Sleep Position Detection for Closed-Loop Treatment of Sleep-Related Breathing Disorders.

Reliable detection of sleep positions is essential for the development of technical aids for patients with position-dependent sleep-related breathing disorders. We compare personalized and generalizable sleeping position classifiers using unobtrusive eight-channel pressure-sensing mats. Data of six male patients with confirmed position-dependent sleep apnea was recorded during three subsequent nights. Personalized position classifiers trained using leave-one-night-out cross-validation on average reached an F1-score of 61.3% for supine/non-supine and an F1-score of 46.2% for supine/lateral-left/lateral-right classification. The generalizable classifiers reached average F1-scores of 62.1% and 49.1% for supine/non-supine and supine/lateral-left/lateral-right classification, respectively. In-bed presence ("bed occupancy") could be detected with an average F1-score of 98.1%. This work shows that personalized sleep-position classifiers trained with data from two nights have comparable performance to classifiers trained with large interpatient datasets. Simple eight-channel sensor mattresses can be used to accurately detect in-bed presence required for closed-loop systems but their use to classify sleep-positions is limited.

Stochastically modulated inter-pulse intervals to increase the efficiency of functional electrical stimulation cycling.

INTRODUCTION: Functional electrical stimulation cycling has various health benefits, but the mechanical power output and efficiency are very low compared to volitional muscle activation. Stimulation with variable frequency showed significantly higher power output values in experiments with a knee dynamometer. The aim of the present work was to compare stochastic modulation of inter-pulse interval to constant inter-pulse interval stimulation during functional electrical stimulation cycling. METHODS: Seventeen able-bodied subjects participated (n = 17). Quadriceps and hamstring muscle groups were stimulated with two activation patterns: P1-constant frequency, P2-stochastic inter-pulse interval. Power output was measured on functional electrical stimulation ergometer. RESULTS: Overall, mean power output with the stochastically modulated pattern P2 was lower than with P1 (12.57 ± 3.74 W vs. 11.44 ± 3.81 W, P1 vs. P2, p = 0.022), but no significant differences during the first 30 s and the last 30 s were observed. CONCLUSIONS: This study showed that stimulation strategies that use randomized modulation of inter-pulse intervals can negatively affect power output generation during functional electrical stimulation cycling. To minimise voluntary contractions, power measurement and assessment should be focused on the periods where only the quadriceps are stimulated.

Optimisation of the mean boat velocity in rowing.

In rowing, motor learning may be facilitated by augmented feedback that displays the ratio between actual mean boat velocity and maximal achievable mean boat velocity. To provide this ratio, the aim of this work was to develop and evaluate an algorithm calculating an individual maximal mean boat velocity. The algorithm optimised the horizontal oar movement under constraints such as the individual range of the horizontal oar displacement, individual timing of catch and release and an individual power-angle relation. Immersion and turning of the oar were simplified, and the seat movement of a professional rower was implemented. The feasibility of the algorithm, and of the associated ratio between actual boat velocity and optimised boat velocity, was confirmed by a study on four subjects: as expected, advanced rowing skills resulted in higher ratios, and the maximal mean boat velocity depended on the range of the horizontal oar displacement.

Virtual Reality to control active participation in a subacute stroke patient during robot-assisted gait training.

Virtual Reality (VR) provides a promising medium to enrich robot assisted rehabilitation. VR applications present the opportunity to engage patients in therapy and control participation. The aim of this study was to investigate two strategies to control active participation of a stroke patient focusing on the involvement of the paretic leg in task solution. A subacute stroke patient with a severe hemiparesis performed two experiments on the driven gait orthosis Lokomat. Patient activity was quantified by weighted interaction torques measured in both legs (experiment A) and the paretic leg only (experiment B). The patient was able to successfully implement both the bilateral and unilateral control modality. Both control modes increased the motor output of the paretic leg, however the paretic leg control mode resulted in a much more differentiated regulation of the activity in the leg. Both control modes are appropriate approaches to enhance active participation and increase motor output in the paretic leg. Further research should evaluate the therapeutic benefit of patients with hemiparesis using the unilateral control mode depending on the severity of their impairment.

