Volume 51, Issue 5_6

Several analysis techniques have been developed for time series to detect interactions in multidimensional dynamic systems. When analyzing biosignals generated by unknown dynamic systems, awareness of the different concepts upon which these analysis techniques are based, as well as the particular aspects the methods focus on, is a basic requirement for drawing reliable conclusions. For this purpose, we compare four different techniques for linear time series analysis. In general, these techniques detect the presence of interactions, as well as the directions of information flow, in a multidimensional system. We review the different conceptual properties of partial coherence, a Granger causality index, directed transfer function, and partial directed coherence. The performance of these tools is demonstrated by application to linear dynamic systems.

This article proposes a modular, computer-based methodology to describe and compare medical problems using data mining methods. The methodology focuses on a mathematical formulation of typical classification problems, systematic extraction of interpretable features from time series, and an evaluation adapted to problem-specific preferences and limitations (computational power, interpretability, etc.). The approach is applied to instrumented gait analysis and to the individual design of myoelectric controllers for hand prostheses.

By restricting analysis to single averaged strides considered to be characteristic for the individual under investigation, current methods in gait analysis do not exploit the full dynamics of continuous locomotion. Therefore, a novel approach is presented that is based on long-term measurements of kinematic data during treadmill walking. The method consists of reconstructing the system attractor in the embedding space and then analyzing its geometric structure. Estimating the dimension of movement trajectories correlates well with the notion of controlling multiple degrees of freedom during performance of complex movement tasks such as walking. The influence of walking speed on the complexity of physiologic walking was investigated in 10 healthy subjects walking on a treadmill at seven fixed speeds. The results suggest that human walking becomes more complex at slower speeds. This may be associated with results from EMG studies demonstrating more irregular EMG patterns at very slow walking speeds. This study emphasizes that tools from non-linear dynamics are well suited for providing more insight into motor control in humans.

Recently, locomotion therapy on a treadmill has become part of rehabilitation programs for neurological gait disorders (spinal cord injury, hemiplegia). Instrumental gait analysis is an important tool for quantification of therapy progress in terms of functional changes in a patient's gait patterns. Whereas most of current applications focus on diagnostic assessment of gait, the current paper presents an extension of movement analysis offering enhanced therapeutic options. Specifically, the conceptual basis for application of real-time movement feedback in rehabilitation medicine is outlined and is put into context with recent developments in the field. A first technical realization of these concepts is presented and first results are reported. Furthermore, open questions towards a universal environment for movement feedback in rehabilitation medicine are discussed and future lines of research are identified.

Investigations of back muscle fatigue are important for understanding the role of muscle strain in the development of low back pain. The aim of this contribution is to review the two main techniques used for in vivo investigations of metabolic and electrophysiological changes, namely magnetic resonance phosphorous spectroscopy ( 31 P MRS) and surface electromyography (SEMG), and to report some of our recent results on simultaneous measurements using these techniques during isometric back-muscle contraction in volunteers. Since it appears that electrophysiological and metabolic factors are simultaneously involved in the processes of fatigue and muscle recovery during load application, simultaneous acquisition of complete information is quite promising for obtaining new insights into the metabolic origin of electrophysiological changes or vice versa . Performing these measurements simultaneously, however, is more intricate owing to the occurrence of signal artifacts caused by mutual signal interferences of both techniques. Besides these mutual disturbances, further experimental difficulties are related to spatial limitations within the bore of clinical whole-body high-field magnetic resonance (MR) systems (1.5 T) and the sensitivity of MR measurements to motion-induced artifacts. Our own experimental results are presented, and problems that occur using both techniques simultaneously, as well as possibilities to resolve them, are discussed. The results shed light on the interrelation of electrophysiological and metabolic changes during fatigue of the back muscle while performing an exercise.

Exoskeleton robots are mechanical constructions attached to human body parts, containing actuators for influencing human motion. One important application area for exoskeletons is human motion support, for example, for disabled people, including rehabilitation training, and for force enhancement in healthy subjects. This paper surveys two exoskeleton systems developed in our laboratory. The first system is a lower-extremity exoskeleton with one actuated degree of freedom in the knee joint. This system was designed for motion support in disabled people. The second system is an exoskeleton for a human hand with 16 actuated joints, four for each finger. This hand exoskeleton will be used in rehabilitation training after hand surgeries. The application of EMG signals for motion control is presented. An overview of the design and control methods, and first experimental results for the leg exoskeleton are reported.

