[Selective Heating of Membrane-forming Holes in Teflon Film Exposed to Decimeter Waves].

Calculations of heating of membrane-forming holes in Teflon film exposed to decimeter waves were performed. The dependence of the temperature increment in holes on the geometry of holes, electrolyte concentration, and decimeter wave frequency was studied. The kinetics of heating depending on the hole diameter was also obtained. It was concluded that the observed in the experiment effects of the decimeter wave on bilayer lipid membranes resulted from the elevated concentration of decimeter electromagnetic waves in membrane-forming hole that led to selective heating of electrolyte in hole and bilayer lipid membranes.

[Frequency dependence of heating of human skin exposed to millimeter waves].

In this paper we studied experimentally the frequency dependence of heating of human skin exposed to millimeter waves. Theoretical modeling of obtained data was performed using the hybrid bio-heat equation. It was found that the skin heating and SAR increased with increasing the exposure frequency. The frequency dependence of heating was entirely resulted from that of reflection from the skin. Unlike temperature, the frequency dependence of the SAR was due to the increased absorption of millimeter wave energy within the thin surface layer of the skin.

[Problems of using a thermocouple for measurements of skin temperature rise during the exposure to millimeter waves].

The possibility of using thermocouples for the artifact-free measurements of skin temperature during millimeter wave exposure was studied. The distributions of the specific absorption rate (SAR) in the human skin were calculated for different orientations of the thermocouple relative to the E-field of exposure. It was shown that, at the parallel orientation of a thermocouple relative to the E-field, SAR significantly increased at the tip of the thermocouple. This can result in an overheating of the thermocouple. At the perpendicular orientation of a thermocouple, the distortions of the SAR were insignificant. The data obtained confirm that the skin temperature can be measured with a thermocouple during exposure under the condition that the thermocouple is located perpendicular to the E-vector of the electromagnetic field. For the accurate determination of SAR from the rate of the initial temperature rise, it is necessary to fit the temperature kinetics measured with the thermocouple to the solution of the bio-heat transfer equation.

[Effect of microwaves on bilayer lipid membranes: role of a membrane-forming hole in the Teflon film].

The distributions of specific abcorption rate (SAR) and E-field in a membrane-forming hole of Teflon film and surrounding electrolyte were calculated for 0.9 GHz exposure. It was found that the specific absorption rate in the membrane-forming hole increased greatly with increasing thickness of the Teflon film, and electrolyte concentration and decreasing diameter of the hole. The previously demonstrated significant changes in the conductivity of modified bilayer lipid membranes induced by microwave exposure can be explained by a local increase in specific absorption rate and subsequent elevation of temperature in the membrane-forming hole of the Teflon film.

Influence of blood flow and millimeter wave exposure on skin temperature in different thermal models.

Recently we showed that the Pennes bioheat transfer equation was not adequate to quantify mm wave heating of the skin at high blood flow rates. To do so, it is necessary to incorporate an "effective" thermal conductivity to obtain a hybrid bioheat equation (HBHE). The main aim of this study was to determine the relationship between non-specific tissue blood flow in a homogeneous unilayer model and dermal blood flow in multilayer models providing that the skin surface temperatures before and following mm wave exposure were the same. This knowledge could be used to develop multilayer models based on the fitting parameters obtained with the homogeneous tissue models. We tested four tissue models consisting of 1-4 layers and applied the one-dimensional steady-state HBHE. To understand the role of the epidermis in skin models we added to the one- and three-layer models an external thin epidermal layer with no blood flow. Only the combination of models containing the epidermal layer was appropriate for determination of the relationship between non-specific tissue and dermal blood flows giving the same skin surface temperatures. In this case we obtained a linear relationship between non-specific tissue and dermal blood flows. The presence of the fat layer resulted in the appearance of a significant temperature gradient between the dermis and muscle layer which increased with the fat layer thickness.

Millimeter wave reflectivity used for measurement of skin hydration with different moisturizers.

