PubMed Health⌕ Search

Biomedical subjects

J Silny

Publications and source records attributed to J Silny.

At least 55 records · Page 3Linked to original sources
PubMed1994

[Cardiopulmonary exercise capacity before and after heart transplantation].

The aim of heart transplantation is to improve survival and exercise capacity of patients with endstage heart failure. Fifteen patients (1 female, 14 male) with a mean age of 48 years (ranging from 25-62) underwent cardiopulmonary exercise testing (CPX) before heart transplantation. 10/15 patients showed an oxygen uptake of < 4 ml/min/kg (Weber E) at the anaerobic threshold and 5/15 an oxygen uptake between 5 and 8 ml/min/kg (Weber D), so that a severe respectively very severe limitation of exercise capacity was documented before transplantation. Up to now 9/15 patients underwent heart transplantation. Cardiopulmonary exercise test could be repeated in 7 of these 9 patients, 12 up to 22 weeks following operation. Exercise capacity improved from former Weber-class E to class B in 2/5 patients, to class C in 2/5 patients, and to class D in 1/5 patient. Both patients with a preoperative class D improved to class C. Thus, in all cardiac recipients exercise capacity increased, whereas normal values were not reached. The denervation of cardiac allografts leads to a higher heart rate at rest, a delayed increase and diminished slope of exercise response and reduced heart rates at maximal effort. In 17 heart transplant recipients (3 female, 14 male) with a mean age of 53 years (ranging from 25-62), we investigated the exercise capacity with respect to the abnormal rate regulation of the donor heart, which was quantified by comparing the corresponding rate regulation of the remaining part of recipient's atrium driven by the sinus mode.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Influence of weak static and 50 Hz magnetic fields on the redox activity of cytochrome-C oxidase.

The effects of static and 50 Hz magnetic fields on cytochrome-C oxidase activity were investigated in vitro by strictly controlled, simultaneous polarographic measurements of the enzyme's high- and low-affinity redox reaction. Cytochrome-C oxidase was isolated from beef heart. Control experiments were carried out in the ambient geomagnetic and 50 Hz magnetic fields at respective flux densities of 45 and 1.8 microT. The experimentally applied fields, static and time-varying, were generated by Helmholtz coils at flux densities between 50 microT and 100 mT. Exposures were timed to act either on the combined enzyme-substrate interchange or directly on the enzyme's electron and proton translocations. Significant changes as high as 90% of the overall cytochrome-C oxidase activity resulted during exposure (1) to a static magnetic field at 300 microT or 10 mT in the high-affinity range, and (2) to a 50 Hz magnetic field at 10 or 50 mT in the low-affinity range. No changes were observed at other flux densities. After exposure to a change-inducing, static or time-varying field, normal activity returned.

Animals↗
PubMed1993

Clinical application of a noninvasive multi-electrode array EMG for the recording of single motor unit activity.

Using a recently developed noninvasive EMG recording technique with multi-electrode arrays we investigated the pattern and distribution of motor unit action potentials (MUAP) following maximal voluntary contraction of the musculus abductor pollicis brevis. An additional parameter, i.e. muscular conduction velocity (CV) in single motor units, was calculated from the multi-electrode array EMG recordings. From 63 healthy children of various age the normal EMG pattern and CV were derived and compared to the EMG of diagnosed patients known to suffer from Duchenne muscular dystrophy and from spinal muscular atrophy. In normal individuals the muscular CV in neonates was lowest at 1-2 m/s and gradually reached a plateau of 2.9-4 m/s from the age of 4 years onwards. The EMG in 31 children with Duchenne muscular dystrophy showed an abnormal pattern with low amplitude action potentials. In 30 out of 31 patients a significantly lower muscular CV was found. In 10 children with spinal muscular atrophy the EMG showed action potentials of abnormally large amplitude and a reduced recruitment of firing motor units. The muscular CV remained within the normal range. Compared to classical needle EMG the application of this new noninvasive EMG technique in children is painless and offers an easy-to-handle diagnostic tool to differentiate between neuromuscular diseases of denervating or of myopathic origin.

