Biomedical subjects

J Silny

Publications and source records attributed to J Silny.

At least 37 records · Page 2Linked to original sources

PubMed1999

Procedure for the semi-automatic detection of gastro-oesophageal reflux patterns in intraluminal impedance measurements in infants.

The diagnosis of gastro-oesophageal reflux (GOR) is of great interest for paediatric gastroenterologists. pH monitoring is the commonly used procedure for GOR diagnosis but a major amount of postprandial GOR is missed due to the mostly non-acidic gastric contents in infants. The multiple intraluminal impedance technique is based on the recording of the impedance changes during bolus transport inside the oesophagus. It is the first method which allows the pH-independent, long-term registration of GOR. The use of the impedance technology in clinical practice has been limited so far by the time-consuming, visual evaluation of the impedance traces. The new approach of a semi-automatic analysis of the impedance measurements allows the automated detection of reflux patterns. It is based on event marking and an optimised feature description of the impedance traces combined with a fuzzy system for pattern recognition. The classifier is developed and tested on 50 investigations in infants. Compared to the comprehensive, multiple visual evaluation the achieved precision is 75% sensitivity and 48% positive prediction. In comparison to a single visual evaluation the analysis of the automatically proposed patterns corresponds to a 96% reduction of the evaluation time with no loss of precision. Thus the applicability of the impedance technology is enhanced significantly. A combined measurement of pH and impedance gives evidence about the occurrence of GOR, its pH and the acidic exposure of the oesophagus.

Algorithms↗

PubMed1999

N30 and the effect of explorative finger movements: a model of the contribution of the motor cortex to early somatosensory potentials.

OBJECTIVES: The source of the N30 potential in the median nerve somatosensory evoked potentials (SEP) has been previously attributed to a pre-central origin (motor cortex or the supplementary motor area, SMA) or a post-central located generator (somatosensory cortex). This attribution was made from results of lesion studies, the behavior of the potential under pathological conditions, and dipole source localization within spherical volume conductor models. METHODS: The present study applied dipole source localization and current density reconstruction within individual realistically shaped head models to median nerve SEPs obtained during explorative finger movements. RESULTS: The SEPs associated with movement of the stimulated hand showed a minor reduction of the N20 amplitude and a markedly reduced amplitude for the frontal N30 and parietal P27, exhibiting a residual frontal negativity around 25 ms. The brain-stem P14 remained unchanged. Mapping of the different SEPs (movement of the non-stimulated hand minus movement of the stimulated hand) showed a bipolar field pattern with a maximum around 30 ms post-stimulus. In eight out of ten normal subjects, both the N30 and the gN30 (subtraction data) sources resided within the pre-central gyrus, more medially than the post-centrally located N20. Two subjects, in contrast, showed rather post-centrally localized sources in this time range. A model of the cortical SEP sources is introduced, explaining the data with respect to previously described findings of dipole localization, and from lesion studies and the alterations seen in motor diseases. CONCLUSIONS: The results provide evidence for a pre-central N30 generator, predominantly tangentially oriented, located within the motor cortex, while no sources were detected elsewhere. It is suggested that the mechanisms underlying the 'gating' effect during explorative finger movements in the 30 ms time range predominantly arise in the motor cortex.

Adult↗

PubMed1999

Gastroesophageal reflux and respiratory phenomena in infants: status of the intraluminal impedance technique.

