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The changes of microregional perfusion in a hamster cheek pouch membrane were investigated. The vessel network of the membrane was visualized by preparing a transparent chamber, which was heated with circulating water at 42 degree C. Blood perfusion was monitored by using a laser Doppler flowmeter (LDF), which was used either in a conventional way by positioning the probe stationary or in a novel way by constantly moving the probe over the surface of the chamber (scanning). When a segment of tissue was subjected to the LDF scanning, the profile of scanned LDF values was well correlated with the distribution of vessels. Therefore, this scanning technique was useful in localizing the probe in tissues with respect to vessels. Since the scanning can be repeated every other minute, this technique also offered continuous monitoring of tissue blood flow at multiple sites. Upon heating, different vessels individually responded to the first and second heatings followed by coolings, suggesting a heterogeneous heat response in the connective tissue of the hamster cheek pouch membrane. This scanning technique proved very useful in collecting information for the study of the heterogeneous nature of blood flow in normal and tumour tissues.

The occurrence of differential heating and differential thermal sensitivity between malignant tumors and normal tissues is thought to be due to limited heat dissipation and energy depletion in many solid tumors which in turn results from an inadequately functioning tumor microcirculation (Jain and Ward-Hartley 1984; Song 1984, 1991; Vaupel and Kallinowski 1987; Reinhold 1988; Vaupel et al. 1988a; Vaupel 1990). As a consequence of the latter pathophysiological condition, supply and drainage function are restricted in many solid tumors or, at least, in some tumor areas, thus creating a hostile metabolic microenvironment characterized by tissue hypoxia, acidosis, and energy depletion. Thermal sensitivity has been shown to depend greatly on tumor pH, and on energy and nutritional status of the tumors treated. Although no conclusive evidence is so far available concerning the ranking of these pivotal factors, there is no doubt that the rate and homogeneity of blood perfusion plays a paramount role in determining the metabolic and energy status.