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Elucidation of the biological effects of microwave exposure requires a careful review and critical analysis of the literature. This requires differentiating established effects and mechanisms from speculative and unsubstantiated reports. Most of the experimental data support the concept that the effects of microwave exposure are primarily, if not wholly, a response to hyperthermia or altered thermal gradients in the body. There are, nevertheless, large areas of confusion, uncertainty, and actual misinformation.

The treatment of a neuron as an information processor is complicated by the nonlinear, time-varying, and distributed parameter attributes of the classical Hodgkin-Huxley neuron model. In this paper, we fit data from experiments on spontaneously firing snail neurons to a much simpler integrate and fire model featuring random process descriptions of the input current density, threshold, and reset potentials. The method of generalized least squares is used to show that the integrate and fire model explains 99.6 percent of the variation in the data used to describe the population behavior of neurons on the visceral ganglion of the Helix Aspersa snail. Experimental histograms suggest that most of the random variation in the interspike interval is caused by the randomness in the input current density and comparatively little by the random fluctuations in threshold and reset potentials, although the latter are still significant from an information processing viewpoint. Residuals from the regression are used to estimate the range of the input current density random process. The residuals also show that slight, but significant, autocorrelation exists in the input current densities. This suggests that information in addition to the mean input current density is being transmitted in the interspike interval code.

To determine if microwaves disrupt the hydrogen bonding between DNA strands of the double helix, Hamrick (1973) constructed DNA melting curves after exposure of DNA to continuous-wave (CW) 2.45-GHz microwaves at 67 W/kg for 16 hr and up to 160 W/kg for 1 hr. Temperature was controlled, usually at 37°C, but for some experiments at 40°C, 45°C, and 50°C. All melting curves were virtually identical to those for unexposed, temperature-matched controls.

A number of investigators have reported that the blood and blood-forming system are not affected by acute or chronic microwave exposure (Barron and Baraff, 1958; Daily, 1943; Drogichina et al., 1966; Tyagin, 1957; Hyde and Friedman, 1968; Budd et al., 1970; Spalding et al., 1971). Effects on hematopoiesis have nevertheless been found by others (Petrov, 1970; Sadchikova and Orlova, 1958; Michaelson et al., 1961, 1964, 1965, 1967; Kitsovskaya, 1964; Baranski and Czerski, 1966; Baranski, 1971, 1972; Goncharova et al., 1966; Sacchitelli and Sacchitelli, 1960; Vacek, 1972; Czerski et al., 1974a,b; Ivanov, 1962).

A portable microprocessor-based noninvasive cardiopulmonary heart rate monitor is described for use in situations in which direct contact with the subject is either impossible or undesirable. Low-power Doppler microwaves are employed to measure the chest movements associated with the expansion and contraction of the heart and the lung. After proper analogue signal conditioning, the signal is digitised and processed by an Intel-85 microprocessor system. Pattern-recognition techniques are applied to extract the heart and respiration rates. The algorithm is tested on anaesthetised rats. The system has also been tested on a limited number of human subjects. Results indicate that the meter can detect the desired physiological signals, with good accuracy, of a standing or supine human subject wearing ordinary clothing.

This paper presents direct measurements of acoustic pressure wave propagation in cat brains irradiated with pulsed 2.45-GHz microwaves. Short rectangular microwave pulses (2 microseconds, 15 kW peak power) were applied singly through a direct-contact applicator located at the occipital pole of a cat's head. Acoustic pressure waves were detected by using a small hydrophone transducer, which was inserted stereotaxically into the brain of an anesthetized animal through a matrix of holes drilled on the skull. The measurements clearly indicate that pulsed microwaves induce acoustic pressure waves which propagate with an acoustic wave velocity of 1523 m/s.

