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Results for “RADIO WAVES”

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At least 505 records · Page 28Linked to original sources

PubMed1997

Role of modulation on the effect of microwaves on ornithine decarboxylase activity in L929 cells.

The effect of 835 MHz microwaves on the activity of ornithine decarboxylase (ODC) in L929 murine cell was investigated at an SAR of approximately 2.5 W/kg. The results depended upon the type of modulation employed. AM frequencies of 16 Hz and 60 Hz produced a transient increase in ODC activity that reached a peak at 8 h of exposure and returned to control levels after 24 h of exposure. In this case, ODC was increased by a maximum of 90% relative to control levels. A 40% increase in ODC activity was also observed after 8 h of exposure with a typical signal from a TDMA digital cellular telephone operating in the middle of its transmission frequency range (approximately 840 MHz). This signal was burst modulated at 50 Hz, with approximately 30% duty cycle. By contrast, 8 h exposure with 835 MHz microwaves amplitude modulated with speech produced no significant change in ODC activity. Further investigations, with 8 h of exposure to AM microwaves, as a function of modulation frequency, revealed that the response is frequency dependent, decreasing sharply at 6 Hz an 600 Hz. Exposure with 835 MHz microwaves, frequency modulated with a 60 Hz sinusoid, yielded no significant enhancement in ODC activity for exposure times ranging between 2 and 24 h. Similarly, exposure with a typical signal from an AMPS analog cellular telephone, which uses a form of frequency modulation, produced no significant enhancement in ODC activity. Exposure with 835 MHz continuous wave microwaves produced no effects for exposure times between 2 and 24 h, except for a small but statistically significant enhancement in ODC activity after 6 h of exposure. Comparison of these results suggests that effects are much more robust when the modulation causes low-frequency periodic changes in the amplitude of the microwave carrier.

Animals↗

PubMedDate not supplied

Percutaneous radiofrequency lumbar rhizolysis (rhizotomy).

Low-back pain may arise from degenerative changes in the posterior joints of the lumbar spine. These joints are innervated by a branch of the posterior primary ramus, which follows an antomically constant course. Pain impulses from these joints can be interrupted by coagulating the nerve with a radiofrequency wave, the probe having been placed in the area of the nerve percutaneously. Percutaneous lumbar rhizolysis was carried out under local anesthesia on an outpatient basis in 82 patients, most of whom had multiple level rhizolysis, Rhizolysis was successful in 67% of patients with mechanical low-back pain without evidence of disc herniation and nerve-root compression or psychogenic pain, who had not previously undergone an operation for relief of the pain.

Back Pain↗

PubMed2004

Fast EPR imaging at 300 MHz using spinning magnetic field gradients.

Electron paramagnetic resonance imaging (EPRI) technology has rapidly progressed in the last decade enabling many important applications in the fields of biology and medicine. At frequencies of 300-1200 MHz a range of in vivo applications have been performed. However, the requisite imaging time duration to acquire a given number of projections, limits the use of this technique in many in vivo applications where relatively rapid kinetics occur. Therefore, there has been a great need to develop approaches to accelerate EPRI data acquisition. We report the development of a fast low-frequency EPRI technique using spinning magnetic field gradients (SMFG). Utilizing a 300 MHz CW (continuous wave) EPRI system, SMFG enabled over 10-fold accelerated acquisition of image projections. 2D images with over 200 projections could be acquired in less than 3s and with 20s acquisitions good image quality was obtained on large aqueous free radical samples. This technique should be particularly useful for in vivo studies of free radicals and their metabolism.

Algorithms↗

PubMed2006

[Biologic effects of millimeteric waves (94 GHz). Are there long term consequences?].

Active Denial Systems (ADS) is a millimetric wave radiation emitting technology now included in the non lethal weapon arsenal. Such devices emit electromagnetic, thus agitating water in the skin and causing feeling of heat enough that target individual retreats from the beam. They can be used at up to 1 km from the target. We have reviewed the literature on the interactions of millimetric waves (MMW) with biological systems. An opposition appears between the observations performed in the Former Soviet Union and Russia showing potential interaction sometimes deleterious while generally of good influence and used in therapy. By way of contrast, most of the other studies, performed in USA, address local acute effects, exclusively located on the skin and eyes of the target, and considered as completely reversible.

Electromagnetic Fields↗

PubMed1999

Absence of ocular effects after either single or repeated exposure to 10 mW/cm(2) from a 60 GHz CW source.

