The effect of rate of heating or cooling prior to heating on tumor and normal tissue microcirculatory blood flow.

Single vessel responses to hyperthermia were studied in tumor and normal tissues using a transparent access window chamber. Rates of heating less than or equal to .68 degrees C/minute preserved relatively better vascular function in normal than tumor tissue. A rate of heating of 1.0 degrees C/minute lowered normal tissue statis temperatures so they were no different from tumor. Cooling to 30 degrees C prior to heating slowed normal arteriolar flows to less than 5% of 38 degrees C controls. Heating resulted in increased flow in those vessels, but maximum flows never exceeded 5% of flows achieved in similar vessels which were not cooled first. The implications of this work are that rate of heating and cooling prior to heating can alter normal tissue vascular response to heat in a way that could prove deleterious to maintaining efficient vascular function in that tissue relative to tumor.