title: Repeatability of the measurement of augmentation index in the clinical assessment of arterial stiffness using radial applanation tonometry.
abstract: OBJECTIVE
  Aortic augmentation index (AIx) measured using applanation tonometry is a non-invasive indicator of arterial stiffness. The objective of this study was to assess its repeatability when used by nurses with limited experience of the technique.
  
  
  METHODS
  Blood pressure/augmentation index (BP/AIx) was measured 4 times in 20 consecutive ambulant patients (16 male) after they rested supine for 15 min. Two nurses independently and alternately measured BP/AIx using the same equipment (Omron HEM-757; SphygmoCor with Millar hand-held tonometer). Nurses were blinded to patient medical records and their colleague's AIx/BP. 'Within' and 'between' observer differences were assessed using intra-class correlation coefficients (rI) and 95 % limits of agreement (95 % LoA) derived from Bland-Altman plots.
  
  
  RESULTS
  Mean age was 56 (mean BP 136/79; mean pulse 64). Mean AIx was 24.1 (range 2.8 to 41.0). Both 'between' and 'within' observer repeatability was very high, with intra-class correlation coefficients ranging from 0.92 to 0.98. Mean AIx readings 'between' observers differed by only 0.68 (95 % CI -0.24 to 1.59) with a high rI (0.98; 95 % CI 0.95 to 0.99) and a narrow 95 % LoA (-3.22 to 4.57). The 95 % LoA for 'within' observer repeatability was -6.75 to 7.95. Differences in AIx measurement did not vary over time or with increasing levels of AIx.
  
  
  CONCLUSIONS
  Even when undertaken by relatively inexperienced operators, both 'within' and 'between' observer repeatability of AIx measurement is very high. Such non-invasive assessment of arterial stiffness has the potential to be included in the clinical assessment of ambulant patients.
authors.affiliation: Department of Public Health, University of Aberdeen Medical School, Foresterhill, Aberdeen, Scotland. mike.crilly@abdn.ac.uk
authors.forename: M
authors.initials: M
authors.lastname: Crilly
authors.forename: C
authors.initials: C
authors.lastname: Coch
authors.forename: H
authors.initials: H
authors.lastname: Clark
authors.forename: M
authors.initials: M
authors.lastname: Bruce
authors.forename: D
authors.initials: D
authors.lastname: Williams
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure; D001916:Brachial Artery / Q000502:physiology*; D016022:Case-Control Studies; D004548:Elasticity; D005260:Female; D006801:Humans; D008297:Male; D008365:Manometry / Q000379:methods* / Q000706:statistics & numerical data; D008875:Middle Aged; D015588:Observer Variation; D011361:Professional Competence / Q000706:statistics & numerical data; D011673:Pulsatile Flow / Q000502:physiology*; D011674:Pulse / Q000706:statistics & numerical data*; D017534:Radial Artery / Q000502:physiology*; D012044:Regression Analysis; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014655:Vascular Resistance / Q000502:physiology