HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 291/2/H581    most recent 01279.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (8) Citing Articles via Google Scholar Google Scholar Articles by Cabrales, P. Articles by Tsai, A. G. Search for Related Content PubMed PubMed Citation Articles by Cabrales, P. Articles by Tsai, A. G.

Blood viscosity maintains microvascular conditions during normovolemic anemia independent of blood oxygen-carrying capacity

¹La Jolla Bioengineering Institute; and ²Department of Bioengineering, University of California, San Diego, La Jolla, California

Submitted 5 December 2005 ; accepted in final form 23 February 2006

Responses to exchange transfusion with red blood cells (RBCs) containing methemoglobin (MetRBC) were studied in an acute isovolemic hemodiluted hamster window chamber model to determine whether oxygen content participates in the regulation of systemic and microvascular conditions during extreme hemodilution. Two isovolemic hemodilution steps were performed with 6% dextran 70 kDa (Dex70) until systemic hematocrit (Hct) was reduced to 18% (Level 2). A third-step hemodilution reduced the functional Hct to 75% of baseline by using either a plasma expander (Dex70) or blood adjusted to 18% Hct with all MetRBCs. In vivo functional capillary density (FCD), microvascular perfusion, and oxygen distribution in microvascular networks were measured by noninvasive methods. Methylene blue was administered intravenously to reduce methemoglobin (rRBC), which increased oxygen content with no change in Hct or viscosity from MetRBC. Final blood viscosities after the entire protocol were 2.1 cP for Dex70 and 2.8 cP for MetRBC (baseline, 4.2 cP). MetRBC had a greater mean arterial pressure (MAP) than did Dex70. FCD was substantially higher for MetRBC [82 (SD 6) of baseline] versus Dex70 [38 (SD 10) of baseline], and reduction of methemoglobin to oxyhemoglobin did not change FCD [84% (SD 5) of baseline]. PO₂ levels measured with palladium-meso-tetra(4-carboxyphenyl)porphyrin phosphorescence were significantly changed for Dex70 and MetRBC compared with Level 2 (Hct 18%). Reduction of methemoglobin to oxyhemoglobin partially restored PO₂ to Level 2. Wall shear rate and wall shear stress decreased in arterioles and venules for Dex70 and did not change for MetRBC or rRBC. Increased MAP and shear stress-mediated factors could be the possible mechanisms that improved perfusion flow and FCD after exchange for MetRBC. Thus the fall in systemic and microvascular conditions during extreme hemodilution with low-viscosity plasma expanders seems to be, in part, from the decrease in blood viscosity independent of the reduction in oxygen content.

microcirculation; extreme hemodilution; plasma expander; intravascular oxygen; methemoglobin; methylene blue; functional capillary density

This article has been cited by other articles:

				B. Y. Salazar Vazquez, P. Cabrales, A. G. Tsai, P. C. Johnson, and M. Intaglietta Lowering of Blood Pressure by Increasing Hematocrit with Non Nitric Oxide Scavenging Red Blood Cells Am. J. Respir. Cell Mol. Biol., February 1, 2008; 38(2): 135 - 142. [Abstract] [Full Text] [PDF]

				P. Cabrales and A. G. Tsai Plasma viscosity regulates systemic and microvascular perfusion during acute extreme anemic conditions Am J Physiol Heart Circ Physiol, November 1, 2006; 291(5): H2445 - H2452. [Abstract] [Full Text] [PDF]