Tremors of the arm are a common symptom of many neurological disorders, including Parkinson’s disease and multiple sclerosis (MS), and can be severely disabling. The complexity of the movements makes it difficult to identify the mechanisms that give rise to the tremor. Engineering researchers from the University of Bristol are working with the charity MS Research to change the way arm tremors are diagnosed and assessed. They aim to provide clinicians with a more detailed, quantitative, and objective representation of each patient’s tremor characteristics, so that the treatment strategy can be optimised for that individual.
Methods
Tremor patients are fitted with MTx sensors on the hand, lower arm, upper arm, shoulder, and sternum. With the sensors in place, they carry out a series of movements that are commonly used by clinicians when assessing tremor by visual observation or that reflect daily tasks. The Xbus Master is used to transmit sensor data to a nearby computer via Bluetooth. This equipment is well suited to the application as the sensors can be applied quickly and comfortably to patients with a wide range of disabilities and movement restrictions. Furthermore, the system can easily be incorporated into any clinical environment; any available PC can serve as the host computer and, unlike camera-based systems, it imposes no requirements on the layout of the room.
Analysis
Each sensor unit outputs real-time estimates of orientation in three dimensions, using Xsens's Kalman filter to ensure robustness to noise. The recordings are used to reconstruct the movements of the individual parts of the arm,1 with 15 degrees-of-freedom (3 per sensor unit). The subject’s height and weight are used to make reasonable assumptions for the inertial properties of those limb segments.2 Inverse dynamics calculations1 are then carried out in SimMechanicsTM, yielding estimates of the torques applied at individual joints to generate the movements.
The cross-correlations between torques in individual joints are used to automatically identify, within the movement, key patterns of coordinated forcing that cannot be discerned by the unaided eye. These forcing patterns are being used to determine, for each individual patient, whether a particular joint is primarily responsible for initiating or perpetuating the tremor. Further studies will then investigate the hypothesis that mechanical suppression of the tremor at only these ‘driving’ joints will yield a reduction of tremor in the other joints as well. For details, see the references below.
Summary
The Xbus system is being used to quantify tremor movements, yielding insights with new levels of detail and accuracy, while enabling automated identification of key movement patterns. The choice of equipment ensures that the system can be easily implented in any modern clinical environment.
Disclaimer
This publication includes independent research commissioned by the National Institute for Health Research (NIHR) under the Invention for Innovation (i4i) programme. The views expressed in this publication are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health.
References
[1] L. P. Ketteringham, "Measuring and controlling upper limb tremor in individuals with multiple sclerosis". PhD thesis, Department of Mechanical Engineering, University of Bristol, UK, 2010.
[2] D. G. Western, L. P. Ketteringham, S. A. Neild, R. A. Hyde, R. J. S. Jones, and A. M. Davies-Smith, “Validation of Inverse Dynamics Modelling and Correlation Analysis to Characterise Upper-Limb Tremor,” to be published in the proceedings of the International Conference on Neurorehabilitation, Toledo, Spain, 14-16 Nov. 2012.
Personnel
Dr. David Western, Dr. Laurence Ketteringham, and Dr. Simon Neild
david.western@bristol.ac.uk
Dept. of Mechanical Engineering
University of Bristol
Dr. Rosie Jones and Ms. Angela Davies-Smith
MS Research
www.ms-research.org.uk
