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At least 541 records · Page 30Linked to original sources
PubMed1989

RF currents induced in an anatomically-based model of a human for plane-wave exposures (20-100 MHz).

The three-dimensional finite-difference time-domain (FDTD) method has been used to calculate local, layer-averaged and whole-body averaged specific absorption rates (SARs) and internal radiofrequency (RF) currents in a 5628-cell, anatomically-based model of a human for plane-wave exposures from 20-100 MHz. The conditions of exposure of the human considered are: 1) isolated from ground, and 2) feet in contact with ground. Also considered are various separations of the model from ground and the use of insulating, rubber-soled footwear close to the grounded resonance frequency of 45 MHz. The calculated results are in agreement with the experimental data of Hill and others. While the existence of large foot currents has been known previously, substantial RF currents (600-800 mA) induced over much of the body are obtained for E-polarized fields suggested in the 1982 ANSI RF safety guideline.

Electric Conductivity↗
PubMed2003

Sensitivity of the acoustic waveguide biosensor to protein binding as a function of the waveguide properties.

The aim of this work is to study the effect of operating frequency, piezoelectric substrate and waveguide layer thickness on the sensitivity of the acoustic waveguide sensor during the specific binding of an antibody by a protein. Shear horizontal (SH) wave devices consisting of (a) a LiTaO3 substrate operating at 104 MHz, (b) a quartz substrate operating at 108 MHz and (c) a quartz substrate operating at 155 MHz were coated with a photoresist polymer layer in order to produce acoustic waveguide devices supporting a Love wave. The effect of the thickness of the polymer layer on the Love wave was assessed by measuring the amplitude and phase of the wave before and after coating. The sensitivity of the above three biosensors was compared during the detection of the specific binding of different concentrations of Immunoglobulin G in the range of 0.7-667 nM to a protein A modified surface. Results indicate that the thickness of the polymer guiding layer is critical for obtaining the maximum sensitivity for a given geometry but a trade-off has to be made between the theoretically determined optimum thickness for waveguiding and the device insertion loss. It was also found that increasing the frequency of operation results in a further increase in the device sensitivity to protein detection.

Acoustics↗
PubMedDate not supplied

[Synchronization of the frequency of cardiovascular fatalities with physical time cues].

Investigations were carried out to correlate the frequency of cardiovascular catastrophes (daily mortality rate of patients with ischemic heart disease), heliogeomagnetic activity (solar radiation in the wave band 10.7 cm, H, D and Z components of the geomagnetic field), synchronization and desynchronization of circaseptidian rhythms, and total number of cardiovascular catastrophes in different seasons. The raw data sets were treated with due account of the discrete pattern of random sequences and noise in the medical data set, finite analysis interval and informativity of the derivatives of the parameters used. The occurrence of cardiovascular catastrophes showed circaseptidian rhythms whose level depended on the above three factors. The results obtained are discussed with respect to possible synchronization and desynchronization of endogenous biorhythms by time cues, relating them to the mechanism of human adaptation to the environment.

Biological Clocks↗
PubMed2005

A numerical evaluation of SAR distribution and temperature changes around a metallic plate in the head of a RF exposed worker.

