Biomedical subjects

F Heinmets

Publications and source records attributed to F Heinmets.

At least 19 recordsLinked to original sources

PubMed1991

A study of deoxyribonucleotide metabolism and its relation to DNA synthesis. Supercomputer simulation and model-system analysis.

A model system (1) was established to analyze purine and pyrimidine metabolism. This system has been expanded to include macrosimulation of DNA synthesis and the study of its regulation by terminal deoxynucleoside triphosphates (dNTPs) via a complex set of interactions. Computer experiments reveal that our model exhibits adequate and reasonable sensitivity in terms of dNTP pool levels and rates of DNA synthesis when inputs to the system are varied. These simulation experiments reveal that in order to achieve maximum DNA synthesis (in terms of purine metabolism), a proper balance is required in guanine and adenine input into this metabolic system. Excessive inputs will become inhibitory to DNA synthesis. In addition, studies are carried out on rates of DNA synthesis when various parameters are changed quantitatively. The current system is formulated by 110 differential equations.

Animals↗

PubMed1989

Thermoregulatory responses of rats exposed to 9.3-GHz radiofrequency radiation.

Ketamine-anesthetized Sprague-Dawley rats were exposed in H orientation to far-field 9.3-GHz continuous-wave (CW) and pulsed (2 microseconds, 500 pps) radiofrequency radiation (RFR) at average power densities of 30 and 60 mW/cm2 (whole-body average specific absorption rates of 9.3 and 18.6 W/kg, respectively). Irradiation was conducted to cyclicly increase colonic temperature from 38.5 to 39.5 degrees C. Colonic, tympanic, and subcutaneous temperatures, ECG, blood pressure, and respiratory rate were continuously recorded during experimentation. At both power densities, the subcutaneous and tympanic temperature increases significantly exceeded the colonic temperature increase. At both exposure levels, heart rate increased significantly during irradiation and returned to baseline when exposure was discontinued. Blood pressure and respiratory rate did not significantly change during irradiation. There were no significant differences between the effects of CW and pulsed RFR exposure. The levels of subcutaneous heating and heart rate change were greater, and the times required to achieve and to recover from a 1 degree C colonic temperature increase were longer than in previous studies conducted at 2.8 GHz. Results of these studies indicate that the carrier frequency used during irradiation markedly affects the pattern of heat distribution and the physiological responses of RF-irradiated animals.

Animals↗

PubMed1989

Supercomputer analysis of purine and pyrimidine metabolism leading to DNA synthesis.

A model-system is established to analyze purine and pyrimidine metabolism leading to DNA synthesis. The principal aim is to explore the flow and regulation of terminal deoxynucleoside triophosphates (dNTPs) in various input and parametric conditions. A series of flow equations are established, which are subsequently converted to differential equations. These are programmed (Fortran) and analyzed on a Cray chi-MP/48 supercomputer. The pool concentrations are presented as a function of time in conditions in which various pertinent parameters of the system are modified. The system is formulated by 100 differential equations.

Computer Systems↗

PubMed1988

Physiological measurements during radio-frequency irradiation.

Conventional techniques for monitoring physiological parameters are not suitable for use during RFR exposure. This research note describes transduction methods involving the use of fluorocarbon leads and a pneumatic pressure transducer for reliable measurement of the ECG and respiratory rate in anesthetized or restrained rats during radiofrequency irradiation.

Animals↗

PubMed1988

Physiological effects of 2.8 GHz radio-frequency radiation: a comparison of pulsed and continuous-wave radiation.

