title: Baroreflex sensitivity during sleep in infants: impact of sleeping position and sleep state.
abstract: OBJECTIVE
  The prone sleeping position is a major risk for the sudden infant death syndrome (SIDS) and has been associated with lowered blood pressure and impaired blood pressure control. This study aimed to assess the effects of sleeping position, sleep state, and postnatal age on baroreflex control of heart rate.
  
  
  METHODS
  Term infants (n = 31) were studied at 2-4 weeks, 2-3 months, and 5-6 months with daytime polysomnography.
  
  
  METHODS
  Blood pressure and heart rate were recorded during quiet (QS) and active (AS) sleep in both the supine and prone positions. In each condition, three 1-2 minute baseline measurements and three 15° head-up tilts were performed.
  
  
  RESULTS
  Baroreflex sensitivity (BRS) was assessed using cross-spectral analysis (BRS(SP)) and sequence analysis (BRS(SEQ)) in the baseline condition and with BRS(SP) during head-up tilting (BRS(SP) Tilt). BRS was usually lower prone compared to supine, reaching significance at 2-3 months (BRS(SP), P < 0.05; BRS(SP) Tilt, P < 0.05) and 5-6 months (BRS(SEQ), P < 0.05). BRS was lower in AS than QS supine at 5-6 months for all BRS estimates (P < 0.05). During QS, BRS increased with postnatal age in both sleeping positions (P < 0.05 for all BRS estimates); during AS, the postnatal age-related increase was limited to the prone position (BRS(SEQ), P < 0.05).
  
  
  CONCLUSIONS
  Sleeping position, sleep state and postnatal age all affect infant baroreflex function. Reduced BRS in the younger infants sleeping prone could increase the vulnerability to hypotensive events during sleep and thus play a vital role in conditions where circulatory failure may be involved, such as SIDS.
authors.affiliation: The Ritchie Centre, Monash Institute of Medical Research, Monash University, Melbourne, Victoria, Australia.
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Yiallourou
authors.forename: Scott A
authors.initials: SA
authors.lastname: Sands
authors.forename: Adrian M
authors.initials: AM
authors.lastname: Walker
authors.forename: Rosemary S C
authors.initials: RS
authors.lastname: Horne
mesh_terms: D000367:Age Factors; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn / Q000502:physiology*; D008297:Male; D017286:Polysomnography; D016684:Prone Position / Q000502:physiology*; D012890:Sleep / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*