title: Impact of volunteer-related and methodology-related factors on the reproducibility of brachial artery flow-mediated vasodilation: analysis of 672 individual repeated measurements.
abstract: Brachial artery flow-mediated dilation (FMD) is a popular technique to examine endothelial function in humans. Identifying volunteer and methodological factors related to variation in FMD is important to improve measurement accuracy and applicability.
  
  
  
  Volunteer-related and methodology-related parameters were collected in 672 volunteers from eight affiliated centres worldwide who underwent repeated measures of FMD. All centres adopted contemporary expert-consensus guidelines for FMD assessment. After calculating the coefficient of variation (%) of the FMD for each individual, we constructed quartiles (n = 168 per quartile). Based on two regression models (volunteer-related factors and methodology-related factors), statistically significant components of these two models were added to a final regression model (calculated as β-coefficient and R). This allowed us to identify factors that independently contributed to the variation in FMD%.
  
  
  
  Median coefficient of variation was 17.5%, with healthy volunteers demonstrating a coefficient of variation 9.3%. Regression models revealed age (β = 0.248, P < 0.001), hypertension (β = 0.104, P < 0.001), dyslipidemia (β = 0.331, P < 0.001), time between measurements (β = 0.318, P < 0.001), lab experience (β = -0.133, P < 0.001) and baseline FMD% (β = 0.082, P < 0.05) as contributors to the coefficient of variation. After including all significant factors in the final model, we found that time between measurements, hypertension, baseline FMD% and lab experience with FMD independently predicted brachial artery variability (total R = 0.202).
  
  
  
  Although FMD% showed good reproducibility, larger variation was observed in conditions with longer time between measurements, hypertension, less experience and lower baseline FMD%. Accounting for these factors may improve FMD% variability.
authors.affiliation: aDepartment of Physiology, Radboud Institute for Health Sciences, Radboud University Medical Center, Nijmegen, The Netherlands bResearch institute for Sport and Exercise Sciences, Liverpool John Moores University, Liverpool, United Kingdom cTop Institute for Food and Nutrition (TIFN), Wageningen dUnilever R&D Vlaardingen, Vlaardingen eDivision of Human Nutrition, Wageningen University, Wageningen fDepartment of Human Biology gDepartment of Biomedical Engineering, Maastricht University Medical Centre, Maastricht, The Netherlands hSchool of Sports Science, Exercise and Health, The University of Western Australia, Nedlands, Australia iUniversity of Pisa, Pisa, Italy.
authors.forename: Anke C C M
authors.initials: AC
authors.lastname: van Mil
authors.forename: Arno
authors.initials: A
authors.lastname: Greyling
authors.forename: Peter L
authors.initials: PL
authors.lastname: Zock
authors.forename: Johanna M
authors.initials: JM
authors.lastname: Geleijnse
authors.forename: Maria T
authors.initials: MT
authors.lastname: Hopman
authors.forename: Ronald P
authors.initials: RP
authors.lastname: Mensink
authors.forename: Koen D
authors.initials: KD
authors.lastname: Reesink
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Green
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Ghiadoni
authors.forename: Dick H
authors.initials: DH
authors.lastname: Thijssen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001916:Brachial Artery / Q000502:physiology*; D003935:Diagnostic Techniques, Cardiovascular / Q000592:standards* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D014664:Vasodilation / Q000502:physiology*; D014838:Volunteers / Q000706:statistics & numerical data; D055815:Young Adult