title: Brachial-to-radial SBP amplification: implications of age and estimated central blood pressure from radial tonometry.
abstract: OBJECTIVE
  The reference standard for noninvasive estimation of central blood pressure (BP) is radial tonometry calibrated using brachial SBP and DBP. Brachial-to-radial-SBP amplification (B-R-SBPAmp) may introduce error into central BP estimation, but the magnitude of such amplification is uncertain. This study aimed to determine the magnitude and effect of ageing on B-R-SBPAmp; the effect of B-R-SBPAmp on radial tonometry estimated central SBP; and correlates of B-R-SBPAmp.
  
  
  METHODS
  Forty young (28 ± 5 years) and 20 older (60 ± 8 years) healthy participants underwent brachial and radial artery ultrasound to identify SBP from the first Doppler flow inflection during BP cuff deflation (first Korotkoff sound). Impedance cardiography, ultrasound, tonometry and anthropometric data were collected to explore B-R-SBPAmp correlates.
  
  
  RESULTS
  Radial SBP was significantly higher than brachial SBP in younger (118 ± 12 versus 110 ± 10  mmHg; P < 0.001) and older (135 ± 12 versus 121 ± 11  mmHg; P < 0.001) participants. The magnitude of B-R-SBPAmp (radial minus brachial SBP) was higher in older than younger participants (14 ± 7 versus 8 ± 7  mmHg; P = 0.002), independent of sex and heart rate. Estimated central SBP was higher in both age groups when radial waveforms were recalibrated using radial (versus brachial) SBP (P < 0.001). The central SBP change relative to B-R-SBPAmp was associated with augmentation index (r = 0.739, P < 0.001), independent of age, sex and heart rate. Age, male sex and high-density lipoprotein each positively related to B-R-SBPAmp in multiple regression analysis (P < 0.05).
  
  
  CONCLUSIONS
  Major B-R-SBPAmp occurs in healthy people and is higher with increasing age. Furthermore, B-R-SBPAmp contributes to underestimation of radial tonometry derived central SBP.
authors.affiliation: aMenzies Institute for Medical Research, University of Tasmania, Hobart bSchool of Health Sciences, University of Tasmania, Launceston, Tasmania, Australia *Dean S. Picone and Rachel E.D. Climie contributed equally to this article.
authors.forename: Dean S
authors.initials: DS
authors.lastname: Picone
authors.forename: Rachel E D
authors.initials: RE
authors.lastname: Climie
authors.forename: Kiran D K
authors.initials: KD
authors.lastname: Ahuja
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Keske
authors.forename: James E
authors.initials: JE
authors.lastname: Sharman
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D001795:Blood Pressure Determination; D001916:Brachial Artery / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008365:Manometry; D008875:Middle Aged; D017534:Radial Artery / Q000502:physiology*; D055815:Young Adult