In recent years, hyperthermia has been used to treat malignant tumors, and attempts have been made to improve its therapeutic efficacy. However, since the highest temperature currently used in whole clinical body hyperthermia is around 42°C, its therapeutic efficacy still remains less than satisfactory. Generally, the safety limit for the highest temperature for the body is thought to be around 42°C. However, the critical temperature for cell lethality is considered to be around 43°C, and cell lethality is remarkably increased by elevating temperatures above 43°C. Rapid tumor cell killing can be achieved by maintaining the body temperature at 43°C for 90 mintues.
In our present experiment, 5 Japamese monkeys were kept under hyperthermia maintained at 43°C for 90 minutes. After the experiment, 4 monkeys survived, and no abnormal findings were noted. Systolic arterial pressure was significantly elevated as the body temperature rose to 42°C and declined somewhat aftef reaching 43°C. Thereafter systolic pressure remained at 110-123 mmHg. The heart rate increased with rising body temperature and remained the highest when the temperature was at 43°C for 90 min. With normalization of the temperature, the heart rate dropped to 170 beats/min, but was still higher than the preheating level. According to a blood gas analysis, PaO2 was persistency elevated above 400 mmHg during hyperthermia. In serum electrolytes, the K ion was elevated during hyperthermia then declined below the preheating level after normalization of the temperature.
Although there are species differences between man an monkey, our results suggest potential clinical applications for hyperthermia at 43°C, which will contribute to a dramatic increase in its therapeutic efficacy.
