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Biomedical subjects

N Leitgeb

Publications and source records attributed to N Leitgeb.

At least 19 recordsLinked to original sources
PubMed2006

Electromagnetic shielding mats: facts and fiction.

The use of electricity is accompanied by electric and magnetic fields which, intended or not, became a part of our environment. However, fear from environmental electromagnetic fields (EMFs) is widespread and so is business with fear. A number of more or less serious products including miracle products are placed on the market partly at excessive costs. By numerical simulation the efficiency of electromagnetic shielding mats was investigated and claims of manufacturers and their cited expert opinions checked. It could be shown that such products do not fulfil the justified expectations of customers, neither in the extremely low frequency (ELF) nor in the radiofrequency (RF) range. On the contrary, these mats usually make things even worse. The connection to ground, if available, might increase the belief on shielding efficiency, but in fact it even enhances fields instead of improving shielding. The electric conductivity of the mat material plays a minor role in the ELF range and enhances field increase in the RF range. It can not explain the enormous price differences. It could be shown that positive reports can be explained by result picking and exceptional arrangements of selected field sources. Overall, the investigation showed that manufacturer's claims about the shielding effectiveness are misleading and fool the customers about the real situation. Therefore, acquisition and use of electromagnetic shielding mats must be strongly discouraged.

Electricity↗
PubMed2005

[Inefficiency of electrical pollution-shielding mats. 1: low frequency range].

Despite of the fact that environmental electric and magnetic fields are magnitudes below the existing limits, fear from electromagnetic pollution increase and so does business with fear by offering more or less plausible products with partly excessively high prices . Based on numerical simulation the claims of manufacturers on the efficiency of electromagnetic shielding mats were tested. It is pretended that electric fields can be shielded to 98% and more, and transferred to earth by earth cables (if attached). It could be shown that in general such products do not fulfil the justified expectations of customers, but in contrary even cause the opposite. To connect the mats with earth potential by an attached cable might increase the beliefs on a protective effect, however, this is not capable to enhance the shielding effect but in most cases this causes even the contrary by partly considerably increasing electric field exposure. The electric conductivity of the used shielding mats plays a neglectable role and cannot explain the considerable price differences. The investigation demonstrates that in spite of references made to expert's opinions manufacturer's claims about the shielding efficiency are misleading and fooling clients about the real situation.

Computer Simulation↗
PubMed2005

[Inefficiency of electrosmog-shielding mats. Part 2: radio frequency range].

It could already be shown that electromagnetic shielding mats do not reduce but even enhance electric field exposure in daily life situations. By measurements and numerical simulations the claims of manufacturers were checked who pretend that radio frequency electromagnetic fields can be shielded to 99% and more, and transferred to earth by earth cables (if attached). It could be shown that in the radio frequency range such products do not fulfil the justified expectations of customers, but in most cases even cause the opposite. The results depend on the electric properties of the material. Good electric conductivity of shielding mats even considerably increases electromagnetic field exposure. To connect the mats with earth potential by an attached cable might increase the beliefs on a protective effect, however, this is not capable to enhance the shielding effect. The investigation demonstrates that in spite of references made to experts opinions manufacturers claims about the shielding efficiency of radio frequency fields are misleading and fool clients about the real situation. Overall, acquisition and use of electrosmog shielding mats must be discouraged. If at all, shielding can be reached by placing a shielding cover between the source and the person. However, even in this case, efficiency is much lower than promised by manufacturers and decreases even more if it is taken into account that the head naturally remains uncovered and hence unshielded.

Electromagnetic Fields↗
PubMed2004

[Investigation of sleep disorders in the vicinity of high frequency transmitters].

To investigate the potential impact of RF electromagnetic fields of transmitters on the sleep quality of nearby residents, a new study design is presented. In a double-blind crossover field study the effect of on-site shielding, rather than of additional exposure, is investigated. For improved sleep quality differentiation the polysomnographic parameters are expanded by additional parameters. The feasibility study showed that checking the raw data and correcting the software-generated results by visual reading of the polysomnographic recordings is essential. Long-term RF measurement showed that exposure may vary considerably throughout the night, as well as from one night to the next. This variation may be greater than the GSM contribution itself. Mostly, the contributions of USW radio frequency fields dominated over GSM. Thus, continuous broadband RF recording is required for reliable interpretation of the results, in particular with regard to the potential role of mobile telephony emissions. Results show that simple sleep monitoring systems based on single-channel EEG analysis without acces to original biosignals are not adequate for sleep studies.

Cross-Over Studies↗
PubMed2003

[Influence of body size on the electric current perception threshold].

Although the threshold for electric current perception is of great importance for safety considerations and safety regulations, important aspects remain unsolved, e.g. the role of age or body size. In the present study measurements of the perception threshold were performed in 790 persons aged between 18 and 82 years randomly selected from the general population. For the first time, the composition and size of the sample were selected such as to allow extrapolation to the general population. The results reveal not only statistically significant gender differences in the perception threshold but also statistically significant relationships between perception threshold and body size. The assumption that the differences in body size between men and women are responsible for the gender-specific difference in electric current perception threshold was not confirmed in this study.

Adolescent↗
PubMed2001

[Risk from electric current greater than assumed].

Despite its importance for the assessment of the effects of electric current and for technical safety considerations, not only does the electric perception threshold remain uncertain, but essential questions are still unanswered and contradictions unresolved. Via measurements at 908 persons randomly selected from the general population, including 708 adults (349 men, 359 women aged between 16 and 60 years), the problems of extrapolation to the general population and adequate statistical representation have now been overcome for the first time. The results show that existing assumptions about electric current perception need to be drastically corrected. It has been shown that the assumed electric perception threshold has been too high by a factor of 10, and that women are substantially more sensitive than men. This means that present gender-specific differences in electrosensitivity need revising. On the basis of the evidence of significant underestimation of the reaction variability in the general population, present assumptions on safety limits and safety factors urgently need to be reviewed. By no means can a relaxation of safety regulations be justified.

