The importance of constancy of period in checking implanted pacemakers.
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Electrocardiography↗
Biomedical subjects
J Silny
Publications and source records attributed to J Silny.
[Pulsating electromagnetic fields in treatment of injuries and illnesses of the locomotor system--an overview and meta-analysis].
AIM: Recently, pulsating electromagnetic fields have gained wide attraction in the treatment of various orthopaedic diseases. The purpose of this study is to evaluate the scientific evidence for the effectiveness of this therapeutic tool. METHOD: All clinical studies which deal with pulsating electromagnetic fields in the treatment of orthopaedic conditions are reviewed. To elucidate the physiological basis of the method, important experimental studies are considered. RESULTS: 37 clinical studies with 3379 patients are evaluated, of which only a minority were performed as prospective studies with control groups. The results of the studies, performed on patients with various orthopaedic conditions, are not unequivocal and partly inconsistent. In view of the physiological basis many questions remain unanswered. CONCLUSIONS: At present the use of pulsating electromagnetic fields in the treatment of orthopaedic diseases is not scientifically proven.
Clinical Trials as Topic↗
[Electrical fields in the knee joint induced by external magnetic fields: results of an experimental study].
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.
Electromagnetic Fields↗
The interference threshold of cardiac pacemakers in electric 50 Hz fields.
The aim of the study was to determine a 'worst-case' and a 'real-case' interference threshold for implanted cardiac pace-makers (CPM) in electric 50 Hz fields as they appear in high-voltage plants, e.g. beneath high voltage overhead lines. For this purpose the resulting electrical potential distribution within the thorax area of volunteers from an external homogeneous electrical 50 Hz field was measured. Different factors such as different body geometries as well as inspiration and expiration of the lung were considered. Measurements showed that 1 per 1 kV m(-1) unimpaired electrical field strength (RMS) an interference voltage of about 180 microVpp as real-case value an 400 microVpp as worst-case value would occur at the input of a unipolar ventricularly controlled, left pectorally implanted cardiac pacemaker. Therefore, it is possible under worst-case conditions but unlikely under practice-relevant conditions that an implanted cardiac pacemaker is disturbed by present electric 50 Hz fields beneath high voltage overhead lines.
Adult↗
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.
Adult↗
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.
Computer Simulation↗
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.
Animals↗
[Improved objective measurement of refraction with the aid of visual evoked potentials (VEP) (author's transl)].
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Accommodation, Ocular↗
A new procedure for the registration of the visual-evoked cortical potential by multichannel recording of the gradient distribution.
A new bipolar multichannel visual-evoked cortical potential (VECP) procedure is presented, which can supply objective information on visual field losses. The electrical potential is recorded from 11 electrodes applied to the back of the head in the form of an equidistant rectangular grid. Each neighbouring pair of electrodes feeds one of 14 bipolar channels. The adjacent horizontal and vertical channels are used to calculate an approximation to the direction and amplitude of the electrical field gradients. The gradient distribution is represented by a map of arrows (gradient map) for every instant of the sweep, so that the whole sweep can be plotted as a time series of gradient maps. The maps are easy to scale and are well suited for visual evaluation. Twenty normal subjects were stimulated using checkerboard reversal, partial field patterns to simulate visual field defects. The stimulated area varied between full-, half- and quarter-field, and the particular area stimulated could be clearly seen in the resulting gradient maps. Additionally, we developed a computerized classification procedure that detected 86% of the disturbed visual fields from the gradient recordings.
Adult↗
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.
Adult↗
A noninvasive EMG technique for investigating the excitation propagation in single motor units.
A new EMG recording technique which is based on a spatially filtering surface multi-electrode array enables, with its high spatial resolution, the noninvasive investigation of single motor unit (MU) excitations. This recording technique was applied to study the propagation velocity within single, superficial MUs of lower arm muscles. The conduction velocity (CV) was estimated by time shifts between action potentials (APs) recorded at different positions along the muscle fibres. Several signal characteristics to define this time shift were compared in regard of their influence on the reliability of CV values. Best results were obtained by calculating the time shift between main peak maxima, with a standard deviation found for the CV values from single APs in the range of 4 to 25%. The disturbance by signal noise could be reduced by the application of approximating cubic spline functions. The CV values showed a remarkable variability between different sites along the single MU muscle fibres.
Action Potentials↗