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At least 703 records · Page 39Linked to original sources
PubMed1980

Microwave-induced pressure waves in a model of muscle tissue.

Microwave-induced mechanical stress waves were studied in simulated muscle tissue. Pulsed microwave energy at 5.655 GHz induced pressure waves that were recorded with a hydrophone transducer. Each pulse produced a peak power density greater than 1.5 kW/cm2. Microwave absorption measurements within the model showed energy deposition to be mostly confined to a region within 2 cm of the irradiated surface. The average specific absorption rate (SAR) at the surface of the sample was about 100 W/kg. The microwave-induced stress wave propogated at a velocity of 1,600 m/sec with peak pressures of approximately 300 pascals and was detectable after having traveled a total distance of 0.61 m on a path that included two reflections at model-container interfaces.

Absorption↗
PubMed1980

Effect of microwaves (2450-MHz) on the immune system in mice: studies of nucleic acid and protein synthesis.

CBA/J adult male mice were given single or triple exposures to 2450-mHz microwaves in an environmentally controlled wave guide facility. The average absorbed dose rate for a single exposure varied from 12 to 15 mW/g. Sham-exposed mice served as controls. Lymphoid cells were collected and tested for metabolic activity on days 3, 6, and 9 following a single exposure, and on days 9, 12, and 16 following triple exposures on days 0, 3, and 6. Cells were cultured in vitro for four hours to seven days before their metabolic rates were assayed. Under these conditions, microwaves failed to produce any detectable change in deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and protein synthesis, as measured by the incorporation of methyl(3H)-thymidine (3H-TDR) (DNA substrate), 3H-uridine (3H-UR) (RNA substrate), and 3H-leucine (protein substrate) by spleen, bone marrow, and peripheral blood lymphocytes (PBL) in vitro. These data suggest that microwave-induced increases in the frequency of complement-receptor (CR)- or surface-immunoglobulin (sIg)-bearing cells were not associated with a concomitant increase in cell proliferation and/or protein synthesis, and favor the concept that microwaves under these conditions stimulate already existing B-cell precursors for maturation.

Animals↗
PubMed1980

Effects of 2.45-GHz microwave radiation on embryonic quail hearts.

Although exposure to nonionizing electromagnetic radiation has been reported to cause a variety of systemic alterations during embryonic development, there are few reports of the induction of specific physiology or morphologic changes in the myocardium. This study was designed to examine the effects of microwave radiation on cardiogenesis in Japanese quail embryos exposed during the first eight days of development to 2.45-GHz continuous-wave microwaves at power densities of 5 or 20 mW/cm2. The specific absorption rates were 4.0 and 16.2 mW/g, respectively. The ambient temperature for each exposure was set to maintain the embryonated eggs at 37.5 degree C. This did not preclude thermal gradients in the irradiated embryos since microwaves may not uniformly absorbed. The test exposure levels did not induce changes in either the morphology of the embryonic heart or the ultrastructure of the myocardial cells. Analysis of the enzymatic activities of lactate dehydrogenase, glutamic oxaloacetic transaminase, and creatine phosphokinase failed to reveal any statistically significant differences between the nonexposed controls and those groups exposed to either 5 or 20 mW/cm2. The data indicate that 2.45-GHz microwave radiation at 5 or 20 mW/cm2 has no effect on the measured variables of the Japanese quail myocardium exposed during the first eight days of development.

Animals↗
PubMed1981

Fluorescence depolarization studies of red cell membrane fluidity. The effect of exposure to 1.0-GHz microwave radiation.

The internal viscosity of human red blood cell membranes was investigated during exposure to continuous wave 1.0-GHz microwave radiation using fluorescence measurements of a lipid seeking molecular probe, diphenyl-hexatriene. Samples were exposed in a Crawford cell arranged so that fluorescence was measured during microwave exposure; specific absorption rates calculated from electrical measurements were approximately 0.6, 2 and 15 W/kg. Measurements were obtained at selected temperatures between 15 degrees C and 40 degrees C and as a function of the duration of exposure at 23 degrees C. Arrhenius-type plots of the temperature profile data were linear and showed no difference between exposed and control samples. The exposure duration data also showed no difference between exposed and control samples except for a small effect of elevated temperature at the highest exposure. The activation energy for motion of the fluorescent probe in its environment within the membrane lipid was not affected by the application of the microwave energy and no evidence for a lipid phase transition was found. These results indicate that the increased cation efflux from red cells, observed by others at certain transition temperatures during microwave exposure, was more likely to have been caused by alteration of the membrane bound protein than by changes in the lipid constituents of the red cell membrane.

