title: Laser Doppler flowmetry measurement of changes in human optic nerve head blood flow in response to blood gas perturbations.
abstract: OBJECTIVE
  The objective of this study was to establish the ability of laser Doppler flowmetry to detect relative changes in human optic nerve head hemodynamics caused by physiologic blood gas perturbations.
  
  
  METHODS
  Laser Doppler flowmetry permits the noninvasive assessment of relative blood velocity, volume, and flow (flux) in a sample volume of the nerve head. Such measurements were performed in two groups of healthy subjects. The first group (n = 11) was tested during normal room air breathing and then while breathing 100% oxygen (isocapnic hyperoxia). The second group (n = 10) was also tested under normal conditions as well as during isoxic hypercapnia (+ 15% end-tidal carbon dioxide). Results were analyzed by paired t tests.
  
  
  RESULTS
  Hyperoxia created a significant 25% (p = 0.002) decrease in optic nerve head blood flow, with blood volume decreased by 9% (p = 0.095) and blood velocity reduced by 13% (p = 0.154) compared to the room air condition. During hypercapnia, optic nerve head blood flow was increased by 28% (p = 0.012), with blood volume increased by 22% (p = 0.017) and blood velocity increased by 9% (p = 0.218) as compared to the normal room air condition.
  
  
  CONCLUSIONS
  Blood flow in the optic nerve head capillaries changes in response to hyperoxia and hypercapnia as demonstrated in the brain and retina. Laser Doppler flowmetry permits the noninvasive assessment of these responses in humans under conditions within the physiologic range.
authors.affiliation: Department of Ophthalmology, Indiana University School of Medicine, Indianapolis 46202, USA.
authors.forename: A
authors.initials: A
authors.lastname: Harris
authors.forename: D R
authors.initials: DR
authors.lastname: Anderson
authors.forename: L
authors.initials: L
authors.lastname: Pillunat
authors.forename: K
authors.initials: K
authors.lastname: Joos
authors.forename: R W
authors.initials: RW
authors.lastname: Knighton
authors.forename: L
authors.initials: L
authors.lastname: Kagemann
authors.forename: B J
authors.initials: BJ
authors.lastname: Martin
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D001810:Blood Volume; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000503:physiopathology*; D018496:Hyperoxia / Q000503:physiopathology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D008875:Middle Aged; D009898:Optic Disk / Q000098:blood supply*; D012039:Regional Blood Flow