title: Effect of isovolumic hemodilution on oxygen delivery to the optic nerve head.
abstract: BACKGROUND
  To investigate the effect of isovolumic hemodilution on the tissue oxygenation of the optic nerve head (ONH).
  
  
  METHODS
  In 9 miniature pigs (6 - 12 kg), hemodilution was performed by replacing 100 - 140 ml of blood by an equivalent volume of 6 % hydroxyethyl starch in saline. The blood flow parameters in the ONH microcirculation, namely velocity (BVel), volume (BVol) and flow (BF), were measured by laser Doppler flowmetry. Microelectrodes placed at approximately 50 micrometer from the disk surface and the phosphorescence quenching technique were used to measure pO 2 in the vitreous (pO 2 (vitr)) and in the ONH capillary blood (pO 2 (blood)), respectively. Arterial blood pressure, hematocrit (Hct) and gas content were documented.
  
  
  RESULTS
  In all animals, hemodilution reduced Hct by 30 +/- 6 %. All the flow parameters increased markedly. Simultaneously, pO 2 (blood) (baseline: 31 +/- 3 mm Hg) dropped to approximately 75 % of its initial value, while pO 2 (vitr) (baseline: 26 +/- 8 mm Hg) increased by 15 +/- 8 %.
  
  
  CONCLUSIONS
  Hemodilution leads to an increase of pO 2 (vitr) reflecting a similar rise of the ONH tissue pO 2. This effect results from an enhanced blood perfusion of the ONH, which over-compensates the decrease of the blood O 2 content.
authors.affiliation: Laboratoire d'Optique et de Biophysique, Institut de Recherche en Ophtalmologie, Sion, Switzerland.
authors.forename: Stéphane R
authors.initials: SR
authors.lastname: Chamot
authors.forename: Benno L
authors.initials: BL
authors.lastname: Petrig
authors.forename: Constantin J
authors.initials: CJ
authors.lastname: Pournaras
authors.forename: Charles E
authors.initials: CE
authors.lastname: Riva
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D006438:Hemodilution / Q000379:methods*; D006895:Hydroxyethyl Starch Derivatives / Q000494:pharmacology; D017078:Laser-Doppler Flowmetry; D009898:Optic Disk / Q000098:blood supply*; D010101:Oxygen Consumption / Q000502:physiology*; D013556:Swine, Miniature; D014822:Vitreous Body / Q000098:blood supply
chemical_list: D006895:Hydroxyethyl Starch Derivatives