BACKGROUND/AIMS: A new non-invasive method for determining the free water content in human skin has been developed. The method analyzes the reflection of millimeter (mm) wavelength electromagnetic waves. The amount of reflection of mm waves depends on an electrical property (namely, the permittivity) of the skin, and this depends upon the free water content of the various skin layers. The aim of the present study was to use the mm wave reflectometry method for determination of free water content in healthy skin treated with different hydrating substances. METHODS: Skin lotion, pure water, glycerol, and petroleum jelly (an occlusive substance) were used for hydration of skin. The amount of free water was calculated using the permittivity values of skin layers found from fitting a three layer skin model to measured reflection data. The skin model consisted of (1) the stratum corneum (SC), (2) the viable epidermis plus the dermis, and (3) fat layers. RESULTS: Mm wave reflection was significantly affected by the water content of the thick SC of the palm but not by the very thin SC of the forearm. Treatment of the forearm and palm skin with different hydrating substances produced notable changes of the free water content in the SC, but not in the viable epidermis or dermis. The greatest hydration was produced by pure water and skin lotion, and the lowest by petroleum jelly. However, petroleum jelly produced prolonged retention of water in the SC following its hydration by other moisturizers. The content of free water was found to return to its baseline value after removal of moisturizers in as short a time as 8.3 min. CONCLUSION: The study shows that mm wave reflectometry can be used as a sensitive technique for the non-invasive determination of water content in living skin.

Reflection and penetration depth of millimeter waves in murine skin.

Millimeter (mm) wave reflectivity was used to determine murine skin permittivity. Reflection was measured in anesthetized Swiss Webster and SKH1-hairless mice in the 37-74 GHz frequency range. Two skin models were tested. Model 1 was a single homogeneous skin layer. Model 2 included four skin layers: (1) the stratum corneum, (2) the viable epidermis plus dermis, (3) fat layer, and (4) muscle which had infinite thickness. We accepted that the permittivity of skin in the mm wave frequency range results from the permittivity of cutaneous free water which is described by the Debye equation. Using Fresnel equations for reflection we determined the skin parameters best fitting to the reflection data and derived the permittivity of skin layers. The permittivity data were further used to calculate the power density and specific absorption rate profiles, and the penetration depth of mm waves in the skin. In both murine models, mm waves penetrate deep enough into tissue to reach muscle. In human skin, mm waves are mostly absorbed within the skin. Therefore, when extrapolating the effects of mm waves found in animals to humans, it is important to take into account the possible involvement of muscle in animal effects.

Millimeter wave dosimetry of human skin.

To identify the mechanisms of biological effects of mm waves it is important to develop accurate methods for evaluating absorption and penetration depth of mm waves in the epidermis and dermis. The main characteristics of mm wave skin dosimetry were calculated using a homogeneous unilayer model and two multilayer models of skin. These characteristics included reflection, power density (PD), penetration depth (delta), and specific absorption rate (SAR). The parameters of the models were found from fitting the models to the experimental data obtained from measurements of mm wave reflection from human skin. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. The thin SC produced little influence on the interaction of mm waves with skin. On the contrary, the thick SC in the palm played the role of a matching layer and significantly reduced reflection. In addition, the palmar skin manifested a broad peak in reflection within the 83-277 GHz range. The viable epidermis plus dermis, containing a large amount of free water, greatly attenuated mm wave energy. Therefore, the deeper fat layer had little effect on the PD and SAR profiles. We observed the appearance of a moderate SAR peak in the therapeutic frequency range (42-62 GHz) within the skin at a depth of 0.3-0.4 mm. Millimeter waves penetrate into the human skin deep enough (delta = 0.65 mm at 42 GHz) to affect most skin structures located in the epidermis and dermis.

Human skin permittivity determined by millimeter wave reflection measurements.

Millimeter wave reflection from the human skin was studied in the frequency range of 37-74 GHz in steps of 1 GHz. The forearm and palm data were used to model the skin with thin and thick stratum corneum (SC), respectively. To fit the reflection data, a homogeneous unilayer and three multilayer skin models were tested. Skin permittivity in the mm-wave frequency range resulted from the permittivity of cutaneous free water which was described by the Debye equation. The permittivity increment found from fitting to the experimental data was used for determination of the complex permittivity and water content of skin layers. Our approach, first tested in pure water and gelatin gels with different water contents, gave good agreement with literature data. The homogeneous skin model fitted the forearm data well. Permittivity of the forearm skin obtained with this model was close to the skin permittivity reported by others. To fit reflection from the palmar skin with a thick SC, a skin model containing at least two layers was required. Multilayer models provided better fitting to both the forearm and palmar skin reflection data. The fitting parameters obtained with different models were consistent with each other.