This study was designed to examine ocular effects associated with exposure to millimeter waves (60 GHz). Rabbits served as the primary experimental subjects. To confirm the results of the rabbit experiments in a higher species, the second phase of the study used nonhuman primates (Macaca mulatta). First, this study used time-resolved infrared radiometry to assess the field distribution patterns produced by different antennas operating at 60 GHz. These results allowed us to select an antenna that produced a uniform energy distribution and the best distance at which to expose our experimental subjects. The study then examined ocular changes after exposure at an incident power density of 10 mW/cm(2). Acute exposure of both rabbits and nonhuman primates consisted of a single 8 h exposure, and the repeated exposure protocol consisted of five separate 4 h exposures on consecutive days. One eye in each animal was exposed and the contralateral eye served as the sham-exposed control. After postexposure diagnostic examinations, animals were euthanized and the eyes were removed. Ocular tissue was examined by both light and transmission electron microscopy. Neither microscopic examinations nor the diagnostic procedures performed on the eyes of acute and repeatedly exposed rabbits found any ocular changes that could be attributed to millimeter-wave exposure at 10 mW/cm(2). Examination of the primates after comparable exposures also failed to detect any ocular changes due to exposure. On the basis of our results, we conclude that single or repeated exposure to 60 GHz CW radiation at 10 mW/cm(2) does not result in any detectable ocular damage.

Animals↗

PubMed1982

Trigeminal evoked potentials in the cat.

Electrical stimulation of the infraorbital nerve in the cat resulted in a series of far-field evoked potentials at the vertex. The wave form of these potentials is similar to the auditory brain stem evoked response and the somatosensory far-field response; it is multicomponent, the amplitudes of individual components are of the order of 1 microV, and the latencies are all less than 4 msec. The anatomical origins of these evoked potentials were investigated. The results indicated that contributions due to the afferent trigeminal nerve, the principal sensory nucleus, and the spinal trigeminal nucleus are involved.

Animals↗

PubMed1993

[The influence of repetitive delivery of radiofrequency current in catheter ablation].

The single delivery of radiofrequency current to the cardiac tissue can produce discrete small and shallow area of homogeneous coagulation necrosis. Little is known, however, concerning the influence of repetitive deliveries of radiofrequency current to the identical site of the ventricular myocardium. Therefore, in animal experiments using 8 dogs, we investigated the influences of those applications on the ventricular myocardium from the histological and electrocardiographical aspects. The used frequencies of radiofrequency current were 13.56 MHz (RF-50), 520 kHz (Hatt 200 S) and 500 kHz (LL-50). Released power was 25 Watts in current and 20 seconds in duration. The innings of application were 10, 20 and 30 times per one ablation session. The depth of ablated lesion became greater as the applied innings increased in any generator of radiofrequency current. The ablated lesion by the delivery over 20 times reached from the ventricular endocardium to the epicardium. In contrast, surface area produced by repetitive application was determined by the size and length of the tip of electrode catheter. T wave inversion and isolated premature ventricular contraction on electrocardiogram were observed only during repetitive radiofrequency energy application. Thus, since the repetitive delivery of radiofrequency energy to the identical myocardium caused the deep ablated lesion reached to the epicardium, caution should be taken against myocardial perforation in a clinical setting. However, this application could be useful for the ablation of deeper lesion responsible for ventricular tachycardia.

Animals↗

PubMed2005

An RF phased array applicator designed for hyperthermia breast cancer treatments.

An RF phased array applicator has been constructed for hyperthermia treatments in the intact breast. This RF phased array consists of four antennas mounted on a Lexan water tank, and geometric focusing is employed so that each antenna points in the direction of the intended target. The operating frequency for this phased array is 140 MHz. The RF array has been characterized both by electric field measurements in a water tank and by electric field simulations using the finite-element method. The finite-element simulations are performed with HFSS software, where the mesh defined for finite-element calculations includes the geometry of the tank enclosure and four end-loaded dipole antennas. The material properties of the water tank enclosure and the antennas are also included in each simulation. The results of the finite-element simulations are compared to the measured values for this configuration, and the results, which include the effects of amplitude shading and phase shifting, show that the electric field predicted by finite-element simulations is similar to the measured field. Simulations also show that the contributions from standing waves are significant, which is consistent with measurement results. Simulated electric field and bio-heat transfer results are also computed within a simple 3D breast model. Temperature simulations show that, although peak temperatures are generated outside the simulated tumour target, this RF phased array applicator is an effective device for regional hyperthermia in the intact breast.

Algorithms↗

PubMed2003

Effects of ELF magnetic field on membrane protein structure of living HeLa cells studied by Fourier transform infrared spectroscopy.