BACKGROUND: The coincidence of recurrent respiratory symptoms and gastroesophageal reflux (GER) is a well-known phenomenon in infants. Twenty-four-hour pH metry is the presumed gold standard of diagnostic tools for this symptom complex, but with this method, only acid (pH <4) and alkaline (pH >7) GER can be detected. Gastroesophageal reflux with an esophageal pH in the physiological range (pH 5-6.8) may represent many cases of clinically relevant GER unrecognized by pH metry. In this study the intraluminal multiple electrical impedance (IMP) procedure for complete registration of GER was compared with pH metry for its diagnostic value in the presence of respiratory symptoms. METHODS: Twenty-two infants with recurrent regurgitation or pulmonary problems were investigated simultaneously with IMP, pH metry, and polygraphy during two feeding periods. Heart rate, oxygen saturation, sleep states, and oronasal flow were recorded, among other parameters. RESULTS: Three hundred sixty-four occurrences of GER were detected by IMP; only 11.4% had a pH less than 4 and were therefore recognized by pH metry. Three hundred twelve (84.8%) occurrences were associated with breathing abnormalities, and 11.9% of these were detected by pH metry. Nineteen instances were accompanied by a decrease of oxygen saturation of more than 10% of the initial value. Only three (15.8%) of these had a pH less than 4. The remaining 16 reflux episodes were recognized by IMP only. After software-aided preselection, 165 instances of apnea were visually validated, 49 of which were accompanied by GER. Thirty-eight (77.6%) of these were exclusively recorded by IMP. CONCLUSIONS: The use of pH metry alone cannot detect most GER incidents accompanied by respiratory symptoms and therefore does not appear to be suitable for this approach. The pH-independent IMP technique promises to be a reliable tool for presumably GER-associated respiratory symptoms.

Electric Impedance↗

PubMed1999

Multiple intraluminal electrical impedancometry for recording of upper gastrointestinal motility: current results and further implications.

This review focuses on current aspects of the novel technology of multiple intraluminal electrical impedance measurement. It presents methodological features, summarizes current results, and discusses potential implications for further research. The impedance technique assesses a bolus transport and its associated peristalsis. Validation studies showed a good analogy between physically deduced impedance characteristics and characteristics derived from cineradiography and manometry. From the impedance tracings, it is possible to distinguish between resting states, bolus transit, and wall contraction. Characteristics of a peristaltic wave can be obtained. In human studies, esophageal and small intestinal peristaltic patterns can quantitatively and qualitatively be assessed. A high resolution recording of bolus movements with interesting details of transport and mixing can be obtained. On the basis of several prior characterized impedance tracings duodenal contractile patterns have been classified, and the interdigestive and postprandial states characterized. For reflux evaluation the impedance technique was especially useful for the detection of nonacid gastroesophageal reflux, which is not detectable by pH monitoring. In summary, the main impact of the impedance technique is its capability to characterize esophageal and intestinal chyme transport. Important data on luminal chyme transport have been obtained. This technique is developing into an interesting investigative tool to complement standard techniques for study of upper GI motility, in particular for basic research.

Cineradiography↗

PubMed1999

Patterns of gas and liquid reflux during transient lower oesophageal sphincter relaxation: a study using intraluminal electrical impedance.

BACKGROUND: Belching has been proposed as a major mechanism underlying acid gastro-oesophageal reflux in normal subjects. However, the presence of oesophageal gas has not been measured directly but only inferred from manometry. AIMS: To investigate, using intraluminal electrical impedance, the patterns of gas and liquid reflux during transient lower oesophageal sphincter (LOS) relaxations, the main mechanism of acid reflux in normal subjects. METHODS: Impedance changes associated with the passage of gas were studied in vitro, and in vivo in cats. Oesophageal manometry, pH, and intraluminal electrical impedance measurements were performed in 11 normal subjects after a meal. RESULTS: Gas reflux caused a sudden increase in impedance that propagated rapidly to the proximal oesophagus whereas liquid reflux induced a retrogressively propagated fall in impedance. Impedance showed gas or liquid reflux during most (102/141) transient LOS relaxations. When acid reflux occurred, impedance showed evidence of intraoesophageal retrograde flow of liquid in the majority (78%) of events. Evidence of gas retroflow was found in almost half (47%) of acid reflux episodes. When present together, however, liquid preceded gas on 44% of occasions. Overall, gas reflux occurred as the initial event in only 25% of acid reflux episodes. CONCLUSIONS: These findings suggest that in upright normal subjects, although belching can precipitate acid reflux, most acid reflux occurs as a primary event.