Adolescent↗
PubMed1993

[Do heart transplant patients benefit from rate-adjusted electrostimulation?].

Exercise capacity of heart transplant recipients is limited in comparison to normals and, due to cardiac denervation, exercise-induced heart-rate response is blunted in these patients. In order to evaluate the effect of rate-responsive atrial pacing on exercise capacity, 13 patients (three female, 10 male; age: 53 +/- 7 years) were studied 2-35 months after orthotopic heart transplantation. Spiroergometry with breath-to-breath gas analysis was performed during a progressive supine bicycle test with a starting workload of 25 watts and increments of 15 watts every minute. In comparison to 10 normals (two female, eight male; age: 51 +/- 7 years) maximal heart rate (127 +/- 17 vs. 146 +/- 12 min-1), maximal work load (107 +/- 27 vs. 208 +/- 42 watts) and oxygen consumption at the anaerobic threshold (9 +/- 2 vs. 18 +/- 4 ml/kg/min) were significantly reduced in heart transplant recipients (p < 0.05). During the exercise test the p-waves of the remaining part of the recipients' atria were registered via a transoesophageal catheter. The maximal rate of the innervated recipients sinus node (146 +/- 15 min-1) was equal to the maximal heart rate of the control group. The exercise protocol was repeated during atrial stimulation of the transplanted hearts. To achieve a physiological adaptation of the heart rate, the pacing rates were adjusted to the rates of the recipients sinus node. In comparison to the previous tests an improvement of cardiopulmonary exercise capacity was not observed during rate adaptive pacing.

Adult↗
PubMed1992

[Electrocardiographic diagnosis of acute graft rejection after heart transplantation].

In order to evaluate the diagnostic value of standard-ECG (ST-ECG) and precordial mapping-ECG with 63 unipolar leads (PM-ECG) for detection of acute cardiac allograft rejection, 15 patients (12 male, 3 female; age range 24-64 years) were studied. ST-ECG and PM-ECG were recorded along with 94 endomyocardial biopsies. Twenty-four acute rejections were detected histologically. Using the ST-ECG, a reduction of the QRS-amplitude-sum (lead I, II, III, V1 and V6) greater than or equal to 5% in comparison with the ECG obtained 1 week before was found to be the best diagnostic criterion (sensitivity 63%, specificity 74%, positive predictive value 48%, negative predictive value 85%). By analysing the PM-ECG a drop of the QRS-amplitude greater than or equal to 12% in greater than or equal to 14/63 precordial leads was determined to be the most reliable parameter (sensitivity 79%, specificity 71%, positive predictive value 49%, negative predictive value 91%). In contrast to the high sensitivity of PM-ECG, ST-ECG was less suitable for detection of acute rejection. However, taking into account the high negative predictive value of PM-ECG, acute rejection could be excluded with high probability, if the QRS-amplitudes of the PM-ECG remained stable. This may lead to a lower frequency of routinely performed endomyocardial biopsies.

Adult↗
PubMed1991

[Risks of electromagnetic fields for humans].

Different kinds of electromagnetic fields are treated regarding their possible effects on the human organism. Only scientific findings are taken as a basis for these considerations. According to the latest state of research only strong magnetic fields of low frequency and strong electromagnetic fields of high frequency can be critical for humans if exposed for a prolonged period. Possible causes for this threat are either the incidence of heart fibrillation or grave burnings of the body. Fields with such a strong intensity, however, are found only in few specific technical environments where they usually can be avoided by the specialists there. An impairment of well-being may also occur in connection with almost all other kinds of fields due to direct or indirect influence when the strength of the field becomes very high. An exception to that is only the static magnetic field where there are different findings from in-vivo- as well as in-vitro-experiments which, however, do not fit into these categories. Since the mechanisms of these effects are not understood yet, it is impossible to make statements about the medical relevance of the observed effects. Considering the variability and the partial inconsistency of the results found in magnetic fields it must be concluded that additional studies are necessary to validate these findings statistically. Last not least this also applies to the presumed and in public controversially discussed connection between the promotion of cancer and relatively weak time-varying magnetic fields, which in these low intensities occur not only in households, cars and trains, but also in almost all working environments.(ABSTRACT TRUNCATED AT 250 WORDS)

Electromagnetic Fields↗
PubMed1991

Influence of tissue inhomogeneities on noninvasive muscle fiber conduction velocity measurements--investigated by physical and numerical modeling.