The development of innovative driver assistance systems requires the evaluation of the predisposed hypotheses such as acceptance and driving safety. For this purpose, the conduction of experiments with end-users as subjects is necessary. Analysis and evaluation are based on the recording of numerous sensor values and system variables. Video, gaze and physiological data are recorded for the analysis of gaze distraction and emotional reactions of subjects to system behaviour. In this paper, a modular data streaming and processing architecture is suggested and a concept for this architecture is defined for consistent data evaluation, which integrates off-the-shelf products for data analysis and evaluation.

Rapid magnetic resonance imaging (MRI) makes it possible to detect the fast kinetics of tissue response after intravenous administration of a paramagnetic contrast medium (CM), reflecting the status of tissue microcirculation. In this paper, the basic physical and tracer kinetic principles of dynamic relaxivity and susceptibility contrast-enhanced MRI are reviewed. Quantitative analysis of data acquired is broken up into an MR-specific part, in which the signal variation observed is related to the CM concentration in the tissue, and an MR-independent part, in which the computed concentration time series are analyzed by tracer kinetic modeling to estimate well-defined physiological tissue parameters. The clinical application of dynamic MRI techniques is demonstrated by two representative studies.

Commercially available cardiac pacemakers and implantable cardioverters/defibrillators (ICDs) predominantly use an intracardiac-derived electrocardiogram (ECG) for the detection of arrhythmias. To achieve automatic control of the heart frequency in accordance with cardiovascular strain and improved detection of life-threatening arrhythmias, it is desirable to monitor the heart by an input signal correlated with the hemodynamic state. One possible approach to derive such a signal is to measure the inotropy (mechanical contraction strength of the heart muscle). For this purpose, an optoelectronic measurement system has been designed. The fundamental function of the system has been shown in earlier investigations using an isolated beating pig heart. In this paper the design of two algorithms for use in pacemakers and ICDs based on a fiber optic sensor signal is presented.

Radiofrequency (RF) ablation using high-frequency current has become an important treatment method for patients with non-resectable liver tumors. Tumor recurrence is associated with tissue cooling in the proximity of large blood vessels. This study investigated the influence of blood flow rate on tissue temperature and lesion size during monopolar RF ablation at a distance of 10 mm from single 4- and 6-mm vessels using two different approaches: 1) an ex vivo blood perfusion circuit including an artificial vessel inserted into porcine liver tissue was developed; and 2) a finite element method (FEM) model was created using a novel simplified modeling technique for large blood vessels. Blood temperatures at the inflow/outflow of the vessel and tissue temperatures at 10 and 20 mm from the electrode tip were measured in the ex vivo set-up. Tissue temperature, blood temperature and lesion size were analyzed under physiological, increased and reduced blood-flow conditions. The results show that changes in blood flow rate in large vessels do not significantly affect tissue temperature and lesion size far away from the vessel. Monopolar ablation could not produce lesions surrounding the vessel due to the strong heat-sink effect. Simulated tissue temperatures correlated well with ex vivo measurements, supporting the FEM model.

The blood parameters oxygen saturation and hematocrit were determined by two different spectral sensors using reflectance spectra from 550 to 900 nm and partial transmission spectra centered at 660 nm. The spectra were analyzed by the method of partial least squares. One sensor consists of a miniature integrating sphere, while the other was fiber-guided. The results show that the geometry of the sensors and different blood flows do not influence the spectral analysis significantly. Independent of the sensor geometry, both hematocrit and oxygen saturation could be determined with an absolute predicted root mean square error of less than 3%. Furthermore, the analysis showed that hematocrit prediction requires eight wavelength regions and oxygen saturation prediction requires four wavelength regions using reflectance spectroscopy. This implies that if the measurement is restricted to reflectance, a spectrometer is indispensable for determining both blood parameters. Hematocrit determination could be improved using reflectance measurements in combination with transmission.

