Monitoring Variations of Biological Impedances at Microwave Frequencies

Two interferometer systems for monitoring time-varying biological impedances at 915 MHz and 913 GHz were developed. The systems compare the phase of the signal scattered from a region of biological tissue to that of a reference signal, using a phase sensitive detector. The phase changes of the scattered signal are an indication of the net changes within the test region due to various physiological processes, for example, the displacements of blood vessels during the cardiac cycle. The systems were tested with simulation models and their detection characteristics were found to be a linear function of the phase changes for return losses within the test region as high as 60 dB. Because of the interference between the signal scattered from the test region and the signal reflected at the antenna-tissue interface, the maximum range of operation of the systems was limited to a fraction of a wavelength in the test medium. Copyrigh

Evaluating the biological effects of intermittent 1.9 GHz pulse-modulated radiofrequency fields in a series of human-derived cell lines

Several recent studies have suggested that radiofrequency (RF) fields may cause changes in a variety of cellular functions that may eventually lead to potential long-term health effects. In the present study, we have assessed the ability of non-thermal RF-field exposure to affect a variety of biological processes (including apoptosis, cell cycle progression, viability and cytokine production) in a series of human-derived cell lines (TK6, HL60 and Mono-Mac-6). Exponentially growing cells were exposed to intermittent (5 min on, 10 min off) 1.9 GHz pulse-modulated RF fields for 6 h at mean specific absorption rates (SARs) of 0, 1 and 10 W/kg. Concurrent negative (incubator) and positive (heat shock for 1 h at 43°C) controls were included in each experiment. Immediately after the 6-h exposure period and 18 h after exposure, cell pellets were collected and analyzed for cell viability, the incidence of apoptosis, and alterations in cell cycle kinetics. The cell culture supernatants were assessed for the presence of a series of human inflammatory cytokines (TNFA, IL1B, IL6, IL8, IL10, IL12) using a cytometric bead array assay. No detectable changes in cell viability, cell cycle kinetics, incidence of apoptosis, or cytokine expression were observed in any of RF-field-exposed groups in any of the cell lines tested, relative to the sham controls. However, the positive (heat-shock) control samples displayed a significant decrease in cell viability, increase in apoptosis, and alteration in cell cycle kinetics (G2/M block). Overall, we found no evidence that non-thermal RF-field exposure could elicit any detectable biological effect in three human-derived cell lines