[Electromagnetic fields, electric current and bone healing - what is the evidence?]. / Elektromagnetische Felder, elektrischer Strom und Knochenheilung: was ist gesichert?

For more than 30 years the potential effects of electrical stimulation on bone healing have been investigated. Up to now this therapy is controversial and not established as a standardised treatment option. This systematic review and metaanalysis focuses on the potential effects of electromagnetic fields and high-frequency electric fields on bony healing. In a systematic literature search randomised clinical trials were identified and analysed. Those studies with the primary endpoint "rate of bony healing" were combined in a metaanalysis which was performed with the "random effects" model. We found a total of 14 randomised clinical trials. These studies included a total of 915 patients. The majority of these studies used pulsed electromagnetic fields (PEMF). Out of the 14 studies nine were suitable for the metaanalysis which revealed a cumulative odds ratio of 3.5 and a 95 % confidence interval of 1.94-6.3. When performing a subgroup analysis a statistically significant result could not be confirmed by the studies with a higher methodological quality. In view of the heterogeneous physical parameters with different frequencies, time course, flux densities and in view of the methodological deficits, a general conclusion seems difficult. Recommendations or standards of therapy are so far not available.

The influence of anatomical and physiological parameters on the interference voltage at the input of unipolar cardiac pacemakers in low frequency electric fields.

The problem of electromagnetic interference of electronic implants such as cardiac pacemakers has been well known for many years. An increasing number of field sources in everyday life and occupational environment leads unavoidably to an increased risk for patients with electronic implants. However, no obligatory national or international safety regulations exist for the protection of this patient group. The aim of this study is to find out the anatomical and physiological worst-case conditions for patients with an implanted pacemaker adjusted to unipolar sensing in external time-varying electric fields. The results of this study with 15 volunteers show that, in electric fields, variation of the interference voltage at the input of a cardiac pacemaker adds up to 200% only because of individual factors. These factors should be considered in human studies and in the setting of safety regulations.

Evaluation and comparison of 50 Hz current threshold of electrocutaneous sensations using different methods.

Leakage currents, tiny currents flowing from an everyday-life appliance through the body to the ground, can cause a non-adequate perception (called electrocutaneous sensation, ECS) or even pain and should be avoided. Safety standards for low-frequency range are based on experimental results of current thresholds of electrocutaneous sensations, which however show a wide range between about 50 microA (rms) and 1000 microA (rms). In order to be able to explain these differences, the perception threshold was measured repeatedly in experiments with test persons under identical experimental setup, but by means of different methods (measuring strategies), namely: direct adjustment, classical threshold as amperage of 50% perception probability, and confidence rating procedure of signal detection theory. The current is injected using a 1 cm2 electrode at the highly touch sensitive part of the index fingertip. These investigations show for the first time that the threshold of electrocutaneous sensations is influenced both by adaptation to the non-adequate stimulus and individual, emotional factors. Therefore, classical methods, on which the majority of the safety investigations are based, cannot be used to determine a leakage current threshold.The confidence rating procedure of the modern signal detection theory yields a value of 179.5 microA (rms) at 50 Hz power supply net frequency as the lower end of the 95% confidence range considering the variance in the investigated group. This value is expected to be free of adaptation influences, and is distinctly lower than the European limits and supports the stricter regulations of Canada and USA.

[Chiparray-based identification of gene expression in HUVECs treated with low frequency electric fields]. / Chiparray-basierte Identifikation von differenziell exprimierten Genen in humanen Nabelschnurendothelzellen (HUVEC) nach in vitro Stromexposition.