The 1998 International Commission for Non-Ionising Radiation (ICNIRP) Guidelines for human exposure to radiofrequency (RF) fields contain a recommendation to assess the potential impact of metallic implants in workers exposed up to the allowable occupational field limits. This study provides an example of how numerical electromagnetic (EM) and thermal modelling can be used to determine whether scattered RF fields around metallic implants in workers exposed to allowable occupational ambient field limits will comply with the recommendations of relevant standards and guidelines. A case study is performed for plane wave exposures of a 50 mm diameter titanium cranioplasty plate, implanted around 5-6 mm under the surface of the forehead. The level of exposures was set to the ambient power flux density limits for occupational exposures specified in the 1998 ICNIRP guidelines and the current 1999 IEEE C95.1 standard over the frequency range 100-3000 MHz. Two distinct peak responses were observed. There was a resonant response for the whole implant at 200-300 MHz where the maximum dimension of the implant is around a third of the wavelength of the RF exposure. This, however, resulted in relatively low peak specific energy absorption rate (SAR) levels around the implant at the exposure limits. Between 2100-2800 MHz, a second SAR concentrating mechanism of constructive interference of the wave reflected back and forth between the air-scalp interface and the scalp-plate interface resulted in higher peak SARs that were within the allowable limits for the ICNIRP exposures, but not for the IEEE C95.1 exposures. Moreover, the IEEE peak SAR limits were also exceeded, to a lesser degree, even when the implant was not present. However, thermal modelling indicated that the peak SAR concentrations around the implant did not result in any peak temperature rise above 1 degrees C for occupational exposures recommended in the ICNIRP guidelines, and hence would not pose any significant health risk.

Body Burden↗
PubMed2003

[Effects of 50 to 60 Hz and of 20 to 50 kHz magnetic fields on the operation of implanted cardiac pacemakers].

UNLABELLED: The effect of 50 Hz and 60 Hz (frequencies of current distribution) and 20 kHz to 50 kHz (frequencies of induction cooktop) magnetic interference on implanted pacemakers have been assessed with the present generation of device technology. Sixty patients implanted in 1998 and 1999 with dual chamber pacemakers from 9 different manufacturers were monitored with telemetry while passing through, and standing between a system of two coils. They generated a 50 Hz or a 60 Hz magnetic field at 50 microT. Then, patients used a cooktop at different power. The recordings were made with the standard setting of "medically correct" sensing parameters chosen for the patients. Then pacemakers were reprogrammed to the unipolar mode, with the highest atrial (A) and ventricular (V) sensitivity that did not induce muscular inhibition while moving. Between each exposure (50 Hz, 60 Hz or 20 kHz to 50 kHz), the pacemaker programmation was controlled. At the end of the tests, pacemakers will be reprogrammed with the standard setting. The medical observer being blind to the existence or not of the magnetic field. No pacemaker was influenced by the vicinity of the magnetic field at medically correct settings. At unipolar high sensitivity, no inhibition nor reprogramming was observed. Transient reversion to interference mode was observed in 6 cases, 3 transient acceleration due to atrial detection of the interference, and one T wave detection by the ventricular lead. All were observed with the 60 Hz, and only 3 with the 50 Hz magnetic field. One device (Biotronik) shifted out of its special program (hysteresis research) during the tests with the induction cooktop, but it maintained its standard program, and the event could not be repeated despite further testing. CONCLUSION: Actual pacemakers do not present any electromagnetic interference with 50 Hz and 60 Hz or induction cooktop frequency working. They are insensitive with medically correct settings. Unusual high sensitivity leads only to noise reversion mode, or transient ventricular tracking.

Dose-Response Relationship, Radiation↗
PubMed2003

RF nonlinear interactions in living cells-I: nonequilibrium thermodynamic theory.

Some biological experiments report effects that depend on low frequency modulation of a radiofrequency (RF) carrier. Such effects require nonlinear responses in biological preparations, which we show could be observed with great generality by the unique frequency signatures that would appear in the scattered RF energy. Following Illinger [Illinger (1982): Bioelectromagnetics 3:9-16], we considered a two part physical system. The greater part, dominated by the properties of water, interacts linearly with the RF field and is described by equilibrium thermodynamics. However, another, much smaller part, e.g., certain biological molecules and molecular subgroups, supports nonlinear interactions and is described by nonequilibrium thermodynamics. For example, a nonlinear interaction might result from scattering of RF photons from oscillators located in a region of strong field gradients, such as at membrane surfaces. A second nonlinear mechanism could appear if stress (elastic) waves were launched within the confines of the exposure vessel by RF heating. Amplitude modulation at angular frequency Omega of a carrier wave with angular frequency omega (omega << omega) produces two peaks in elastic stress in the cell structure during each period; that is, there is "full-wave demodulation." As a result of coherent nonlinear charge motion, modulation products could appear at frequencies omega +/- 2 omega and, in general, at omega +/- n 2 omega (n = 1, 2, em leader ) if vibrational harmonics at 2 n omega also are excited. Although in principle microwaves can alter the stability of a thermodynamic system by pumping a chemical transition, the degree of nonlinear coupling required for an observable instability is so great that its probability is effectively zero, unless field intensity is extremely high. A companion paper suggests an extremely sensitive method and the related instrumentation for detection of the spectrum scattered by living cells during exposure to amplitude modulated RF energy.

