Biomedical subjects

N Kuster

Publications and source records attributed to N Kuster.

7 recordsLinked to original sources

PubMed1998

Differences in energy absorption between heads of adults and children in the near field of sources.

This paper was motivated by a recent article in which the levels of electromagnetic energy absorbed in the heads of mobile phone users were compared for children and adults at the frequencies of 835 MHz and 1,900 MHz. Significant differences were found, in particular substantially greater absorption in children's heads at 835 MHz. These findings contradict other studies in which no significant changes had been postulated. The clarification of this issue is crucial to the mobile communications industry since current SAR evaluations as required by the FCC are only performed with phantoms based on the heads of adults. In order to investigate the differences in absorption between adults and children due to their differing anatomies, simulations have been performed using head phantoms based on MRI scans of an adult (voxel size 2 x 2 x 1 mm3) and two children (voxel size 2 x 2 x 1.1 mm3) of the ages of 3 and 7 y. Ten different tissue types were distinguished. The differences in absorption were investigated for the frequencies of 900 MHz and 1,800 MHz using 0.45 lambda dipoles instead of actual mobile phones. These well-defined sources simplified the investigation and facilitated the comparison to previously published data obtained from several numerical and experimental studies on phantoms based on adults. All simulations were performed using a commercial code based on the finite integration technique. The results revealed no significant differences in the absorption of electromagnetic radiation in the near field of sources between adults and children. The same conclusion holds when children are approximated as scaled adults.

Adult↗

PubMed1997

Effect of global system for mobile communication microwave exposure on the genomic response of the rat brain.

The acute effect of global system for mobile communication (GSM) microwave exposure on the genomic response of the central nervous system was studied in rats by measuring changes in the messenger RNAs of hsp70, the transcription factor genes c-fos and c-jun and the glial structural gene GFAP using in situ hybridization histochemistry. Protein products of transcription factors, stress proteins and marker proteins of astroglial and microglial activation were assessed by immunocytochemistry. Cell proliferation was evaluated by bromodeoxyuridine incorporation. A special GSM radiofrequency test set, connected to a commercial cellular phone operating in the discontinuous transmission mode, was used to simulate GSM exposure. The study was conducted at time averaged and brain averaged specific absorption rates of 0.3 W/kg (GSM exposure), 1.5 W/kg (GSM exposure) and 7.5 W/kg (continuous wave exposure), respectively. Immediately after exposure, in situ hybridization revealed slight induction of hsp70 messenger RNA in the cerebellum and hippocampus after 7.5 W/kg exposure, but not at lower intensities. A slightly increased expression of c-fos messenger RNA was observed in the cerebellum, neocortex and piriform cortex of all groups subjected to immobilization, but no differences were found amongst different exposure conditions. C-jun and GFAP messenger RNAs did not increase in any of the experimental groups. 24 h after exposure, immunocytochemical analysis of FOS and JUN proteins (c-FOS, FOS B, c-JUN JUN B, JUN D), of HSP70 or of KROX-20 and -24 did not reveal any alterations. Seven days after exposure, neither increased cell proliferation nor altered expression of astroglial and microglial marker proteins were observed. In conclusion, acute high intensity microwave exposure of immobilized rats may induce some minor stress response but does not result in lasting adaptive or reactive changes of the brain.

Animals↗

PubMed1997

Exposure setup to test effects of wireless communications systems on the CNS.

This paper presents an exposure setup designed for in vivo studies of possible effects on the central nervous system due to the electromagnetic exposure from handheld mobile communications equipment. The setup consists of a carousel on which 10 rats, each restrained in a radially positioned tube, are exposed to the electromagnetic field emanating from a dipole antenna at the center. The rats are positioned with their snouts at a distance of 35 mm from the dipole antenna. The tubes restrain the movement of the animals to such an extent as to allow for well defined exposure conditions, yet without totally immobilizing them. Numerical and experimental dosimetric analysis of the setup was conducted using rats weighing 250-300 g at a frequency of 900 MHz. A detailed rat phantom derived from MRI scans was developed for the numerical assessment with a commercially available code based on the finite integration technique. The results were validated by measurements of the temperature rise in selected points of a rat cadaver. The dosimetric analysis shows that the setup is eminently suitable for central nervous system studies. It enables well defined field strengths to be induced in the brain tissue, whereby the variations in the specific absorption rate averaged over the brain tissue caused by movement and varying animal sizes was shown to be less than +/-16%. The specific absorption rate distribution in the brain is nonhomogeneous but comparable to that induced in the brain of a human using a handheld wireless phone. The efficiency of the exposure is about 0.20+/-0.05 mW g(-1) for the brain average value per 100 mA feedpoint current. The whole-body average specific absorption rate is considerably lower, i.e., about half of that of the brain averaged value. In addition, the setup has been proven to be practical in use, and the stress levels caused by restraining the animals in this setup are deemed by neurologists and veterinary scientists to be very low.

Animals↗

PubMed1996

Numerical and experimental dosimetry of Petri dish exposure setups.