Ketamine-anesthetized female Sprague-Dawley rats were exposed individually to far-field 2.8 GHz continuous wave (CW) and pulsed (2 microseconds, 500 pps) radio-frequency radiation (RFR) at average power densities of 30, 45, and 60 mW/cm2 [specific absorption rates (SAR) of 8.4, 12.6, and 16.8 W/kg, respectively] and to pulsed RFR at 75 mW/cm2 (SAR = 21 W/kg). Intermittent exposures were conducted to repeatedly increase colonic temperature from 38.5 to 39.5 degrees C. Colonic, tympanic, and subcutaneous temperatures, electrocardiogram, respiratory rate, and arterial blood pressure were continuously monitored and recorded. The time required to effect a 1 degree C colonic temperature increase varied inversely with the average power density used during exposure; however, the rate of cooling was independent of the heating rate. During pulsed irradiation, heart rate increased significantly at average power densities above 30 mW/cm2; heart rate increase during CW exposure was not significant. Heart rate returned to baseline when exposure was discontinued. Blood pressure and respiratory rate did not significantly change during irradiation. Pulsed RFR exposure caused a significantly greater increase in subcutaneous and tympanic temperatures than did CW exposure; however, no significant difference was noted between the effects of CW or pulsed RFR upon the rats' colonic temperature responses (heating and cooling time), heart rate, blood pressure, and respiratory rate.

Animals↗

PubMed1988

Thermal responses to 5.6-GHz radiofrequency radiation in anesthetized rats: effect of chlorpromazine.

Anesthetized rats were exposed to 5.6-GHz continuous wave radiofrequency radiation at an average power density of 60 mW/cm2 (average specific absorption rate 12 W/kg). Exposure was performed to raise colonic temperature from 38.5 to 39.5 degrees C. Following acute administration of chlorpromazine, body temperature exhibited a faster return to baseline temperature when exposure was discontinued. When exposure was initiated at 38.5 degrees C and continued until lethal temperatures resulted, chlorpromazine-treated animals exhibited significantly shorter survival times than saline-treated animals. Thus, although chlorpromazine enhanced thermo-regulatory efficiency at colonic temperatures below 39.5 degrees C, the drug caused increased susceptibility to terminal radiofrequency radiation exposure. The present results, when compared to previous studies of irradiation at 2.8 GHz, indicate that the effects of chlorpromazine on thermal responses to RFR during intermittent and terminal exposure are similar at both 2.8 and 5.6 GHz.

Animals↗

PubMed1985

Effects of psychotropic drugs on thermal responses to radiofrequency radiation.

An increase in body temperature is a primary effect of exposure to high levels of radiofrequency radiation; therefore, pharmacological agents which may modify thermoregulation are of interest. The present study investigated the effects of chlorpromazine, amitriptyline, and haloperidol on thermal responses in anesthetized rats exposed to 2.8 GHz radiofrequency radiation. Exposure was performed at an average power density of 60 mW X cm-2 (average whole body absorption rate, 14 W X kg-1), and was of sufficient duration to increase colonic temperature from 38.5 to 39.5 degrees C. Administration of chlorpromazine (5 mg X kg-1) resulted in a slower rate of colonic temperature rise during radiation exposure and a faster return to baseline temperature when exposure was discontinued. Administration of amitriptyline (10 mg X kg-1), haloperidol (0.1 mg X kg-1), or saline did not significantly affect thermal responses. A more rhythmic pattern of respiration occurred following chlorpromazine administration; the change in pattern was not seen after amitriptyline, haloperidol, or saline administration. The results indicate that acute administration of chlorpromazine can counteract hyperthermia during exposure to radiofrequency radiation, when colonic temperature is not allowed to rise above 39.5 degrees C.

Amitriptyline↗

PubMed1984

Heart rate changes due to 5.6-GHz radiofrequency radiation: relation to average power density.

Effects of intermittent exposure to 5.6-GHz radiofrequency radiation (RFR) on heart rate, blood pressure, and respiratory rate were examined in anesthetized rats. During exposure to 60 mW/cm2 which resulted in a 1 degree C change in colonic temperature, heart rate increased; the values returned to control levels after exposure was discontinued. No changes in mean arterial blood pressure or in respiratory rate were observed. Exposure to 30 mW/cm2 caused no significant changes in heart rate, blood pressure, or respiratory rate. The data indicate that heart rate changes during exposure to 5.6-GHz RFR are related to the average power density applied, and thus to the rate of change in temperature, and not simply to the absolute change in temperature.

Animals↗

PubMed1984

A new method of SAR determination in animals exposed to microwave/radiofrequency radiation (MW/RFR).

