Affiliations: [a] Department of Neurology and Neurosurgery, McGill University, Montreal, QC, Canada | [b] School of Physical and Occupational Therapy, McGill University, Montreal, QC, Canada | [c] Department of Physiology, University of Montreal, Montreal, QC, Canada | [d] CRIR Research Centre – Jewish Rehabilitation Hospital, Laval, QC, Canada | [e] Department of Otolaryngology-Head and Neck Surgery, Royal Victoria Hospital, McGill University, Montreal, QC, Canada
Correspondence:
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Corresponding author: Mindy Levin, School of Physical and Occupational Therapy, McGill University, 3654 Promenade Sir William Osler, Montreal, H3G 1Y5, Canada. Tel.: +1 514 398 3994; E-mail: [email protected]; Website: www.mcgill.ca/spot
Abstract: When arm and trunk segments are involved in reaching for objects within arm's reach, vestibulospinal pathways compensate for trunk motion influence on arm movement. This compensatory arm-trunk synergy is characterised by a gain coefficient of 0 to 1. Vestibular patients have less efficient arm-trunk synergies and lower gains. To assess the clinical usefulness of the gain measure, we used a portable ultrasound-based device to characterize arm-trunk coordination deficits in vestibular patients. Arm-trunk coordination without vision was measured in a Stationary Hand Task where hand position was maintained during trunk movement, and a Reaching Task with and without trunk motion. Twenty unilateral vestibular patients and 16 controls participated. For the Stationary Hand task, patient gains ranged from g=0.94 (good compensation) to 0.31 (poor compensation) and, on average, were lower than in controls (patients: 0.67 ± 0.19; controls: 0.85 ± 0.07; p< 0.01). Gains were significantly correlated with clinical tests (Sensory Organization; r=0.62, p< 0.01, Foam Romberg Eyes Closed; r=0.65, p< 0.01). For the Reaching Task, blocking trunk movement during reaching modified hand position significantly more in patients (8.2 ± 4.3 cm) compared to controls (4.5 ± 1.7 cm, p< 0.02) and the amount of hand position deviation was correlated with the degree of vestibular loss in a sub-group (n=14) of patients. Measurement of the Stationary Task arm-trunk gain and hand deviations during the Reaching Task can help characterize sensorimotor problems in vestibular-deficient patients and track recovery following therapeutic interventions. The ultrasound-based portable device is suitable for measuring vestibulospinal deficits in arm-trunk coordination in a clinical setting.
Keywords: Motor control, vestibular deficiency, rehabilitation, arm-trunk coordination, measurement
