title: Peak and time-integrated shear rates independently predict flow-mediated dilation.
abstract: BACKGROUND
  To determine whether peak and time-integrated shear rates independently predict flow-mediated dilation (FMD).
  
  
  METHODS
  Eleven physically active (25 ± 5 years old) male subjects were tested. FMD was defined as the shear rate-diameter relationship. Hierarchical linear modeling was used to estimate brachial artery diameter change with repeated measures of shear rate nested within each subject. Two models were tested: 1) FMD was induced using ischemia-induced hyperemia (2, 4, 6, and 10 minutes); and 2) FMD was induced following transient (ischemia) and steady-state (forearm heating and handgrip exercise) increases in shear rate. For both models we determined whether peak, in addition to time-integrated shear rates, explained a significant portion of variation for diameter change.
  
  
  RESULTS
  Model 1: Time integrated shear rates explained most of the variation for diameter change. However, peak shear rate explained an additional significant portion of variation. Model 2: The transient condition resulted in significantly (p = 0.012) smaller diameter change per shear rate change than the steady-state condition. However, when specifying peak shear rate as a covariate, the difference between conditions became nonsignificant (p = 0.138).
  
  
  CONCLUSIONS
  Peak and time-integrated shear rates independently predict FMD. Future studies using the FMD test should consider both parameters.
authors.affiliation: Department of Kinesiology, University of Georgia, Ramsey Center, Athens, GA 30602, USA.
authors.forename: Lee
authors.initials: L
authors.lastname: Stoner
authors.forename: Kevin K
authors.initials: KK
authors.lastname: McCully
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology; D001916:Brachial Artery / Q000000981:diagnostic imaging* / Q000502:physiology*; D018737:Hand Strength; D006801:Humans; D006940:Hyperemia / Q000000981:diagnostic imaging / Q000503:physiopathology; D007511:Ischemia / Q000000981:diagnostic imaging / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D014463:Ultrasonography; D014664:Vasodilation