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A New Simplified Bioheat Equation for the Effect of Blood Flow on Local Average Tissue Temperature
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1985
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Recent studies have shown that the isotropic blood perfusion term in the classic bioheat equation is negligible due to microvascular organization, and that incomplete countercurrent exchange in thermally significant microvessels is the primary mechanism for blood‑tissue energy transfer. The authors aim to derive a simplified three‑dimensional bioheat equation that captures the effect of blood flow on blood‑tissue heat transfer. They formulate a tensor conductivity expression that depends on local vascular geometry and flow velocity in countercurrent vessels, yielding a compact bioheat equation that incorporates this mechanism. The resulting model predicts that tissue behaves as an anisotropic heat‑transfer medium and that directed perfusion between countercurrent vessels markedly influences heat transfer in vessels smaller than 70 µm.
A new simplified three-dimensional bioheat equation is derived to describe the effect of blood flow on blood-tissue heat transfer. In two recent theoretical and experimental studies [1, 2] the authors have demonstrated that the so-called isotropic blood perfusion term in the existing bioheat equation is negligible because of the microvascular organization, and that the primary mechanism for blood-tissue energy exchange is incomplete countercurrent exchange in the thermally significant microvessels. The new theory to describe this basic mechanism shows that the vascularization of tissue causes it to behave as an anisotropic heat transfer medium. A remarkably simple expression is derived for the tensor conductivity of the tissue as a function of the local vascular geometry and flow velocity in the thermally significant countercurrent vessels. It is also shown that directed as opposed to isotropic blood perfusion between the countercurrent vessels can have a significant influence on heat transfer in regions where the countercurrent vessels are under 70-μm diameter. The new bioheat equation also describes this mechanism.