PURPOSE: After high-voltage electric injury, patients often show progressive tissue necrosis and thrombosis of blood vessels even remote from the entry and exit sites of electrical current. Recently, we were able to demonstrate IN VIVO and VITRO the release of several prothrombotic factors. In this study, we report on IN VITRO studies performed to characterize gene expression profiles using a DNA-microarray in HUVECs (human umbilical vein endothelial cells) exposed to low frequency electrical current. METHODS: HUVECs were plated and grown to confluence in a culture chamber. They were exposed to 25 periods of 50 Hz sinusoidal waves. The periods had field strength of 60 V/cm and duration of 100 ms. Periods were interrupted by 10-second intervals to prevent significant joule heating. Control HUVECs were treated identically except that no electric field was applied. Samples from control and treated cells were taken after six and 24 hours. A PIQOR Immunology Array (Milteny Biotech) containing 1076 cDNAs was used for gene expression analysis. Hybridization of Cy3- and Cy5-labelled samples, image capture, and signal quantification of hybridized arrays were performed. Local background was subtracted from the signal to obtain the net signal intensity and the ratio of Cy5/Cy3. The ratios were normalized to the median of all ratios and the mean of the ratios of four corresponding spots was computed. More than two-fold increases or decreases of the gene expression were regarded as relevant. RESULTS: A total of 413 genes (1s + s) respectively 345 genes (2s + s) could be detected. The results obtained display a distinct expression pattern of up-regulated genes known to be important for hemostasis (e.g. UPA, UPAR, ECE1, PAFAH1B1, PGT, INOS, ENOS, TPA, ICAM1, VCAM1, PAI1, PAI2, VWF, PTGDR, F3, THBD), which was most evident after 24 hours. This expression profile might lead to a hypercoagulated state. Furthermore, the expression of genes involved in angiogenesis was reduced whereas the expression of those involved in platelet formation was increased. CONCLUSION: Our results indicate that low frequency electrical fields induce a distinct signature of differential gene expression in exposed HUVECs. This might explain the clinical observation of thrombosis and progressive tissue necrosis after electrical injury.

Duodenal motility is not affected during duodenotomy in pigs.

The effects of surgical procedures on intestinal motility are still under debate. In order to quantify the effects of duodenotomy on duodenal motility, the present study used the electric impedance technique (IMP). Ten pigs (32-40 kg) were instrumented under general anaesthesia with a central venous catheter (CVC) and a percutaneous enterogastrostomy (PEG). Duodenal phases I-III and the duration of the migrating motor complex (MMC) were measured by an IMP catheter, which was introduced non-invasively into the proximal duodenum via the PEG by endoscopy, or through surgical placement in an invasive manner via duodenotomy. There were no significant differences in the length of interdigestive phases I-III between the groups. In tendency, pigs after laparotomy and duodenotomy demonstrated slightly prolonged median duration of phase I (P = 0.1) and phase III (P = 0.7), while phase II (P = 0.1) and the MMC cycle length (P = 0.6) seemed to be shortened as compared to pigs of the PEG group. In conclusion, simple laparotomy with duodenotomy did not affect the proximal duodenal motility activity measured by the impedance technique.

Relationship between bolus transit and LES-relaxation studied with concurrent impedance and manometry.

BACKGROUND/AIMS: Neuromuscular mechanisms regulating esophageal bolus transport are well studied. However, detailed data about the relationship between bolus transit and lower esophageal sphincter (LES)-relaxation during conventional motility testing are still lacking. METHODOLOGY: We performed systematic studies in 25 normal subjects, employing a catheter that integrates the two techniques impedancometry and manometry in a single instrument for simultaneous recording and analysis of the relationship between bolus transit and LES relaxation after swallowing saline or yogurt. RESULTS: 195 swallows were analyzed. LES relaxation occurred frequently later than UES relaxation. The mean latency between bolus entry into the esophagus and LES relaxation was 3.6 +0.2 sec. Two types of swallow-induced LES relaxation were observed: (a) LES relaxation preceding bolus transit (46 cases or 24%) and (b) LES relaxation occurring during bolus transit (149 cases or 76%). In the later case, during 114 (76%) cases of this deglutition, the position of the bolus was very close to the LES. CONCLUSIONS: During deglutition, LES relaxation seems to be modulated by bolus transit and occurs predominantly upon arrival of the bolus in the distal esophagus.

Effects of propofol and fentanyl on duodenal motility activity in pigs.

