Thermal bradycardia during radiofrequency irradiation.

The present study was performed to determine if any heart rate or blood pressure changes occur during intermittent exposure to radiofrequency radiation (RFR), and to determine if parasympathetic blockade due to atropine has any effect on these changes or on thermal responses. Anesthetized rats were exposed to 2.8 GHz pulsed RFR at an average power level of 60 mW/cm2 (average specific absorption rate, 14 W/kg). During an initial exposure period to raise colonic temperature to 39.5 degrees C, heart rate decreased significantly. This thermal bradycardia is similar to that reported by other investigators during environmental heat exposure. Intermittent exposure to radiation, which was designed to result in 1 degree C colonic temperature changes, did not significantly affect heart rate or mean arterial blood pressure, before or after atropine administration. The time courses of these 1 degree C temperature changes were not altered significantly by atropine. Following administration of atropine, the thermal bradycardia during the initial heating period was still evident. Thus, factors other than vagal activity are responsible for the phenomenon. It is possible that the bradycardia is a consequence of a general reduction in metabolism, which occurs also during environmental heat exposure.