475 doi:10.1067/mpd.2001.114475 ANOVA Analysis of variance AS Active sleep QS Quiet sleep SIDS Sudden infant death syndrome Objective: To investigate whether the prone sleeping position impaired arousal from sleep in healthy infants and whether this impairment was related to cardiorespiratory variables, temperature, or age. Study design: Healthy term infants (n = 24) were studied with daytime polysomnography on 3 occasions: 2 to 3 weeks after birth, 2 to 3 months after birth, and 5 to 6 months after birth. Multiple measurements of arousal threshold (cm H 2 O) in response to air-jet stimulation applied alternately to the nares were made in both active sleep and quiet sleep when infants slept both prone and supine. Results: Arousal thresholds were significantly higher in both active sleep and quiet sleep when infants slept prone at 2 to 3 weeks and 2 to 3 months, but not at 5 to 6 months. These increases were independent of any sleep position–related change in either rectal or abdominal skin temperature, respiratory rate, oxygen saturation, or heart rate. Conclusions: The prone position significantly impairs arousal from both active sleep and quiet sleep in healthy term infants. This impairment in arousability occurred with no clinically significant changes in cardiorespira- tory variables or body temperature. Decreased arousability from sleep in the prone position provides an important insight into its role as a risk factor for sudden infant death syndrome. (J Pediatr 2001;138:811-6)