Holger Nahrstaedt

Automatic Control of a Drop‐Foot Stimulator Based on Angle Measurement Using Bioimpedance

The topic of this contribution is iterative learning control of a drop-foot stimulator in which a predefined angle profile during the swing phase is realized. Ineffective dorsiflexion is compensated by feedback-controlled stimulation of the muscle tibialis anterior. The ankle joint measurement is based on changes in the bioimpedance (BI) caused by leg movements. A customized four-channel BI measurement system was developed. The suggested control approach and the new measurement method for the joint angle were successfully tested in preliminary experiments with a neurologically intact subject. Reference angle measurements were taken with a marker-based optical system. An almost linear relation between joint angle and BI was found for the angle range applicable during gait. The desired angle trajectory was closely tracked by the iterative learning controller after three gait cycles. The final root mean square tracking error was below 5 degrees.

Automated Detection and Evaluation of Swallowing Using a Combined EMG/Bioimpedance Measurement System

Introduction. Developing an automated diagnostic and therapeutic instrument for treating swallowing disorders requires procedures able to reliably detect and evaluate a swallow. We tested a two-stage detection procedure based on a combined electromyography/bioimpedance (EMBI) measurement system. EMBI is able to detect swallows and distinguish them from similar movements in healthy test subjects. Study Design. The study was planned and conducted as a case-control study (EA 1/019/10, and EA1/160/09, EA1/161/09). Method. The study looked at differences in swallowing parameters in general and in the event of penetration during swallows in healthy subjects and in patients with an oropharyngeal swallowing disorder. A two-stage automated swallow detection procedure which used electromyography (EMG) and bioimpedance (BI) to reliably detect swallows was developed. Results. Statistically significant differences between healthy subjects and patients with a swallowing disorder were found in swallowing parameters previously used to distinguish between swallowing and head movements. Our two-stage algorithm was able to reliably detect swallows (sensitivity = 96.1%, specificity = 97.1%) on the basis of these differences. Discussion. Using a two-stage detection procedure, the EMBI measurement procedure is able to detect and evaluate swallows automatically and reliably. The two procedures (EMBI + swallow detection) could in future form the basis for automated diagnosis and treatment (stimulation) of swallowing disorders.

Swallow Detection Algorithm Based on Bioimpedance and EMG Measurements

Abstract Image-based swallowing assessment tools like videofluoroscopy and endoscopy allow experts manual investigation of a few individual swallows. However, these tools are expensive and can only be used by clinicians. Systems which utilize easily attachable, inexpensive and non-invasive sensors at the throat could be a real progress for diagnosis and therapy. This contribution investigates the use of a combined electromyography (EMG) and bioimpedance (BI) measurement at the throat to automatically detect swallowing events. The absolute value of the measured BI completely describes the swallowing process, i.e. the closure of the larynx. There is a typical reproducible drop in BI during a swallow. The muscle activity needed for the laryngeal movement during a swallow is measured using EMG. The presented algorithm involves a valley detection in order to perform a segmentation of the BI signal. Additionally, only BI valleys that coincide with EMG activity are selected for feature extraction. In the second part of the algorithm, extracted features of the BI and integrated EMG are fed into a support vector machine (SVM) which is able to separate BI valleys related to swallowing events from valleys which are not caused by swallowing. The detection algorithm has been tested on data from nine healthy subjects. The data set contained 1370 swallows of different bolus sizes and consistency and was effected by other movements and speech. The combined BI/EMG segmentation detected 99.3% of all swallowing events. The subsequently applied classifier showed a sensitivity of 96.1% and a specificity of 97.1% for the test data.

A bioimpedance measurement device for sensing force and position in neuroprosthetic systems

This contribution investigates the use of bioimpedance measurements on the limbs for the control of electrically stimulated muscles. Movements of the limbs and muscle contractions cause changes in the absolute value of the complex impedance. A four-electrode bioimpedance measurement system will be presented which can be used while the electrical muscle stimulation of the neuroprostheses is active. A constant sinusoidal current at 50 kHz with an amplitude of less than 0.25 mA is generated by a programmable function generator connected to a voltage controlled current source and is applied via two current electrodes.

Iterativ Lernende Regelung einer Gang-Neuroprothese Iterative Learning Control of a Gait Neuroprosthesis

Zusammenfassung Dieser Beitrag beschreibt den Entwurf einer linearen Iterativ Lernenden Regelung (ILR) im Zeitbereich für die automatische Anpassung einer Neuroprothese bei Schlaganfallpatienten. Eine unzureichende Fußhebung in der Schwungphase des Ganges soll durch die gezielte Stimulation des Fußhebers kompensiert werden. Für die Erfassung des Gelenkwinkels wird ein neuartiges Messverfahren verwendet, bei welchem durch Bewegung hervorgerufene Bio-Impedanz-Änderungen im Bein registriert werden. Für die Regelung ist ferner eine Gangphasenerkennung mittels Drucksensoren unter der Fußsohle notwendig, um die Stimulation exakt mit der Schwungphase zu synchronisieren. Ein erster Test des Regelungskonzepts und des neuen Ansatzes zur Winkelmessung wurde an einem gesunden Probanden durchgeführt.