Effect of cyclophosphamide and 61.22 GHz millimeter waves on T-cell, B-cell, and macrophage functions.

The present study was undertaken to investigate whether millimeter waves (MMWs) at 61.22 GHz can modulate the effect of cyclophosphamide (CPA), an anti-cancer drug, on the immune functions of mice. During the exposure each mouse's nose was placed in front of the center of the antenna aperture (1.5 x 1.5 cm) of MMW generator. The device produced 61.22 +/- 0.2 GHz wave radiation. Spatial peak Specific Absorption Rate (SAR) at the skin surface and spatial peak incident power density were measured as 885 +/- 100 W/kg and 31 +/- 5 mW/cm(2), respectively. Duration of the exposure was 30 min each day for 3 consecutive days. The maximum temperature elevation at the tip of the nose, measured at the end of 30 min, was 1 degrees C. CPA injection (100 mg/kg) was given intraperitoneally on the second day of exposure to MMWs. The animals were sacrificed 2, 5, and 7 days after CPA administration. MMW exposure caused upregulation in tumor necrosis factor-alpha (TNF-alpha) production in peritoneal macrophages suppressed by CPA administration. MMWs also caused a significant increase in interferon-gamma (IFN-gamma) production by splenocytes and enhanced proliferative activity of T-cells. Conversely, no changes were observed in interleukin-10 (IL-10) level and B-cell proliferation. These results suggest that MMWs accelerate the recovery process selectively through a T-cell-mediated immune response.

Local heating of human skin by millimeter waves: effect of blood flow.

We investigated the influence of blood perfusion on local heating of the forearm and middle finger skin following 42.25 GHz exposure with an open ended waveguide (WG) and with a YAV mm wave therapeutic device. Both sources had bell-shaped distributions of the incident power density (IPD) with peak intensities of 208 and 55 mW/cm(2), respectively. Blood perfusion was changed in two ways: by blood flow occlusion and by externally applied vasodilator (nonivamide/nicoboxil) cream to the skin. For thermal modeling, we used the bioheat transfer equation (BHTE) and the hybrid bioheat equation (HBHE) which combines the BHTE and the scalar effective thermal conductivity equation (ETCE). Under normal conditions with the 208 mW/cm(2) exposure, the cutaneous temperature elevation (DeltaT) in the finger (2.5 +/- 0.3 degrees C) having higher blood flow was notably smaller than the cutaneous DeltaT in the forearm (4.7 +/- 0.4 degrees C). However, heating of the forearm and finger skin with blood flow occluded was the same, indicating that the thermal conductivity of tissue in the absence of blood flow at both locations was also the same. The BHTE accurately predicted local hyperthermia in the forearm only at low blood flow. The HBHE made accurate predictions at both low and high perfusion rates. The relationship between blood flow and the effective thermal conductivity (k(eff)) was found to be linear. The heat dissipating effect of higher perfusion was mostly due to an apparent increase in k(eff). It was shown that mm wave exposure could result in steady state heating of tissue layers located much deeper than the penetration depth (0.56 mm). The surface DeltaT and heat penetration into tissue increased with enlarging the irradiating beam area and with increasing exposure duration. Thus, mm waves at sufficient intensities could thermally affect thermo-sensitive structures located in the skin and underlying tissue.

Millimeter wave-induced suppression of B16 F10 melanoma growth in mice: involvement of endogenous opioids.

Millimeter wave treatment (MMWT) is widely used in Eastern European countries, but is virtually unknown in Western medicine. Among reported MMWT effects is suppression of tumor growth. The main aim of the present "blind" and dosimetrically controlled experiments was to evaluate quantitatively the ability of MMWT to influence tumor growth and to assess whether endogenous opioids are involved. The murine experimental model of B16 F10 melanoma subcutaneous growth was used. MMWT characteristics were: frequency, 61.22 GHz; average incident power density, 13.3 x 10(-3) W/cm2; single exposure duration, 15 min; and exposure area, nose. Naloxone (1 mg/kg, intraperitoneally, 30 min prior to MMWT) was used as a nonspecific blocker of opioid receptors. Five daily MMW exposures, if applied starting at the fifth day following B16 melanoma cell injection, suppressed subcutaneous tumor growth. Pretreatment with naloxone completely abolished the MMWT-induced suppression of melanoma growth. The same course of 5 MMW treatments, if started on day 1 or day 10 following tumor inoculations, was ineffective. We concluded that MMWT has an anticancer therapeutic potential and that endogenous opioids are involved in MMWT-induced suppression of melanoma growth in mice. However, appropriate indications and contraindications have to be developed experimentally before recommending MMWT for clinical usage.

