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Biomedical subjects

A G Pakhomov

Publications and source records attributed to A G Pakhomov.

13 recordsLinked to original sources
PubMed2002

Electromagnetic field standards in Central and Eastern European countries: current state and stipulations for international harmonization.

Electromagnetic field standards in the West are based on well-established acute biological effects that could be considered as signaling a potentially adverse health effect. The specific absorption rate, which is proportional to the tissue heating (thermal effects), represents the basic restriction of exposure to Radio-Frequency (RF) fields. On the other hand, Eastern European standards are designed to protect from potential non-thermal effects that might be caused by chronic exposure to very low intensities, where a so-called "power load" (a product of field intensity and duration of exposure) represents the basic limitation. Thus, electromagnetic field standards in Eastern European countries differ considerably from those which are proposed by the International Commission of Non-ionizing Radiation Protection and the Standards Coordinating Committee 28 of the Institute of Electrical and Electronics Engineers, Inc. In the present paper, the strategies for development of exposure limit values in electromagnetic fields standards currently in force in Eastern and Central European countries are discussed. Some differences as well as similarities of the national health and safety standards and the main obstacles to harmonization of these standards with those being established by Western national and international organizations and agencies are presented.

Electromagnetic Fields↗
PubMed2000

Comparative effects of extremely high power microwave pulses and a brief CW irradiation on pacemaker function in isolated frog heart slices.

The existence of specific bioeffects due to high peak power microwaves and their potential health hazards are among the most debated but least explored problems in microwave biology. The present study attempted to reveal such effects by comparing the bioeffects of short trains of extremely high power microwave pulses (EHPP, 1 micros width, 250-350 kW/g, 9.2 GHz) with those of relatively low power pulses (LPP, 0.5-10 s width, 3-30 W/g, 9.2 GHz). EHPP train duration and average power were made equal to those of an LPP; therefore both exposure modalities produced the same temperature rise. Bioeffects were studied in isolated, spontaneously beating slices of the frog heart. In most cases, a single EHPP train or LPP immediately decreased the inter-beat interval (IBI). The effect was proportional to microwave heating, fully reversible, and easily reproducible. The magnitude and time course of EHPP- and LPP-induced changes always were the same. No delayed or irreversible effects of irradiation were observed. The same effect could be repeated in a single preparation numerous times with no signs of adaptation, sensitization, lasting functional alteration, or damage. A qualitatively different effect, namely, a temporary arrest of preparation beats, could be observed when microwave heating exceeded physiologically tolerable limits. This effect also did not depend on whether the critical temperature rise was produced by LPP or EHPP exposure. Within the studied limits, we found no indications of EHPP-specific bioeffects. EHPP- and LPP-induced changes in the pacemaker rhythm of isolated frog heart preparation were identical and could be entirely attributed to microwave heating.

Animals↗
PubMed1998

Current state and implications of research on biological effects of millimeter waves: a review of the literature.

In recent years, research into biological and medical effects of millimeter waves (MMW) has expanded greatly. This paper analyzes general trends in the area and briefly reviews the most significant publications, proceeding from cell-free systems, dosimetry, and spectroscopy issues through cultured cells and isolated organs to animals and humans. The studies reviewed demonstrate effects of low-intensity MMW (10 mW/cm2 and less) on cell growth and proliferation, activity of enzymes, state of cell genetic apparatus, function of excitable membranes, peripheral receptors, and other biological systems. In animals and humans, local MMW exposure stimulated tissue repair and regeneration, alleviated stress reactions, and facilitated recovery in a wide range of diseases (MMW therapy). Many reported MMW effects could not be readily explained by temperature changes during irradiation. The paper outlines some problems and uncertainties in the MMW research area, identifies tasks for future studies, and discusses possible implications for development of exposure safety criteria and guidelines.

Animals↗
PubMed1997

Search for frequency-specific effects of millimeter-wave radiation on isolated nerve function.