Quantitative description of the state of awareness of patients in vegetative and minimally conscious state.

Clinical scales represent the golden standard in characterizing awareness for patients in vegetative or in a minimally conscious state. Clinical scales suffer from problems of sensitivity, specificity, subjectivity, and inter-rater reliability. This leads to a misdiagnosis rate of up to 40% and consequences associated with inappropriate treatment decisions. In this study, objective measures including physiological and neurological signals are used to quantify the patient status. Using linear backward regression analysis, 13 variables (based on frequency analysis of the electrocardiogram, heart rate variability, amplitude and latency of the P300, skin conductance responses, changes in the blood pressure and respiration signal) were found to be sufficient to describe 74.7% of the variability of the scores. In this regression model, the P300, electrocardiogram and the blood pressure signal account for most of the variability. More patient data and additional measures will enable refinement of the methods. This new objective-measurement based model of the state of awareness will complement the clinical scales in order to increase the quality of diagnosis.

Comparison of visual and haptic feedback during training of lower extremities.

We compared the effects of visual and haptic modalities on the adaptation capabilities of healthy subjects to the virtual environment. The visual cueing (only the reference motion is presented) and visual feedback (the reference motion as well as the current tracking deviation are presented) were provided by a real-time visualization of a virtual teacher and a virtual self - avatar, using optical measurements. The subjects had to track the virtual teacher during stepping-in-place movements. The haptic feedback was provided by the actuated gait orthosis Lokomat programmed with the same stepping movements employing an impedance control algorithm. Both setups included auditory cueing. The stepping task was performed by engaging different modalities separately as well as combined. The results showed that (1) visual feedback alone yielded better tracking of the virtual teacher than visual cueing alone, (2) haptic feedback alone yielded better tracking than any visual modality alone, (3) haptic feedback and visual feedback combined yielded better tracking than haptic feedback alone, and (4) haptic feedback combined with visual cueing did not improve tracking performance compared to haptic feedback alone. In general, we observed a better task performance with the haptic modality compared to visual modality.

Temporal and spatial patterns of cortical activation during assisted lower limb movement.

Human gait is a complex process in the central nervous system that results from the integrity of various mechanisms, including different cortical and subcortical structures. In the present study, we investigated cortical activity during lower limb movement using EEG. Assisted by a dynamic tilt table, all subjects performed standardized stepping movements in an upright position. Source localization of the movement-related potential in relation to spontaneous EEG showed activity in brain regions classically associated with human gait such as the primary motor cortex, the premotor cortex, the supplementary motor cortex, the cingulate cortex, the primary somatosensory cortex and the somatosensory association cortex. Further, we observed a task-related power decrease in the alpha and beta frequency band at electrodes overlying the leg motor area. A temporal activation and deactivation of the involved brain regions as well as the chronological sequence of the movement-related potential could be mapped to specific phases of the gait-like leg movement. We showed that most cortical capacity is needed for changing the direction between the flexion and extension phase. An enhanced understanding of the human gait will provide a basis to improve applications in the field of neurorehabilitation and brain-computer interfaces.

Robot-aided rehabilitation of neural function in the upper extremities.

Repetitive movements can improve muscle strength and movement coordination in patients with neurological disorders and impairments. Robot-aided approaches can serve to enhance the rehabilitation process. They can not only improve the therapeutic outcome but also support clinical evaluation and increase the patient motivation. This chapter provides an overview of existing systems that can support the movement therapy of the upper extremities in subjects with neurological pathologies. The devices are compared with respect to technical function, clinical applicability, and clinical outcomes.

New technologies and concepts for rehabilitation in the acute phase of stroke: a collaborative matrix.