The effects of exposure to a 50 Hz magnetic field (maximum of 41.7 to 43.6 mT) on the membrane protein structures of living HeLa cells were studied using attenuated total reflection infrared spectroscopy. One min of such exposure shifted peak absorbance of the amide I band to a smaller wave number, reduced peak absorbance of the amide II band, and increased absorbance at around 1600 cm(-1). These results suggest that exposure to the ELF magnetic field has reversible effects on the N-H inplane bending and C-N stretching vibrations of peptide linkages, and changes the secondary structures of alpha-helix and beta-sheet in cell membrane proteins.

Albumins↗

PubMedDate not supplied

[The effect of SHF waves on the evoked potentials in the cat spinal cord].

In experiments with adult cats there revealed a pronounced effect of SHF radiation on the electrogenesis of spinal cord, the beam density being 15 mW/cm2 and time of exposure 10 min. The estimates of the induced somatosensory brain potentials indicate that there is a phase of a 20 per cent response inhibition with the effect reaching maximum 2-3 h following irradiation. Subsequently, potential characteristics are exponentially restored to be the same with the control values. The evidence is presented that the synaptic neuron contacts within the reflex arc are highly susceptible to SHF radiation.

Animals↗

PubMed1993

Effect of Gd-DTPA and/or magnetic field and radiofrequency exposure on sister chromatid exchange in human peripheral lymphocytes.

The effects of a magnetic field, radiofrequency, and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) on the sister chromatid exchange (SCE) in human peripheral lymphocytes were investigated. Whole blood was taken from a nonsmoker and samples were exposed to magnetic force (1.5 T) alone, and to a magnetic force combined with radiofrequency waves (63.86 MHz, specific absorption rate, SAR, 0.4 W/kg). Gd-DTPA was then added to other blood samples in varying amounts and concentrations. After exposure to the conditions described above, these blood samples were cultured for 69 hours. Slides were made for an SCE evaluation. As the concentration of Gd-DTPA added to the blood increased, the SCE frequency also increased. However, the addition of Gd-DTPA at the clinical concentrations normally used did not affect the SCE frequency.

Gadolinium DTPA↗

PubMed1984

[Cerebral hemodynamics in the early recovery period after reconstructive surgery on the cerebral vessels during decimeter-wave therapy].

Using REG data, the effect of decimeter electromagnetic wave therapy (DEMWT) on the cerebral hemodynamics was studied in patients in the early recovery period following reconstructive surgery on the cerebral vessels. The results of the study suggest that the use of DEMWT increases considerably the compensatory-adaptive functions of the body and improves significantly the cerebral hemodynamics which is paralleled by the regression of neurologic symptomatology. DEMWT represents a physiological and pathologically-substantiated method for treating the given category of patients.

Adolescent↗

PubMedDate not supplied

The short wavelength-sensitive cone electroretinogram in diabetes: relationship to systemic factors.

The short wavelength-sensitive (S-) cone electroretinogram (ERG) is selectively reduced in diabetic patients both with and without retinopathy, but the exact mechanism of the vulnerability of the S-cone system is still unclear. This study examined relationships of the S-cone ERG to systemic factors in diabetes. Cone ERGs to different color flash stimuli were examined in the presence of bright white background illumination in 17 diabetic patients without retinopathy and in 17 diabetics with background retinopathy. Relationships of the amplitude and implicit time of the S-cone ERG to the following systemic factors were statistically analyzed: patients' age, hemoglobin A1 level, method of diabetic control, presence of retinopathy, and presence of nephropathy. The amplitude of the S-cone ERG b-wave was significantly reduced in diabetics treated with insulin and in those associated with nephropathy. No significant correlation was found between the S-cone ERG and patient's age, hemoglobin A1 level and presence or absence of retinopathy. A selective reduction of the S-cone ERG is observed in patients whose metabolic control has been poor for a longer period, suggesting that microvascular changes may play a role in the S-cone ERG impairment.

Adult↗

PubMed1993

Results of deep prostatic hyperthermia applied with Thermex II in 525 benign prostatic hyperplasias.

Deep prostatic hyperthermia (DPH) with radiofrequency waves has been found to be of considerable beneficial value in benign prostatic hyperplasia. This study was performed on 525 patients. Madsen's criteria were used for symptom scoring. All the treatments were performed at 44.5 degrees C. Mean follow-up was 18 months. DPH is well tolerated and no severe complications were noted. Statistically meaningful changes of improvement were seen in mean flow rate and residual volume in 51% of the patients.

Adult↗

PubMed1985

Effects of ELF (1-120 Hz) and modulated (50 Hz) RF fields on the efflux of calcium ions from brain tissue in vitro.