The determination of conduction velocity in the muscle fibers of single motor units from noninvasive recordings of single motor unit action potentials can be improved by the method of spatially filtering multielectrode EMG. The use of this conduction velocity as a diagnostic tool requires a high reliability of the detected values. However, experiments did reveal that the measured conduction velocity values showed remarkably high fluctuations depending on the recording site along the muscle fibers which could not be attributed to the influence of the endplate and tendon region. The present work examines the hypothesis that the observed fluctuations in propagation velocity were caused by electrically inhomogeneous tissue, regions of different electrical conductivity which are located between the excited muscle fibers and the recording electrodes and which cause a deformation of the extracellular electric current field. The investigation was performed by means of a physical model as well as by finite element model calculations. In both models single, simple shaped (cylindrical) inhomogeneity regions with a conductivity of 0.1 to 10 times that of the surrounding medium and diameters ranging between 1.6 and 2.7 mm were placed between excitation sources and recording site. The results indicate that the observed conduction velocity fluctuations of up to some 10% can be well attributed to inhomogeneity effects of the tissue conductivity. Based on these results, one may look for signal processing methods to cut down such fluctuations in conduction velocity measurements.

Computer Simulation↗
PubMed1990

Results with multichannel topographical bipolar recordings of the visual evoked potential in normals and amblyopes.

The method currently used to record topographical voltage distributions of visual evoked potentials is that of monopolar recording with respect to some arbitrary reference electrode. As an alternative we investigated the method of bipolar topographical recording of the checkerboard reversal evoked potential in four amblyopic patients and ten normal persons. The recordings were performed with a system of 14 bipolar channels, arranged in a rectangular grid with an interelectrode distance of 15% of the inion-nasion distance and centered 3 cm above the inion. The gradient distributions of the visual evoked potential obtained from normal persons showed at the time of component P2 a maximum about 3 cm above the inion. The healthy eyes of the amblyopic patients showed similar distributions and latencies. The amblyopic eyes showed normal or reduced amplitudes and normal or increased latencies with large checks and low amplitudes with smaller checks. The topographical distributions recorded with the bipolar recording system showed shifts of the maxima with the larger patterns in three of four amblyopic eyes. A technical comparison showed that these shifts can be recorded by the bipolar recording method with higher accuracy than with the monopolar method, promising a better understanding and more accurate diagnosis of amblyopia.

Adult↗
PubMed1990

[ECG in acute myocardial infarct. Continuous registration in thrombolytic therapy].

For 35 patients with acute myocardial infarction undergoing thrombolytic therapy (31 patients with streptokinase and 4 with rt-PA), the treatment effect was assessed angiographically and correlated with ECG changes. These ECG changes were found by continuous registration of eight "strategically" located precordial leads in patients with anterior myocardial infarction, and five precordial leads plus three limb leads in those with posterior myocardial infarction. In 31 patients (group A), successful reperfusion could be verified by angiography, while in 4 patients the infarct-related vessel remained closed. In 3 further cases (group B), recanalization could be achieved only by additional mechanical intervention. The average duration of ECG surveillance was 87 min in group A and 85 min in group B. A significant change of R-amplitudes during this period of time could not be observed. ST-60-value of group A (total of ST-elevations and depressions 60 msec after S of all surveillance electrodes, divided by number of electrodes) was reduced under thrombolysis from 0.377 mV (SD +/- 0.270) to 0.133 mV (SD +/- 0.118) (p less than 0.004). This means a reduction of 64%, while the corresponding values in group B did not change (0.535 mV, respectively 0.546 mV) before and after therapy. When only the electrode with the highest ST-60-value was checked before therapy ("sensitive lead"), reduction in group A was as high as 71%. Except for two patients, all other 29 patients with successful reperfusion either precordially or in the limb leads showed a reduction of ST-segment abnormalities (ST 60) of more than 50% during surveillance time. This could not be observed in any of the unsuccessfully treated patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Use of the scanning laser ophthalmoscope for recording pattern electroretinography and visual evoked cortical potentials].