To investigate the effects of propofol and fentanyl on the postprandial duodenal motility the intraluminal impedance technique was used. Six pigs were instrumented with a central venous catheter, a percutaneous enterogastrostomy (PEG), and an impedance catheter, which was introduced via the PEG into the duodenum through endoscopy. Over the following 3 d, duodenal motility was measured for 8-hour periods. Measurements were taken on each subject under 3 different sets of conditions: in the conscious unrestrained pig, during propofol sedation, and during sedation with propofol-fentanyl. Both, after morning feeding and during gastric nutrition via the PEG, duodenal feeding patterns and duodenal phase II of the migrating motor cycle were shortened during propofol and propofol-fentanyl sedation. In contrast, the duration of phase I was prolonged by propofol and propofol-fentanyl. In conclusion, either propofol or propofolfentanyl sedation shortens duodenal feeding patterns, as well as phase II of the migrating motor cycle.

Electrical potentials derived from articular cartilage: the significance of polarization potentials.

Changes of electrical potentials in cartilage tissue under mechanical compression have been detected in several studies. As polarization potentials are known to occur at the interface between metals and electrolytes, the question remains open whether the measured electrical potentials in relation to mechanical compression are interfered with polarization potentials. Using a porcine model, whole knee joints were explanted and exposed to uniaxial loading of up to 250 N. Under similar conditions, a tube filled with normal saline was prepared with three gold-plated electrodes. Changes of voltage derived from the electrodes placed in normal saline could be detected only when the force was applied instantly by a hydraulically controlled pump. In comparison, mechanically induced electrical potentials could be derived from cartilage tissue when exposed to both sudden force and force induced more slowly by an electric engine. While the electrical response derived from cartilage tissue correlated with the extent of the applied force, there was no such correlation between the potential changes from normal saline and the applied mechanical force. In conclusion, polarization potentials derived from metal electrodes in contact with electrolyte solution are pressure dependent. However, those electrical potential changes obtained from the cartilage tissue under compressive force revealed no obvious influence by polarization potentials.

[Acid and non-acid gastro-esophageal reflux in newborns. Preliminar results using intraluminal impedance]. / Reflujo gastroesofágico ácido y no ácido en el recién nacido. Datos preliminares de estudio con impedancia intraesofágica.

Preterm infants present often Gastroesophageal refluxes (GER). Esophageal pH monitoring to reflux detection is of limited use in this infants because their gastric pH is normally higher than 4 for 90% of the time. Other methods such as the Intraluminal Impedance Technique (MII) technique and the use of micromanometric catheters try to palliate the difficulties for measuring GER by pH monitoring. The aim of this study, in a first step, was to obtain the normal Intraluminal Impedance values on control children and, in a second step, to study the relationship between GER and cardiorespiratory episodes using simultaneous recording of the end-tidal fraction of expired CO2, 02 saturation by pulse-oximetry, respiratory frequency, esophageal impedance and manometry, gastro-esophageal pHmetry, and electrocardiography in selected patients. Data from simultaneous pH and Intraluminal Impedance during 24 hours in 7 control preterms showed 89 acid refluxes, 192 non-acid refluxes, 79.36% of all refluxes reached the proximal esophagus. Therefore the impedance is an innocuous method which opens new horizons in the study of such a common illness as the GER in the preterm infants.

Unipolar cardiac pacemakers in electromagnetic fields of high voltage overhead lines.

Experimental studies have shown that both electric and magnetic extremely low frequency fields are able to disturb a cardiac pacemaker (CPM) at certain field strengths. However, the simultaneous influence of multiphase electric and magnetic fields beneath high voltage overhead lines (HVOLs) has not yet been investigated. Therefore, the distribution of the electric and the magnetic field as well as the phase angle between both components for an exemplary HVOL was numerically calculated. The calculations show that the phase difference of the capacitive and the inductive induced voltage on the input of an implanted cardiac pacemaker is position-dependent. Based on these and our earlier results a worst-case-scenario for two virtual patients beneath an exemplary HVOL was derived. It turned out that although the interference of CPMs by the electromagnetic fields (EMFs) of HVOLs cannot be ruled out, the life-threatening interference condition 'inhibition by EMF' is unlikely. Due to various factors depending on technical parameters and the individual patient a definite answer about the disturbance of an implanted CPM beneath HVOLs can be given by studies with real CPM patients only.

