To compare the effects of ketamine anesthesia and mild restraint on microwave-induced thermal and cardiovascular changes, rats were irradiated in two states: 1) unanesthetized, restrained, and 2) ketamine-anesthetized (150 mg/kg).
|Distance between exposed object and exposure source||150 cm|
|Chamber||The Eccosorb RF-shielded anechoic chamber was maintained at 27 ± 0.5°C and 20 ± 5% humidity.|
|Setup||A rat was restrained in a vented Plexiglas cage and placed within the exposure chamber on a stand made of 2-inch thick high density Styrofoam. The rat was positioned along the boresight and exposed in H-orientation (left lateral exposure, long axis of the body parallel to the magnetic field).|
|Additional info||The exposure was interrupted when the colonic temperature had increased from 37.8 ± 0.2°C to 39.5°C, and it was resumed when the temperature had returned to 38.5°C. This procedure was repeated for three cycles after which anaesthesia was provided by an i.m. injection of ketamine. After 10 to 15 min and the start sequence, three additional cycles were completed. Four animal carcasses were irradiated for one additional cycle immediately after euthanasia. The rise and recovery times were 4.1 ± 0.2 min and 12.7 ± 0.9 min for unanaesthetized animals, 7.1 ± 0.4 min and 14.3 ± 0.7 min for anaesthetized animals, and 10.6 ± 1.0 min and 10.7 ± 0.1 min for dead animals, respectively.|
The time required for colonic temperature to increase 1°C was significantly longer in the anesthetized animals; however, the time to return to baseline was similar under both conditions. Heart rate and blood pressure significantly increased during exposure in the unanesthetized state, but remained virtually unchanged in the anesthetized state. The subcutaneous temperature increase during irradiation was significantly greater in the anesthetized state.
The differences in responses of anesthetized and mildly restrained rats should be considered when conducting studies on thermoregulatory responses to microwave exposure.