Broadening of the RF Power-Density Window for Calcium-ion Efflux from Brain Tissue

Blackman et al. [1], [2] have reported enhanced efflux of calcium ions from chicken forebrains, exposed in vitro in a 50 ¿stripline to 147 MHz radiation, modulated sinusoidally at 16 Hz. When the spacing between the sample tubes was 3.8 cm on center, enhancement occurred at an incident power density of 0.83 mW/cm2, but not at 0.11, 0.5S, 1.11, or 1.38 mW/cm2. When the spacing between sample tubes was reduced to 1.9 cm, significant enhanced efflux was observed at incident power densities of 0.55, 0.83, 1.11, and 1.38 mW/cm2. This broadening of the effective power-density range is explained herein by calculations which show that the more closely spaced samples interact electrically in a way that both lowers and broadens the range of spatial variation-of absorbed power density (MW/cm3) within the sample for a given incident power density (mW/cm2). Electrical coupling among the samples allows several different values of incident power to yield exactly the same value of power absorbed at given points within the brain sample. Because the absorbed power density must be directly related to the power that interacts with the brain to enhance the efflux of calcium ions, the electromagnetic conditions for efflux enhancement in coupled and uncoupled brains are the same if the absorbed power density is the same. Ranges of absorbed power density are identified that could be effective in enhancing the efflux of calcium ions from the brain tissue.