Comparison of dose dependences for bioeffects of continuous‐wave and high‐peak power microwave emissions using gel‐suspended cell cultures†

Abstract

The study compared bioeffects of continuous wave (CW) microwaves and short, extremely high power pulses (EHPP) at the same carrier frequency (9.3 GHz) and average power (1.25 W). The peak transmitted power for EHPP was 250 kW (0.5-micro s pulse width, 10 p.p.s.), producing the E field of 1.57 MV/m in the waveguide. A biological endpoint was the density of yeast cells, achieved after a 6 h growth period in a solid nutrient medium (agarose gel) during EHPP or CW exposure. Owing to power losses in the medium, the specific absorption rate (SAR) ranged from 3.2 kW/kg at the exposed surface of the sample to 0.6 mW/kg at 24 mm depth. Absorption and penetration of EHPP was identical to CW, producing peak SAR values 200 000 times higher than the average SAR, as high as 650 MW/kg at the surface. CW and EHPP exposures produced highly nonuniform but identical heating patterns in exposed samples. Following the exposure, the samples were sliced in a plane perpendicular to the wave propagation, in order to separate cell masses exposed at different SAR levels. Cell density in the slices was determined by nephelometry and compared to unexposed parallel control samples. Cell density was strongly affected by irradiation, and the changes correlated well with the local temperature rise. However, the data revealed no statistically significant difference between CW and EHPP samples across the entire studied range of SAR levels (over six orders of magnitude). A trend (P<0.1) for such a difference was observed in slices that were exposed at a time average SAR of 100 W/kg and higher, which corresponded to peak SAR above 20 MW/kg for the EHPP condition. These numbers could be indicative of a threshold for a specific (not merely thermal) exposure effect if the trend is confirmed by future studies.

Effects of high power microwave pulses on synaptic transmission and long term potentiation in hippocampus

“…This conclusion is consistent with our previous studies in isolated frog heart slices and yeast cells [Pakhomov et al, 1999[Pakhomov et al, , 2000b[Pakhomov et al, , 2002, but contrasts positive findings of other authors [Deviatkov et al, 1994[Deviatkov et al, , 1998Tambiev et al, 1989;Bolshakov et al, 2000a,b]. Coincidentally, all these ''positive effect'' studies tested the same carrier frequency and the same pulse duration (10 GHz and 10 ns).…”

“…Our previous studies explored EHPP effects in isolated, spontaneously beating frog heart slices [Pakhomov et al, 1999[Pakhomov et al, , 2000b and in gel suspended yeast cells [Pakhomov et al, 2002]. All observed effects were consistent with the thermal paradigm and provided no proof of EHPP-specific effects.…”

“…Microwave exposures were performed essentially the same way as described before [Pakhomov et al, 2002]. EHPP were generated by a model 337X magnetron transmitter (Applied Systems Engineering, Inc.) with the peak output of 230-260 kW.…”

Review of possible modulation‐dependent biological effects of radiofrequency fields

“…The scope of the review was limited to modulations used in telecommunications. The well-established auditory responses [Elder and Chou, 2003] and other biological effects from pulsed microwaves with high peak power [e.g., Pakhomov et al, 2000Pakhomov et al, , 2002Pakhomov et al, , 2003 were not reviewed.…”

Cellular effects of acute exposure to high peak power microwave systems: Morphology and toxicology

“…Studies using cell preparations to investigate effects of pulsed microwaves have also been conducted. No deleterious effect was seen in yeast exposed to 9.2 GHz microwaves at roughly 1.67 MV/m in the sample [Pakhomov et al, ]. In other experiments in the same laboratory and at the same frequency, changes seen in spontaneous contractions of frog heart slices exposed to pulsed or continuous wave exposure were attributed to tissue heating [Pakhomov et al, ,, ].…”