title: Brachial artery endothelial function is stable across the morning in young men.
abstract: BACKGROUND
  The morning hours are associated with increased cardiovascular (CV) risk, and vascular endothelial function (VEF) is a strong predictor of CV disease. A diurnal rhythm in VEF has been established but the morning variation in VEF is not well-documented. Thus, we tested if VEF is impaired across the vulnerable morning period.
  
  
  METHODS
  After overnight fasts, eight healthy men (age 26.3 ± 3 yr) underwent assessments of VEF under standardized testing conditions every 2 h from 0700 to 1300 h on two separate days. VEF was estimated following 5 min brachial artery occlusions by hyperemic flow-mediated dilation (FMD).
  
  
  RESULTS
  There was no significant change in FMD or hyperemic shear stimulus across the 6 h vulnerable period on either day, despite changes in physical activity and meals across these periods.
  
  
  CONCLUSIONS
  In this healthy group of young men, VEF is stable across the vulnerable morning period when typical behaviors occurred (breakfast and physical activity). Future research should focus on the roles of sleep, physical inactivity during sleep and endogenous circadian rhythm in VEF.
authors.affiliation: Oregon Institute of Occupational Health Sciences, Oregon Health and Science University, L 606/RJH 1553 A, 97139, Portland, Oregon, USA. thosar@ohsu.edu.
authors.forename: Saurabh S
authors.initials: SS
authors.lastname: Thosar
authors.affiliation: Department of Kinesiology, School of Public Health, Indiana University Bloomington, Bloomington, Indiana, 47405, USA. chcwiggi@indiana.edu.
authors.forename: Chad C
authors.initials: CC
authors.lastname: Wiggins
authors.affiliation: Oregon Institute of Occupational Health Sciences, Oregon Health and Science University, L 606/RJH 1553 A, 97139, Portland, Oregon, USA. sheast@ohsu.edu.|Department of Public Health and Preventive Medicine, Oregon Health & Science University, Portland, Oregon, 97239, USA. sheast@ohsu.edu.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Shea
authors.affiliation: Department of Kinesiology, School of Public Health, Indiana University Bloomington, Bloomington, Indiana, 47405, USA. wallacej@indiana.edu.
authors.forename: Janet P
authors.initials: JP
authors.lastname: Wallace
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001916:Brachial Artery / Q000000981:diagnostic imaging* / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D004730:Endothelium, Vascular / Q000000981:diagnostic imaging* / Q000502:physiology*; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D033081:Shear Strength / Q000502:physiology; D014463:Ultrasonography / Q000379:methods; D014655:Vascular Resistance / Q000502:physiology