The process of developing a successful stroke rehabilitation methodology requires four key components: a good understanding of the pathophysiological mechanisms underlying this brain disease, clear neuroscientific hypotheses to guide therapy, adequate clinical assessments of its efficacy on multiple timescales, and a systematic approach to the application of modern technologies to assist in the everyday work of therapists. Achieving this goal requires collaboration between neuroscientists, technologists and clinicians to develop well-founded systems and clinical protocols that are able to provide quantitatively validated improvements in patient rehabilitation outcomes. In this article we present three new applications of complementary technologies developed in an interdisciplinary matrix for acute-phase upper limb stroke rehabilitation - functional electrical stimulation, arm robot-assisted therapy and virtual reality-based cognitive therapy. We also outline the neuroscientific basis of our approach, present our detailed clinical assessment protocol and provide preliminary results from patient testing of each of the three systems showing their viability for patient use.

Robot-aided neurorehabilitation of the upper extremities.

Task-oriented repetitive movements can improve muscle strength and movement co-ordination in patients with impairments due to neurological lesions. The application of robotics and automation technology can serve to assist, enhance, evaluate and document the rehabilitation of movements. The paper provides an overview of existing devices that can support movement therapy of the upper extremities in subjects with neurological pathologies. The devices are critically compared with respect to technical function, clinical applicability, and, if they exist, clinical outcomes.

fMRI-Compatible Electromagnetic Haptic Interface.

A new haptic interface device is suggested, which can be used for functional magnetic resonance imaging (fMRI) studies. The basic component of this 1 DOF haptic device are two coils that produce a Lorentz force induced by the large static magnetic field of the MR scanner. A MR-compatible optical angular encoder and a optical force sensor enable the implementation of different control architectures for haptic interactions. The challenge was to provide a large torque, and not to affect image quality by the currents applied in the device. The haptic device was tested in a 3T MR scanner. With a current of up to 1A and a distance of 1m to the focal point of the MR-scanner it was possible to generate torques of up to 4 Nm. Within these boundaries image quality was not affected.

Optimised robot-based system for the exploration of elastic joint properties.

Numerous publications provide measured biomechanical data relating to synovial joints. However, in general, they do not reflect the non-linear elastic joint properties in detail or do not consider all degrees of freedom (DOF), or the quantity of data is sparse. To perform more comprehensive, extended measurements of elastic joint properties, an optimised robot-based approach was developed. The basis was an industrial, high-precision robot that was capable of applying loads to the joint and measuring the joint displacement in 6 DOF. The system was equipped with novel, custom-made control hardware. In contrast to the commonly used sampling rates that are below 100 Hz, a rate of 4 kHz was realised for each DOF. This made it possible to implement advanced, highly dynamic, quasi-continuous closed-loop controllers. Thus oscillations of the robot were avoided, and measurements were speeded up. The stiffness of the entire system was greater than 44 kNm(-1) and 22 Nm deg(-1), and the maximum difference between two successive measurements was less than 0.5 deg. A sophisticated CT-based referencing routine facilitated the matching of kinematic data with the individual anatomy of the tested joint. The detailed detection of the elastic varus-valgus properties of a human knee joint is described, and the need for high spatial resolution is demonstrated.

Impact of laparoscopic adjustable gastric banding on plasma ghrelin, eating behaviour and body weight.

BACKGROUND: Plasma ghrelin, an orexigenic peptide derived from the stomach and duodenum, increases following weight loss and might contribute to weight regain. The aim of the present study was to evaluate the effect of laparoscopic adjustable gastric banding (LAGB) on body weight and body composition as well as plasma ghrelin in relation to eating behaviour in morbidly obese patients. MATERIALS AND METHODS: This study was performed in 23 morbidly obese subjects who underwent standardized LAGB. Fasting plasma ghrelin was measured before and 6 months after surgery and was correlated with body weight, body composition, and eating behaviour. RESULTS: Six months after LAGB, body weight decreased significantly by -15.7 +/- 1.4 kg (mean +/- SEM, P = 0.0001) which was accompanied by an increased cognitive restraint of eating (P = 0.001), and by a decreased disinhibition of eating and susceptibility to hunger (P = 0.0001). Plasma ghrelin increased (P = 0.016) by 27.2% from 100.39 +/- 12.90 to 127.22 +/- 13.15 fmol mL(-1). The change in plasma ghrelin correlated with changes in body weight (r = -0.49, P = 0.02), BMI (r = -0.42, P = 0.048) and fat mass (r = -0.519, P = 0.013), but not with changes of fat-free mass and of the three dimensions of eating behaviour. CONCLUSION: Weight loss following LAGB leads to an increase in fasting plasma ghrelin and is accompanied by a decrease in hunger, disinhibition of eating and an increase in cognitive restraint. Thus, changes in eating behaviour, which promote reduction of food intake and not fasting ghrelin, determines weight loss achieved by LAGB.