Reflujo gastroesofágico ácido y no ácido en el recién nacido. Datos preliminares de estudio con impedancia intraesofágica / Acid and non-acid gastro-esophageal reflux in newborns. Preliminar results using intraluminal impedance

El reflujo gastroesofágico (RGE) es un hecho muy común en niños pretérmino. La prueba gold standard hasta ahora para medir el reflujo, la pHmetría, se ve limitada en estos niños debido a que supH gástrico es superior a 4 un 90% del tiempo. Nuevos métodos como la impedanciometría, y los catéteres de micromanometría,intentan paliar el déficit existente hasta ahora en este campo. Los objetivos de nuestro estudio son en una primera fase obtener valores normales de impedanciometría en niños controles y estudiar,en una segunda fase, la relación entre RGE y enfermedad respiratoria en recién nacidos pretérmino, con un registro multivariable de impedancia y pH para identificar los episodios de reflujo y las variaciones del electrocardiograma (ECG), la saturación de O2 (SO2), la frecuencia respiratoria (FR) y el CO2 espirado (ETCO2), para objetivar si los episodios de reflujo tienen alguna relación con la enfermedad respiratoria. Hemos estudiado hasta ahora a 7 niños pretérmino, con controles mediante monitorización durante 24 horas de pHmetría + impedancia. Nº de reflujos ácidos: 89. Nº de reflujos pH>4: 192. Reflujos que llegan a esófago distal: 79,36%.La impedancia, por tanto, se trata de un método inocuo que abre nuevos horizontes en el estudio de una enfermedad tan común como el RGE (AU)

Preterm infants present often Gastroesophageal refluxes (GER). Esophageal pH monitoring to reflux detection is of limited use in this infants because their gastric pH is normally higher than 4 for 90% of the time. Other methods such as the Intraluminal Impedance Technique (MII) technique and the use of micromanometric catheters try to palliate the difficulties for measuring GER by pH monitoring. The aim of this study, in a first step, was to obtain the normal Intraluminal Impedance values on control children and, in a second step, to study the relationship between GER and cardiorespiratory episodes using simultaneous recording of the end-tidal fraction of expired CO2, O2 saturation by pulse-oximetry, respiratory frequency, esophageal impedance and manometry, gastro-esophageal pHmetry, and electrocardiography in selected patients. Data from simultaneous pH and Intraluminal Impedance during 24 hours in 7 control preterms showed 89 acid refluxes, 192 non-acid refluxes, 79.36% of all refluxes reached the proximal esophagus. Therefore the impedance is an innocuous method which opens new horizons in the study of such a common illness as the GER in the preterm infantsPreterm infants present often Gastroesophageal refluxes(GER). Esophageal pH monitoring to reflux detection is of limited use in this infants because their gastric pH is normally higher than 4 for 90% of the time. Other methods such as the Intraluminal Impedance Technique (MII) technique and the use of micromanometric catheterstry to palliate the difficulties for measuring GER by pH monitoring. The aim of this study, in a first step, was to obtain the normal Intraluminal Impedance values on control children and, in a second step, to study the relationship between GER and cardiorespiratory episodes using simultaneous recording of the end-tidal fraction of expired CO2,O2 saturation by pulse-oximetry, respiratory frequency, esophageal impedance and manometry, gastro-esophageal pHmetry, and electrocardiographyin selected patients. Data from simultaneous pH and Intraluminal Impedance during 24 hours in 7 control preterms showed 89 acid refluxes, 192 non-acid refluxes, 79.36% of all refluxes reached the proximal esophagus.Therefore the impedance is an innocuous method which opens new horizons in the study of such a common illness as the GER in the preterm infants (AU)

Effects of a single dose of ketamine on duodenal motility activity in pigs.

