title: Physiological factors in hyperthermia.
abstract: The blood flow in normal tissues, i.e., skin and muscle, increases remarkably when heated at temperatures commonly used in hyperthermia (42 degrees -45 degrees C), whereas that in tumor appears to increase slightly when heated at temperatures below 41 degrees -42 degrees C but drastically decreases at temperatures above 42 degrees C. Histopathological studies of the heated tumors demonstrated a pronounced hyperemia, vascular occlusion, and hemorrhage. Due to the vascular occlusion, the dissipation of heat in the tumors becomes inefficient, and the temperatures in the tumor rise higher than those in normal tissues during hyperthermia at temperatures above 42 degrees C. The pH in tumors significantly decreases upon heating. The acidic conditions in the tumors enhances the thermal killing of tumor cells and inhibits the repair of thermal damage and development of tolerance to heat. The mechanism of the decrease in blood flow and pH in the heated tumors is not clear, but these two phenomena seem closely related. The preferential effect of hyperthermia on tumors may be attributed to the higher temperature relative to normal tissue temperature during heating and also to the decrease in the pH upon heating.
mesh_terms: D000818:Animals; D001810:Blood Volume; D002279:Carcinoma 256, Walker / Q000098:blood supply / Q000628:therapy; D006224:Cricetinae; D005260:Female; D006358:Hot Temperature / Q000627:therapeutic use*; D006863:Hydrogen-Ion Concentration; D008325:Mammary Neoplasms, Experimental / Q000098:blood supply / Q000628:therapy; D051379:Mice; D009374:Neoplasms, Experimental / Q000098:blood supply* / Q000628:therapy; D051381:Rats; D011919:Rats, Inbred Strains; D012039:Regional Blood Flow; D012517:Sarcoma, Yoshida / Q000098:blood supply / Q000628:therapy