Animals↗
PubMed2006

Evaluation of stray radiofrequency radiation emitted by electrosurgical devices.

Electrosurgery refers to the passage of a high-frequency, high-voltage electrical current through the body to achieve the desired surgical effects. At the same time, these procedures are accompanied by a general increase of the electromagnetic field in an operating room that may expose both patients and personnel to relatively high levels of radiofrequency radiation. In the first part of this study, we have taken into account the radiation emitted by different monopolar electrosurgical devices, evaluating the electromagnetic field strength delivered by an electrosurgical handle and straying from units and other electrosurgical accessories. As a summary, in the worst case a surgeon's hands are exposed to a continuous and pulsed RF wave whose magnetic field strength is 0.75 A m(-1) (E-field 400 V m(-1)). Occasionally stray radiation may exceed ICNIRP's occupational exposure guidelines, especially close to the patient return plate. In the second part of this paper, we have analysed areas of particular concern to prevent electromagnetic interference with some life-support devices (ventilators and electrocardiographic devices), which have failed to operate correctly. Most clinically relevant interference occurred when an electrosurgery device was used within 0.3 m of medical equipment. In the appendix, we suggest some practical recommendations intended to minimize the potential for electromagnetic hazards due to therapeutic application of RF energy.

Electrocardiography↗
PubMed1993

Radiofrequency catheter ablation of sustained intra-atrial reentrant tachycardia in adult patients. Identification of electrophysiological characteristics and endocardial mapping techniques.

BACKGROUND: Information about electrophysiological characteristics and radiofrequency ablation of intra-atrial reentrant tachycardia has not been reported before. We proposed that induction and termination of intra-atrial reentrant tachycardia by atrial extrastimuli or rapid atrial pacing and resetting the response pattern by atrial extrastimuli during intra-atrial reentrant tachycardia could ensure the mechanism of reentry and that the earliest site of endocardial activation and concealed entrainment pace mapping with the shortest stimulus-P wave interval could localize a critical area responsible for intra-atrial reentrant tachycardia and radiofrequency ablation. METHODS AND RESULTS: Seven patients with refractory atrial tachycardia were referred for electrophysiological studies and radiofrequency ablation. Electrophysiological studies and endocardial mapping found (1) 10 atrial foci with atrial tachycardia cycle length of 406 +/- 41 ms; (2) atrial tachycardia had induction and termination by atrial extrastimuli (8 of 10) or rapid atrial pacing (10 of 10); (3) atrial tachycardia had increasing (6 of 10) or mixed (flat and increasing, 4 of 10) resetting response pattern, with resetting interval of 57 +/- 13 ms (14 +/- 4% of atrial tachycardia cycle length); (4) exit sites of atrial tachycardia in right atrial free wall (6 of 10), right atrial septum (3 of 10), and midposterior left atrium (1 of 10); and (5) earliest activation site had timing relative to P wave by -37 +/- 7 ms, and concealed entrainment pace mapping had shortest stimulus-P interval 23 +/- 3 ms. By the endocardial activation pace-mapping technique, radiofrequency energy (8 +/- 1 pulses, 31 +/- 3 W, 101 +/- 11 seconds) successfully eliminated the 10 atrial foci without recurrence (follow-up, 16 +/- 5 months). CONCLUSIONS: Mechanism of intra-atrial reentrant tachycardia could be confirmed by the electrophysiological characteristics, and radiofrequency ablation energy delivered to a critical area in the atrial reentrant circuit is safe and effective for the treatment of intra-atrial reentrant tachycardia.