We have previously shown that 16-Hz, sinusoidal electromagnetic fields can cause enhanced efflux of calcium ions from chick brain tissue, in vitro, in two intensity regions centered on 6 and 40 Vp-p/m. Alternatively, 1-Hz and 30-Hz fields at 40 Vp-p/m did not cause enhanced efflux. We now demonstrate that although there is no enhanced efflux associated with a 42-Hz field at 30, 40, 50, or 60 Vp-p/m, a 45-Hz field causes enhanced efflux in an intensity range around 40 Vp-p/m that is essentially identical to the response observed for 16-Hz fields. Fields at 50 Hz induce enhanced efflux in a narrower intensity region between 45 and 50 Vp-p/m, while radiofrequency carrier waves, amplitude modulated at 50 Hz, also display enhanced efflux over a narrow power density range. Electromagnetic fields at 60 Hz cause enhanced efflux only at 35 and 40 Vp-p/m, intensities slightly lower than those that are effective at 50 Hz. Finally, exposures over a series of frequencies at 42.5 Vp-p/m reveal two frequency regions that elicit enhanced efflux--one centered on 15 Hz, the other extending from 45 to 105 Hz.

Animals↗

PubMed1990

New experimental technique for detecting the effect of low-frequency electric fields on enzyme structure.

A new experimental approach has been developed to determine kinetic and thermodynamic parameters of the inactivation of an enzyme under labile conditions both with and without exposure to electrical currents as sources of perturbation. Studies were undertaken to investigate if low-frequency electric currents can accelerate the thermal inactivation of an enzyme through interactions with dipole moments in enzymatic molecules and through related mechanical stresses. The experiments were conducted with the enzyme acid phosphatase. The enzyme was exposed to a 50-Hz current at different densities (10 to 60 mA/cm2 rms) or to a sinusoidal or square-wave current at an average density of 3 mA/cm2 and frequencies from, respectively, 50 Hz to 20 kHz and 500 pulses per second (pps) to 50,000 pps. Positive-control experiments were performed in the presence of a stabilizer or a deactivator. The results indicate that the technique is sensitive to conformational changes that otherwise may be impossible to detect. However, exposure to electric currents under the experimental conditions described herein showed no effects of the currents.

Acid Phosphatase↗

PubMed1984

[Role of ultrasonic dopplerography in monitoring the effectiveness of treatment of patients who have sustained a stroke with decimeter-range electromagnetic waves].

The data on the high therapeutic efficiency of the local use of decimeter electromagnetic waves (DEMW) in stroke survivors are presented (a course of therapy consisted of 10-12 procedures). Doppler sonography proved to be a highly effective method of monitoring the treatment results. The technique makes it possible to ascertain some aspects of the mechanism of DEMW therapeutic action and provides the researcher with complete information on the intensity and the rate of the collateral circulation development.

Adult↗

PubMed2005

Atrial pacemaker complex preserved radiofrequency maze procedure reducing the incidence of sick sinus syndrome in patients with atrial fibrillation.

BACKGROUND: The Cox maze III procedure can effectively restore sinus rhythm in most patients with permanent atrial fibrillation (AF). However, previous studies have shown that the maze procedure results in significant sinus node dysfunction, and, consequently, a considerable number of patients required postoperative pacemaker implantation. HYPOTHESIS: This study investigates the hypothesis that the modification of the Cox III maze procedure, to avoid injuring the sinus node and the atrial physiologic pacemaker complex, will reduce the incidence of sick sinus syndrome following surgery. METHODS AND RESULTS: This study investigated 71 patients with permanent AF and mitral valve disease who were undergoing concomitant open-heart surgery. Most atrial incisions in the Cox maze III procedure were replaced with radiofrequency ablation, and the intercaval counterablation was moved posterolaterally to avoid injury to the sinus node and atrial pacemaker complex. At a mean (+/- SD) follow-up time of 46.5 +/- 24 months, 59 patients (83.1%) regained sinus rhythm without receiving antiarrhythmic drug therapy or undergoing electrical cardioversion. The transmitral atrial wave was observed in 44 patients (62%), and the transtricuspid atrial wave was also observed in 53 patients (74.6%). Late sinus node dysfunction developed in only two patients (2.8%), who received permanent pacemaker implantation. CONCLUSION: This modified radiofrequency maze procedure produces few patients with sick sinus syndrome and effectively restores sinus rhythm and atrial transport function in most patients with permanent AF undergoing concomitant open-heart surgery.

Atrial Fibrillation↗