A microwave-induced thermoelastic tissue imaging system is suggested as a new and promising imaging modality. It appears to possess some unique features that may allow it to become as useful as these other methods and to permit non-invasive tissue imaging of tissue characteristics which are not identifiable by other techniques. It uses nonionizing radiation and relies on a beam of impinging microwave to launch an acoustic wavefront into tissue. There is a direct relation between the pattern of absorbed microwave pulses and the induced thermoelastic pressure waves in biological tissues. Moreover, regions of differing permittivity would exhibit differential absorption. This thermoelastic wave of pressure would propagate through the tissue and be detected by a two-dimensional array of piezoelectric transducers positioned on the body surface to give an image of the intervening tissue structure. Signals from the outputs of this transducer array are then amplified and band-limited at a signal conditioning stage. A computer-controlled data acquisition system samples and converts them to digital form for further processing. A hybrid parralel/serial design of dividing the array into segments and collecting data from each segment sequentially is used. Image processing algorithms are applied to digitized pictures for enhancing the images. The processed two-dimensional image is displayed on a color monitor. An example showing the image of a human hand model illustrates the potential usefulness of microwave-induced thermoelastic tissue imaging.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Knowledge of the physiologic or pathophysiologic status of the heart and vessels as a transportation system for blood, and lungs as the site of gas exchange are factors that can greatly assist medical practitioners in the management of cardiovascular and pulmonary diseases. In light of prevalence of mortality and morbidity associated with heart, vascular and lung diseases, considerable efforts have been devoted to the development of noninvasive diagnostic techniques which not only are safe, but also offer the possibility of earlier detection as well as quantification of these disease states. Most recently, the advantage afforded by non-contact and remote sensing has engendered a great deal of excitement regarding the use of such technologies for monitoring patients with critical burns and premature developments, and personnel fell prey to such hazardous environments as fire, chemical or nuclear contamination and natural or man-caused disasters.

A prototype microwave-induced thermoelastic tissue imaging system was designed to acquire and process two-dimensional projections of various sizes test tubes filled with tissue equivalent materials. A test object is immersed in a tank of water at whose surface single microwave pulses of 2 mu s at a carrier frequency of 2450 MHz are launched. Thermoelastic waves induced at the water surface are detected, on propagating through the object material, by a 20*20 piezoelectric transducer array at the bottom of the water tank. A computer-controlled data acquisition system samples and converts the amplified and bandlimited signals into digital form. The system produces images interactively through the use of image processing techniques. Results are presented to demonstrate the potential use of microwave-induced thermoelastic waves as a possible medical imaging modality. >

Dielectric properties of tissue materials have been extensively studied (Schwan, 1957, 1963, 1965). A basic understanding has been achieved of the mechanisms and structures that determine the electromagnetic properties of tissue materials. It has been demonstrated that tissue materials are nearly nonmagnetic, and thus have permeabilities close to that of free space and are independent of frequency. On the other hand, the electrical properties of tissue materials have been shown to display a characteristic dependence on frequency. They possess very high dielectric constants compared with many other types of homogeneous liquids and solids. This is because biological tissues are nonhomogeneous, and are composed of cells, macromolecules, and other membrane-bound substances. An example of the frequency-dependent character of tissue materials is given in Fig. 4-1. There are three principal regions of dispersions described as α, β, and γ, respectively. Each dispersion is defined by either a single relaxation frequency or a small group of relaxation frequencies.

Although protective clothing and eye shields have been developed and demonstrated as providing effective shielding in some circumstances (Glaser and Heimer, 1971; Christianson and Rutkowski, 1967; Wadey, 1956), their use is not recommended. Reflections can increase the hazard to other people, and faults, such as open circuits, can act as secondary sources to actually increase the hazard to the wearer. In high-radiation fields, arcing problems may arise (Klascius, 1971).

Reproductive efficiency concerns the capacity of the dam or sire to effect a conception and bear and rear offspring. Changes in this capacity might be due to alterations in behavior, physiology, or morphology.

The propagation of electromagnetic waves in biological materials is governed by the dielectric constant, conductivity, source configuration, and the geometrical factors that describe the tissue structure. These parameters also determine the quantity of energy a given biological body extracts from the propagating wave. When the radius of curvature of the body surface is large compared to the wavelength and beam width of the impinging radiation, planar tissue models may be used to estimate the absorbed energy and its distribution inside the body. Otherwise, the absorbed energy will be dictated by the size of the body, the curvature of its surface, the ratio of body size to wavelength, and the source characteristics.

