Microvascular thermal equilibration in rat spinotrapezius muscle

The current study investigates heat exchange in the thermally significant countercurrent paired vessels of the rat spinotrapezius muscle. Detailed tissue surface temperatures under normal (after the microvascular surgery) and pharmacologically vasodilated states were measured using high-resolution infrared thermography. During vasodilation, a measurable thermal disturbance was observed above the first-order feeding vessel pair. The measured tissue temperatures were compared with those predicted by modifying the theoretical model for two-dimensional muscle preparations given by Zhu et al. (Zhu, L., D. E. Lemons, and S. Weinbaum. Ann. Biomed. Eng. 24:109-123, 1996). They were found in good agreement. The Weinbaum-Jiji k(eff) theory (Weinbaum, S., and L. M. Jiji. J. Biomech. Eng. 107:131-139, 1985) for heat exchange between the paired vessels and their surrounding tissue was also examined in this muscle. A close agreement was obtained between the theoretically predicted k(eff) and the measured value calculated using a fin approximation for the tissue layer. This experimental study revealed for the first time the nonequilibration between blood vessels and the surrounding tissue, where the enhancement in k(eff) due to the incomplete countercurrent heat exchange is comparable to the tissue axial conduction.