Dose-Response Relationship, Radiation↗
PubMed1982

Investigation of the effects of continuous-wave, pulse- and amplitude-modulated microwaves on single excitable cells of Chara corallina.

Single internodal excitable cells of Chara corallina were exposed to CW, pulse-modulated and sinusoidally modulated S-band microwave fields in a temperature-controlled waveguide exposure chamber. All electrical measurements were made external to the waveguide (ie, under no impressed microwave field). The dependent variables measured before, during, and after exposure to the S-band microwave fields included: resting potential, amplitude of the action potential, rise and decay time of the action potential, conduction velocity, and excitability. Cells maintained at 22 +/- 0.1 degrees C during exposure showed no consistent or statistically significant microwave-dependent alterations in any of the dependent variables.

Chlorophyta↗
PubMed1982

Reduced weight in mice offspring after in utero exposure to 2450-MHz (CW) microwaves.

Time-bred CD-1 mice (100) were sham-irradiated or irradiated with 2450-MHz (CW) microwaves at 28 mW/cm2 for 100 minutes daily from the 6th through 17th day of gestation. The offspring were examined either as fetuses after hysterotomy on the 18th day of gestation or as naturally born neonates on the 1st and 7th day of age. Fetuses of half of the dams were examined on the 18th day of gestation. The incidence of pregnancy and the numbers of live, dead, resorbed, and total fetuses were similar in both groups. The mean weight was significantly lower (10%) in live microwave-irradiated fetuses, and ossification of sternal centers was significantly delayed. In the offspring that were born naturally, the mean weight of microwave-irradiated 7-day-old suckling mice was significantly lower (10%) than that of the sham-irradiated group. Survival rates of neonates in these two groups were not different. These data demonstrate that the decreased fetal weight seen in microwave-irradiated mice is retained at least 7 days after birth. Evidence from other published studies is presented to show that the retarded growth is persistent and might be interpreted as permanent stunting.

Animals↗
PubMed1982

Effects of X-band microwave exposure on rabbit erythrocytes.

Rabbit erythrocytes were exposed in vitro to continuous wave (CW) and pulse-modulated X-band microwaves in wave guide exposure chambers. Erythrocytes were exposed as whole (heparinized) blood suspensions or as washed cells in 1:1 isotonic buffered K+-free saline suspensions. Statistically significant increases in K+ efflux relative to thermal controls were detected when red cells were exposed in whole blood suspensions to either CW or pulsed 8.42-GHz microwaves at SARs that resulted in equilibrium sample temperatures of approximately 24 degrees C. Under the same exposure conditions, no statistically significant K+ efflux occurred in the case of 1:1 red cell suspensions. Measured differences in sample heating rates and temperature gradients between microwave-exposed and heated control suspensions may account in part for the differential effect of microwave exposure but such effects do not appear to explain the results of this study fully.

Animals↗
PubMed1983

A microwave-hyperthermia model of febrile convulsions.

While convulsions associated with fever represent a serious problem in pediatric medicine, conventional animal models of febrile convulsions suffer numerous technical limitations. A microwave-hyperthermia model that eliminates these problems was tested. Microwave energy was used to increase the core temperature of 13- and 17-day-old rats, resulting in convulsions similar to febrile convulsions in human infants. Rats were irradiated for 10 min in circularly polarized waveguides at 918 MHz, CW (average SAR = 9.4 W/kg at 13 days and 18.0 W/kg at 17 days as determined by twin-well calorimetry). Day 17 irradiated rats were less susceptible to convulsions that were day 13 irradiated rats, indicating an age-dependent decline in susceptibility. Contrary to findings of earlier models using infrared or hot-oven heating, convulsions induced with microwave hyperthermia impaired neither brain growth nor subsequent performance during behavioral testing. Simultaneous measurement of brain and rectal temperatures during microwave irradiation revealed differential heating rates that favor thermal homeostasis in brain tissue.