This investigation was aimed at correlating changes of blood-brain-barrier permeability with the quantity and distribution of absorbed microwave energy inside the brain of adult Wistar rats anesthetized by sodium pentobarbital. Through use of thermographic methods and a direct-contact applicator at the animal's head, the pattern of absorbed microwave energy was determined. Indwelling catheters were placed in the femoral vein and in the left external carotid artery. Evans blue and sodium fluorescein in isotonic saline were used as visual indicators of barrier permeation. Exposure to pulsed 2,450-MHz radiation for 20 min at average power densities of 0.5, 1, 5, 20, 145 or 1,000 mW/cm2, which resulted in average specific absorption rates (SARs) of 0.04, 0.08, 0.4, 1.6, 11.5 or 80.0 mW/g in the brain, did not produce staining, except in the pineal body, the pituitary gland, and the choroid plexus - regions that normally are highly permeable. Except for these regions, staining was also absent in the brains of sham-exposed animals. The rectal temperature, as monitored by a copper-constantan thermocouple, showed a maximum increase of less than 0.75 degrees C from a mean pre-exposure temperature of 36.6 degrees C. The highest brain temperature recorded in a similar group of animals usingmore » a thickfilm carbon thermistor was less than 41.0 degrees C.« less

1. 1. Five electrophoretically separable lactate dehydrogenase (LDH) isozymes were found in muscle tissue while heart tissue exhibited variation in its isozyme number. 2. 2. Muscle LDH exhibited a higher pyruvate substrate optimum than did heart LDH, 4.0 and 1.6 mM respectively, and showed less substrate inhibition. 3. 3. The pH optimum for muscle LDH was lower than that for heart LDH, pH 7.2 and 7.6 respectively.

A microprocessor-based noninvasive arterial pulse wave analyzer is described which detects the peripheral, arterial pulse of an individual and extracts from the pulse waveform clinically important features. Continuous-wave Doppler microwaves (24.125 GHz) are employed to measure the arterial wall movements associated with the pressure pulse wave. Through the use of feature extraction techniques, key landmarks are located on the pulse contour. Then the pulse rate, the foot-to-systolic peak time period, and the foot-to-dicrotic notch time period are calculated. Preliminary results are presented which indicate that the arterial pulse wave analyzer can accurately determine the movement of the arterial wall and is able to analyze the pulse wave contour for clinically important features.

There has been a concerted effort to assess the sensitivity of the central nervous system (CNS) to “low levels’ of microwave energy. To date there is no convincing evidence of the existence of “low-intensity” microwave effects on the human CNS. Animal studies suggest that the mechanisms that are the basis for reported effects, involve microwave-induced nonuniform temperature distributions and/or thermal gradients (Cleary, 1977).

Fixed ratio performance changes of rats exposed to near zone 918 MHz radiation have been observed to occur at incident power levels of 40 mW/cm/sup 2/corresponding to peak absorbed power densities of 32-36 W/kg. No change in behavior was indicated for incident and peak absorbed power densities of up to 20 mW/cm/sup 2/and 18 W/kg, respectively.

Although there is growing awareness of the need for cryo-preservation of solid organs for transplantation, whole-organ survival rate after freezing and thawing has changed little over the last quarter of a century (1). Nevertheless, a great deal has been learned concerning mechanisms of failure and avenues of inquiry which may lead to successful recovery of frozen organs for transplantation.

The intrinsic measurement error of a dual video camera-based three-dimensional (3-D) machine vision system is analyzed. The sources of error are assumed to stem from common arrangement inaccuracies and limited precisions of the imaging device. The resultant error equation for a point in 3-D space is related to system parameters such as pixel resolution, camera focal length, camera position, separation and orientation. For normal camera to object distances, the accuracy of the vision system is strongly influenced by camera orientation errors and least affected by limited resolution of the imaging device.The intrinsic measurement error of a dual video camera-based three-dimensional (3-D) machine vision system is analyzed. The sources of error are assumed to stem from common arrangement inaccuracies and limited precisions of the imaging device. The resultant error equation for a point in 3-D space is related to system parameters such as pixel resolution, camera focal length, camera position, separation and orientation. For normal camera to object distances, the accuracy of the vision system is strongly influenced by camera orientation errors and least affected by limited resolution of the imaging device.

Progress in understanding electromagnetic interaction with biological systems is closely linked to the advances in measurement capability. Measurement provides the means to describe physical phenomena in quantitative terms. As our ability to describe these phenomena with precision and reliability increases, the opportunity of advancing our understanding of the laws of nature increases and the capability of making use of this understanding also increases. Furthermore, the growing significance of international cooperation to arrive at a meaningful safety standard has made valid measurement a necessary means for the international exchange of scientific and engineering results.