Aged↗
PubMed2006

Modest increase in temperature affects ODC activity in L929 cells: Low-level radiofrequency radiation does not.

The effects of low-level radiofrequency (RF) radiation and elevated temperature on ornithine decarboxylase (ODC) activity were investigated in murine L929 fibroblasts. The cells were exposed at 900 MHz either to a pulse-modulated (pulse frequency 217 Hz; GSM-type modulation) or a continuous wave signal at specific absorption rate (SAR) levels of 0.2 W kg(-1) (0.1-0.3 W kg(-1)) and 0.4 W kg(-1) (0.3-0.5 W kg(-1)) for 2, 8, or 24 h. RF radiation did not affect cellular ODC activity. However, a slight increase in temperature (0.8-0.9 degrees C) in the exposure system lead to decreased ODC activity in cell cultures. This was verified by tests in which cells were exposed to different temperatures in incubators. The results show that ODC activity is sensitive to small temperature differences in cell cultures. Hence, a precise temperature control in cellular ODC activity studies is needed.

Animals↗
PubMed2006

Impact of localized inhomogeneity on the surface-wave velocity and bulk-wave reflection in solids.

The effect of a weak surface, near-surface and interfacial inhomogeneity on the frequency dependence of the surface wave velocity and of the SH (shear horizontal) wave reflectivity in isotropic elastic media is studied analytically and numerically. The inhomogeneity is modeled as an infinite planar layer with continuously varying properties. Weak inhomogeneity may markedly affect the dispersion of the Rayleigh velocity and especially of the reflectivity. It is demonstrated how this effect, particularly pronounced at high frequency, depends on the extent of inhomogeneity. The material data for damaged and ideal concrete and several simple examples of inhomogeneity profiles are utilized for the numerical calculations based on the Peano expansion. The use of explicit low- and high-frequency approximations is also exemplified. Among these, simple WKB asymptotics are shown to be particularly helpful for the Rayleigh velocity in the case of a prominent inhomogeneity attached to the surface and for the reflection on weak interfaces.

Models, Theoretical↗
PubMed1985

Viability and phagocytosis of neutrophils exposed in vitro to 100-MHz radiofrequency radiation.

Rabbit polymorphonuclear leucocytes (PMN, neutrophils) obtained from peritoneal exudate were exposed in vitro for one-half or one hour to continuous wave or amplitude-modulated (20-Hz) 100-MHz RF radiation in a temperature-controlled coaxial exposure chamber at field strengths from 2.5 to 4.1 V/cm (SARs of 120 to 341 W/kg). RF exposure at 37 +/- 0.2 degrees C had no detectable effect on PMN viability or phagocytosis compared to sham-exposed cells simultaneously subjected to the same time-temperature regime. Temperature control studies indicated that at 37 degrees C no effect on PMN viability would be expected but phagocytosis would be reduced by approximately 6%/degrees C temperature increase. The absence of an effect of RF exposure suggests that there was minimal undetected intrasample heating and that phagocytosis was not affected by 100-MHz RF radiation under the conditions of this study.

Animals↗
PubMed1980

Power density, field intensity, and carrier frequency determinants of RF-energy-induced calcium-ion efflux from brain tissue.