Adolescent↗

PubMed1999

Electrical hypersensitivity in humans--fact or fiction?

The phenomenon of the so-called electrical hypersensitivity in the weak electromagnetic fields of everyday life, potentially causing different health symptoms, is reviewed under consideration of current results from in-vivo and in-vitro investigations as well as of statistical data. Electrical hypersensitivity cannot be explained by means of the known and validated influence mechanisms of electromagnetic fields in humans, as their thresholds are at least 50 times higher for harmless effects, and more than 1000 times higher for adverse effects than the strengths of the environmental fields. Present statistical data reveal clear inconsistencies in many respects. The prevalence varies by a factor 1000 although the reporting countries have comparable field and exposure situations. Neither the apparently random combination of symptoms on the side of the suffering patients nor the problematic attribution of the symptoms to certain electromagnetic field situations do support the hypothesis of a electrical hypersensitivity. On the other hand, the statistical data must be considered unsubstantiated because of the small number of cases and the procedures of survey. Consequently, there is a need for additional, systematic investigations of this group of patients under participation of different medical and biomedical disciplines.

Air Pollution, Indoor↗

PubMed1998

Estimation of the relationship between the noninvasively detected activity of single motor units and their characteristic pathological changes by modelling.

Neuromuscular disorders are often related to specific changes in the structure of single motor units (MUs). One approach for the detection of these changes is high-spatial-resolution EMG (HSR-EMG), which allows non-invasive recording of the activity of a single MU. Early investigations with patients suffering from various neuromuscular disorders have shown that there is a distinct difference between the HSR-EMG signals of healthy volunteers, patients with muscular disorders, and patients with neuronal disorders. In this study, the relationship between typical HSR-EMG patterns and characteristic pathological changes in the structure of the MUs is considered. Therefore, a muscle model has been developed which is adapted to the physiological properties of the m. abductor pollicis brevis. The effects of the loss of single muscle fibres (muscular disorders) and the loss of entire MUs (neuronal disorders) on the HSR-EMG pattern have been simulated. These simulations show the same HSR-EMG patterns as seen in patients and healthy volunteers. As a consequence, it can be assumed that the muscle model is an appropriate tool for the simulation of HSR-EMG signals. Furthermore, the simulation results support the hypothesis that the typical changes in the HSR-EMG pattern found in patients with neuromuscular disorders can be attributed to the characteristic changes in the structure of the MUs.

Action Potentials↗

PubMed1998

[Combined pH measurement and multiple impedance variation assessments--validation of a new technique for detection of non-acid reflux in the esophagus].

In 10 patients with gastroesophageal reflux disease, defective lower esophageal sphincter and normal motility pH and impedance were measured parallel over 24 hours. All patients had a reflux score > 40 with a total of 736 reflux episodes registered by the pH metry of which 724 (sensitivity: 98.9%) were recognized by impedancemetry and with additional 292 reflux phases registered at a stomach pH > 4 by the impedancemetry of which none was recognized by the pH metry as a reflux of pH > 7. With the multiple impedancemetry a reliable recognition of gastroesophageal reflux is possible, independently of the pH and this makes it possible to recognize gastroesophageal reflux also at a non acid milieu of the stomach, e.g. under acid suppression medication or after stomach resection.

Electric Impedance↗

PubMed1997

Diagnostic yield of noninvasive high spatial resolution electromyography in neuromuscular diseases.

High Spatial Resolution electromyography (HSR-EMG), a new kind of noninvasive surface EMG based on a spatial filtering technique, was evaluated with respect to the diagnosis of neuromuscular diseases. HSR-EMG measurements were recorded from 61 healthy subjects and 72 patients with different neuromuscular diseases and analyzed quantitatively. The results indicate that a few parameters such as muscular conduction velocity, dwell time over root mean square, autocorrelation function, and chi-value are sufficient to recognize and classify specific signal alterations due to neuromuscular disorders. A diagnostic evaluation procedure calculating automatically the most probable diagnosis from the parameter results could assign the correct diagnosis to about 81% of the investigated patients and healthy subjects. Myopathic disorders were recognized with a sensitivity of 85% (specificity: 97%), neuropathic disorders with a sensitivity of 68% (specificity: 98%). We conclude that HSR-EMG shows a diagnostic validity similar to that described in literature for needle EMG. Moreover, the noninvasive technique provides the advantage of a simple and painless application.

