title: Decreased heart rate variability is associated with increased transcranial Doppler velocities in children with sickle cell disease.
abstract: OBJECTIVE
  To explore the relationship between 24-hour blood pressure (BP) variability, heart rate (HR) variability, and transcranial Doppler velocity (TCDV) in a cohort of pediatric sickle cell disease (SCD) patients.
  
  
  METHODS
  This is a retrospective study of 11 children aged 8-18 years with SCD who previously underwent 24-hour ambulatory BP monitoring and TCDV measurements.
  
  
  METHODS
  Medical records were reviewed for TCDV and 24-hour ABP data. TCDV in the right and left middle cerebral artery were examined, and the highest velocity was recorded. HR and BP standard deviations were used as markers of variability. The relationships between daytime, nighttime, and 24-hour blood pressures and heart rate variability were determined.
  
  
  RESULTS
  Mean age, body mass index and hemoglobin levels were 11.2 ± 3.0 years, 18.7 ± 3.4 kg/m2, and 9.1 ± 1.7 g/dL, respectively. Median transcranial Doppler velocity was 136cm/s (125-142). Decreased day, night, and 24-hour heart rate variability were significantly associated with increased transcranial Doppler velocity (R = -.69, P = .02; R = -.82 P =.002; R = -.66, P = .03, respectively). BP variability did not correlate with TCDV. Nighttime BP indexes were higher than daytime.
  
  
  CONCLUSIONS
  In this small cohort, decreased heart rate variability assessed by the standard deviation of HR was associated with increased transcranial Doppler velocities in children with SCD. No correlation between measurements of BP variability and TCDV was found. Our study provides new information on heart rate and blood pressure variability and TCDV; a surrogate marker of stroke risk in sickle cell disease. Larger multicenter studies are needed to confirm our findings.
authors.forename: Jenna B
authors.initials: JB
authors.lastname: Jones
authors.forename: Ibrahim F
authors.initials: IF
authors.lastname: Shatat
authors.forename: Brent M
authors.initials: BM
authors.lastname: Egan
authors.forename: Remberto C
authors.initials: RC
authors.lastname: Paulo
mesh_terms: D000293:Adolescent; D000755:Anemia, Sickle Cell / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001783:Blood Flow Velocity / Q000502:physiology*; D001794:Blood Pressure / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory; D002560:Cerebrovascular Circulation / Q000502:physiology*; D002648:Child; D002940:Circadian Rhythm / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D020768:Middle Cerebral Artery / Q000000981:diagnostic imaging / Q000503:physiopathology; D012189:Retrospective Studies; D017585:Ultrasonography, Doppler, Transcranial