With a scanning laser ophthalmoscope (SLO) variable patterned stimuli can be projected onto the retina. During alternation of these patterns visual evoked cortical potentials and pattern ERGs can be recorded. The configurations of the SLO-elicited potentials and peak latencies correspond to those evoked during conventional stimulation. During pattern stimulation the fundus and alternating pattern stimuli are observed simultaneously on a video monitor. Thus the examiner always knows the exact location of the stimulus on the retina. Scanning laser ophthalmoscopy could be a clinically interesting method of recording evoked potentials, because it enables the patient's retina to be viewed continuously at low light levels and makes electrophysiological examination of a defined region of the retina possible.

Electroretinography↗
PubMed1989

[The development of stereoscopic vision in the first months of life].

Dynamic random dot patterns generated on a TV screen by a special pattern generator are proven to be adequate stimuli for testing stereopsis. The registration of transient visual evoked cortical potentials (VECP) to these random dot stimuli offers objective proof of stereopsis. Using different disparities in older people a typical amplitude behaviour in the dynamic random dot stereo VECP with maximum amplitudes to medium sized disparities was found. Compared to 20 adults and 30 children with normal vision, in 26 children with negative TNO- and Titmus-tests for stereoscopic vision treated for strabismus no dynamic random dot stereo VECPs could be recorded. The development of stereoscopic vision in the first 12 months of life was investigated in five babies. First positive components in the dynamic random dot stereo VECP could be found in the 4th to 6th months of life in all children. From these results the assumption, that stereoscopic vision develops in later childhood, must be revised in favour of a much earlier period of infancy.

Adult↗
PubMed1988

Changes in vertebral end plates in congenital spine deformities.

The authors investigated morphologically material from 30 patients with congenital spine deformities operated on at the 2nd Orthopaedic University Department in Brno, and the spines of two patients who underwent a spinal operation and later died from other causes, and also the spines of young, healthy road accident victims. In the course of operations for congenital deformities of the spine representative tissue samples were taken (hemivertebrae, quarter vertebrae, etc.), along with the adjacent parts of intervertebral disks. The authors concentrated mainly on the growth defects of deformed vertebrae and microscopic changes in the adjacent cartilage plates. In this way light was thrown on some questions of both defects of formation and defects of segmentation of the mesenchymal base of the spine. The defects of ossification and growth disorders observed are, in the authors' opinion, an important component in the occurrence of congenital deformities and idiopathic scolioses and have a major effect on their progression.

Female↗
PubMed1987

Localization of significant coronary arterial narrowings using body surface potential mapping during exercise stress testing.

The ability of body surface potential mapping to localize coronary arterial narrowings during exercise stress testing was investigated. An array of 48 chest wall electrodes, simultaneously recorded, was used. Digital filtering and signal processing, data reduction techniques and discriminant analysis were applied to process the information. Forty patients whose coronary angiograms showed a single significant narrowing of either the left anterior descending or right coronary artery were selected for further study. On the basis of body surface potential mapping, the site of coronary arterial narrowing was correctly classified in 88% of the patients.

Coronary Disease↗
PubMed1987

Evidence of pericentral stereopsis in random dot VECP.

Dynamic random dot patterns generated on a TV screen by a special pattern generator are proven to be adequate stimuli for testing stereopsis. In our experimental set-up we use red-green coded striped or checkered patterns of various size and disparity as stimuli, which are viewed through red-green glasses (anaglyph method). The registration of transient visual evoked cortical potential (VECP) to these random dot stimuli offers objective proof of stereopsis. There is a typical amplitude behavior with maximum amplitudes at medium disparities. By recording the specific stereo VECP while masking the central retinal areas stepwise (artificial central scotoma) we can objectively show intact stereopsis of corresponding pericentral retinal areas. This peripheral stereopsis is demonstrable in the VECP by central scotomas up to eight degrees.

Cerebral Cortex↗