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A W Guy

Publications and source records attributed to A W Guy.

At least 37 records · Page 2Linked to original sources
PubMed1988

Influence of microwaves on the beating rate of isolated rat hearts.

Previous reports have shown that microwave exposure can decrease the beating rate of isolated rat hearts. These experiments were conducted at room temperature and with the hearts exposed to air. We observed arrhythmia frequently at room temperature, and the variation of heart beat was so large that it makes the results difficult to reproduce. Therefore, we employed a double-circulating system to provide perfusion through the coronary artery and around the outside of the heart to maintain the rat hearts at 37.7 degrees C. No arrhythmias were observed in our experiments, and the hearts were beating for at least 1 h. The effects of 16-Hz modulated 2,450-MHz pulsed microwaves (10 microseconds, 100 pps) on the beating rate of 50 isolated rat hearts were studied. Results showed no statistically significant changes of heart rate in exposed groups at SARs of 2 and 10 W/kg compared with the control group. The effect seen at 200 W/kg was shown to be similar to that resulting from heating the heart.

Animals↗
PubMed1988

Acute low-level microwave exposure and central cholinergic activity: studies on irradiation parameters.

Sodium-dependent high-affinity choline uptake was measured in the striatum, frontal cortex, hippocampus, and hypothalamus of rats after acute exposure (45 min) to pulsed (2 microseconds, 500 pps) or continuous-wave 2,450-MHz microwaves in cylindrical waveguides (Guy et al.: Radio Science 14:63-74, 1979) or miniature anechoic chambers (Guy: Journal of Microwave Power 14:327-338, 1979). In all exposure conditions, the average whole-body specific absorption rate was at 0.6 W/kg. Decrease in choline uptake was observed in the frontal cortex after microwave exposure in all of the above irradiation conditions. Regardless of the exposure system used, hippocampal choline uptake was decreased after exposure to pulsed but not continuous-wave microwaves. Striatal choline uptake was decreased after exposure to either pulsed or continuous-wave microwaves in the miniature anechoic chamber. No significant change in hypothalamic choline uptake was observed under any of the exposure conditions studied. We conclude that depending on the parameters of the radiation, microwaves can elicit specific and generalized biological effects.

Animals↗
PubMed1988

Superficial- and deep-tissue temperature increases in anesthetized dogs during exposure to high specific absorption rates in a 1.5-T MR imager.

Superficial- and deep-tissue heating was measured in five dogs during high-specific-absorption-rate radiofrequency (RF) irradiation to see whether significant temperature changes could be produced by a 1.5-T clinical magnetic resonance imager. The RF power output employed was 6.3 times that required for routine imaging. Temperature probes were placed in both deep and superficial tissues, and temperatures were recorded before, during, and after exposure. In each dog, there was a linear temperature increase of several degrees during RF exposure; the maximal average change was 4.6 degrees C in the urinary bladder. The temperature increase was slightly greater in deep tissues than in superficial tissues. The calculated specific absorption rate, based on the temperature change, averaged 7.9 W/kg for all five dogs. These findings argue for continued caution in the design and operation of imagers capable of high specific absorption rates, particularly when they are used for imaging infants or patients with altered thermoregulatory capability.

Absorption↗
PubMed1987

Thermal cataract formation in rabbits.

Intraocularly circulating hot water was used to produce cataracts in nine eyes of seven rabbits by maintaining their retrolental temperatures between 43 degrees C and 45 degrees C. A rapid rate of heating (1.3 degrees C/min) plus a sharp temperature gradient across the eye may have been contributing factors in the consistent production of cataracts at these temperatures. Biomicroscopy and light microscopy showed lens changes similar to those associated with acute exposure to microwave radiation. These findings support the assumption that microwave cataractogenesis is due to the local production of elevated temperatures.

Animals↗
PubMed1987

Effects of low-level microwave irradiation on hippocampal and frontal cortical choline uptake are classically conditionable.

In previous research, we found that sodium-dependent high-affinity choline uptake in the hippocampus and frontal cortex of the rat was lowered after acute (45 min) exposure to low-level 2450-MHz pulsed microwaves (power density 1 mW/cm2; average whole body specific absorption rate, 0.6 W/kg; 2 mu sec pulses, 500 pps). In the present experiment, we investigated developments of tolerance and classical conditioning to these effects of microwaves. Rats were exposed to microwaves in cylindrical waveguides in 10 daily sessions (45 min per session). In an 11th session, we subjected the rats to either microwave (study of tolerance) or sham exposure (study of conditioned effect) for 45 min, and immediately measured choline uptake in the hippocampus and frontal cortex. We found that tolerance, a decrease in response to microwaves, developed to the effect of microwaves on choline uptake in the hippocampus, but not in the frontal cortex. Conditioned effects were also observed: an increase in choline uptake in the hippocampus and a decrease in uptake in the frontal cortex. These data suggest that the effects of microwaves on choline uptake in the hippocampus and frontal cortex are classically conditionable, probably to cues in the exposure environment.