Meaningful evaluation of physiological changes resulting from microwave/radiofrequency radiation (MW/RFR) exposure depends upon accurate dose level determination. Comparison of experimental results from different investigators also requires firm establishment of dose levels. Review of the current literature reveals considerable inconsistency in this area. Therefore, a reliable method of specific absorption rate (SAR) determination in living animals must be established. In this article, we propose a new procedure for SAR determination which does not interfere with other complementary measurements required during experimentation. This simple and reliable method utilizes both the rate of temperature increase during irradiation and the rate of cooling following exposure. Current experiments suggest that the proposed method is an effective technique for local and whole-body SAR determination and allows an accurate evaluation of MW/RFR bio-effects.

Absorption↗

PubMed1984

Increased susceptibility to radiofrequency radiation due to pharmacological agents.

The effects of chlorpromazine, methysergide, and propranolol on thermal responses to 2.8 GHz radiofrequency radiation were examined in anesthetized rats. During intermittent exposure at an average power density of 60 mW X cm-2 (specific absorption rate, 14 W X kg-1), when colonic temperature was not allowed to rise above 39.5 degrees C, none of the pharmacological agents had any significant effects on thermal responses. When exposure was continued until lethal temperatures resulted, animals which were administered chlorpromazine, methysergide, or propranolol exhibited significantly shorter survival times than saline-treated animals. Propranolol administration caused the greatest decrease in survival time and resulted in a significantly lower lethal temperature than that which occurred in saline-treated animals.

Animals↗

PubMed1983

Thermal bradycardia during radiofrequency irradiation.

The present study was performed to determine if any heart rate or blood pressure changes occur during intermittent exposure to radiofrequency radiation (RFR), and to determine if parasympathetic blockade due to atropine has any effect on these changes or on thermal responses. Anesthetized rats were exposed to 2.8 GHz pulsed RFR at an average power level of 60 mW/cm2 (average specific absorption rate, 14 W/kg). During an initial exposure period to raise colonic temperature to 39.5 degrees C, heart rate decreased significantly. This thermal bradycardia is similar to that reported by other investigators during environmental heat exposure. Intermittent exposure to radiation, which was designed to result in 1 degree C colonic temperature changes, did not significantly affect heart rate or mean arterial blood pressure, before or after atropine administration. The time courses of these 1 degree C temperature changes were not altered significantly by atropine. Following administration of atropine, the thermal bradycardia during the initial heating period was still evident. Thus, factors other than vagal activity are responsible for the phenomenon. It is possible that the bradycardia is a consequence of a general reduction in metabolism, which occurs also during environmental heat exposure.

Animals↗

PubMed1982

Pilot experiments on temperature cycling in rats exposed repetitively to radiofrequency radiation (RFR).

A series of temperature cycling experiments during Radiofrequency Radiation (RFR) exposure of rats was performed. It is evident that this type of exposure procedure permits the introduction of high doses of electromagnetic energy into biological systems while the systems are maintained at physiologically acceptable temperatures. Experiments were carried out at various power densities (50-200 mW/cm2) using continuous wave (CW) and pulsed radiation while the carrier frequency was maintained at 2.06 GHz. It was observed that single-day RFR exposures at power levels used in this series produced no observable effect on temperature regulation of rats in terms of heat dissipation efficiency.

Animals↗

PubMed1981

A new approach to microwave hyperthermia therapy for cancer.

High frequency electromagnetic fields are used currently in clinical therapy of cancer. A considerable research effort is spent on improving field application techniques. The main difficulty encountered is the establishment of a sufficient temperature difference between normal and cancerous tissue for effective therapy. Therefore I propose a temperature cycling technique in field applications which should permit achieving higher temperatures in the tumor region while temperatures in normal tissue remain within a physiological range. It is expected that by this technique an improvement in cancer cure rate could be obtained.

Electromagnetic Phenomena↗

PubMed1978

Electron reactions with cytochrome c in ethylene glycol/water glass at-196 degrees C.

Low temperature gamma-irradiation and spectroscopy are used to study electron reactions with cytochrome c in aquo organic glass at-196 degrees C. Spectral data suggests that cytochrome c is reduced by electron at 196 degrees C. Raising the glass temperature reveals further changes in spectrum, suggesting that conformational changes may occur in cytochrome c molecule during stabilization of reductive process.

Animals↗

PubMed1974