Effects of 2.8-GHz microwaves on restrained and ketamine-anesthetized rats

To compare the effects of ketamine anesthesia and mild restraint on microwave-induced thermal and cardiovascular changes, sixteen Fischer 344 rats were irradiated in two states: 1) unanesthetized, restrained, and 2) ketamine-anesthetized (150 mg/kg, I.M.). Individual animals were exposed in H orientation to far-field continuous-wave 2.8-GHz microwaves. Irradiation was conducted at a power density of 60 mW/cm2 (whole-body average specific absorption rate of 14.4 W/kg) to cyclicly increase colonic temperature from 38.5 to 39.5 degrees C. Colonic and subcutaneous temperatures, aortic blood pressure, and heart rate were continuously monitored. The time required for colonic temperature to increase 1 degree C was significantly longer in the anesthetized state; however, the time to return to baseline was similar under both conditions. Heart rate and blood pressure significantly increased during irradiation in the unanesthetized state, but remained virtually unchanged in the anesthetized state. The subcutaneous temperature increase during exposure was significantly greater in the anesthetized state. The differences in responses of anesthetized and mildly restrained animals should be considered when conducting experiments on thermoregulatory responses to microwave irradiation.