Intrinsic Metabolic Regulation of Blood Flow, O2 Extraction and Tissue O2 Delivery in Dog Skeletal Muscle
In a recent systems analysis of intrinsic microvascular control of tissue oxygen deliveryl, we proposed that O2 delivery to skeletal muscle cells was autoregulated in accordance with their metabolic requirements through local metabolic control of blood flow and O2 extraction. We also suggested that blood flow is regulated through feedback regulation of arteriolar tone, and O2 extraction is modulated through precapillary sphincter control of capillary surface area and capillary-to-cell diffusion distance. Our analysis, which includes as a major feature the assumption that precapillary sphincter sensitivity to metabolic control is greater than that of the arterioles, suggests that: 1) When the venous oxygen reserve is large, increased extraction is the major mechanism by which tissue oxygen delivery is maintained in accordance with cellular requirements, whenever the O2 availability-to-demand ratio is reduced. Under these conditions, the contribution of local flow regulation is minimal. 2) As the prevailing venous oxygen reserve decreases, the contribution of the arteriolar flow control system increases and the importance of the precapillary sphincter control of O2 extraction diminishes. Indeed, at a venous oxygen saturation of 25 per cent, blood flow responses account for over 90 per cent of the total compensation. 3) Thus, as metabolic stresses become greater, the major locus of intrinsic microvascular control of tissue oxygen delivery moves from the normally more sensitive sphincters to the upstream arterioles. In this manner, adequate tissue oxygenation is maintained over a wide range of metabolic stresses, the relative contribution of blood flow and O2 extraction to the regulation of tissue oxygen delivery being determined by the prevailing venous oxygen level. The data presented in this paper represent the experimental basis of our analysis.
KeywordsSkeletal Muscle Cell Total Compensation Blood Flow Response Oxygen Difference Step Decrease
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