Local heating of human skin by millimeter waves: a kinetics study.

Heating rates of human skin exposed locally to 42.25 GHz mm waves, coming from a waveguide (WG) opening or a YAV device designed for therapeutic application, were studied in vivo using infrared (IR) thermography. For both radiators, the power density distribution was described by a circularly symmetrical Gaussian type function on the exposed skin surface. Insertion of a small thermocouple (d = 0.1 mm) in the exposed area did not produce any significant artifact, either in the power density distribution or kinetics measurement, providing it was perpendicular to the E vector. The heating kinetics in the skin exposed with either the WG opening or the YAV device were well fitted to solutions of the 2-D bio-heat transfer equation for homogeneous tissue. Changes in irradiating beam size (1-8 mm) had no detectable effect on the initial (0.3-3.0 s) phase of the heating kinetics. However, the amplitude of the kinetics decreased substantially with decreasing the beam size. As the temperature rise in the time interval necessary for reliable measurement of the initial temperature rise rate was very small, an accurate experimental determination of specific absorption rate (SAR) becomes practically impossible at the low intensities normally used in our experiments. The correct SAR values may be found from fitting of the model to the heating kinetics. Bioelectromagnetics 24:571-581, 2003.

Distortion of millimeter-wave absorption in biological media due to presence of thermocouples and other objects.

Specific absorption rate (SAR) distributions in the vicinity of a thermocouple or air bubble in water and in the presence of hair or sweat duct in skin were calculated using analytical and two-dimensional impedance methods. The objects were exposed to uniform 42.25 GHz plane electromagnetic fields. Insertion of a 0.1-mm thermocouple or similarly sized air bubble into water produced a strong localized disturbance of the otherwise uniform SAR distribution. However, the average of SAR values immediately surrounding the thermocouple was close to the undisturbed uniform average SAR. This allows measuring the average SAR during exposure of both unbounded and bounded media using calibrated small thermocouples (up to 0.1 mm). The SAR distribution in the vicinity of a hair was qualitatively similar to that produced by an air bubble. The maximal value of SAR was more than three times higher than the overall average SAR value in the skin. Sweat ducts produced a smaller disturbance of the millimeter-wave (mm-wave) field.

Millimeter wave power density in aqueous biological samples.

Power density distribution inside a water sample placed between two parallel lossy dielectric plates (Polystyrene) was calculated using Fresnel equations for the frequency range of 42.25-53.57 GHz. Due to the multiple internal reflections from the sample boundaries, the distribution of the power density within the thin sample is more uniform than that within a semi-infinite medium. The power density in a sample depends on the thicknesses of the sample and the adjacent dielectric plates. For the given frequency range the sample thickness optimal for power density uniformity varies between 0.28 and 0.33 mm. The front plate has a significant effect on the magnitude of the power density within the sample but little effect on the power density distribution. The thicker the rear plate, the greater is the non uniformity of the power density distribution within the sample. Based on the calculated data, we determined the dimension of an exposure chamber providing the optimal power density distribution uniformity for mm-wave irradiation.

Peripheral neural system involvement in hypoalgesic effect of electromagnetic millimeter waves.

In a series of blind experiments, using the cold water tail-flick test (cTFT) as a quantitative indicator of pain, the hypoalgesic effect of a single exposure of mice to low power electromagnetic millimeter waves (MW) was studied. The MW exposure characteristics were: frequency = 61.22 GHz; incident power density = 15 mW/cm2; and duration = 15 min. MW treatment was applied to the glabrous skin of the footpad. Exposure of an intact murine paw to the MW resulted in a statistically significant hypoalgesia as measured in the cTFT. These mice were able to resist cold noxious stimulation in the cTFF more than two times longer than animals from the sham-exposed group. A unilateral sciatic nerve transection was used to deafferent the area of exposure in animals from one of the experimental groups. This surgery, conducted six days before the MW treatment, completely abolished the hypoalgesic effect of the exposure to MW. The results obtained support the conclusion that the MW-skin nerve endings interaction is the essential step in the initiation of biological effects caused by MW. Based on our past and present results we recommend that in order to obtain a maximum therapeutic effect, densely innervated skin areas (head, hands) need to be used preferentially for exposure to MW in clinical practice.