Animals↗
PubMed1984

Microwave bioeffects in the erythrocyte are temperature and pO2 dependent: cation permeability and protein shedding occur at the membrane phase transition.

Microwave exposure (2450 MHz, 60 mW/g, CW) of rabbit erythrocytes increases Na passive transport only at membrane phase transition temperatures (Tc) of 17-19 degrees C. This permeability effect is enhanced for relative hypoxia which is characteristic of intracellular oxygen tension (pO2 less than or equal to 5 mm Hg). Neither the permeability nor the pO2 effects are observed in temperature-matched (+/- 0.05 degrees C), sham-exposed controls. In addition, at Tc, microwave exposure is observed to induce the shedding or release of two erythrocyte proteins not seen in sham-exposed controls. Moreover, the enhanced shedding of at least seven other proteins all of molecular weight less than or equal to 28,000 D was detected in the microwave-treated samples. Using sensitive silver staining we estimate that approximately 450 fg of protein were shed per erythrocyte. These results demonstrate that temperature and pO2 are important influences on both functional and structural responses of cell membranes to microwave radiation.

Animals↗
PubMed1985

Effects of continuous-wave, pulsed, and sinusoidal-amplitude-modulated microwaves on brain energy metabolism.

A comparison of the effects of continuous-wave, sinusoidal-amplitude-modulated, and pulsed square-wave-modulated 591-MHz microwave exposures on brain energy metabolism was made in male Sprague-Dawley rats (175-225 g). Brain NADH fluorescence, adenosine triphosphate (ATP) concentration, and creatine phosphate (CP) concentration were determined as a function of modulation frequency. Brain temperatures of animals were maintained between -0.1 and -0.4 degrees C from the preexposure temperature when subjected to as much as 20 mW/cm2 (average power) CW, pulsed, or sinusoidal-amplitude modulated 591-MHz radiation for 5 min. Sinusoidal-amplitude-modulated exposures at 16-24 Hz showed a trend toward preferential modulation frequency response in inducing an increase in brain NADH fluorescence. The pulse-modulated and sinusoidal-amplitude-modulated (16 Hz) microwaves were not significantly different from CW exposures in inducing increased brain NADH fluorescence and decreased ATP and CP concentrations. When the pulse-modulation frequency was decreased from 500 to 250 pulses per second the average incident power density threshold for inducing an increase in brain NADH fluorescence increased by a factor of 4--ie, from about 0.45 to about 1.85 mW/cm2. Since brain temperature did not increase, the microwave-induced increase in brain NADH and decrease in ATP and CP concentrations was not due to hyperthermia. This suggests a direct interaction mechanism and is consistent with the hypothesis of microwave inhibition of mitochondrial electron transport chain function of ATP production.

Adenosine Triphosphate↗
PubMed1986

Behavioral and physiological effects of chronic 2,450-MHz microwave irradiation of the rat at 0.5 mW/cm2.

Adult male Long-Evans rats were intermittently exposed to 2450 MHz CW microwaves at an average power density of 0.5 mW/cm2 for 90 days. The resulting SAR was 0.14 W/kg (range 0.11 to 0.18 W/kg). The animals were exposed 7 h/day, 7 days/wk, for a total of 630 h in a monopole-above-ground radiation chamber while housed in Plexiglas holding cages. Daily measures of body mass and food and water intake indicated no statistically significant effects of microwave exposure. Monthly assessment of reactivity to electric footshock, levels of cholinesterase and sulfhydryl groups in blood, and 17-ketosteroids in urine revealed no reliable differences between 14 sham-exposed and 14 microwave-exposed rats. After the 90 days of exposure, seven rats, randomly chosen from each group, were assessed for open-field behavior, shuttlebox performance, and schedule-controlled (IRT schedule) lever pressing for food pellets. Statistically significant differences between microwave-exposed and sham-exposed rats were observed in shuttlebox performances and lever pressing. Post mortem measures of mass of several organs and microscopic examination of adrenal tissue revealed no differences between the two groups of animals.