Adolescent↗

PubMed1997

Inverse localization of electric dipole current sources in finite element models of the human head.

The paper describes finite element related procedures for inverse localization of multiple sources in realistically shaped head models. Dipole sources are modeled by placing proper monopole sources on neighboring nodes. Lead field operators are established for dipole sources. Two different strategies for the solution of inverse problems, namely combinatorial optimization techniques and regularization methods are discussed and applied to visually evoked potentials, for which exemplary results are shown. Most of the procedures described are fully automatic and require only proper input preparation. The overall work for the example presented (from EEG recording to visual inspection of the results) can be performed in roughly a week, most of which is waiting time for the computation of the lead field matrix or inverse calculations on a standard and affordable engineering workstation.

Cerebral Cortex↗

PubMed1997

Noninvasive approach to motor unit characterization: muscle structure, membrane dynamics and neuronal control.

The standard surface EMG reflects the compound activity of a high number of motor units which is finally due to its low spatial resolution in the detection of the potential distribution on the skin surface. Therefore, detailed information about the structural and functional characteristics of the muscle consisting of populations of motor units, like the functional anatomy, the excitation spread or the innervation pattern cannot be obtained from the standard surface EMG. A novel noninvasive EMG-procedure with high spatial resolution (HSR-EMG) allows in contrast to the standard surface EMG even the detection of the single motor unit activity. In this way, the noninvasive determination of detailed information about the muscle structure, the membrane dynamics and the neuronal control becomes possible. First applications of the HSR-EMG have shown that especially the noninvasively measured conduction velocity of the excitation is highly affected by physiological details, like the muscle temperature, the relative muscle fibre diameter or inhomogeneities in the connective tissue forming part of the volume conductor around the muscle. From the results of the HSR-EMG investigations it can be concluded that the information about the structural and functional characteristics of the muscle as well as a deeper insight in the active state of the muscle is essential for a correct interpretation of the standard surface EMG.

Animals↗

PubMed1997

Improvement of spatial resolution in surface-EMG: a theoretical and experimental comparison of different spatial filters.

The conventional bipolar surface electromyography (EMG) technique detects, due to its low spatial resolution, the superimposed electromyographic activity of a large number of motor units (MU's). In superficial muscles the isolated action potentials of the most superficial MU's can be recorded noninvasively by means of surface electrodes, if the method of spatial filtering, in connection with electrode arrays, is used. Up to now, only filters with an anisotropic transfer function have been used. As the surface potential distribution generated by the excitation of the MU's contains spatial frequencies in the anisotropic range of those filters, it can be assumed that isotropic spatial filters detect the single MU activity more effectively. In the present study, different isotropic and anisotropic filters have been compared by means of theoretical field simulations and experiments in volunteers. A tripole model for an excited MU was used as the basis for simulating the spatial extension of the filter response for each of the investigated filters. The spatial extension is an indicative of the spatial resolution. For the experimental validation, the total number of single motor units was not directly investigated, but the signal-to-noise ratio (SNR) has been determined. Therefore, the potential distribution generated on the skin surface during maximum voluntary contraction has been simultaneous spatially filtered with each of the investigated filters. The simulations show that an isotropic spatial filtering procedure reduces the spatial extension of the filter response and improves the spatial resolution of the EMG-recording arrangement in comparison to anisotropic spatial filters up to 30%. In other words, the spatial selectivity of the arrangement is increased. This improvement in the filter performance is more pronounced for MU's located close to the skin surface than for MU's more distantly located. Additionally, this theoretical improvement in selectivity depends on the direction of the excitation spread relative to the filter alignment. However, the investigations also show that isotropic filters offer an advantage, compared to anisotropic filters, only when the investigated MU is located extremely close to the filter input. The results of the simulations can be confirmed by the experimental investigations. An improvement of 11% in the SNR, relative to anisotropic spatial filters, can be established when using an isotropic spatial filter. This experimental improvement in selectivity is less than the theoretical improvement because the experimentally investigated MU's have less portion in the anisotropic range of the filters than the simulated one at best.