In order to investigate the effects of a single dose of ketamine on duodenal motility, the present study focused on the electric impedance technique. Five pigs (32 to 40 kg, CVC group) were instrumented with a central venous catheter 1 d before measurements. The next day, general anesthesia was started and maintained via central venous catheter by propofol and fentanyl. In contrast, the pigs of the KETA group (n = 5) received ketamine intramuscularly prior to the induction of anesthesia by the injection of propofol-fentanyl via an ear vein. An intraluminal impedance catheter was manually introduced into the proximal duodenum. Measurements were recorded for 4 h. The KETA group showed a median duration of phase II that was shortened by 35%, while phase I was prolonged by 73% (P < 0.05). In conclusion, when gastrointestinal motility has to be investigated, the effects of a single dose of ketamine, even for premedication, should be taken into consideration.

Impedance characteristics of esophageal motor function in achalasia.

Detailed data on patterns of esophageal bolus transport in patients with achalasia are still lacking. To study these we applied the novel technique of multichannel intraluminal impedance measurements. Ten patients with achalasia were studied using a 16 channel system. Liquid and semisolid boluses of 10 mL were applied with the patients in a supine position. Patterns of bolus transport were determined and analyzed as compared to results obtained from 20 healthy subjects. The healthy subjects featured a unique typical primary peristalsis pattern independent of bolus viscosity. In contrast, achalasia patients demonstrated different impedance characteristics, including: (i) significantly lower baseline esophageal impedance during the resting state as compared with healthy volunteers (999 omega +/- 108 versus 2749 omega +/- 113); (ii) failed bolus transport through the esophagus in all cases; (iii) impedance evidence of luminal content regurgitation in 35% of the swallows (iv) impedance evidence of pathological air movement within the proximal esophagus during deglutition in 38% of the swallows, so called air trapping. Thus, impedance characteristics of achalasia have been defined and can be attributed to known symptoms of achalasia. They can be used as basic findings for further classification of pathological bolus transports in other esophageal motility disorders.

50-Hz magnetic field exposure influences DNA repair and mitochondrial DNA synthesis of distinct cell types in brain and kidney of adult mice.

Despite several recent investigations, the impact of whole-body magnetic field exposure on cell-type-specific alterations due to DNA damage and DNA repair remains unclear. In this pilot study adult mice were exposed to 50-Hz magnetic field (mean value 1.5 mT) for 8 weeks or left unexposed. Five minutes after ending exposure, the mice received [(3)H]thymidine and were killed 2 h later. Autoradiographs were prepared from paraffin sections of brains and kidneys for measuring unscheduled DNA synthesis and mitochondrial DNA synthesis, or in situ nick translation with DNA polymerase-I and [(3)H]dTTP. A significant (P<0.05) increase in both unscheduled DNA synthesis and in situ nick translation was only found for epithelial cells of the choroid plexus. Thus, these two independent methods indicate that nuclear DNA damage is produced by long-lasting and strong magnetic field exposure. The fact that only plexus epithelial cells were affected might point to possible effects of magnetic fields on iron transport across the blood-cerebrospinal fluid barrier, but the mechanisms are currently not understood. Mitochondrial DNA synthesis was exclusively increased in renal epithelial cells of distal convoluted tubules and collecting ducts, i.e., cells with a very high content of mitochondria, possibly indicating increased metabolic activity of these cells.

The interference of electronic implants in low frequency electromagnetic fields.

