Effect of isovolumic hemodilution on oxygen delivery to the optic nerve head.
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.
Chamot
Stéphane R
SR
Laboratoire d'Optique et de Biophysique, Institut de Recherche en Ophtalmologie, Sion, Switzerland.
Petrig
Benno L
BL
Pournaras
Constantin J
CJ
Riva
Charles E
CE
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
D006895:Hydroxyethyl Starch Derivatives