Theory and Experiment for the Effect of Vascular Microstructure on Surface Tissue Heat Transfer—Part I: Anatomical Foundation and Model Conceptualization

Abstract

A new theoretical model supported by ultrastructural studies and high-spatial resolution temperature measurements is presented for surface tissue heat transfer in a two-part study. In this first paper, vascular casts of the rabbit thigh prepared by the tissue clearance method were serially sectioned parallel to the skin surface to determine the detailed variation of the vascular geometry as a function of tissue depth. Simple quantitative models of the basic vascular structures observed were then analyzed in terms of their characteristic thermal relaxation lengths and a new three-layer conceptual model proposed for surface tissue heat transfer. Fine wire temperature measurements with an 80-micron average diameter thermocouple junction and spatial increments of 20 micrometers between measurement sites have shown for the first time the detailed temperature fluctuations in the microvasculature and have confirmed the fundamental assumptions of the proposed three-layer model for the deep tissue, skeletal muscle and cutaneous layers.

UTCI-Fiala multi-node model of human heat transfer and temperature regulation

“…Body elements are built of annular concentric tissue layers (section A-A″ in Figure 1) : brain, lung, bones, muscles, viscera, fat, and skin (Fiala et al 1999) and subdivided into a total of 63 spatial sectors (Table 1). Skin is modelled as two layers (Weinbaum et al 1984): cutaneous plexus, i.e. blood-perfused inner layer; and outer skin which contains sweat glands but no thermally significant blood vessels.…”

Modelling of temperature and perfusion during scalp cooling

“…In the outer layer, the blood temperature T A is equal to the local tissue temperature T (Weinbaum et al 1984), eliminating the perfusion term in (1). This is modelled by setting perfusion w b for the outer skin to zero.…”

“…Since anatomical differences in blood vessels in the skin affect heat transfer (Weinbaum et al 1984), the skin was modelled with two layers, an inner and an outer skin layer. In the outer layer, the blood temperature T A is equal to the local tissue temperature T (Weinbaum et al 1984), eliminating the perfusion term in (1).…”

Ultrasound–biophysics mechanisms

“…Even though the bioheat transfer equation has shortcomings (Weinbaum et al, 1984), it is easy to implement analytically and is perhaps the most widely used thermal model of living tissue. Analyses based on the bioheat transfer equation (NCRP, 1983;Curley, 1993) were used to develop some of the ODS's thermal indices (ODS, 2004).…”