Microcirculatory Function, Tissue Oxygenation, Microregional Redox Status and ATP Distribution in Tumors Upon Localized Infrared-A-Hyperthermia at 42°C

Abstract

Since local hyperthermia (HT) affects microenvironmental parameters, the aim of the study was to analyze the impact of 42°C-HT on microcirculatory function, tumor pO₂, microregional redox status and ATP distribution in experimental rat tumors. Subcutaneously growing DS-sarcomas were treated with localized HT using infrared-A radiation resulting in a mean tumor temperature of 42°C. The relative red blood cell (RBC) flux in the tumor was assessed using the laser Doppler technique and the mean tumor pO₂ measured continuously using O₂-sensitive catheter electrodes. In a second series of experiments, the microregional distribution of the mitochondrial redox status and ATP concentration was measured. Although the average RBC flux increased by 63%, tumor pO₂ rose only by approx. 6%. No distinct changes were seen in the mitochondrial redox status. The microregional distribution of the redox status as well as of the ATP concentration showed considerable heterogeneity. In conclusion, although 42°C-HT leads to a distinct improvement in tumor perfusion, there is practically no change in the oxygenation status. The latter finding can be explained by an equivalent increase in the oxygen consumption rate of the cells which increases by approx. 58% at 42°C compared to normothermia.