Reflection and absorption of millimeter waves by thin absorbing films.

Reflection, transmission, and absorption of mm-waves by thin absorbing films were determined at two therapeutic frequencies: 42. 25 and 53.57 GHz. Thin filter strips saturated with distilled water or an alcohol-water solution were used as absorbing samples of different thicknesses. The dependence of the power reflection coefficient R(d) on film thickness (d) was not monotonic. R(d) passed through a pronounced maximum before reaching its steady-state level [R(infinity)]. Similarly, absorption, A(d), passed two maximums with one minimum between them, before reaching its steady-state level [A(infinity)]. At 42.25 GHz, A(d) was compared with absorption in a semi-infinite water medium at a depth d. When d < 0.3 mm, absorption by the film increased: at d = 0.1 mm the absorption ratio for the thin layer sample and the semi-infinite medium was 3.2, while at d = 0.05 mm it increased up to 5.8. Calculations based on Fresnel equations for flat thin layers adequately described the dependence of the reflection, transmission, and absorption on d and allowed the determination of the refractive index (n), dielectric constant (epsilon), and penetration depth (delta) of the absorbing medium for various frequencies. For water samples, epsilon was found to be 12.4-19.3j, delta = 0.49 mm at 42.25 GHz, and epsilon = 9.0-19.5j, delta = 0.36 mm at 53.57 GHz. The calculated power density distribution within the film was strongly dependent on d. The measurements and calculations have shown that the reflection and absorption of mm-waves by thin absorbing layers can significantly differ from the reflection and absorption in similar semi-infinite media. The difference in reflection, absorption, and power density distribution in films, as compared to semi-infinite media, are caused by multiple internal reflections from the film boundaries. That is why, when using thin phantoms and thin biological samples, the specifics of the interaction of mm-waves with thin films should be taken into account.

Hypoalgesic effect of millimeter waves in mice: dependence on the site of exposure.

Based on a hypothesis of neural system involvement in the initial absorption and further processing of the millimeter electromagnetic waves (MW) signal, we reproduced, quantitatively assessed and compared the analgesic effect of a single MW treatment, exposing areas of skin possessing different innervation densities. The cold water tail flick test (cTFT) was used to assess experimental pain in mice. Three areas of exposure were used: the nose, the glabrous skin of the right footpad, and the hairy skin of the mid back at the level of T5-T10. The MW exposure characteristics were: frequency = 61.22 GHz; incident power density = 15mW/cm2; and duration = 15 min. The maximum hypoalgesic effect was achieved by exposing to MW the more densely innervated skin areas--the nose and the footpad. The hypoalgesic effect in the cTFT after MW exposure to the murine back, which is less densely innervated, was not statistically significant. These results support the hypothesis of neural system involvement in the systemic response to MW.

Effects of millimeter waves on ionic currents of Lymnaea neurons.

The effects of mm-waves 60.22-62.22 GHz and 75 GHz on A-type K+ currents and the effects of 61.22 GHz on Ca2+ currents of Lymnaea neurons were investigated using a whole-cell voltage-clamp technique. The open end of a rectangular waveguide covered with a thin Teflon film served as a radiator. Specific absorption rates at the waveguide outlet, inserted into physiological solution, were in the range of 0-2400 W/kg. Millimeter wave irradiation increased the peak amplitudes, activation rates, and inactivation rates of both ion currents. The changes in A-type K+ current were not dependent on the irradiation frequency. It was shown that the changes in the amplitudes and kinetics of both currents resulted from the temperature rise produced by irradiation. No additional effects of irradiation on A-type K+ current other than thermal were found when tested at the phase transition temperature or in the presence of ethanol. Ethanol reduced the thermal effect of irradiation. Millimeter waves had no effect on the steady-state activation and inactivation curves, suggesting that the membrane surface charge and binding of calcium ions to the membrane in the area of channel locations did not change.