Effects of a short-term exposure to millimeter waves (CW, 40-52 GHz, 0.24-3.0 mW/cm2) on the compound action potential (CAP) conduction were studied in an isolated frog sciatic nerve preparation. CAPs were evoked by either a low-rate or a high-rate electrical stimulation of the nerve (4 and 20 paired pulses/s, respectively). The low-rate stimulation did not alter the functional state of the nerve, and the amplitude, latency, and peak latency of CAPs could stay virtually stable for hours. Microwave irradiation for 10-60 min at 0.24-1.5 mW/cm2, either at various constant frequencies or with a stepwise frequency change (0.1 or 0.01 GHz/min), did not cause any detectable changes in CAP conduction or nerve refractoriness. The effect observed under irradiation at a higher field intensity of 2-3 mW/cm2 was a subtle and transient reduction of CAP latency and peak latency along with a rise of the test CAP amplitude. These changes could be evoked by any tested frequency of the radiation; they reversed shortly after cessation of exposure and were both qualitatively and quantitatively similar to the effect of conventional heating of 0.3-0.4 degree C. The high-rate electrical stimulation caused gradual and reversible decrease of the amplitude of conditioning and test CAPs and increased their latencies and peak latencies. These changes were essentially the same with and without irradiation (2.0-2.7 or 0.24-0.28 mW/cm2), except for attenuation of the decrease of the test CAP amplitude. This effect was observed at both field intensities, but was statistically significant only for certain frequencies of the radiation. Within the studied limits, this effect appeared to be dependent on the frequency rather than on the intensity of the radiation, but this observation requires additional experimental confirmation.

Absorption↗
PubMed1995

Microwave influence on the isolated heart function: I. Effect of modulation.

Dependence of the microwave effect on modulation parameters (pulse width, duty ratio, and peak intensity) was studied in an isolated frog auricle preparation. The rate and amplitude of spontaneous auricle twitches were measured during and after a 2 min exposure to 915 or 885 MHz microwaves and were compared to preexposure values. The studied ranges of modulation parameters were: pulse width, 10(-6)-10(-2) s; duty ratio, 7:100000, and peak specific absorption rate, 100-3000 W/kg. Combinations of the parameters were chosen by chance, and about 400 various exposure regimes were tested. The experiments established that no regime was effective unless the average microwave power was high enough to induce preparation heating (0.1-0.4 degree C). The twitch rate instantly increased, and the amplitude decreased, as the temperature rose; similar changes could be induced by equivalent conventional heating. The data provide evidence that the effect of short-term microwave exposure on the isolated heart pacemaker and contractile functions depends on pulse modulation just as much as modulation determines the average absorbed power. These functions demonstrated no specific dependence on exposure parameters such as frequency or power windows.

Animals↗
PubMed1995

Microwave influence on the isolated heart function: II. Combined effect of radiation and some drugs.

The combined effects of microwave radiation and some drugs were studied in an isolated frog auricle preparation. The experiments established that exposure to pulse-modulated 915 MHz microwaves for up to 40 min had no effect on either the rate or the amplitude of spontaneous auricle twitches, unless the average absorbed power was high enough to produce preparation heating. Treatment of the preparation with saline containing (0.6-3.0) 10(-5) M of propranolol or (0.5-1.5) 10(-7) M of atropine altered neither its pacemaker nor its contractile functions; these drugs also had no effect when they were combined with nonthermal microwave irradiation. Caffeine (1 mM) strongly increased the average heart power, which was calculated as the product of twitch rate and amplitude. The caffeine effect appeared to be significantly augmented (by about 15%, P < 0.02) under exposure to burst-type pulsed microwaves (pulse width, 1.5 msec; pause, 2.5 msec; 8 pulses/burst, 16 bursts/s; average SAR, 8-10 W/kg). By itself, this modulation was not effective; the heating of the preparation and saline during exposure was approximately 0.1 degrees C, which could not account for the detected changes. The experimental results demonstrate that caffeine treatment increases the microwave sensitivity of the frog auricle preparation and reveals primarily subthreshold, nonthermal microwave effect.

Animals↗
PubMed1991

[Synaptic transmission in the frog spinal cord exposed to intensive microwave radiation].