Electronic implants such as cardiac pacemakers or nerve stimulators can be impaired in different ways by amplitude-modulated and even continuous electric or magnetic fields of strong field intensities. For the implant bearer, possible consequences of a temporary electromagnetic interference may range from a harmless impairment of his well-being to a perilous predicament. Electromagnetic interferences in all types of implants cannot be covered here due to their various locations in the body and their different sensing systems. Therefore, this presentation focuses exemplarily on the most frequently used implant, the cardiac pacemaker. In case of an electromagnetic interference the cardiac pacemaker reacts by switching to inhibition mode or to fast asynchronous pacing. At a higher disturbance voltage on the input of the pacemaker, a regular asynchronous pacing is likely to arise. In particular, the first-named interference could be highly dangerous for the pacemaker patient. The interference threshold of cardiac pacemakers depends in a complex way on a number of different factors such as: electromagnetic immunity and adjustment of the pacemaker, the composition of the applied low-frequency fields (only electric or magnetic fields or combinations of both), their frequencies and modulations, the type of pacemaker system (bipolar, unipolar) and its location in the body, as well as the body size and orientation in the field, and last but not least, certain physiological conditions of the patient (e.g. inhalation, exhalation). In extensive laboratory studies we have investigated the interference mechanisms in more than 100 cardiac pacemakers (older types as well as current models) and the resulting worst-case conditions for pacemaker patients in low-frequency electric and magnetic fields. The verification of these results in different practical everyday-life situations, e.g. in the fields of high-voltage overhead lines or those of electronic article surveillance systems is currently in progress. In case of the vertically-oriented electric 50 Hz fields preliminary results show that per 1 kV/m unimpaired electrical field strength (rms) an interference voltage of about 400 microVpp as worst-case could occur at the input of a unipolar ventricularly controlled, left-pectorally implanted cardiac pacemaker. Thus, already a field strength above ca. 5 kV/m could cause an interference with an implanted pacemaker. The magnetic fields induces an electric disturbance voltage at the input of the pacemaker. The body and the pacemaker system compose several induction loops, whose induced voltages rates add or subtract. The effective area of one representing inductive loop ranges from 100 to 221 cm2. For the unfavourable left-pectorally implantated and atrially-controlled pacemaker with a low interference threshold, the interference threshold ranges between 552 and 16 microT (rms) for magnetic fields at frequencies between 10 and 250 Hz. On this basis the occurrence of interferences with implanted pacemakers is possible in everyday-life situations. But experiments demonstrate a low probability of interference of cardiac pacemakers in practical situations. This apparent contradiction can be explained by a very small band of inhibition in most pacemakers and, in comparison with the worst-case, deviating conditions.

Relevance of ineffective oesophageal motility during oesophageal acid clearance.

BACKGROUND: Oesophageal clearance of acid reflux consists of an initial volume clearance followed by neutralisation of the acidified mucosa by swallowed saliva (chemical clearance). Ineffective oesophageal motility (IOM), a frequent finding in patients with gastro-oesophageal reflux disease (GORD), has been claimed to underlie prolonged acid clearance by affecting oesophageal emptying and saliva transport. Intraluminal impedance allows non-radiological monitoring of movement of oesophageal liquids. AIMS: To evaluate the relevance of IOM during oesophageal volume and chemical clearance using combined pH impedance measurements. SUBJECTS: Impedance was validated with fluoroscopy to study volume clearance in three healthy subjects. Acid clearance tests were performed in 10 healthy subjects in the upright and supine positions, before and after oesophageal peristaltic disruption with sildenafil 50 mg. METHODS: After instillation of an acid bolus, simultaneous manometry, pH, and impedance were used to study oesophageal motility, chemical clearance, and volume clearance, respectively. RESULTS: Impedance allowed assessment of volume clearance accurately, showing a strong correlation with fluoroscopy (r(2)=0.89). Sildenafil provoked a graded impairment in oesophageal motility in healthy subjects without affecting saliva secretion. In the upright position, volume clearance was slightly prolonged only with severe IOM (>80% abnormal peristaltic sequences). In the supine position, severe IOM significantly prolonged chemical and volume clearance. Moderate IOM (30-80% abnormal peristalsis) had no effect. With normal peristalsis and moderate IOM, clearance times were similar in the upright and supine positions. Severe IOM however had a greater impact on clearance in the supine than in the upright position. CONCLUSION: Ineffective oesophageal motility has little effect on oesophageal clearance during upright acid reflux. With supine reflux, only severe IOM is associated with prolonged oesophageal clearance.

Current density threshold for the stimulation of neurons in the motor cortex area.

