Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “MICROWAVES”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 757 records · Page 42Linked to original sources
PubMed1992

Microwave thermal balloon angioplasty in the normal rabbit.

The feasibility of utilizing microwave energy for thermal angioplasty was evaluated in 28 normal New Zealand white rabbits. Angioplasty catheters were inserted via bilateral femoral arteriotomy and balloon angioplasty was performed on the external iliac arteries. There were three variables in the microwave angioplasty procedure: peak temperature, energy duration, and peak balloon pressure. At 1 week after the angioplasty, animals were put to death and the iliac arteries were removed after perfusion fixation. Histologic analysis was performed. Injuries to the medial and intimal proliferation were evaluated using an index based on the circumferential extent and depth of abnormality. There was no relationship noted between intimal proliferation or medial injury and energy duration of peak balloon pressure. There was a direct relationship between peak temperature and medial injury. Furthermore, there was an inverse relationship between medial injury and intimal proliferation. The axial extent of change induced by microwave energy was 1.6 cm. Microwave thermal energy delivery through a balloon angioplasty catheter is feasible and can be performed conveniently.

Angioplasty, Balloon↗
PubMed1986

Microwave sterilization of hydrophilic contact lenses.

We used standard 2,450-MHz microwave irradiation to achieve sterilization of hydrophilic contact lenses contaminated with a variety of bacterial, fungal, and viral corneal pathogens. A three-dimensional rotisserie was used to overcome the problem of "cold spots" within the microwave oven. The contact lenses became dehydrated in approximately two minutes. Rehydration with normal saline restored their shape and appearance. The time necessary to prohibit all growth of the bacterial and fungal organisms studied ranged from 45 seconds to eight minutes. All viral contaminants were completely inactivated after four minutes of microwave exposure. Refractive properties were unaffected after 101 exposures to microwaves for ten minutes. Slit-lamp examination and scanning electron microscopy disclosed minute particles on the surface of these contact lenses but no damage to the lens matrix from irradiation.

Bacteria↗
PubMed1979

Characterization of iron-sulphur centres of plant mitochondria by microwave power saturation.

The electron spin relaxation of iron-sulphur centres and ubisemiquinones of plant mitochondria was studied by microwave power saturation of the respective EPR signals. In the microwave power saturation technique, the experimental saturation data were fitted by a least-squares procedure to a saturation function which is characterized by the power for half-saturation (P1/2) and the inhomogeneity parameter (b). Since the theoretical saturation curves were based on a one-electron spin system, it became possible to differentiate between EPR signals of iron-sulphur centres which have similar g values but different P1/2 values. If the difference in the P1/2 values of the overlapped components was small, no significant deviation from these theoretical saturation curves was observed, as shown for the overlapped signals of centre S-3 and the Ruzicka centre of mung bean mitochondria. By contrast, the microwave power saturation data for the g = 1.93 signal (17--26 K) of Arum maculatum submitochondrial particles reduced by succinate could not be fitted using one-electron saturation curves. Reduction by NADH resulted in a stronger deviation. Since the iron-sulphur centres of Complex I were present only in an unusually low concentration in A. maculatum mitochondria, it was proposed that an iron-sulphur centre of the external NADH dehydrogenase contributes to the spectrum of centre S-1. For mung bean mitochondria, the g = 1.93 signal below 20 K could be attributed mainly to centre N-2. The microwave power saturation technique was also suitable for detecting magnetic interactions between paramagnetic centres. From the saturation data of the complex spectrum attributable to centre S-3 and an interacting ubisemiquinone pair in mung bean mitochondria (oxidized state) followed that centre S-3 has a faster electron spin relaxation than the ubisemiquinone molecules. It is noteworthy that the differences in the relaxation rates were maintained despite the interaction between centre S-3 and the ubisemiquinones. Furthermore, a relaxation enhancement was observed for centre S-1 of A. maculatum submitochondrial particles upon reduction of centre S-2 by dithionite. This indicated a magnetic interaction between centres S-1 and S-2.

Electron Spin Resonance Spectroscopy↗
PubMed1979

Permeability of the blood-brain barrier to mannitol in the rat following 2450 MHz microwave irradiation.