Adolescent↗
PubMed1994

Quantitative assessment of fracture healing. The value of computerised sonometry in a correlative animal experiment in sheep.

Usually follow-up of the healing process of bone fractures is by subjective assessment of standard X-rays, based on the clinician's personal experience. It is therefore impossible to completely avoid misjudgements in the evaluation of the mechanical stability. Other authors have reported that the mechanical response of bony structures to a knock impulse allows a definitive statement about the stiffness of a fracture. The practicability of computerised sonometry in computer-aided evaluation of the mechanical vibration reaction and the acoustic transmission of sound through osseous structures for assessing stability has been proved in experimental and clinical studies. We designed an animal study that would allow a systematic correlation between the diagnostic investigations in general use. As a main goal, this study tries to correlate sonography with other quantitative techniques, even if they are not used under everyday clinical conditions. Our results show that methods based on direct assessment of the mechanical stability between fracture fragments allow a more exact evaluation of fracture healing. This study helps to classify the results of computerised sonometry together with other diagnostic procedures used for the evaluation of fracture healing, and furthermore provides a basis for clinical interpretation of the findings of a new, non-invasive technique for precise quantitative assessment of fracture healing.

Animals↗
PubMed1994

Early detection of delayed union in lower leg fractures using a computerised analysis of mechanical vibration reactions of bone for assessing the state of fracture healing.

Standard X-ray techniques are used to follow up the healing process of bone fractures. However, these methods allow only indirect conclusions about the stability of the healing bone, depending on the experience of the clinician. In addition, by radiologic means, delayed union or non-union can only be diagnosed on the basis of the absence of specific changes such as callus formation. Therefore, efforts have been made to develop alternative methods for monitoring the healing process. The measuring principle of a non-invasive method is based on evaluation of changes in mechanical vibration reactions. The measuring system is composed of two sound transducers, an amplifier module and an AD converter attached to a PC. The assessment of 150 healthy individuals as well as an initial measuring series after treatment of tibial fractures with an external fixator system revealed highly significant differences between intact and fractured tibias. Thus, computerised sonometry is capable of supplying quantitatively recordable information about the stability of a fractured bone at any time in the healing process. Furthermore, this non-invasive technique allows early diagnosis of disorders in the repair process by the absence of change in the parameters.

Biomechanical Phenomena↗
PubMed1993

[Computerized sonometry--use of a noninvasive procedure for evaluating stability after fractures].

Common techniques to assess the healing process of fractures are usually related to the experience of the clinician. However, standard x-rays allow only indirect conclusions on the stability of the healing bone. In addition to the radiological examination delayed union or non-union can only be diagnosed in the absence of specific changes such as callus formation. Computerised sonometry comprises the analysis of mechanical vibration as well as sound transmission during or after bone healing. This non-invasive method allows for assessing the stiffness of the bone quantitatively and gives objective data on bone stability.

Auscultation↗
PubMed1993

[Analysis of epidemiologic studies of magnetic field-induced cancer risk].

Since 1979 in numerous epidemiological studies with different design and conflicting results the possibility of a relationship between cancer and exposure to magnetic fields was investigated. By combined evaluation of 39 studies it can be stated that the time dependence of the results seems to support the hypothesis that no risk should be expected or that it is at least lower than presently assumed.

Brain Neoplasms↗
PubMed1990

[Ultrasonic diagnosis of fractures].

For the first time, sonographic callus diagnosis concentrates not on the fracture gap but on the conversion process within the surrounding callus region to determine healing and reloadability of fractures. On evaluation of callus texture in relation to the adjacent muscle tissue a sensitive diagnostic parameter can be determined from B-scan images even in a clinical routine situation which is suitable for the monitoring of healing as well as determination of the fracture status. The results of a clinical study are presented and a parameter range is determined which can be used as a criterium for tibia fracture stability and reloadability. Principal agreement of parameter dependence on healing time is shown by fibula fracture diagnosis, too.

Bone and Bones↗
PubMed1990

[Cyclotron resonance as a cause of biological effects of weak electric and magnetic fields?].

Even weak electric and magnetic fields have been found to cause interaction effects in vitro only within small frequency ranges. The existence of such "frequency windows" may be explained by a cyclotron resonance model which also takes the influence of the earth's magnetic field into consideration. In this paper analytical relations are developed which permit the determination of energy uptake and motion curve diameter. On the basis of this calculations it can be concluded that, giving consideration to interparticle interactions and the limitations of motion curve dimensions due to the limited dimensions of cells and cellular interspaces, energy uptake in vivo is many orders of magnitude below thermal energy, and can therefore be neglected.

Biophysical Phenomena↗
PubMed1988

[Technical aspects of ultrasound equipment today and tomorrow].

From the very beginning any progress in the technique of instruments used in sonography has been strongly dependent upon the general technical progress, and any such progress must take place within the physically postulated marginal conditions. Now that the image quality has been considerably improved, the present situation is characterised by the fact that sonographic diagnosis is developing from a qualitative method into a quantitative one. This will be made possible by means of computerised tissue differentiation which is already being utilised in practice by means of trend analyses, by new sonography parameters (multiparameter imaging) and by the use of digital reconstruction methods. Another substantial improvement in the technique of instruments will be brought about mainly by the extremely rapid strides made by digital technique, by further development of the weak point represented by the transducers, and by improved possibilities of display.

Equipment Design↗