The aim of this study was to determine a current density threshold for exciting the motor cortex area of the brain. The current density threshold for excitation of nerve fibres (20 microm in diameter) found in the literature is approximately 1 A/m(2) at frequencies lower than 1 kHz. In consideration of a safety factor of 100, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommends to restrict the exposure to 0.01 A/m(2). The electromagnetic stimulation of neurons in the motor cortex is used in the clinical diagnosis of nerve lesions and neuropathy by means of magnetic or electrical transcranial stimulation. Combining medical data from clinical studies and technical specifications of the Magstim Model 200 stimulator, we were able to compute the current density threshold for the excitation of the human motor cortex by means of the finite element method (FEM). A 3D-CAD head model was built on the basis of magnetic resonance imaging (MRI) slices and segmented into four anatomical structures (scalp, skull, brain, and ventricular system) with different conductivities. A current density threshold for the stimulation of the motor cortex area of the upper limbs of 6 and 2.5 A/m(2) at 2.44 kHz and 50 Hz, respectively, was calculated. As these values lie above the recommended ICNIRP values by two orders of magnitude there is no need for lower safety standards with regard to stimulation of the brain.

[Electrical fields in the knee joint induced by external magnetic fields: results of an experimental study]. / Elektrische Felder im Kniegelenk durch externe Magnetfelder: Ergebnisse einer experimentellen Untersuchung.

AIM: Magnetic fields are used in the treatment of osteoarthritis. So far the efficiency has not been scientifically proven. The comparability of induced electrical fields with those produced endogenously within the cartilage tissue is unknown. METHOD: The study was performed on a knee joint model which was exposed to magnetic fields (2mT and 4.9 mT, 50 Hz). The measurements were performed using small spherical electrodes within the knee joint located at positions defined by three cartesian coordinates. The electrical potentials were amplified 100-fold and plotted on an oscilloscope. The results were checked by post-mortem examinations on a human knee joint. RESULTS: In relation to the magnetic flux density and the steric orientation of the electrodes, we found electric field strengths between 60 and 410 micro V/cm. When performing the procedure on the human knee joint, field strengths of up to 400 micro V/cm were measured. CONCLUSIONS: Electrical fields in the knee joint which are induced by external magnetic fields can be verified. When compared with the endogenous electrical potentials, the measured values were about 30 times smaller. Given these results, we can make no conclusions about therapeutic efficiency.

Electrical phosphenes: on the influence of conductivity inhomogeneities and small-scale structures of the orbita on the current density threshold of excitation.

Electrical and magnetic phosphenes, perceptions of light as a result of non-adequate stimulation of the eye by electrical current or magnetic induction, respectively, are one of the cornerstones to justify limit values for extreme low-frequency fields specified by statutory regulations. However, the mechanism and place of action, as well as the excitation threshold, remain unknown until now. We suggest that the origin of phosphene excitation is the synaptic layer of the eye. The current density threshold value for electrical phosphene excitation was numerically quantified for this area on the basis of a detailed geometrical model in original submillimetre resolution and specifically measured conductivities in the LF range. The threshold values found were 1.8 A m-2 at 60 Hz and 0.3 A m-2 at 25 Hz. These values are comparable with values of other excitable tissues. It has been shown that the current density threshold for phosphene generation depends on small-scale structures not taken into account by previous models.

The interference threshold of unipolar cardiac pacemakers in extremely low frequency magnetic fields.

The effective induction loop area of implanted cardiac pacemaker (CPM) systems in magnetic fields was determined. The results were verified in a tank model placed in the centre of a Helmholtz-coil-arrangement. Both a left and a right pectorally implanted unipolar dual chamber CPM system were simulated. On this basis and with the results of benchmark-tests the interference thresholds for a collection of modern CPMs in extremely low frequency (ELF) magnetic fields were estimated. The investigations clearly showed that there are two loops, the CPM-lead-tissue-loop and the body loop, responsible for the magnitude of the disturbance voltage on the input of a cardiac pacemaker. The effective induction loop areas rangedfrom 100 to 221 cm2. For a left pectorally implanted, atrially controlled CPM system the interference thresholds for the magnetic induction lay between 16 and 552 micro T (RMS) for frequencies of the magneticfield between 10 and 250 Hz. Thus, there is a limited possibility for an interference of implanted CPM by ELF magnetic fields in everyday life.