Cooperative strategies for robot-aided gait neuro-rehabilitation.

Task-oriented repetitive movements can improve muscular strength and movement coordination in patients with impairments due to neurological or orthopedic lesions. The application of robotics and automation technology can serve to assist, enhance, evaluate, and document neurological and orthopedic rehabilitation of the lower and upper extremities. This review presentation will give an overview of patient-cooperative techniques to the robot-aided gait rehabilitation of paralyzed patients. Patient-cooperative means that the technical system considers the patient intention and efforts rather than imposing any predefined movement or inflexible strategy. It is hypothesized that cooperative approaches have the potential to improve the therapeutic outcome compared to classical rehabilitation strategies. Three new cooperative strategies are presented in this review. In all three strategies the patient's movement effort is detected and processed in three different ways. First, the data is used to offer the patient an increased freedom of movement by a certain amount of robot compliance. Second, the robot behavior is adapted to the patient movement efforts. In the third strategy the recorded movement data are displayed to the patient in order to improve the patient efforts by biofeedback principles.

In vivo kinematic measurement during laparoscopic cholecystectomy.

BACKGROUND: Despite the rapid development of computer-assisted surgery, studies on kinematic measurement for surgical innovation are rare. This study describes a system for kinematic measurement in real operating theater environments. Six laparoscopic cholecystectomies were recorded and analyzed. In addition to a demonstration of the feasibility of the method, basis data for the development of an actuated laparoscopic camera holder are evaluated. METHODS: The positions of four receivers were recorded by an electromagnetic motion acquisition system. Analysis of the data was performed postoperatively with matlab. Parameters such as coordinates, velocities, angles, angular velocities, workspaces in typical phases of an operation, and subareas of the coordinate ranges were computed. RESULTS: The workspace during the operation in situ before (II) and after (V) removal of the gallbladder at the upper camera end was as follows: (X, Y, Z; given in cm): II: 65.5 . 42.7 . 27.3 (subarea 90% = 8.3. 14.0.6.3); V: 57.4.33.3.26.2, (90% = 10.3.16.5.7.9). Workspaces at the lower camera end were smaller: II: 14.8.9.7.15.4; (90% = 3.5.3.1.4.3). During these operation phases, velocities up to 82.9 cm/s were documented. Most of the measured velocities were much smaller. The camera -tilt-angles in left/right (alphax) and head/ feet (alphay) direction were as follows: alphax: -69 degrees to +69 degrees and alphay: -74 degrees to +48 degrees. CONCLUSION: This study demonstrates the feasibility of real-time kinematic measurement in the operation environment. The information might be of future value not only as basis data for the development of camera holders, but also for further investigations on robotics, ergonomics, and simulation.

[Initial results with the Munich knee simulator]. / Erste Ergebnisse mit dem Münchner Kniesimulator.

In orthopaedics more than 50 different clinical knee joint evaluation tests exist that have to be trained in orthopaedic education. Often it is not possible to obtain sufficient practical training in a clinical environment. The training can be improved by Virtual Reality technology. In the frame of the Munich Knee Joint Simulation project an artificial leg with anatomical properties is attached by a force-torque sensor to an industrial robot. The recorded forces and torques are the input for a simple biomechanical model of the human knee joint. The robot is controlled in such way that the user gets the feeling he moves a real leg. The leg is embedded in a realistic environment with a couch and a patient on it.

Model-based control of FES-induced single joint movements.