Animals↗
PubMed1987

Dosimetry associated with exposure to non-ionizing radiation: very low frequency to microwaves.

The interpretation of the effects in biological systems exposed to electromagnetic (EM) fields requires knowledge of the internal fields and absorbed energy. The quantification of the specific absorption rate (SAR) is called dosimetry. The SAR given in units of watts per kilogram is a complex function of the source configuration, shape and size of the exposed subjects, orientation of the subject with respect to the source, and the frequency. The average and maximum SAR in the exposed subject may vary over many orders of magnitude for a given exposure level. In order to relate observed biological effects in exposed laboratory animals to safe exposure levels for man, both the fields within the environment and SAR within the exposed tissues must be determined. The environmental fields and the SAR can often be determined from EM theory, but in most cases one must rely on instrumentation such as field survey meters for quantifying the exposure fields and electric field probes, thermocouples, thermistors, fiber optic probes, thermography, and calorimetry for quantifying the SAR in the tissues or equivalent models. A combination of techniques, each valid for a particular model over a particular frequency range, have been used to determine average and peak SARs in humans and animals exposed to plane wave radiation. Though it has been considerably more difficult to quantify these quantities for near field and partial-body exposure conditions, progress is continually being made in this area.

Animals↗
PubMed1987

Low-level microwave irradiations affect central cholinergic activity in the rat.

Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain.

Animals↗
PubMed1986

Effects of low-level microwave irradiation on amphetamine hyperthermia are blockable by naloxone and classically conditionable.

In a series of experiments, we investigated the effects of pulsed low-level microwave irradiation on amphetamine-induced hyperthermia in the rat. Rats were irradiated in a 2,450-MHz cylindrical waveguide exposure system at 1 mW/cm2, 2 mus pulses, 500 pps, average SAR of 0.6 W/kg. Acute (45 min) exposure to microwaves attenuated amphetamine-induced hyperthermia. This effect was blocked by pretreatment of the animals with the narcotic antagonist naloxone. In another experiment, rats were subjected to ten daily sessions of microwave exposure (45 min/session). On day 11, amphetamine-induced hyperthermia was studied in the animals immediately after a session of either microwave or sham exposure. Similar to the acute effect, amphetamine-induced hyperthermia was attenuated in rats irradiated with microwaves (unconditioned effect). In the sham-irradiated animals we observed a potentiation of the amphetamine-induced hyperthermia, which was a conditioned effect of microwaves. Thus, the conditioned effect (potentiation) was opposite in direction to the unconditioned effect (attenuation). No tolerance developed to the unconditioned effect after subchronic exposure. Furthermore, both conditioned and unconditioned effects of microwaves on amphetamine-induced hyperthermia could be blocked by treatment with naloxone. These data suggest that microwave irradiation may activate endogenous opioids, which in turn alter the actions of psychoactive drugs, and the effect of microwaves on drug action can be classically conditioned.

Amphetamine↗
PubMed1986

Low-level microwave irradiation attenuates naloxone-induced withdrawal syndrome in morphine-dependent rats.

The effect of microwave irradiation on naloxone-induced withdrawal syndrome was studied in rats made morphine dependent by subcutaneous implantation of morphine pellets. Morphine-dependent rats were either exposed to pulsed low-level microwaves (2450 MHz, 1 mW/cm2, 500 pps, 2 musec pulses) or sham-irradiated for 45 min before the naloxone injection. We found that microwave-exposed rats showed significantly less weg-dog-shakes and had higher body temperature than the sham-exposed animals during withdrawal. There was no significant difference in the incident of diarrhea between the two groups of animals. These data further support the results of our previous research suggesting that pulsed low-level microwave irradiation activates endogenous opioids in the rat.

Animals↗
PubMed1986

Effects of pulsed microwave radiation on the contractile rate of isolated frog hearts.

Hearts from 81 frogs were divided into 10 groups and placed individually in a temperature-controlled waveguide filled with Ringer's solution. Hearts of Group A served as controls. Hearts of the other nine groups were treated with pulsed microwaves (2450 MHz, 10 microseconds, 100 pps) that ranged from a specific-absorption rate (SAR) of 2 to 200 W/kg. In several groups, an electrocardiogram was used to synchronize microwave irradiation with the heartbeat. In one group of frog hearts exposed at 200 W/kg, the heart rate slowed down sharply 25 minutes after irradiation, by which time the temperature of the Ringer's solution had risen by 7 degrees C. In another group exposed at 200 W/kg but under constant temperature, the heartbeat almost paralleled that of the control group. Other groups, including exposures of frog hearts to 16 Hz modulated CW or pulsed fields at SARs from 3 mW/kg to 8.55 W/kg, showed no effects of pulsed microwave irradiation on heartbeats; no brachycardia or tachycardia were found at constant temperatures.

Animals↗
PubMed1985

Specific absorption rate in rats exposed to 2,450-MHz microwaves under seven exposure conditions.