Einfluss der Körperposition auf die Atem-Schluck-Koordination

BACKGROUND To allow passage of food, the swallowing process closes off the larynx and interrupts respiratory flow. Both the timing of the interruption of respiratory flow and the body position can affect the results of the swallowing process. OBJECTIVE The effect of body position on the swallowing process and the coordination of breathing and swallowing is investigated. MATERIALS AND METHOD A combined EMG/bioimpedance measurement system and a piezoelectric sensor were used to investigate coordination of breathing and swallowing of a range of food consistencies in three different body positions (90°, 45° and 0°) in healthy subjects. RESULTS Investigations were carried out on 21 healthy subjects (12 ♂, 9 ♀). 762 swallows were recorded. Changing body position was found to have a statistically significant effect on swallow-related parameters (maximum laryngeal elevation and speed of laryngeal elevation) and breathing pattern (pre- and post-swallow breathing phases). The laryngeal elevation as well as the speed of the laryngeal elevation is influenced significantly by the consistency to be swallowed. The breathing pattern changes from saliva to solid food of inspiration/swallow/inspiration to expiration/swallow/expiration. A change of body position influences the parameters specific for swallowing and the breathing patterns significantly. CONCLUSIONS This study demonstrates that body position affects coordination of breathing and swallowing and swallow-related parameters in healthy subjects. Our results indicate that patients should be enabled to adopt a position in which they are sitting at an angle of at least 45°.

Efficacy of EMG/bioimpedance-triggered functional electrical stimulation on swallowing performance

In order to support swallowing, the efficacy of functional electrical stimulation for different stimulation settings of the submental musculature has been investigated. The stimulation was administrated at rest and synchronously to voluntary initiated swallows. The onset of a swallow was detected in real-time by a combined electromyography/ bioimpedance measurement at the neck in order to trigger the stimulation. The amplitude and speed of larynx elevation caused by the FES has been assessed by the observed change in bioimpedance whereas a reduction of bioimpedance corresponds to an increase in larynx elevation. Study results from 40 healthy subjects revealed that 73% of the subjects achieved a larger and faster larynx elevation during swallowing with triggered FES and therefor a better protection of their airways. However, we also observed a decrease in larynx elevation compared to normal swallowing in 11 out of the 40 subjects what might not benefit from such a treatment. The largest improvement of larynx elevation and speed during swallowing could be achieved with three stimulation channels formed by four electrodes in the submental region.

Effect of body position on coordination of breathing and swallowing

BACKGROUND To allow passage of food, the swallowing process closes off the larynx and interrupts respiratory flow. Both the timing of the interruption of respiratory flow and the body position can affect the results of the swallowing process. OBJECTIVE The effect of body position on the swallowing process and the coordination of breathing and swallowing is investigated. MATERIALS AND METHOD A combined EMG/bioimpedance measurement system and a piezoelectric sensor were used to investigate coordination of breathing and swallowing of a range of food consistencies in three different body positions (90°, 45° and 0°) in healthy subjects. RESULTS Investigations were carried out on 21 healthy subjects (12 ♂, 9 ♀). 762 swallows were recorded. Changing body position was found to have a statistically significant effect on swallow-related parameters (maximum laryngeal elevation and speed of laryngeal elevation) and breathing pattern (pre- and post-swallow breathing phases). The laryngeal elevation as well as the speed of the laryngeal elevation is influenced significantly by the consistency to be swallowed. The breathing pattern changes from saliva to solid food of inspiration/swallow/inspiration to expiration/swallow/expiration. A change of body position influences the parameters specific for swallowing and the breathing patterns significantly. CONCLUSIONS This study demonstrates that body position affects coordination of breathing and swallowing and swallow-related parameters in healthy subjects. Our results indicate that patients should be enabled to adopt a position in which they are sitting at an angle of at least 45°.

Multisensor Classification System for Triggering FES in Order to Support Voluntary Swallowing.

In dysphagia the ability of elevating the larynx and hyoid is usually impaired. Electromyography (EMG) and Bioimpedance (BI) measurements at the neck can be used to trigger functional electrical stimulation (FES) of swallowing related muscles. Nahrstaedt et al.1 introduced an algorithm to trigger the stimulation in phase with the voluntary swallowing to improve the airway closure and elevation speed of the larynx and hyoid. However, due to non-swallow related movements like speaking, chewing or head turning, stimulations might be unintentionally triggered. So far a switch was used to enable the BI/EMG-triggering of FES when the subject was ready to swallow, which is inconvenient for practical use. In this contribution, a range image camera system is introduced to obtain data of head, mouth, and jaw movements. This data is used to apply a second classification step to reduce the number of false stimulations. In experiments with healthy subjects, the amount of potential false stimulations could be reduced by 47% while 83% of swallowing intentions would have been correctely supported by FES.

BIOIMPEDANCE- AND EMG-TRIGGERED FES FOR IMPROVED PROTECTION OF THE AIRWAY DURING SWALLOWING

Dysphagia has a huge impact on the quality of life. Especially, the ability to elevate larynx and hyoid in order to guarantee airway protection is decreased in dysphagia during swallowing. In this contribution, EMG and Bioimpedance (BI) measurements at the neck are used for triggering functional electrical stimulation (FES) of the submental muscles at the transition from the oral phase to the pharyngeal phase of swallowing. It was demonstrated on a first patient that airway closure and elevating speed are improved using swallowing-triggered FES.