To explain a carrier frequency dependence reported for radiofrequency (RF)-induced calcium-ion efflux from brain tissue, a chick-brain hemisphere bathed in buffer solution is modeled as a sphere within the uniform field of the incident electromagnetic wave. Calculations on a spherical model show that the average electric-field intensity within the sample remains the same at different carrier frequencies if the incident power density (Pi) is adjusted by an amount that compensates for the change in complex permittivity (epsilon *r) and the change of wavelength, as a function of carrier frequency. The resulting formula for transforming Pi is seen to follow the pattern of both positive and negative demonstrations of calcium-ion efflux that have been observed at carrier frequencies of 50, 147, and 450 MHz. Indeed, all results obtained at these three frequencies, when related by Pi's that produce the same average electric-field intensity within the sample, are seen to be in agreement; no prediction is contradicted by an experiment.

Animals↗
PubMed1990

Glioma proliferation modulated in vitro by isothermal radiofrequency radiation exposure.

Isothermal (37 +/- 0.2 degrees C) exposure of glioma cells (LN71) for 2 h to 27 or 2450 MHz continuous-wave radiofrequency (RF) radiation in vitro modulated the rates of DNA and RNA synthesis 1, 3, and 5 days after exposure. The alterations indicate effects on cell proliferation and were not caused by RF-induced cell heating. The dose response for either frequency of the radiation was biphasic. Exposure to specific absorption rates (SARs) of 50 W/kg or less stimulated incorporation rates of tritiated thymidine (3H-TdR) and tritiated uridine (3H-UdR), whereas higher SARs suppressed DNA and RNA synthesis. Statistically significant time-dependent alterations were detected for up to 5 days postexposure, suggesting a kinetic cellular response to RF radiation and the possibility of cumulative effects on cell proliferation. General mechanisms of effects are discussed.

Cell Division↗
PubMed1994

Estimation of Bloch model MT spin system parameters from Z-spectral data.

Previous studies have described magnetization transfer (MT) Z-spectra in terms of a two-pool Bloch model, with six spin-system parameters KA, F, T1A, T1B, T2A, and T2B. By simulation, we show that a process including nonlinear constrained optimization can be used to accurately and uniquely estimate spin-system parameters from MT Z-spectra prepared by continuous wave (CW) RF irradiation. Experiments producing Z-spectra by pulsed RF irradiation give substantially different magnetization values, relative to MT acquisitions obtained by CW RF irradiation, at small offset frequencies, with a consequence that only T2B can be uniquely determined. However, several equalities and bounds involving four of the other parameters (KA, F, T1A, and T1B) are derived, which are applicable to pulsed data. These relationships allow calculation of "free pool" magnetization corresponding to complete saturation of the restricted pool, without requiring that this complete saturation be experimentally achieved. MT experimental data from pulsed RF irradiation on boiled egg albumin, obtained using a clinical whole-body MRI system, are analyzed using an optimization algorithm and the derived expressions.

Algorithms↗
PubMed1999

Relaxation effects in a system of a spin-1/2 nucleus coupled to a quadrupolar spin subjected to RF irradiation: evaluation of broadband decoupling schemes.

We have investigated the suitability and performance of various decoupling methods on systems in which an observed spin-1/2 nucleus I (13C or 15N) is scalar-coupled to a quadrupolar spin S (2H). Simulations and experiments have been conducted by varying the strength of the irradiating radiofrequency (RF) field, RF offset, relaxation times, and decoupling schemes applied in the vicinity of the S-spin resonance. The T1 relaxation of the quadrupolar spin has previously been shown to influence the efficiency of continuous wave (CW) decoupling applied on resonance in such spin systems. Similarly, the performance of broadband decoupling sequences should also be affected by relaxation. However, virtually all of the more commonly used broadband decoupling schemes have been developed without consideration of relaxation effects. As a consequence, it is not obvious how one selects a suitable sequence for decoupling quadrupolar nuclei with exotic relaxation behavior. Herein we demonstrate that, despite its simplicity, WALTZ-16 decoupling is relatively robust under a wide range of conditions. In these systems it performs as well as the more recently developed decoupling schemes for wide bandwidth applications such as GARP-1 and CHIRP-95. It is suggested that in macromolecular motional regimes, broadband deuterium decoupling can be achieved with relatively low RF amplitudes (500-700 Hz) using WALTZ-16 multiple pulse decoupling.

