A method to qualitatively assess arm use in stroke

Authors: Kaspar Leuenberger Roman Gonzenbach Susanne Wachter Andreas Luft Roger Gassert

Publish Date: 2016/04/22

Volume: 55, Issue: 1, Pages: 141-150

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Abstract

Wearable sensor technology has enabled unobtrusive monitoring of arm movements of stroke survivors in the home environment However the most widely established method based on activity counts provides quantitative rather than qualitative information on arm without functional insights and is sensitive to passive arm movements during ambulatory activities We propose a method to quantify functionally relevant arm use in stroke survivors relying on a single wristworn inertial measurement unit Orientation of the forearm during movements is measured in order identify gross arm movements The method is validated in 10 subacute/chronic stroke survivors wearing inertial sensors at 5 anatomical locations for 48 h Measurements are compared to conventional activity counts and to a test for gross manual dexterity Duration of gross arm movements of the paretic arm correlated significantly better with the Box and Block Test r=095 than conventional activity counts when walking phases were included r=069 and similar results were found when comparing ratios of paretic and nonparetic arms for gross movements and activity counts The proposed gross arm movement metric is robust against passive arm movements during ambulatory activities and requires only a singlesensor module placed at the paretic wrist for the assessment of functionally relevant arm useFunctional recovery and regain of independence following neurological injury are commonly assessed via clinical scores comprising capacity and time measures and subjective questionnaires 11 Objective information on arm use in the home environment could provide a valuable complement to insights gained from clinical assessmentsWearable sensor technology has enabled unobtrusive monitoring of arm movements in the natural environment with accelerometry representing the most established approach Activity counts AC derived from the acceleration signals provide quantitative information about arm activity such as total duration 27 28 and intensity of movements 5 23 However AC provide only information about the amount of arm use but not about functional arm use For example accelerometry in wristworn applications is sensitive to any kind of movements eg passive arm swinging during ambulatory activities which leads to an overestimation of realworld arm activity 1 12 Ambulatory activities can be detected by means of accelerometry 18 33 and upper extremity activity can be adjusted accordingly 22 but this requires additional temporally synchronized sensors which may negatively impact patient compliance To reject the influence of ambulatory activities the ratio of arm use between paretic and nonparetic arm is commonly used 2 26 28 29 30 However ratios are a relative measure of intensity or duration of use and therefore are not suitable to capture potential changes in absolute activity or useWhereas clinical tests assess function and impairment accelerometry measures only the effects of impairment in the form of reduced activity levels or reduced duration of arm use but does not consider motion patterns In contrast to accelerometers only inertial measurement units IMUs comprising accelerometers and gyroscopes angular rate sensors can be used to precisely measure and monitor movements of body segments and have been proposed for portable motion capture of gait 6 13 or arm movements 35 36 The inclusion of gyroscopes is especially beneficial as they allow to measure angular displacement during highly dynamic activities Inertial sensors worn in a clinical setting during assessments such as the Functional Ability Scale of the Wolf Motor Function Test 7 10 19 20 or the FuglMeyer Assessment 3 have allowed the reconstruction of these scores based on the recorded signals demonstrating that qualitative information of arm movements can also be extracted Still there is a need for a metric motivated by the characteristics of typical object grasping and manipulation movements complementing the quantitative measures of accelerometers with measures of functional arm use Singlesensor setups are preferable because there is no risk of swapping sensors and no need for sophisticated synchronization and compliance in patients as well as clinicians is increasedWe propose a novel method to qualitatively assess functional arm use in the home environment relying on only a single wristworn sensor module To evaluate this method we monitored 10 subacute/chronic stroke survivors in their home environment during 48 h using five inertial measurement units IMUs placed on wrists shanks and waist We compare our method against setups involving sensors worn at multiple anatomical locations and investigate its ability to reject influence of ambulatory activities on arm use Performance measures are compared with clinical measures for gross manual dexterityThe goal of this work is to assess functional arm use as in the case of reaching to and manipulating an object with a single wristworn IMU IMUs are subject to drift especially in the horizontal plane and measurement of absolute wrist orientation can therefore not be guaranteed The use of magnetometers could add an absolute reference in the horizontal plane and reduce drift but these are “difficult to use in the vicinity of ferromagnetic metals” 16 which are often encountered in daily settings eg doors elevators speakers Robust measurement of wrist orientation and position relative to the trunk during ADL would require absolute tracking as provided by magnetic sensing 8 24 However when considering only short time windows of sensor recordings the effects of drift can be neglected and angular displacements can be measured reliablyReaching and manipulation movements performed during ADL typically involve grasping objects placed on a table or shelf and displacing them by moving the arm over a certain angle in the horizontal or vertical plane or a combination of the two During walking in return the forearm is mostly oriented toward the ground and swings passively It has been shown that during ADL wrist position is mostly constrained around the sagittal plane 8 and above the waist 31 and thus absolute orientation with respect to the trunk which could be influenced by sensor drift in the horizontal plane is not essential We assume that forearm elevation the angle between the forearm axis and a horizontal plane and/or yaw the angle between the forearm axis and the sagittal plane change significantly during functional arm use Based on these assumptions we propose to infer functional arm use by measuring the relative angular change in forearm orientation induced by such movementsTo derive a metric subsequently called gross arm movements GM based on these assumptions thresholds for forearm elevation and lateral movement have to be determined By observing reaching and manipulation tasks we defined a threshold of 30circ for angular change in elevation and/or yaw in order to identify such movements Fig 2 Further by constraining the elevation of the forearm to a range of 30circ to +30circ the influence of pro and supination movements of the forearm which we assume is not indicative of functional movements on the proposed metric can be reduced This is an issue as pronosupination movements at forearm postures around pm 90circ are indistinguishable from lateral movement with the available sensor information Furthermore this guarantees that the analysis of arm movements is not affected by singularities where subsequent behavior can not be predicted occurring at pm 90circ of forearm elevation Additionally by excluding forearm elevation lower than 30circ from the analysis the influence of ambulatory activities can be reduced

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