Anisotropy↗

PubMed1997

Abnormal postprandial duodenal chyme transport in patients with long standing insulin dependent diabetes mellitus.

BACKGROUND: Patients with long standing diabetes mellitus frequently have upper gut dysmotility. Gastroparesis has been well studied, whereas detailed data on duodenal motor function are limited. AIMS: To characterise postprandial duodenal chyme transport in such patients. METHODS: Intraluminal multiple impedance measurement, recently introduced as a novel technique for investigation of chyme transport, was used to study postprandial duodenal chyme flow in 10 patients with long standing insulin dependent diabetes mellitus with gastroparesis, and 10 healthy volunteers. RESULTS: Four distinct transport patterns of chyme, termed bolus transport events (BTEs), were found in both groups and could be characterised as: short distance propulsive; simple long distance propulsive; retrograde; and complex long distance propulsive. Diabetic patients had significantly lower numbers of propulsive BTEs (p < 0.01), and higher proportions of retrograde BTEs and complex long distance BTEs (p < 0.05) than control subjects, whereas the proportion of simple long distance BTEs was significantly lower (p < 0.05). The mean propagation velocities of the BTEs were similar in both groups. CONCLUSION: Abnormal postprandial duodenal chyme transport was found in patients with long standing insulin dependent diabetes mellitus. This is characterised by transport disorganisation and may result in disturbed chyme clearance.

Adult↗

PubMed1997

Dynamics of esophageal bolus transport in healthy subjects studied using multiple intraluminal impedancometry.

The dynamics of a bolus transport through the esophagus are largely unexplored. To study this physiological process, we applied multiple intraluminal impedancometry in 10 healthy subjects. Three different protocols were used: 1) liquid bolus administered with subject supine, 2) liquid bolus with subject upright, or 3) semisolid bolus with subject supine. Transit of different parts of a bolus (bolus head, body, and tail) was analyzed at different anatomic segments, namely the pharynx and the proximal, middle, and distal thirds of the esophagus. A characteristic pattern of bolus transport was seen in all subjects. Impedance changes related to air were observed preceding the bolus head. The bolus head propelled significantly faster than did the bolus body and tail. Pharyngeal bolus transit was significantly faster than esophageal bolus transit. Within the esophagus, bolus propulsion velocity gradually decreased. Bolus transport was significantly accelerated in the upright position and delayed with increase of bolus viscosity. In conclusion, the dynamics of a bolus transport from the pharynx into the stomach are complex. It varies within both different anatomic segments and different parts of the bolus and depends on bolus characteristics and test conditions. The spatial and temporal resolution of a bolus transport can be obtained by the impedance technique.

Adult↗

PubMed1996

Gastroesophageal reflux in infants: evaluation of a new intraluminal impedance technique.