The possibility that pulsed fields produce biological responses other than those elicited by continuous-wave field of the same average power has been conjectured since the early years of research into the biological effect of radiofrequency (RF) energy. However, because of the limited availability of experimental results, few protection guides and exposure standards promulgated by various private organizations or governmental agencies attempted to specify limits to guard against potential hazards of pulsed radiofrequency fields. Indeed, available results have led some to conclude that there is no compelling evidence that pulsed microwave, of the type produced by radar transmitters, cause biological effects not found following exposure under conditions of continuous-wave radiation at the same average power density (Postow and Swicord, 1986). Nevertheless, the accumulation of recent experimental evidence on the biological effects of pulsed and modulated RF field suggests a need to put such interactions in a more meaningful context and a closer examination of the mechanism(s) of such interactions.

When human subjects are irradiated with pulse modulated microwave energy they report the perception of a sound that appears to originate from within or slightly behing the head. Three of the possible mechanisms are examined using first order mathematical approximations and several simplifying assumptions. The results show that while all three (radiation pressure, strictive force and thermal expansion) are capable of producing the phenomenon, the stress resulting from thermal expansion may be so great that it masks the effect of the others completely.

Most of the research on biological effects of microwave/radiofrequency (MW/RF) energies has been done with small rodents having coefficients of heat absorption, field concentration effects, body surface areas, and thermoregulatory mechanisms significantly different from those of man. Even closely related species can differ widely in their responses. The literature is replete with “anomalous” reactions. Thus, results of exposure of common laboratory animals cannot be readily extrapolated to man unless a comparative biology approach and some form of “scaling” among different animal species, and from animal to man, is used in an appropriate manner to obtain quantitatively valid extrapolation relationships from the observed data.

A number of retrospective studies have been done on human populations exposed or believed to have been exposed to RF/MW energies. There have been a few epidemiological studies of MW/RF exposure but these have generally been limited in scope (Silverman, 1979, 1980). Persons exposed while assigned to the military services or occupationally exposed in industrial settings have been the principal groups studied. A few other populations living or working near generating sources or exposed to medical diathermy have been or are being investigated (Silverman, 1979, 1980; Bureau of Radiological Health, 1980; Ruggera, 1980). Information about health status has come from medical records, questionnaires, physical and laboratory examination, and vital statistics. Sources of exposure data include personnel records, questionnaires, environmental measurements, equipment emission measurements, and (assumed adherence to) established exposure limits. Although there have been advances in measurement, microwave dosimetry still presents formidable problems for meaningful assessment in most epidemiological studies (Roberts and Michaelson, 1985; Silverman, 1979, 1980).

An understanding of the interaction of radio and microwave radiation with biological systems requires a knowledge of some of the laws describing the characteristics of radio and microwave radiation. The physical processes of radio and microwave radiation are governed by four principles now known as Maxwell’s equations. These equations represent mathematical expressions of experimental observations. From these four principles or laws of electromagnetics, one may deduce with mathematical vigor and exactness, all macroscopic electromagnetic phenomena.

Power deposition patterns, temperature distribution patterns, and cataractogenesis thresholds have been established in the eyes of rabbits exposed to localized near zone 2450 MHz radiation. There was good agreement between results obtained through theoretical and experimental approaches.

Recordings from elements of the auditory system of cats in response to pulsed microwaves, as well as determinations of thresholds of audibility of humans to the pulses indicate that an auditory sensation may be elicited by pulse energies >20 /spl mu/J/cm/sup 2/, regardless of average or peak power.

Microwave-produced changes in CNS-evoked potentials appear limited to thermal effects, as evidenced by 1) similar changes being elicited by equivalent non-radiation heating, and 2) reduction or even reversal of radiation effects with concurrent brain cooling.

The paper considers multiple scattering effects of millimeter wave propagation in rain. Using the multiple scattering theory developed previously by the authors for beam and plane waves propagating in an isotropically scattering discrete random medium, rainfall attenuations were computed for intensities ranging from 0-100 mm/hr at wavelengths 3-30 mm. The results are compared with existing measurements in the literature. The good agreement between theory and experiment indicates the general applicability of the theory to rainfall attenuation predictions and area rainfall intensity estimations. The theory also agrees with calculations based on existing theory that accounts for drop size distributions. The difference in attenuation of plane and beam waves propagating in rain of the same intensity has found not to exceed 3 db/Km. The limits of applicability of the theory have also been indicated.

