Comparative effects of extremely high power microwave pulses and a brief CW irradiation on pacemaker function in isolated frog heart slices

The existence of specific bioeffects due to high peak power microwaves and their potential health hazards are among the most debated but least explore d problems in microwave biology. The present study attempted to reveal such effects by comparing the bioeffects of short trains of extremely high powe r microwave pulses (EHPP, 1 mu s width, 250-350 kW/g, 9.2 GHz) with those o f relatively low power pulses (LPP, 0.5-10 s width, 3-30 W/g, 9.2 GHz). EHP P train duration and average power were made equal to those of an LPP; ther efore both exposure modalities produced the same temperature rise. Bioeffec ts were studied in isolated, spontaneously bearing slices of the frog heart . In most cases, a single EHPP train or LPP immediately decreased the inter -beat interval (IBI). The effect was proportional to microwave heating, ful ly reversible, and easily reproducible. The magnitude and time course of EH PP- acid LPP-induced changes always were the same. No delayed or irreversib le effects of irradiation were observed. The same effect could be repeated in a single preparation numerous times with no signs of adaptation, sensiti zation, lasting functional alteration, or damage. A qualitatively different effect, namely, a temporary arrest of preparation beats, could be observed when microwave heating exceeded physiologically tolerable limits. This eff ect also did not depend on whether the critical temperature rise was produc ed by LPP or EHPP exposure. Within the studied limits, we found no indicati ons of EHPP-specific bioeffects. EHPP- and LPP-induced changes in the pacem aker rhythm of isolated frog heart preparation were identical and could be entirely attributed to microwave heating. (C) 2000 Wiley-Liss, Inc.