In this study, pH metry was simultaneously applied with a new technique, the intraluminal multiple electrical impedance (IMP) procedure, for measuring gastrointestinal motility for gastroesophageal reflux (GER) detection. Seventeen infants with clinical symptoms of GER disease such as recurrent apnea, aspiration pneumonia, wheezing, and failure to thrive were investigated during two feeding periods. A single catheter combining a pH electrode with seven electrodes for impedance measurements over a distance of 8.5 cm was used for the investigation. In all patients, 185 acid episodes were detected by pH metry. In 106 of these 185 acid episodes, a unique pattern in the IMP readings was noted, indicated by a retrograde esophageal volume flow. These episodes were regarded as acid GER episodes. Seventy-one of the 185 acid episodes occurred during the clearance process of a preceding acid GER characterized by typical IMP readings of an anterograde bolus transport. Eight of 185 acid episodes were missed in the IMP readings for technical reasons. The IMP pattern described as characteristic for a GER was observed in 490 other episodes not detected by pH metry. More than 75% of all GER detected by IMP reached the pharyngeal space; 73% of all GER occurred during feeding and the first 2 postprandial hours and 27% occurred during the remaining time until the next feeding. Even during the latter period, 34% of GER were detected by IMP only; they were missed by pH metry. Volume clearance indicated by IMP was always completed earlier than acidity clearance. The results show that IMP technique facilitates the detection of all GER, whereas pH metry is confined to the measurement of acid GER. Therefore, this technique might improve the evaluation of GER disease and detection of GER in conditions with gastric hypoacidity.

Electric Impedance↗

PubMed1996

Comparison between intraluminal multiple electric impedance measurement and manometry in the human oesophagus.

Conventional oesophageal manometry and intraluminal electrical impedance measurement were simultaneously applied in eight healthy volunteers to study the effect of wet and semisolid bolus viscosities on oesophageal motility and bolus transit. Contraction front velocity measured by electrical impedance and manometry were identical for wet and semisolid swallows and highly associated. Bolus front velocity as measured by electrical impedance was significantly faster than contraction front velocity in both wet and semisolid swallows. Bolus front velocity during semisolid swallows was significantly slower compared to wet swallows. It is concluded that intraluminal electrical impedance measurement is a reliable technique to detect oesophageal motility as well as to differentiate between transit of wet and semisolid bolus consistencies.

Adult↗

PubMed1995

Chyme transport patterns in human duodenum, determined by multiple intraluminal impedancometry.

To get information about the mechanisms involved in chyme transport during the fasting and postprandial states, the novel procedure of multiple intraluminal impedancometry was evaluated in 14 healthy subjects (6 during fasting, 8 after a test meal). All main features of the migrating motor complex (MMC) cycle were determined. During phase II of the MMC cycle and the postprandial period, different transport patterns of chyme, termed bolus transport events (BTEs), were determined. These were 1) simple long-distance propulsive transport (spreading distance > 16 cm), 2) short-distance propulsive transport, and 3) retrograde transport. A significantly lower number of BTEs was recorded during fasting than postprandially. Short-distance propulsive BTEs predominated during fasting (72%), and long-distance propulsive BTEs predominated after the test meal (76%). Retrograde BTEs were recorded during fasting (4%) and postprandially (8%). In the latter state, complex long-distance propulsive BTEs were also observed (5%), consisting of multiple components. A major proportion of gastric contents was found to be continuously transported to jejunum. In conclusion, impedancometry enables us to determine patterns and parameters of chyme transport during fasting and postprandial states.

Adult↗

PubMed1994

Measuring esophageal motility with a new intraluminal impedance device. First clinical results in reflux patients.

BACKGROUND: The study was undertaken to determine the validity of intraluminal impedance measuring for the diagnosis of esophageal motility disorders in reflux patients. METHODS: A new impedance device was used for the detection of esophageal motility patterns in a prospective study with 10 volunteers and 10 patients with reflux esophagitis grade II-III. Perfused manometry was correlated with the impedance tracings. Test meals were saline and curd in three different preparations with liquid to semisolid viscosity. RESULTS: There was a marked delay in esophageal transport with increasing viscosity of the bolus (p < 0.01). A significant (p < 0.001) delay of the bolus transport in the inflamed esophageal areas was seen in reflux patients. A reduced contractility of the lower esophagus and the lower esophageal sphincter was detected by the impedance procedure in reflux patients, indicating that the pathologic motility patterns in reflux esophagitis are most likely secondary to the tissue inflammation. CONCLUSION: We conclude that impedance procedures may give additional significant information about bolus transport and esophageal wall movements.

Adult↗