Cerebral blood flow response to the tissue temperature in tumour and brain tissues

The response of regional-cerebral blood flow (rCBF) to change in the tissue temperature was studied using normal and tumour-bearing monkeys. The local brain was selectively heated by the external microwave irradiation, while the body was kept hypothermic (30.1 +/- 0.1 degrees C, mean +/- standard error) by immersion in a cold water bath. The rCBF in brain and/or tumour tissues was sequentially measured by inhalation hydrogen clearance method. In the normal animal study (n = 7), rCBF changed in response to the tissue temperatures over a range of 29.4-40.7 degrees C with a constant rate 15.2% per degree Celsius change. Similarly, rCBF in the tumour-bearing animals (n = 7) changed proportionately with change in the tissue temperatures over a range of 28.4-42.5 degrees C in tumour and 27.6-41.8 degrees C in brain tissue. The rate in rCBF change per degree Celsius was 6.5% for tumour, which was significantly smaller than that for brain tissue (13.5%) (P less than 0.01). These results indicated that rCBF can be controlled by the defined application of selective heating with temperatures ranging from shallow hypothermia to modest hyperthermia. Vascular response to temperatures in the tumour and brain tissues may play a significant role in the application of heat to brain tumour treatment.