This study evaluated the efficiency of Karl Fischer titration and coulometry for measurement of water content in small intact and defective cartilage specimens. Cartilage from the main weight-bearing zone of the medial condyle of 38 fresh sheep knees was used. Of these, 20 condyles had an intact cartilage, while defects (14 grade I and 4 grade II) were found in the rest. The mechanical hardness was determined as Shore A. Cartilage specimens of approximately 5 mg were analyzed in special devices for moisture measurement and then continuously heated up to 105°C. The actual measurement was performed in an electric cell (coulometry). An electrode was laminated with hygroscopic phosphorus pentoxide. In the electrochemical reaction, H and O are liberated from the electrode. The requirement for electric energy correlates with the amount of water in the specimen. The water content in intact cartilage was 66.9%. Grade I (72.6%) and grade II (77.8%) defects had significantly higher water content. Significantly higher and faster spontaneous evaporation was observed in cartilage defects at room temperature. The water content and spontaneous water evaporation correlated with significantly lower mechanical hardness. The experimental design (combined method of thermogravimetry, Karl Fischer titration, and coulometry) was sufficient for evaluating the water content in small cartilage specimens. It is also possible to measure the temperature-dependent water liberation from cartilage specimens.

TNFα is a potent osteoclastogenic cytokine that has a fundamental role in the pathogenesis of wear particle-induced osteolysis. Wear particles of one composition and their biological effects are well characterised. In contrast, little is known about the effects of mixed particles with respect to mix ratio and particle concentration. We evaluated the effects of different mix ratios of polyethylene and TiAlV particles on TNFα response. We used a human monocytic cell line (THP-1) in this in vitro study. THP-1 monocytes were differentiated to macrophage-like cells and exposed to different mixtures of lipopolysaccharide-detoxified polyethylene and TiAlV particles. TNFα was analysed in culture supernatants using ELISAs. Both polyethylene and TiAlV particles induced a dose- and time-related release of TNFα, with maximum levels after 6 h. A PE/TiAlV mix ratio of 36:1 at 10 8 particles/ml induced significantly higher TNFα concentrations compared to equal particle concentrations of isolated TiAlV (p=0.047) or PE (p=0.044), indicating the synergistic effect of mixed particles. These results provide evidence that TiAlV and polyethylene particles have significant synergistic effects, depending on the mix ratio and particle concentrations. This supra-additive effect can contribute substantially to the pathogenesis of implant particle-induced osteolysis.

Zusammenfassung Die Implantation einer Hüfttotalendoprothese ist ein operativer Eingriff, der in Deutschland häufig aufgrund eines fortgeschrittenen Hüftgelenkschadens sowohl beim Menschen als auch in der Veterinärmedizin beim Hund durchgeführt wird. Das Langzeitergebnis einer Hüfttotalendoprothese wird hauptsächlich durch die aseptische Lockerung der Prothese bestimmt; Abriebpartikel der Gleitpaarung sind für eine Lockerung mit verantwortlich. Zur Analyse der Oberflächenspannungen bei unterschiedlichen Gleitpaarungen wurde ein Finite-Element-Modell generiert, das auf den CAD-Daten einer handelsüblichen Hüfttotalendoprothese basiert. Nach Einleitung einer physiologischen Gelenkkraft wurden Spannungen in den Komponenten der drei Gleitpaarungen Keramik/Polyethylen, Keramik/Keramik und Metall/Polyethylen berechnet. Dabei zeigten sich bei der Gleitpaarung Keramik/Keramik deutlich höhere Spitzenspannungen als bei den beiden übrigen Gleitpaarungen. In weiteren Arbeiten sollen angepasste Prothesen entwickelt werden, die optimale Reib- und Dämpfungseigenschaften der Komponenten sicherstellen.

There is currently renewed interest in articular resurfacing for the treatment of damaged hip-joint cartilage. In contrast to these implants, which involve endoprosthetic replacement of both articulating surfaces, we present a new joint-preserving technique that allows treatment of local osteochondral defects of the femoral head by partial hemi-resurfacing. In this study we describe the operative and technical aspects and problems for partial hemi-resurfacing of the hip joint and critically discuss indications for this procedure in one case. To guarantee an adequate view of the situs, we recommend a surgical approach involving trochanter flip osteotomy, followed by surgical dislocation of the hip joint. Besides partial hemi-resurfacing of the osteochondral defect, this approach allows treatment of associated labral tears and cartilage defects of the hip joint at the same time. For adequate implant fixation, good bone quality is required. Furthermore, osteochondral defects of limited extent and excellent patient compliance are essential for clinical success. In particular, prominence of the implant has to be avoided, which can lead to an irregular joint surface and may induce further cartilage destruction. Long-term studies on statistical populations will show if partial articular hemi-resurfacing is a bone-preserving and useful therapeutic alternative to hemi-resurfacing caps in the treatment of osteochondral hip-joint defects, especially in young patients.