17-Ketosteroids↗
PubMed1986

Intermittent exposure of rats to 2450 MHz microwaves at 2.5 mW cm2: behavioral and physiological effects.

Long-Evans male adult rats were intermittently exposed for 14 weeks to continuous wave (CW) 2450-MHz microwaves at an average power density of 2.5 mW/cm2. The mean specific absorption rate was 0.70 W/kg (+/- 0.02 SEM). The rats were exposed 7 h/day, 7 days/week in a radiation chamber with a monopole above ground, while housed in Plexiglas cages. Weekly measures of body mass and food intake did not indicate statistically significant effects of microwave irradiation. Assessments of threshold for electric-footshock detection revealed a significant difference between microwave and sham-exposed animals. Assessments of cholinesterase and sulfhydryl groups in blood and 17-ketosteroids in urine did not distinguish the two groups of rats. Behavioral measures made at the end of the 14-week exposure included an open-field test, shuttlebox avoidance performance, and schedule-controlled lever-pressing for food pellets. Statistically significant differences between microwave- and sham-exposed rats were observed for these measures. Examination of adrenal tissue, plasma electrolytes, and organ masses after 14 weeks of exposure revealed no difference between the two groups of rats.

17-Ketosteroids↗
PubMed1987

Behavioral effects of chronic exposure to 0.5 mW/cm2 of 2,450-MHz microwaves.

Adult male, Long-Evans rats were exposed 7 h a day for 90 days to continuous wave (CW) 2,450-MHz microwaves at an average power density of 0.5 mW/cm2. Exposures were in a monopole-above-ground radiation chamber with rats in Plexiglas cages. The resulting specific absorption rate (SAR) was 0.14 W/kg (+/- 0.01 SEM). Additional rats served as sham-exposed and home-caged controls. All were evaluated daily for body mass and food and water intakes. Once each 30 days, throughout baseline and exposure phases of the experiment, rats in the sham- and microwave-exposed groups were tested for their sensitivity to footshock. After 90-days of exposure, the rats were evaluated an open field, an active avoidance task and an operant task for food reinforcement. Performance of sham- and microwave-irradiated rats was reliably different on only one measure, the lever-pressing task. The general conclusion reached was that exposure to CW 2,450-MHz microwave radiation at 0.5 mW/cm2 was below the threshold for behavioral effects over a wide range of variables, but did have an effect on a time-related operant task, although the direction of the effect was unpredictable.

Animals↗
PubMed1987

Effects of microwave exposure and temperature on survival of mice infected with Streptococcus pneumoniae.

Female CD-1 mice were injected with an LD50 dose of Streptococcus pneumoniae and then exposed to 2.45 GHz (CW) microwave radiation at an incident power density of 10 mW/cm2 (SAR = 6.8 W/kg), 4 h/d for 5 d at ambient temperatures of 19 degrees C, 22 degrees C, 25 degrees C, 28 degrees C, 31 degrees C, 34 degrees C, 37 degrees C and 40 degrees C. Four groups of 25 animals were exposed at each temperature with an equal number of animals concurrently sham-exposed. Survival was observed for a 10-d period after infection. Survival of the sham-exposed animals increased as ambient temperature increased from 19 degrees C-34 degrees C. At ambient temperatures at or above 37 degrees C the heat induced in the body exceeded the thermoregulatory capacity of the animals and deaths from hyperthermia occurred. Survival of the microwave-exposed animals was significantly greater than the shams (approximately 20%) at each ambient temperature below 34 degrees C. Based on an analysis of the data it appears that the hyperthermia induced by microwave exposure may be more effective in increasing survival in infected mice than hyperthermia produced by conventional methods (ie, high ambient temperature). Microwave radiation may be beneficial to infected animals at low and moderate ambient temperatures, but it is detrimental when combined with high ambient temperatures.

Animals↗
PubMed1988

Microwave effects on acetylcholine-induced channels in cultured chick myotubes.

