title: Hour-to-hour and week-to-week variability and reproducibility of wave reflection indices derived by aortic pulse wave analysis: implications for studies with repeated measurements.
abstract: BACKGROUND
  Wave reflections are implicated increasingly in clinical research.
  
  
  OBJECTIVE
  The purpose of the present study was to investigate whether wave reflection indices are reproducible when measured repeatedly (more than twice) at longer time intervals, namely hour-to-hour and week-to-week, in healthy subjects; something that has not yet been examined.
  
  
  METHODS
  Bland-Altman plots, the interclass correlation coefficients (ICC) and coefficient of variation were used for this purpose. Two series, with measurements repeated in triplicate, were performed in 22 healthy subjects: the first at intervals of 1 h and the second at 1-week time intervals. Augmentation index (AIx), heart rate-corrected AIx (AI@75) and arrival time of reflected waves at the central aorta (tr) were calculated by aortic pulse wave analysis.
  
  
  RESULTS
  AIx and AI@75 presented very good to excellent reproducibility (ICC = 0.86) for hour-to-hour repeated measurements, while tr was also highly reproducible (ICC = 0.79). AIx, AI@75 and tr were substantially reproducible when measured repeatedly with 1-week intervals, providing ICCs greater than 0.70. Bland-Altman plots confirmed these results, indicating that more than 90% of AIx, AI@75 and tr measurements fell within two standard deviations of the mean difference.
  
  
  CONCLUSIONS
  Wave reflections are substantially reproducible even when measurements repeated in triplicate are performed at longer time intervals (hours and weeks). A quantifiable amount of variation was reported, which should be taken carefully into consideration in interventional studies with repeated measurements and in observational studies investigating differences or correlations of these indices.
authors.affiliation: Unit of Biomedical Engineering, First Department of Cardiology, Hippokration Hospital, Medical School, Greece. theopap@mail.ntua.gr
authors.forename: Theodore G
authors.initials: TG
authors.lastname: Papaioannou
authors.forename: Emmanouil N
authors.initials: EN
authors.lastname: Karatzis
authors.forename: Kalliopi N
authors.initials: KN
authors.lastname: Karatzi
authors.forename: Elias J
authors.initials: EJ
authors.lastname: Gialafos
authors.forename: Athanassios D
authors.initials: AD
authors.lastname: Protogerou
authors.forename: Kimon S
authors.initials: KS
authors.lastname: Stamatelopoulos
authors.forename: Christos M
authors.initials: CM
authors.lastname: Papamichael
authors.forename: John P
authors.initials: JP
authors.lastname: Lekakis
authors.forename: Christodoulos I
authors.initials: CI
authors.lastname: Stefanadis
mesh_terms: D000328:Adult; D001011:Aorta / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011674:Pulse; D015203:Reproducibility of Results