The radiotracer method of Oldendorf was used to determine if 2450 MHz continuous wave (CW) microwave energy increases blood-brain barrier permeability to [14C]mannitol, which is normally excluded from entering the brain. Anesthetized, adult rats were irradiated singly for 30 min in the quiet zone of an anechoic chamber, at average power densities from 0.1 to 30 mW/sq.cm. Afterwards each rat received an intracarotid bolus injection of [14C]mannitol/[3H]water mixture and was decapitated 15 sec later. Uptake of [14C]mannitol relative to the highly permeable reference substance, [3H]water, was calculated as the brain uptake index (BUI) for 4 brain regions. Mean BUI values for tissues from the microwave-irradiated rats did not differ significantly from sham-irradiated animals, and a microwave influence on barrier permeability was not evident. Irrespective of treatment, BUI values for cerebellum and medulla were much higher and more variable than values for cortex or diencephalon, and were associated with reduced absorbance or retention of [3H]water. Because of a compromising influence of the vertebral arterial supply on the distribution of intracarotid-injected radiotracers, BUI measurements in caudal brain regions are probably unreliable unless accompanied by data on regional radioisotope concentrations. The absence of such data in an earlier BUI study, suggests that increases in BUI for cerebellum and medulla attributed to microwaves were possibly misinterpreted as differences in barrier permeability to [14C]saccharides, when in fact changes in blood flow and [3H]water influx or egress were responsible.

Animals↗
PubMed1986

Tissue structure of rat brain after microwave irradiation using maximum magnetic field component.

A novel microwave instrument has recently been designed by New Japan Radio Co. Ltd., to provide more homogeneous distribution of the rapidly deposited heat in the rodent brain. Being the first commercial unit which concentrates the maximum magnetic field component of irradiation, rather than the usual electric field, it provides complete enzymatic inactivation in a typical rat brain when a power of 9 kW (90% of maximum) is applied for 0.80 s at the standard operating frequency of 2450 MHz. Tissue structural integrity was investigated in animals sacrificed by this approach or by the usual decapitation to see if any tissue disruption or pressure-induced spreading, a major problem with other microwave devices, might also be of concern for this new unit. Histological examination of tissue samples employed both light and electron microscopy. Using Luxol Fast Blue in the light microscopy, the microwave irradiated tissues exhibited a decreased affinity for the staining agent, an appearance of slight vacuoles, and the disappearance of fine fibrils in the parenchyma. However, the interfacial areas between distinct brain regions remained well preserved. Electron microscopic observation indicated that microwave irradiated tissue caused protein denaturation accompanied by the aggregation of nuclear chromatin, the disappearance of Nissl bodies, ribosomes and neurofilaments, and noticeably irregular myelin sheaths. However, the essential structure of nerve cell membranes and synaptic membranes were maintained, and synaptic vesicles were clearly defined. These results indicated that the rapid heating of brain tissue with maximal magnetic field concentration of the irradiation does not result in significant tissue disruption, pressure-induced spreading or cell breakdown.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Modification of acoustic and tactile startle by single microwave pulses.

Single microwave pulses at 1.25 GHz were delivered to the head and neck of male Long-Evans rats as a prestimulus to acoustic and tactile startle. For acoustic startle, pulses averaging 0.96 microsecond in duration were tested with two specific absorption rate (specific absorption) ranges, 15.0-30.0 kW/kg (16.0-44.2 mJ/kg) and 35.5-86.0 kW/kg (66.6-141.8 mJ/kg), delivered 201, 101, 51, 3, and 1 ms before and 1 ms after onset of a startling noise. The low-intensity pulse did not affect peak amplitude, integral, or latency of the whole-body startle response. The high-intensity pulse at 101 and 51 ms inhibited the startle response by decreasing peak amplitude and integral; at 201 and 51 ms latency was increased. The high-intensity pulse at 1 ms enhanced the startle response by increasing peak amplitude and at 3 ms by increasing integral. For tactile startle, either microwave pulses averaging 7.82 microseconds in duration and 55.9-113.3 kW/kg (525.0-1055.7 mJ/kg) or 94 dB SPL clicks were delivered 157, 107, 57, and 7 ms before and 43 ms after onset of a startling air burst. The microwave pulse at 57 ms inhibited the startle response by decreasing peak amplitude; at 157, 107, 57, and 7 ms it increased latency. The microwave pulse at 43 ms after onset enhanced the startle response by increasing peak amplitude. The acoustic click at 157 and 57 ms inhibited the startle response by decreasing peak amplitude; at 157,2 107, and 57 ms it increased latency.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMedDate not supplied

Cataracts induced by microwave and ionizing radiation.

