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1La Jolla Bioengineering Institute, and 2Department of Bioengineering, University of California-San Diego, La Jolla, California
Submitted 27 June 2005 ; accepted in final form 26 December 2005
The rate of oxygen release from arterioles (
55 µm diameter) was measured in the hamster window chamber model during flow and no-flow conditions. Flow was stopped by microvascular transcutaneous occlusion using a glass pipette held by a manipulator. The reduction of the intra-arteriolar oxygen tension (PO2) was measured by the phosphorescence quenching of preinfused Pd-porphyrin, 100 µm downstream from the occlusion. Oxygen release from arterioles was found to be 53% greater during flow than no-flow conditions (2.6 vs. 1.7 x 10–5 ml O2·cm–2·s–1, P < 0.05). Acute hemodilution with dextran 70 was used to reduce vessel oxygen content, significantly increase wall shear stress (14%, P < 0.05), reduce Hct to 28.4% (SD 1.0) [vs. 48.8% (SD 1.8) at baseline], lower oxygen supply by the arterioles (10%, P < 0.05), and increase oxygen release from the arterioles (39%, P < 0.05). Hemodilution also increased microcirculation oxygen extraction (33% greater than nonhemodilution, P < 0.05) and oxygen consumption by the vessel wall, as shown by an increase in vessel wall oxygen gradient [difference in PO2 between the blood and the tissue side of the arteriolar wall, nonhemodiluted 16.2 Torr (SD 1.0) vs. hemodiluted 18.3 Torr (SD 1.4), P < 0.05]. Oxygen released by the arterioles during flow vs. nonflow was increased significantly after hemodilution (3.6 vs. 1.8 x 10–5 ml O2·cm–2·s–1, P < 0.05). The oxygen cost induced by wall shear stress, suggested by our findings, may be >15% of the total oxygen delivery to tissues by arterioles during flow in this preparation.
oxygen consumption; occlusion; wall shear stress; arteriolar oxygen exit
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