title: Noninvasive measurement of the Bayliss effect in retinal autoregulation.
abstract: OBJECTIVE
  The Bayliss effect describes the reaction of smooth muscle cells in the arterial wall to changes in blood pressure. A rise in mean arterial blood pressure (MAP) causes an autoregulatory myogenic vessel constriction by smooth muscle cells in the arterial wall. The responsiveness of retinal vessels to changes in MAP were analyzed using the Retinal Vessel Analyzer (RVA).
  
  
  METHODS
  Continuous measurement of retinal arterial vessels was performed in 40 healthy volunteers (age 18-56 years.) over a 9-min period. After a 3-min baseline measurement (phase I), isometric exercise caused a rise in MAP over the next 3 min (phase II). During the last 3 min (phase III) recovery was observed. Blood pressure and ECG were documented simultaneously throughout the experiment.
  
  
  RESULTS
  Exercise caused a significant rise of 22.8 (+/-6.0) mm Hg in MAP (phase II vs. phase I: P<0.001). Retinal arterioles showed 5.5% (+/-2.8%) vasoconstriction (P<0.001). During phase III vessel diameters returned to normal, with no difference from phase I (P = 0.179).
  
  
  CONCLUSIONS
  Noninvasive measurement and quantitative analysis of the Bayliss effect in human retinal vessels by means of the RVA is possible. Analysis of retinal arterial autoregulation may provide valuable insight into pathologic conditions such as diabetic or hypertensive retinopathy.
authors: Department of Ophthalmology, Friedrich Schiller University Jena, Germany.
authors: M
authors: M
authors: Blum
authors: K
authors: K
authors: Bachmann
authors: D
authors: D
authors: Wintzer
authors: T
authors: T
authors: Riemer
authors: W
authors: W
authors: Vilser
authors: J
authors: J
authors: Strobel
mesh_terms: D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D015444:Exercise / Q000502:physiology; D005260:Female; D006706:Homeostasis; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008297:Male; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D012016:Reference Values; D012160:Retina / Q000502:physiology*; D012161:Retinal Artery / Q000502:physiology*; D014661:Vasoconstriction