Microwaves most commonly cause anterior and/or posterior subcapsular lenticular opacities in experimental animals and, as shown in epidemiologic studies and case reports, in human subjects. The formation of cataracts seems to be related directly to the power of the microwave and the duration of exposure. The mechanism of cataractogenesis includes deformation of heat-labile enzymes, such as glutathione peroxide, that ordinarily protect lens cell proteins and membrane lipids from oxidative damage. Oxidation of protein sulfhydryl groups and the formation of high-molecular-weight aggregates cause local variations in the orderly structure of the lens cells. An alternative mechanism is thermoelastic expansion through which pressure waves in the aqueous humor cause direct physical damage to the lens cells. Cataracts induced by ionizing radiation (e.g., X-rays and gamma rays) usually are observed in the posterior region of the lens, often in the form of a posterior subcapsular cataract. Increasing the dose of ionizing radiation causes increasing opacification of the lens, which appears after a decreasing latency period. Like cataract formation by microwaves, cataractogenesis induced by ionizing radiation is associated with damage to the lens cell membrane. Another possible mechanism is damage to lens cell DNA, with decreases in the production of protective enzymes and in sulfur-sulfur bond formation, and with altered protein concentrations. Until further definitive conclusions about the mechanisms of microwaves and ionizing radiation induced cataracts are reached, and alternative protective measures are found, one can only recommend mechanical shielding from these radiations to minimize the possibility of development of radiation-induced cataracts.

Animals↗
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↗
PubMed1984

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. A. Effect on the permeability to sodium fluorescein.

Significantly elevated levels of sodium fluorescein (MW 376) were found only in the brains of conscious rats made considerably hyperthermic (colonic temperatures greater than 41.0 degrees C) by exposure to ambient heat (42 +/- 2 degrees C) for 90 min or 2450 MHz CW microwave energy at 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min. For microwave-exposed rats, fluorescein levels within the cortex and hypothalamus appeared to increase with increasing duration of exposure. This trend was not apparent in the cerebellum or medulla. Exposure to ambient heat resulted in increased fluorescein with the cortex, hypothalamus and medulla, but not the cerebellum, and, in general, ambient heat was not as effective as microwave energy in raising tracer concentrations within the brain. By far the greatest elevation of fluorescein dye in the brain occurred in those animals whose blood-brain barrier had been opened osmotically by intracarotid injection of 10 M urea. It is suggested that increased levels of sodium fluorescein found in the brain tissue of ambient heat and microwave-exposed rats most likely represent technically derived artifact and not a breakdown of the blood-brain barrier.

Animals↗
PubMed1984

Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. D. Brain temperature and blood-brain barrier permeability to hydrophilic tracers.

Measurement of temperature within the cerebral cortex, hypothalamus, cerebellum and medulla of rats sham-, heat- or microwave-exposed revealed the presence of a thermal gradient within the brain. In all groups, cerebral cortex and the cerebellum were cooler than the deeper hypothalamus and medulla. Exposure to 2450 MHz CW microwaves or ambient heat (42 +/- 2 degrees C) resulted in measurable elevation of regional brain temperature, but without alteration of temperature gradients normally observed within the brain. Exposure to 20 mW/cm2 (SAR approximately equal to 4 W/kg) for 30, 90 or 180 min induced a small, but significantly (U = 0, P less than 0.05) increased temperature of the colon, and in each region of the brain studied. Exposure to an incident power density of 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min or to ambient heat (42 +/- 2 degrees C) for 90 min resulted in a substantially greater thermal response as indicated by higher colonic and brain temperatures. Comparison of regional brain temperature with individual colonic temperatures is expressed as delta T = t degrees Cbrain--t degrees Ccolon. In general delta T values for ambient heat or microwave-exposed rats did not differ significantly from those of sham-exposed animals. Exposure to microwaves or ambient heat did not alter the general relationships between regional brain and colonic temperatures, i.e., cortical and cerebellar temperatures were always below and hypothalamic and medullary temperatures always above corresponding colonic temperatures. The plotted temperature data (brain vs colonic temperature) indicate a linear relationship between brain and colonic temperatures. Levels of sodium fluorescein (NAFl), horseradish peroxidase (HRP) and [14C]sucrose (described in preceding papers) within the brain show a high correlation (P less than 0.05) with brain temperature. Suppression of blood-brain barrier permeability to hydrophilic tracers was most pronounced at brain temperatures exceeding approximately 40 degrees C and is demonstrated to be temperature dependent.

Animals↗
PubMed1994

Effects of microwave pretreatment on immunocytochemical staining of vibratome sections and tissue blocks of human cerebral cortex stored in formaldehyde fixative for long periods.