A crucial issue of functional electrical stimulation (FES) is the control of motor function by the artificial activation of paralyzed muscles. Major problems that limit the success of current FES systems are the nonlinearity of the target system and the rapid change of muscle properties due to fatigue. In this study, four different strategies, including an adaptive algorithm, to control the movement of the freely swinging shank were developed on the basis of computer simulations and experimentally evaluated on two subjects with paraplegia due to a complete thoracic spinal cord injury. After developing a nonlinear, physiologically based model describing the dynamic behavior of the knee joint and muscles, an open-loop approach, a closed-loop approach, and a combination of both were tested. In order to automate the individual adjustments cited above, we further evaluated the performances of an adaptive feedforward controller. The two parameters chosen for the adaptation were the threshold pulse width and the scaling factor for adjusting the active moment produced by the stimulated muscle to the fitness of the muscle. These parameters have been chosen because of their significant time variability. The first three controllers with fixed parameters yielded satisfactory result. An additional improvement was achieved by applying the adaptive algorithm that could cope with problems due to muscle fatigue, thus permitting on-line identification of critical parameters of the plant. Although the present study is limited to a simplified experimental setup, its applicability to more complex and functional movements can be expected.

A survey study for the development of virtual reality technologies in orthopedics.

Virtual reality (VR) technologies have the potential to support medical education and training. In order to orient the development of medical VR applications towards the actual deficiencies and demands in orthopedics, we performed a survey among 56 orthopedic physicians. They were asked to provide information about the kind of physical joint evaluation tests which they perform most often, the importance of physical joint evaluation in comparison to alternative diagnostic methods, and their opinion about current medical education system as well as the prospects of VR applications in orthopedics. The main conclusion of this survey is that VR applications have the potential to improve the lacking medical education and orthopedic training, e.g. by improving the quality of joint evaluation methods, reducing the high number of unhealthy, risky and expensive alternative diagnostic procedures.

Development of a multi-modal virtual human knee joint for education and training in orthopaedics.

Due to limited simultaneous access to a greater pool of patients an effective training of medical students or young orthopedic physicians is difficult. A knee joint simulator that comprises the properties of a healthy or pathological knee can support medical education and training. In this paper a mechatronic system is presented that provides visual, acoustic, and haptic (force) feedback so that it allows a user to touch and move a virtual shank, bones or muscles within the leg, and simultaneously observe the generated movement, feel the contact force, and hear sounds. These and further features enable the user to study and assess the properties of the knee, e.g. by testing the joint laxity and end-point stiffness in six degrees-of-motion (DOF) and by grasping and pulling at muscles, rupturing ligaments or changing muscle/ligament paths. Such a tool can support training of physical knee evaluation required for diagnosis and therapeutic planning, since any kind of pathology of any subject type can be tested at any time. Furthermore, it can provide a better understanding of functional anatomy, e.g. for the education of medical students.

Using mathematical models and advanced control systems techniques to enhance neuroprosthesis function.

Systems that use electrical stimulation to activate paralyzed muscles, called "neuroprostheses", have restored important functional capabilities to many people with neurologic disorders such as spinal cord injury or stroke. However, the clinical benefits derived from neuroprostheses have been limited by the quality of control of posture and movement that has been achieved. Over the past few decades, engineers have used mathematical models and control systems technology to develop functional neuromuscular stimulation (FNS) control systems that show promise in the laboratory, but these have not yet been incorporated into practical solutions for clinical problems. This article briefly reviews several of the complicating factors in controlling FNS systems and describes the potential roles of biomechanical modeling and advanced control system technology. Three important challenges in FNS control systems research and development are identified: 1) to obtain an improved understanding of the biomechanical system that we are trying to control and how it is controlled by the intact neural system, 2) to develop new control system technology with a particular focus on strategies that mimic those used by biologic systems, and 3) to integrate the knowledge and technologies into useful systems that meet the needs of neuroprosthesis users. The outlook for the future includes many interesting problems; yet more importantly, it includes relevant clinical benefits to be gained through the application of biomechanical models and advanced control systems techniques in neuroprostheses.