Crawford TEM cells are often used to expose cell cultures or small animals in order to study the effects caused by high-frequency fields. They are self-contained, easy-to-use setups that provide a rather homogeneous field distribution in a large area around its center, corresponding approximately to far-field conditions. However, a number of conditions must be met if such TEM cells are intended to be used for in vitro experiments. For instance, poor interaction with the incident field must be maintained to avoid significant field disturbances in the TEM cell. This is best achieved with E-polarization, i.e., when the E-field vector is normal to the investigated cell layer lining the bottom of a synthetic Petri dish. In addition, E-polarization provides the most homogeneous field distribution of all polarizations within the entire layer of cells. In this paper, we present a detailed dosimetric assessment for 60 and 100 mm Petri dishes as well as for a 48-well titer plate at 835 MHz. The dosimetry was performed by using numerical computations. The modeling and the simplifications are validated by a second numerical technique and by experimental measurements. For thin liquid layers, an approximation formula is provided with which the induced field strength for many other experiments conducted in Petri dishes can be assessed reliably.

Absorption↗

PubMed1996

Effects of low energy emission therapy in chronic psychophysiological insomnia.

The treatment of chronic psychophysiological insomnia presents a challenge that has not been met using currently available pharmacotherapy. Low energy emission therapy (LEET) has been developed as a potential alternative therapy for this disorder. LEET consists of amplitude-modulated electromagnetic fields delivered intrabuccally by means of an electrically conducting mouthpiece in direct contact with the oral mucosa. The effect of LEET on chronic psychophysiological insomnia was assessed with polysomnography (PSG) and sleep rating forms on a total of 106 patients at two different centers. Active or inactive LEET was administered for 20 minutes in late afternoon three times a week for a total of 12 treatments. Primary efficacy endpoints evaluating the results were changes from baseline in PSG-assessed total sleep time (TST) and sleep latency (SL). Secondary endpoints were changes in sleep efficiency (SE), sleep stages, and reports by the subjects of SL and TST. There was a significant increase in TST as assessed by PSG between baseline and post-treatment values for the active treatment group (76.0 +/- 11.1 minutes, p = 0.0001). The increase for the inactive treatment group was not statistically significant. The TST improvement was significantly greater for the active group when compared to the inactive group (adjusted for baseline TST; p = 0.020. R1 = 0.20). There was a significant decrease in SL as assessed by PSG between baseline and post-treatment values for the active treatment group (-21.6 +/- 5.9 minutes, p = 0.0006), whereas the decrease noted for the inactive treatment group was not statistically significant. The difference in SL decrease between the two treatment groups was marginally significant (adjusted for baseline SL and center, p = 0.068, R2 = 0.60). The number of sleep cycles per night increased by 30% after active treatment (p = 0.0001) but was unchanged following inactive treatment. Subjects did not experience rebound insomnia, and there were no significant side effects. The data presented in this report indicate that LEET administered for 20 minutes three times a week increased TST and reduced SL in chronic psychophysiological insomnia. LEET is safe and well tolerated and it effectively improved the sleep of chronic insomniacs given 12 treatments over a 4-week period by increasing the number of sleep cycles without altering the percentage of the various sleep stages during the night. The therapeutic action of LEET differs from that of currently available drug therapies in that the sleep pattern noted in insomniacs following LEET treatment more closely resembles nocturnal physiological sleep. This novel treatment may offer an attractive alternative therapy for chronic insomnia.

Adult↗

PubMed1994

Sleep inducing effect of low energy emission therapy.

The sleep inducing effect of a 15 min treatment with either an active or an inactive Low Energy Emission Therapy (LEET) device emitting amplitude-modulated electromagnetic (EM) fields was investigated in a double-blind cross-over study performed on 52 healthy subjects. All subjects were exposed to both active and inactive LEET treatment sessions, with an interval of at least 1 week between the two sessions. LEET consists of 27.12 MHz amplitude-modulated (sine wave) EM fields emitted intrabuccally by means of an electrically conducting mouthpiece in direct contact with the oral mucosa. The estimated local peak SAR is less than 10 W/kg in the oral mucosa and 0.1 to 100 mW/kg in brain tissue. No appreciable sensation is experienced during treatment, and subjects are therefore unable to tell whether they are receiving an active or an inactive treatment. In this study the active treatment consisted of EM fields intermittently amplitude-modulated (sine wave) at 42.7 Hz for 3 s followed by a pause of 1 s during which no EM fields were emitted. During the inactive treatment no EM fields were emitted. Baseline EEGs were obtained and 15 min post-treatment EEGs were recorded and analyzed according to the Loomis classification. A significant decrease (paired t test) in sleep latency to stage B2 (-1.78 +/- 5.57 min, P = 0.013), and an increase in the total duration of stage B2 (1.15 +/- 2.47 min, P = 0.0008) were observed on active treatment as compared with inactive treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1993

Multiple multipole method for simulating EM problems involving biological bodies.

The three-dimensional implementation of the multiple multipole (MMP) method, based on the generalized multipole technique (GMT), is presented. Its performance in simulating electromagnetic problems involving biological bodies is analyzed. In particular, the step-by-step simulation technique and the built-in procedures to validate the solution on numerical basis are discussed and demonstrated in two examples. A comparison is made with other numerical techniques often applied in this field. The advantages of the MMP method are shown to be in its validation capability, in its efficiency for smoothly shaped bodies and in the achievable accuracy, in particular near boundaries. The method is especially suited to handle high-gradient fields in the vicinity of biological bodies. On the other hand, finite difference (FD) techniques are superior for scatterers with complicated angular shapes or inhomogeneous bodies, for which MMP shows rather strong practical limitations. However, in most cases the inhomogeneities of biological bodies modify the field distribution only locally beyond the uncertainties of models. In these cases, inhomogeneities can be stimulated efficiently and with high accuracy by MMP applying the block iterative technique. Other methods are not general enough to compete with FD or MMP in solving EM problems involving biological tissues.

Animals↗