The effects of the microwave antigen-retrieval method were investigated for five antibodies commonly used in neurosciences, i.e., Parvalbumin, Calbindin D28-K, MAP-2, MAP-5 and SMI-32. Immunocytochemical stainings were performed on free-floating vibratome sections of tissue which had been stored in fixative for as long as 10 months to compare the effects of microwave treatment in one of the different metal solutions or in distilled water. Microwave treatment of free-floating vibratome sections led to a severe wrinkling of the sections. Therefore the possibility of pretreatment of a thick tissue slice before vibratome sectioning was investigated. We conclude that microwave pretreatment of tissue slices in an aluminium chloride solution is the preferable antigen-retrieval procedure for the examined antibody staining when the immunocytochemical staining is lost or markedly reduced after storage in formaldehyde fixative for a long period. In particular SMI-32 and MAP-2, but also Parvalbumin staining, improved enormously after such a pretreatment.

Adult↗
PubMed1996

Brain regional levels of adenosine and adenosine nucleotides in rats killed by high-energy focused microwave irradiation.

A high-energy focused microwave system for killing experimental animals was used to rapidly inactivate enzymes and prevent postmortem breakdown of adenine nucleotides and adenosine, thereby enabling accurate measurements of AMP, ADP, ATP and adenosine in rat brain. For comparison, purine levels were measured in brains of rats killed by decapitation, decapitation into liquid nitrogen, or in situ freezing of the brain with liquid nitrogen. Of the three microwave irradiation power levels used, 10, 6.0 or 3.5 kW, rats killed by 10 kW had the highest ATP levels (28.8 nmol/mg protein) and cellular energy charge value (0.8), and the lowest levels of AMP (2.2 nmol/mg protein) and adenosine (19.7 pmol/mg protein). Of the 6 brain regions studied, adenosine levels (pmol/mg protein) ranged from 10 in cerebral cortex to 170 in cerebellum of rats killed using 10 kW microwave irradiation and, for comparison, ranged from 840 in cerebral cortex to 2498 in striatum of rats killed by decapitation. Focused microwave killing permits precise and accurate measurements of purines in discrete regions of rat brain.

Adenine Nucleotides↗
PubMed1991

The effect of microwave and conventional cooking on the temperature profiles and microbial flora of minced beef.

Beef mince samples were cooked to the rare, medium and well done states by microwave and conventional oven methods. The raw samples all contained large numbers of contaminating organisms and low numbers of Listeria monocytogenes were detected in the majority of samples. A substantial proportion of the contaminating flora survived in mince cooked by microwaves to the rare, medium and well done states, prior to a 30-min standing period. Listeria monocytogenes survived in all samples cooked by microwaves to the rare state, prior to the standing period and was still present in one of three after the standing period. It was also detected in one of three samples cooked to medium prior to a standing period. This organism was not detected in mince cooked by conventional oven methods. In all the samples cooked by microwaves with a standing period and samples cooked to rare and medium by conventional oven, survival of some of the microflora occurred. The survival rate decreased with the severity of the cooking treatment.

Animals↗
PubMed1995

Survival of Salmonella species in eggs poached using a microwave oven.

The use of microwave ovens is becoming increasingly popular, but there is little data on the bactericidal effect of this mode of cooking. Following a family outbreak of gastroenteritis due to Salmonella enteritidis PT4, where eggs poached in a microwave oven were the suspected source, we investigated the survival of Salmonella spp. in artificially contaminated eggs cooked in a microwave oven. The survival of six serotypes of Salmonella at various inocula were studied, after cooking the eggs using two recognized poaching methods. Salmonellae were readily recovered after cooking if the yolk was still soft, whichever serotype, inoculum or cooking method was used. The survival of organisms was related to the number of organisms present in the raw eggs. The advice regarding eating lightly cooked eggs should be the same whether microwave or more conventional cooking techniques are used.

Cooking↗
PubMed1989

Formation of N-nitrosamines in microwaved versus skillet-fried bacon containing nitrite.

Differences in volatile N-nitrosamines (NNAs) found in nitrite-cured bacon cooked in an electric skillet and a microwave oven were determined. Samples of bacon were fried in an electric skillet at 171 and 206 degrees C and in a standard microwave oven (rated at 700 W full power) for 45 and 75 sec/slice. The level of NNAs were determined in the cooked bacon and fried-out fat by using gas chromatography-thermal energy analysis. Both N-nitrosopyrrolidine (NPYR) and N-nitrosodimethylamine (NDMA) were detected in the fried-out bacon fat at levels up to 20.8 and 23.3 ng/g, respectively. The total NNAs (NDMA and NPYR) in the skillet-fried bacon was c. 11 ng/g for both the 171 and 206 degrees C fried samples. No NNAs were detected in the bacon or fried-out fat after cooking in a microwave oven for 45 sec/slice. However, excessive cooking of the bacon in a microwave oven (75 sec/slice) does produce levels of NPYR up to 5 ng/g. The minimum detectable level of NPYR was 2.08 ng/g and that of NDMA was 0.76 ng/g. These results indicated that the method of cooking meats containing nitrite could affect the level of NNAs in the cooked product, thereby affecting the level of human exposure to NNAs.

