Jiri Silny

A marker-based measurement procedure for unconstrained wrist and elbow motions

A protocol is proposed to obtain the joint angles of wrist and elbow from tracked triads of surface markers on each limb segment. Cuffs placed on the limb support the rigidity of the triads. Additional markers are used to mark the approximate positions of joints. Corrections of surface marker data for skin motion are derived from a priori knowledge about plausible joint motions. In addition, ill-conditioned states are trapped when the elbow is nearly fully extended. The protocol is applied to sample motions which demonstrate the use and the effect of the corrections. The results show that the model assumptions are reasonable and that accurate joint rotations can be obtained. The correction steps prove to be an essential part of upper-extremity movement analysis.

Spatial Filtering of Noninvasive Multielectrode EMG: Part I-Introduction to Measuring Technique and Applications

Complementary to its conventional applications, surface EMG is also suited to gain more detailed information on the functional state of a muscle, when measurement configurations with smaller pickup areas are used. A new category of suitable measurement configurations is obtained by application of the spatial filtering principle to electromyography. In a spatial filter unit, the signals of several recording electrodes are combined to form one output signal channel. The filter characteristic is determined by the weighting factors used and by the geometrical arrangement of the electrodes. Extended multielectrode arrays and multichannel recording make possible the detection of correlated excitations at different sites of the muscle. Even in high levels of muscle contraction, single motor unit impulses that are suitably shaped by filtering can be repeatedly recognized in the surface EMG signal. In clinical studies, pathologically shaped impulses have been identified indicating multiple innervation zones. The initiation and the propagation of excitation within single motor units can be detected with improved accuracy even from very small muscles.

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

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 motor unit (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 electromyography (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 MUs located close to the skin surface than for MUs 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 MUs have less portion in the anisotropic range of the filters than the simulated one at best.

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.

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.

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.

Spatial Filtering of Noninvasive Multielectrode EMG: Part II-Filter Performance in Theory and Modeling

Spatial filtering, particularly common in the field of engineering, is adapted in theory and practice to the filtering of propagating spatial EMG signals. This technique offers a new flexibility in the design of selective EMG measurement configurations. Longitudinal as well as two-dimensional spatial filters can be used. The conditions for the design of suitable spatial filters are deduced by signal theory. The performances of different selected configurations are compared by means of a given simple model of an excited motor unit. The modeling results compare well to the previously described experimental signals.

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.

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

The hypothesis that the observed fluctuations in propagation velocity are 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, was examined. 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 attributed to inhomogeneity effects of the tissue conductivity.<<ETX>>

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.