EN power deposition in a spherical model of man exposed to HF fields may be derived from a simple approximate equation where the absorbed power due to electric field coupling can be calculated separately from that due to magnetic coupling. The latter is an order of magnitude greater for a plane wave.

Characterstic of electromagnetic pulse transmission in homogeneous spherical models of human and animal heads are studied as a function of time and position. The incident pulse waveform is described by a triple exponential waveform which exhibits close agreement with measured pulse shapes. The transmitted pulse is shown to be proportional to the time rate of change of the incident pulse, with peak occuring at the leading surface of the spheres.

This letter presents a new microwave antenna design with greatly enhanced heating at the tip for interstitial hyperthermia. Temperature distribution patterns surrounding the new balun-fed folded dipole antenna are measured in a saline phantom under transient and steady-state conditions.

Mouse Leukemia L1210 is an extensively used model for cancer chemotherapy studies. An unique microwave irradiation exposure system was used to assay the effects of hyperthermia, microwave irradiation (MWR), and hydrocortisone succinate (HCS) on L1210 cells ability to form colonies in a methylcellulose culture system. MWR was given at 2450 MHz frequency with 1000 mW/cm2 power output for 30 min. L1210 cells were suspended in a medium and then exposed as follows: Sham at 37°C and 42°C; MWR at 37°C and 42°C. All 4 exposure sets were then plated at a cell concentration of 5,000 cells per plate either with no drug, or with 10−5M, 10−6M, 10−7M or 10−8M HCS per plate. At day 8 of culture the colony number was scored in each of the plates. Pre-exposure to MWR, hyperthermia or combination of the two had no effect on the cell's ability to form colonies. HCS when added to culture plates inhibited the colony formation in a dose-dependent fashion. However, no further inhibition was observed by pre-exposing cells to MWR or hyperthermia alone. A significant inhibition (50%) in the colony formation at each HCS concentration was observed by pre-exposing the cells to both MWR and hyperthermia proceeding culture in HCS. We conclude that MWR and hyperthermia when employed together interact with HCS in a synergistic fashion to inhibit growth of L1210 cells.

We have studied the interaction of microwaves with the blood-brain barrier in Wistar rats. Indwelling catheters were placed in the femoral vein. Evans blue in isotonic saline was used as a visual indicator of barrier permeation. Irradiation with pulsed 2450-MHz microwaves for 20 min at average power densities of 0.5 to 2600 mW/cm/sup 2/, which resulted in average specific absorption rages (SARs) of 0.04 to 200 mW/g in the brain, did not produce staining, except in regions that normally are highly permeable. When the incident power density was increased to 3000 mW/cm/sup 2/ (SAR of 240 mW/g), extravasation of Evans blue could be seen in the cortex, hippocampus, and midbrain. The rectal temperature, as monitored by a copper-constantan thermocouple, showed a maximum increase of less than 1.0/sup o/C. the brain temperature recorded in a similar group of animals using a non-field-perturbing thermistor exceeded 43/sup o/C. At the higher power density the extravasation depended on the irradition and euthanization times. In one series of experiments, rats were irradiated at 3000 mW/cm/sup 2/ for 5, 10, 15, and 20 min. Immediately after irradiation all except the 5-min animals exhibited increased permeability in some regions of the brain. Brains of rats euthanized 30more » min after irradiation were free of Evans blue, while those euthanized 10 and 20 min postirradiation showed significant dye staining but with less intensity than those euthanized immediately after irradiation.« less

Colony-forming unit cells from the femurs and tibias of 2-month-old C3H mice were exposed to 2450-MHz CW microwaves in a specially designed fluid-filled waveguide exposure system. The cells were suspended in glass micropipets and exposed to 30 to $1000\ {\rm mW}/{\rm cm}^{2}$ of incident power densities corresponding to specific absorption rates of 60 to 2000 mW/g for 15 min. There was no reduction in the number of colonies formed on days 6 and 12 at $30\ {\rm mW}/{\rm cm}^{2}$ (60 mW/g), but as the exposure was increased up to a level of $1000\ {\rm mW}/{\rm cm}^{2}$ (2000 mW/g) there was a corresponding reduction in the number of colonies formed by microwave-treated cells, compared to sham-exposed cells. Thus, there was a dose-dependent reduction in the number of colonies formed by microwave-exposed bone marrow cells when compared to their sham-exposed counterparts.