Validation of a Step Detection Algorithm during Straight Walking and Turning in Patients with Parkinson’s Disease and Older Adults Using an Inertial Measurement Unit at the Lower Back

INTRODUCTION Inertial measurement units (IMUs) positioned on various body locations allow detailed gait analysis even under unconstrained conditions. From a medical perspective, the assessment of vulnerable populations is of particular relevance, especially in the daily-life environment. Gait analysis algorithms need thorough validation, as many chronic diseases show specific and even unique gait patterns. The aim of this study was therefore to validate an acceleration-based step detection algorithm for patients with Parkinson's disease (PD) and older adults in both a lab-based and home-like environment. METHODS In this prospective observational study, data were captured from a single 6-degrees of freedom IMU (APDM) (3DOF accelerometer and 3DOF gyroscope) worn on the lower back. Detection of heel strike (HS) and toe off (TO) on a treadmill was validated against an optoelectronic system (Vicon) (11 PD patients and 12 older adults). A second independent validation study in the home-like environment was performed against video observation (20 PD patients and 12 older adults) and included step counting during turning and non-turning, defined with a previously published algorithm. RESULTS A continuous wavelet transform (cwt)-based algorithm was developed for step detection with very high agreement with the optoelectronic system. HS detection in PD patients/older adults, respectively, reached 99/99% accuracy. Similar results were obtained for TO (99/100%). In HS detection, Bland-Altman plots showed a mean difference of 0.002 s [95% confidence interval (CI) -0.09 to 0.10] between the algorithm and the optoelectronic system. The Bland-Altman plot for TO detection showed mean differences of 0.00 s (95% CI -0.12 to 0.12). In the home-like assessment, the algorithm for detection of occurrence of steps during turning reached 90% (PD patients)/90% (older adults) sensitivity, 83/88% specificity, and 88/89% accuracy. The detection of steps during non-turning phases reached 91/91% sensitivity, 90/90% specificity, and 91/91% accuracy. CONCLUSION This cwt-based algorithm for step detection measured at the lower back is in high agreement with the optoelectronic system in both PD patients and older adults. This approach and algorithm thus could provide a valuable tool for future research on home-based gait analysis in these vulnerable cohorts

Interhemispheric interactions after stroke

Die nach einem Schlaganfall bei Bewegung der paretischen Hand verstärkte Aktivierung der ungeschädigten Hemisphäre wird in einer Hypothese durch plastische Reorganisation homologer Areale in dieser ungeschädigten Hemisphäre erklärt, begünstigt durch eine Reduktion der inhibitorischen Verbindungen von geschädigter zu ungeschädigter Hemisphäre. Eine andere Hypothese postuliert, dass die verstärkte Aktivierung der ungeschädigten Hemisphäre mit einer verstärkten Inhibition dieser auf die geschädigte Hemisphäre einhergeht. Die vorliegende Arbeit konnte zeigen, dass sich interhemisphärische Inhibition auch indirekt mittels psychophysischer Untersuchung des Bilateralen Defizits, Bimanuellen Advantages und bimanueller Handkraftmessung nachweisen lässt. Überprüft wurde, ob eine verstärkte Interhemisphärische Inhibition zu einem verstärkten Bilateralen Defizit oder reduzierten Bimanuellen Advantage führt. Es konnte ein Bilaterales Defizit bei Messung der Reaktionszeit festgehalten werden; es zeigte sich jedoch kein Bilaterales Defizit bei Testung der Handkraft und kein Bimanuelles Advantage bei Bestimmung der Rhythmizität beider Hände. Die Vermutung, dass bei Schlaganfallpatienten eine erhöhte Interhemisphärische Inhibition zu einem größeren Bilateralen Defizit in der paretischen Hand im Vergleich zur gesunden Hand führt, konnte in der untersuchten Patientengruppen jedoch nicht bestätigt werden. Allerdings zeigte sich ein Trend zu einem generell etwas höheren Bilateralen Defizit bei Schlaganfallpatienten im Vergleich zu den altersgematchten Kontrollen, was eine gegenseitige Erhöhung der Interhemisphärischen Inhibition vermuten lässt. Ein höheres Alter geht in der vorliegenden Studie mit einem niedrigeren Bilateralen Defizit einher, was Ausdruck verringerter gegenseitigen Inhibition der Hemisphären im höheren Alter sein kann. Mittels Psychophysik konnte in dieser Arbeit die Hypothese einer nach Schlaganfall verstärkten Interhemisphärische Inhibition der ungeschädigten Hemisphäre auf die geschädigte Hemisphäre nicht bestätigt werden. Der Vergleich jüngerer zu älterer Schlaganfallpatienten kann Aufschluss über unterschiedliche Erholungs- und Rekrutierungsmechanismen in Gehirnen unterschiedlichen Alters geben.The increased activity in the undamaged brain hemisphere when moving the paretic hand after stroke is explained in one hypothesis by the plastic reorganization of homologue areas in the undamaged hemisphere. This activity is favoured by a reduction of the inhibiting connections between damaged and undamaged hemispheres. Another hypothesis maintains that the increased activity in the undamaged hemisphere comes along with an increased inhibition in the damaged hemisphere. The present work showed that interhemispheric inhibition could also be proved indirectly by psychophysical examination of the bilateral deficit, bimanual advantage and bimanual measuring of the grip force. We investigated whether a stronger interhemispheric inhibition could lead to a stronger bilateral deficit or to a reduced bimanual advantage. Although a bilateral deficit was found when measuring reaction time, no bilateral deficit was noticed when testing grip force and no bimanual advantage was noticed, when measuring rhythmic finger tapping with both hands. The assumption that a higher interhemispheric inhibition in stroke patients would lead to a stronger bilateral deficit in the paretic hand as compared to the healthy hand could not be confirmed in the group of patients examined. Nonetheless, we noticed a tendency towards a generally higher bilateral deficit in stroke patients as compared to age-matched controls, which permits the assumption of a higher reciprocal interhemispheric inhibition. In this study older age correlates with lower bilateral deficit, which can be a sign of reduced reciprocal interhemispheric inhibition in older age. Psychophysical tests used in this study could not confirm the hypothesis about a higher interhemispheric inhibition of the damaged hemisphere by the undamaged one after stroke. The comparison between younger and older stroke patients can provide information about the various recovery and recruiting mechanisms in different-aged brains