Effect of hemodilution on cochlear blood flow measured by laser-Doppler flowmetry.

The effect of hemodilution on cochlear blood flow was studied in guinea pigs. Hypervolemic hemodilution was accomplished by infusion of 10 mg/kg of body weight of dextran 40 (as a 10% solution in normal saline), which resulted in an average hematocrit decrease from 43 to 32%. Normovolemic hemodilution was accomplished by repeated exchange of 3 ml of whole blood with 3 ml of dextran 75 (6% solution in normal saline) every 5 minutes until the hematocrit reached approximately 5%. The cochlear blood flow was measured by laser-Doppler flowmetry. Irrespective of the dilutional technique, the cochlear blood flow increased as hematocrit decreased to a maximum of approximately 200% of original value at a hematocrit near 20%. The blood pressure was not significantly influenced by the hemodilution until hematocrit values below 15% were reached. The enhancement of cochlear blood flow is consistent with the expected reduction of blood viscosity and increase of cardiac output. Normovolemic hemodilution with dextran 75 causes a smaller disturbance of systemic circulation physiology and has a more lasting effect than dextran 40 infusion.