Animals↗
PubMed1995

Ultrasound-guided microwave thermotherapy on a VX-2 carcinoma implanted in rabbit kidney.

A temperature greater than 60 degrees C was maintained for 60 s within a 5-mm radius of a microwave electrode implanted in a rabbit kidney using 2450 MHz at 100 W for 30 s. Histological examination revealed complete coagulation necrosis in that area. VX-2 cells were inoculated into the kidneys of 10 rabbits. One week later, five rabbits received ultrasound-guided microwave thermotherapy, and the remaining five rabbits received no treatment. All rabbits with microwave thermotherapy had a complete response to treatment while all rabbits without therapy died of cancer within 6 weeks of the VX-2 implantation. These results indicate that ultrasound-guided microwave thermotherapy has the potential of being a nephron-salvaging treatment for small renal tumors.

Animals↗
PubMed1990

Measurement of tumor pH during microwave induced experimental and clinical hyperthermia with a fiber optic pH measurement system.

The influence of hyperthermia on tissue pH was investigated using a modified version of the fiber optic monitoring system. This newly developed system was tested for use in tissues and found to be suitable for pH measurement during microwave induced hyperthermia. The fiber optic pH probe (0.7 mm diameter) could be easily used in the electromagnetic fields produced by the microwave applicators, whereas only the display unit required some shielding. Tissue pH of experimental and clinical tumors was measured concurrently with local microwave hyperthermia treatment. The mean initial intratumor pH of a rat rhabdomyosarcoma was 7.03 (SD 0.13, n = 19) and the pH of human subcutis was 7.45 (SD 0.02, n = 8). In rat tumor a primary pH decrease was observed during heating which was fully reversed during cooling. The coefficient of temperature dependence was -0.016 pH unit/degree C (SD 0.004, n = 12). After approximately 1 hr of heating at 43 degrees C a further pH decrease of 0.1-0.3 unit occurred which was not reversed directly after treatment. Measurements during clinical local microwave hyperthermia treatments after radiotherapy revealed similar changes in pH values, primary as well as secondary. The estimated coefficient of temperature dependence for the reversible pH change, which occurred in subcutis as well as in tumor tissue, was -0.016 pH unit/degree C (SD 0.004, n = 12). The fiber optic pH measurement system is expected to be a valuable tool in the thorough investigation of temperature and time related pH changes in tumor during experimental as well as clinical hyperthermia treatment.

Acid-Base Equilibrium↗
PubMed1993

Phantom evaluation of heating of superficial tissues located above interstitial microwave antennas.

PURPOSE: A technique that improves heating of superficial tissues above an implant of microwave interstitial antennas is presented. METHODS AND MATERIALS: Adequate heating of tumor margins is achieved by extending an implant of microwave antennas beyond the tumor boundary by 1-2 cm. When the tumor infiltrates the superficial tissues including the skin, the implant cannot even reach the superficial margin of the tumor since it requires tissue to support the catheters. This may yield cold spots in the tissues above the implant. Measurements in a phantom with varying thickness of the superficial layer above the implant demonstrated inadequate Specific Absorption Rates of energy distribution in this layer. A method that improves these distributions in the superficial layers was developed and tested in this work. This method requires placing a deionized water bolus on the phantom (patient) surface. Additional microwave antennas are placed on top of the bolus above and parallel to the implanted antennas. The Specific Absorption Rates distributions were evaluated for the thicknesses of superficial layer ranging from 1.5 mm to 16 mm and two bolus thicknesses (5 and 10 mm). RESULTS: The adequate Specific Absorption Rates distributions were achieved for all tested thicknesses of the superficial layer (1.5, 4, 8, 12, and 16 mm). The use of the 5 mm bolus versus 10 mm bolus is discussed. The use of additional antennas did not significantly increase stray radiation. CONCLUSION: This method has the potential to optimize heating of superficial tissues located above a microwave antenna implant.

Hyperthermia, Induced↗