Physiological Effects of Hyperthermia

For an efficient application of hyperthermia to tumours, the intensity of the tumour circulation is of utmost importance. Generally, it is assumed that the tumour microcirculation is inferior to that in healthy tissues. This certainly holds if the criterion for comparison is the morphological vascular architecture. There is overwelming evidence, derived using morphological as well as angiographic methods, that the tumour circulation is plainly chaotic. This holds for human tumours as well as for experimental tumours, regardless of the method of investigation used. However, a chaotic vascular pattern in tumours does not per se imply that the blood circulation in the tumours is inferior to, or lower than, the normal tissues in which the tumour grows. Obviously the differences in blood flow between tumour and normal tissue depend upon the tumour and the normal tissue concerned. With regard to the tumours, not only the type of tumour is of importance, but also its size and the site of growth. On the other hand, normal tissue blood flow depends not only on the tissue type, but, for many tissues, also very much on the physiological conditions. In contrast to tumours, many normal tissues can adapt easily to changing demands. In many tissues, such as muscle, fat, skin and intestine, there may be 10- to 30-fold differences, depending upon the conditions. Thus, if one compares the blood flow rate in a tumour, e.g. mammary carcinoma, with that in certain surrounding tissues under normal conditions, e.g. cool skin at 34° C, the circulation in the tumour may appear to be higher than in the normal tissue. However, under conditions of heating this relationship may change considerably. This will be discussed below.