The behavior of cultured myotubes from chick embryos exposed to microwaves has been experimentally analyzed. Recordings of acetylcholine-induced currents have been obtained via patch-clamp techniques using both cell-attached (single-channel current recording) and whole-cell (total current recording) configurations. During the exposure to low-power microwaves the frequency of the ACh-activated single channel openings decreased, while the ACh-induced total current showed a faster falling phase. Channel open time and conductance were not affected by microwave irradiation. It is concluded that the exposure to microwaves increases the rate of desensitization and decreases the channel opening probability. The nonthermal origin and the molecular interaction mechanisms governing these electromagnetic-induced effects are discussed.

Acetylcholine↗
PubMed1989

Lack of behavioral effects in the rhesus monkey: high peak microwave pulses at 1.3 GHz.

The current safety standards for radiofrequency and microwave exposure do not limit the peak power of microwave pulses for general or occupational exposures. While some biological effects, primarily the auditory effect, depend on pulsed microwaves, hazards associated with very high peak-power microwave pulses in the absence of whole-body heating are unknown. Five rhesus monkeys, Macaca mulatta, were exposed to peak-power densities of 131.8 W/cm2 (RMS) while performing a time-related behavioral task. The task was composed of a multiple schedule of reinforcement consisting of three distinct behavioral components: inter-response time, time discrimination, and fixed interval. Trained monkeys performed the multiple schedule during exposure to 1.3-GHz pulses at low pulse-repetition rates (2-32 Hz). No significant change was observed in any behavior during irradiation as compared to sham-irradiation sessions. Generalization of these findings to experimental results with higher peak-power densities, other pulse rates, different carrier frequencies, or other behaviors is limited.

Animals↗
PubMed1991

Naltrexone pretreatment blocks microwave-induced changes in central cholinergic receptors.

Repeated exposure of rats to pulsed, circularly polarized microwaves (2,450-MHz, 2-microseconds pulses at 500 pps, power density 1 mW/cm2, at an averaged, whole-body SAR of 0.6 W/kg) induced biphasic changes in the concentration of muscarinic cholinergic receptors in the central nervous system. An increase in receptor concentration occurred in the hippocampus of rats subjected to ten 45-min sessions of microwave exposure, whereas a decrease in concentration was observed in the frontal cortex and hippocampus of rats exposed to ten 20-min sessions. These findings, which confirm earlier work in the authors' laboratory, were extended to include pretreatment of rats with the narcotic antagonist naltrexone (1 mg/kg, IP) before each session of exposure. The drug treatment blocked the microwave-induced changes in cholinergic receptors in the brain. These data further support the authors' hypothesis that endogenous opioids play a role in the effects of microwaves on central cholinergic systems.

Animals↗
PubMed1991

Immediate post-exposure effects of high-peak-power microwave pulses on operant behavior of Wistar rats.

Behavioral effects of high-peak-power microwave pulses on Wistar rats were studied by operant schedules. Each of twelve rats that had been trained to press a lever to receive food pellets was assigned randomly in groups of four to three different schedules of reinforcement: fixed-ratio (FR), variable-interval (VI), and differential-reinforcement-of-low-rates (DRL). After achieving a steady baseline performance, each animal was exposed for 10 min to 1.25-GHz microwave radiation at 1-MW peak-power (10-microseconds pulse width). Each pulse produced a peak whole-body SA and SAR of 2.1 J/kg and 0.21 MW/kg. Total doses (SAs) were set to 0.50, 1.5, 4.5, and 14 kJ/kg by adjusting the pulse-repetition rate. The corresponding time-averaged whole-body SARs were 0.84, 2.5, 7.6, and 23 W/kg. A microwave-transparent animal holder was used to keep the animal's body axis parallel to the E-field. Exposures at the highest dose caused an average colonic temperature rise of 2.5 degrees C and these animals failed to respond at all for about 13 minutes after the exposure. Their colonic temperatures had decreased to 1.1 degrees C, or less, above their pre-exposure (normal) temperature level when they began to respond. The FR and VI animals failed to reach their baseline levels of performance thereafter, while those on the DRL schedule displayed variable effects. No behavioral effects were found at the lower dose levels. It is concluded that the behavioral perturbations produced by pulsed microwave irradiation were thermal in nature.

Animals↗