The pharmacologic manipulation of blood flow in hyperthermia therapy

Many human tumors treated by hyperthermia do not reach therapeutic temperatures (42 degrees C). The explanation for this difference may be that some tumors react to thermal stress in a manner similar to normal tissues; ie, they increase blood flow during hyperthermia in order to dissipate the heat. Higher temperatures might be achieved in these heat-resistant tumors by administering vasoconstrictive agents in an effort to reduce blood flow. In this preliminary study, we determined the extent to which pharmacologic inhibition of local blood flow might allow higher temperatures to develop in normal muscles exposed to localized radiofrequency hyperthermia. We found that the local muscle temperature rise could be increased by at least 90% in two dogs and six rabbits with the use of a local vasoconstrictive drug.