Computer Simulation↗
PubMedDate not supplied

Health risks of exposure to non-ionizing radiation--myths or science-based evidence.

INTRODUCTION: The non-ionizing radiation (NIR) contains large range of wavelengths and frequencies from vacuum ultraviolet (UV) radiation to static electric and magnetic fields. Biological effects of electromagnetic (EM) radiation depend greatly on wavelength and other physical parameters. OPTICAL RADIATION: The Sun is the most significant source of environmental UV exposure, so that outdoor workers are at risk of chronic over-exposure. Also exposure to short-wave visible light is associated with the aging and degeneration of the retina. Especially hazardous are laser beams focused to a small spot at the retina, resulting in permanent visual impairment. ELECTROMAGNETIC FIELDS: Exposure to EM fields induces body currents and energy absorption in tissues, depending on frequencies and coupling mechanisms. Thermal effects caused by temperature rise are basically understood, whereas the challenge is to understand the suspected non-thermal effects. Radiofrequency (RF) fields around frequencies of 900 MHz and 1800 MHz are of special interest because of the rapid advances in the telecommunication technology. The field levels of these sources are so low that temperature rise is unlikely to explain possible health effects. Other mechanisms of interaction have been proposed, but biological experiments have failed to confirm their existence.

Electromagnetic Fields↗
PubMed2003

Lack of genotoxic effects (micronucleus induction) in human lymphocytes exposed in vitro to 900 MHz electromagnetic fields.

In the present study, we investigated the induction of genotoxic effects in human peripheral blood lymphocytes after exposure to electromagnetic fields used in mobile communication systems (frequency 900 MHz). For this purpose, the incidence of micronuclei was evaluated by applying the cytokinesis-block micronucleus assay. Cytotoxicity was also investigated using the cytokinesis-block proliferation index. The experiments were performed on peripheral blood from 20 healthy donors, and several conditions were tested by varying the duration of exposure, the specific absorption rate (SAR), and the signal [continuous-wave (CW) or GSM (Global System of Mobile Communication) modulated signal]. The following exposures were carried out: (1) CW intermittent exposure (SAR = 1.6 W/kg) for 6 min followed by a 3-h pause (14 on/off cycles); (2) GSM signal, intermittent exposure as described in (1); (3) GSM signal, intermittent exposure as described in (1) 24 h before stimulation with phytohemagglutinin (8 on/off cycles); (4) GSM signal, intermittent exposure (SAR = 0.2 W/kg) 1 h per day for 3 days. The SARs were estimated numerically. No statistically significant differences were detected in any case in terms of either micronucleus frequency or cell cycle kinetics.

Adult↗
PubMed1997

Stress proteins are not induced in mammalian cells exposed to radiofrequency or microwave radiation.

The induction of stress proteins in HeLa and CHO cells was investigated following a 2 h exposure to radiofrequency (RF) or microwave radiation. Cells were exposed or sham exposed in vitro under isothermal (37 +/- 0.2 degrees C) conditions. HeLa cells were exposed to 27- or 2450 MHz continuous wave (CW) radiation at a specific absorption rate (SAR) of 25 W/kg. CHO cells were exposed to CW 27 MHz radiation at a SAR of 100 W/kg. Parallel positive control studies included 2 h exposure of HeLa or CHO cells to 40 degrees C or to 45 microM cadmium sulfate. Stress protein induction was assayed 24 h after treatment by electrophoresis of whole-cell extracted protein labeled with [35S]-methionine. Both cell types exhibited well-characterized responses to the positive control stresses. Under these exposure conditions, neither microwave nor RF radiation had a detectable effect on stress protein induction as determined by either comparison of RF-exposed cells with sham-exposed cells or comparison with heat-stressed or Cd++ positive control cells.

Animals↗