title: The development of the circadian heart rate rhythm (CHR) in Asian infants.
abstract: OBJECTIVE
  To test the hypothesis that term-born Asian infants, at reduced risk to die of Sudden Infant Death Syndrome (SIDS) exhibit a circadian heart rate rhythm (CHR) at a later age than non-Asian term infants.
  
  
  METHODS
  Repeated overnight heart rate (HR) traces obtained with a battery-operated Polar S810i heart-rate monitor at home in 17 Asian Torajan infants in Indonesia, were compared with those of 52 non-Asian infants monitored as part of the Collaborative Home Infant Monitoring Evaluation (CHIME). HR was determined using a moving window averaging technique. A comparison of median HR during quiet sleep (QS) episodes (identified by minimum HR variability), established the presence of CHR.
  
  
  RESULTS
  Seventy three percent of non-Asian CHIME infants ≤7 weeks exhibited CHR compared to 45% of Asian Torajan infants. Between 8 and 12 weeks, 94% of non-Asian CHIME infants exhibited CHR, compared to 33% of Asian Torajan infants (p<0.001). Forty seven and 56% of Asian Torajan infants exhibited the CHR at the age intervals of 16-20 weeks and 21-25 weeks respectively. Active wakefulness percentages as a function of the entire recording and median QS HR were not significantly different in the two groups.
  
  
  CONCLUSIONS
  Despite the fact that Asian Torajan infants were on average a week older than non-Asian CHIME babies, between two and three months of age only one in three exhibited the CHR, compared to virtually all non-Asian CHIME infants. We speculate that the cause of this difference rests in the infants' environment rather than their genetic origin.
authors.affiliation: University of Southern California Division of Neonatal Medicine, LAC+USC Medical Center and Childrens Hospital Los Angeles, Los Angeles, CA 90033, USA. hoppenbrou@earthlink.net
authors.forename: Toke
authors.initials: T
authors.lastname: Hoppenbrouwers
authors.forename: Flavia
authors.initials: F
authors.lastname: Oliveira
authors.forename: Stanislaus
authors.initials: S
authors.lastname: Sandarupa
authors.forename: Michael
authors.initials: M
authors.lastname: Khoo
authors.forename: Michael
authors.initials: M
authors.lastname: Neuman
authors.forename: Rangasamy
authors.initials: R
authors.lastname: Ramanathan
mesh_terms: D000367:Age Factors; D044466:Asian People / Q000706:statistics & numerical data; D002657:Child Development / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007214:Indonesia / Q000453:epidemiology; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008991:Monitoring, Physiologic; D017286:Polysomnography; D013398:Sudden Infant Death / Q000453:epidemiology / Q000208:ethnology / Q000209:etiology