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1 Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA
2 Universite de Technologie de Compiegne, Compiegne Cedex, France
3 Instituto Mexicano del Seguro Social, Centro Medico Siglo XXI, Mexico D.F., Mexico
4 La Jolla Bioengineering Institute, La Jolla, CA, USA
5 Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA; La Jolla Bioengineering Institute, La Jolla, CA, USA
* To whom correspondence should be addressed. E-mail: jmartini{at}bioeng.ucsd.edu.
Hematocrit (Hct) of awake hamsters and CD-1 mice was acutely increased by isovolemic exchange transfusion of packed red blood cells (RBCs) to assess the relation between Hct and blood pressure. Increasing Hct 7 - 13% of baseline decreased mean arterial blood pressure (MAP) by 13 mmHg. Increasing Hct above 19% reversed this trend and caused MAP to rise above baseline. This relationship is described by a parabolic function (R2 = 0.57 and P < 0.05). Hamsters pre-treated with the nitric oxide (NO) synthase inhibitor L-NAME and endothelial NO synthase deficient mice showed no change in MAP when Hct was increased by less than 19%. Nitrate/nitrite (NOx) plasma levels of Hct augmented hamsters increased relative to control and L-NAME treated animals. The blood pressure effect was stable 2 hours after exchange transfusion. These findings suggest that increasing Hct increases blood viscosity, shear stress and NO production, leading to vasodilation and mild hypotension. This was corroborated by measuring A1 arteriolar diameters (55.0 ± 21.5 µm) and blood flow in the hamster window chamber preparation, which showed statistically significant increased vessel diameter (1.04 ± 0.1 relative to baseline) and microcirculatory blood flow (1.39 ± 0.68 relative to baseline) after exchange transfusion with packed RBCs. Larger increases of Hct (> 19% of baseline) led blood viscosity to increase > 50%, overwhelming the NO effect through a significant viscosity dependent increase in vascular resistance, causing MAP to rise above baseline values.
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