Both positive and negative biological effects of microwaves on drug actions in rats exposed to 1-mW/cm2, 2,450-MHz microwaves have been reported by several investigators. We conducted dosimetry studies for seven different exposure conditions to determine whether these different results could be due to the rats having been exposed differently. They included anterior and posterior exposures in a circular waveguide, near field, far field with E- or H-field parallel to the long axis of the body and dorsal exposure in a miniature anechoic chamber with E- or H-field parallel to the long axis of the body. The average specific absorption rates (SARs) in the head, tail, and body of the exposed rats were measured by means of a calorimetry system. The local SARs at eight locations in the brain were determined by temperature measurement with Vitek probes. Intensive coupling of energy to the tail when it was exposed parallel to the E-field was shown by thermography. For the same average incident power density, the average SARs in the heads of rats were about two times higher in the circular waveguide than for other exposures. The local SARs in the brain varied for different exposure conditions. Statistical comparisons of SARs under the different exposure conditions are presented.

Animals↗
PubMed1985

Auditory response in rats exposed to 2,450 MHz electromagnetic fields in a circularly polarized waveguide.

Rats were exposed to 2,450-MHz pulsed microwave fields in a circularly polarized waveguide. The threshold incident energy density per pulse was about 1.5 to 3 microJ/cm2 over the range 1-10 microseconds. The corresponding whole-body averaged specific absorption of energy was 0.9 to 1.8 mJ/kg per pulse. The same response was evoked when the incident energy density or absorbed energy density per pulse was the same, regardless of the pulse widths.

Animals↗
PubMed1985

Absorption of microwave energy by muscle models and by birds of differing mass and geometry.

Spheres composed of phantom muscle of radius 1.5, 2, 3, 4, 6 and 8 cm, as well as birds (parakeets, quail, pigeons, chickens, turkeys) were exposed to far-field plane waves at power densities of incident radiation between 182 and 560 mW/cm2 and at frequencies of 775, 915 and 2450 MHz. Specific absorption rate (SAR) patterns were determined by thermographic techniques for both spheres and birds. The measured SAR patterns in spheres were comparable to those from theoretical predictions. The SAR patterns in birds, however, varied markedly from those obtained from spheres of comparable mass. The results indicate that the geometrically complex animal is not represented by simple geometric models for making absorption studies. Thermograms of birds exposed in the flying position indicated that the SAR is high in the wings. The behavioral response of the birds to the exposure was variable. Threshold power densities for biological or behavioral reactions were determined for each bird at all three frequencies. The lowest power density associated with reactivity by the chicken was 5.8 mW/cm2 (corresponding to SARs of 3.1 W/kg in the head and 3.9 W/kg in the neck) at 775 MHz.

Animals↗
PubMed1984

Theoretical and experimental determination of SAR patterns for spherical tissue models in a rectangular resonant cavity.

Specific absorption rates (SARs) were determined theoretically and experimentally for several spherical models of tissue exposed to electrical fields of TE101 mode in a rectangular cavity of 57.3 MHz resonant frequency. The approximate theoretical SAR can be calculated according to the Mie theory by superposition of four plane waves representing the fields excited in the cavity. The theoretical and thermographically determined SAR patterns in spheres with radii of 5, 7.5, and 10 cm and with conductivities of 0.1, 1, and 10 S/m were compared. For a sphere with radius less than 7.5 cm and conductivity less than 1 S/m, the SAR was quite uniform. When conductivity was increased to 10 S/m, the SAR patterns showed higher absorption in the periphery of the largest sphere (10-cm radius). These characteristics are important in evaluating the scaling technique of exposing a model of a human to very-high-frequency fields to obtain power absorption data in humans exposed to high-frequency or very-low-frequency fields.

Electromagnetic Fields↗
PubMed1984

Effects of acute low-level microwaves on pentobarbital-induced hypothermia depend on exposure orientation.

Two series of experiments were performed to study the effects of acute exposure (45 min) to 2,450-MHz circularly polarized, pulsed microwaves [1 mW/cm2, 2-mus pulses, 500 pps, specific absorption rate (SAR) 0.6 W/kg] on the actions of pentobarbital in the rat. In the first experiment, rats were irradiated with microwaves and then immediately injected with pentobarbital. Microwave exposure did not significantly affect the extent of the pentobarbital-induced fall in colonic temperature. However, the rate of recovery from the hypothermia was significantly slower in the microwave-irradiated rats and they also took a significantly longer time to regain their righting reflex. In a second experiment, rats were first anesthetized with pentobarbital and then exposed to microwaves with their heads either pointing toward the source of microwaves (anterior exposure) or pointing away (posterior exposure). Microwave radiation significantly retarded the pentobarbital-induced fall in colonic temperature regardless of the orientation of exposure. However, the recovery from hypothermia was significantly faster in posterior-exposed animals compared to those of the anterior-exposed and sham-irradiated animals. Furthermore, the posterior-exposed rats took a significantly shorter time to regain their righting reflex than both the anterior-exposed and sham-irradiated animals.

Animals↗