Microwave (6.45 GHz, CW, SAR 0.1-2 W/g) effects on mono- and polysynaptic transmission, temporal and spatial EPSP summation were investigated in isolated frog spinal cord. No changes were observed if the preparation temperature remained constant during irradiation. VHF and conventional heating produced the same effects. The data obtained confirm the thermal mechanism of VHF influences on synaptic transmission processes.

Animals↗
PubMed1988

[Effect of microwave irradiation and temperature on the spontaneous impulse activity of the ventral spinal roots in the frog].

The rate of spontaneous aperiodic activity in ventral roots of isolated, sagittally hemisected frog spinal cord varied from several hundreds up to 4-6 thousand spikes per minute. This rate was the lowest at temperature of 7-11 degrees C; at higher or lower temperatures the activity augmented. Short-term reactions occurred with changes in the temperature: while heating the cord, the activity decreased, and during cooling it intensified. Microwave irradiation (6.45 GHz, specific absorption rates: 0.1, 0.4 and 2 W/g, action duration: 5 min) had no influence on the spike rate if the temperature remained constant. VHF-heating of the preparation and elevation of the superfusing fluid temperature caused the same changes in the activity. The results obtained evidence for the thermal mechanism of neurotropic influence of microwaves.

Animals↗
PubMed1987

[Segmental inhibitory reactions in the spinal cord of the frog in response to orthodromic motor neuron activation].

Ventral root reflexes evoked by a single dorsal root volley were recorded in the isolated frog spinal cord. They varied from asynchronous, low-amplitude response to highly synchronized monosynaptic discharge in different preparations. The response to a testing stimulus could be facilitated or inhibited, respectively. The inhibition was weaker at interstimulus intervals of about 40-50 ms and stronger either at longer (60-100 ms) or at shorter (15-30 ms) intervals, thus testifying to the existence of at least two types of inhibition: early and late. Strychnine effectively blocked the late inhibition and facilitated the early one; d-tubocurarine considerably weakened both types of inhibition. A conclusion is made that the late (presynaptic) inhibition is produced by activation of the inhibitory systems through recurrent motoneuron axon collaterals. Recurrent activation may also take part in the origin of the early (postsynaptic) inhibition.

Animals↗
PubMed1984

[Melanoma of the skin of the concha auriculae].

The results of treatment of 25 cases of malignant cutaneous melanoma of the floor of the auricle are presented. The involvement of the central area of the organ was matched by the least favorable clinical course. All patients of the latter group developed regional metastases. Therefore, a simultaneous removal of primary tumor and fascial-capsular excision of regional lymph nodes should be carried out unless the lymphatics are involved. The involvement of lymphatics makes the case for Crile's operation. In cases of peripheral position of melanoma, the approach to lymph node treatment should consider such factors as tumor invasion degree, growth pattern, histological type, patient's age and condition.

Adolescent↗
PubMed1983

[Treatment of patients with lung cancer who had suffered acute myocardial infarction].

The study was concerned with a comparison of 64 cases of lung cancer with concomitant postinfarctional cardiosclerosis, treated by surgery, radiation and chemotherapy, with similar patients who had not suffered from myocardial infarction. It was found that infarction patients may be given one component of combined treatment or a combination of two (radical surgery followed by a course of postoperative radiation treatment in a dose of 5,000 rad), if required. The long-term results of treatment of patients of both groups were similar.

Adult↗
PubMedDate not supplied

[Non-thermal microwave effect on nerve fiber function].

Effects of microwave radiation (915 MHz, PW, peak SAR 20-30 W/g, pulse duration 1 mcs, 50.000 and 25.000 p.p.s.) were investigated in isolated frog nerve cord preparation. Nerve VHF heating didn't exceed 2.2 degrees C due to intense Ringer's solution perfusion. It was established that nerve irradiation simultaneously with its stimulation lead to significant decrease of action potential amplitude and peak latency. Since the equal conventional heating of the nerve caused the opposite changes (amplitude increase), the results obtained argue for non-thermal mechanism of microwave action.

Action Potentials↗