Abstract
The vestibular system is vital for maintaining balance and stabilizing gaze and vestibular damage causes impaired postural and gaze control. Here we examined the effects of vestibular loss and subsequent compensation on head motion kinematics during voluntary behavior. Head movements were measured in vestibular schwannoma patients before, and then 6 weeks and 6 months after surgical tumor removal, requiring sectioning of the involved vestibular nerve (vestibular neurectomy). Head movements were recorded in six dimensions using a small head-mounted sensor while patients performed the Functional Gait Assessment (FGA). Kinematic measures differed between patients (at all three time points) and normal subjects on several challenging FGA tasks, indicating that vestibular damage (caused by the tumor or neurectomy) alters head movements in a manner that is not normalized by central compensation. Kinematics measured at different time points relative to vestibular neurectomy differed substantially between pre-operative and 6-week post-operative states but changed little between 6-week and > 6-month post-operative states, demonstrating that compensation affecting head kinematics is relatively rapid. Our results indicate that quantifying head kinematics during self-generated gait tasks provides valuable information about vestibular damage and compensation, suggesting that early changes in patient head motion strategy may be maladaptive for long-term vestibular compensation.
Highlights
The vestibular system is vital for maintaining balance and stabilizing gaze and vestibular damage causes impaired postural and gaze control
To investigate the hypothesis that head kinematics are significantly altered as a result of peripheral vestibular loss during voluntary behavior, here we measured and quantified head motion in patients who transitioned through a series of vestibular states characterized by different levels of peripheral damage and central compensation
We chose to use the ten tasks that constitute the Functional Gait Assessment (FGA), since this allowed us to compare our quantitative analysis of head kinematics to the FGA scores that are commonly used in the clinic to assess functional capacity and fall risk in patients with vestibular damage
Summary
The vestibular system is vital for maintaining balance and stabilizing gaze and vestibular damage causes impaired postural and gaze control. Kinematic measures differed between patients (at all three time points) and normal subjects on several challenging FGA tasks, indicating that vestibular damage (caused by the tumor or neurectomy) alters head movements in a manner that is not normalized by central compensation. Following unilateral peripheral vestibular loss patients experience impaired vision and imbalance (e.g.,1,2), as well as aberrant motion and orientation perception (e.g.,3) These symptoms can be debilitating, making it difficult for patients to perform their normal daily activities. To investigate the hypothesis that head kinematics are significantly altered as a result of peripheral vestibular loss during voluntary behavior, here we measured and quantified head motion in patients who transitioned through a series of vestibular states characterized by different levels of peripheral damage and central compensation. FGA Objective Measures Description Speed (distance/duration) Steps/Sec Step length asymmetry: The ratio of integration of the positive vertical accelerations following heel strike of each leg (deafferenated side/ intact side) Step time asymmetry: The ratio of time intervals between vertical acceleration peaks (deafferenated side/ intact side) Average of the standard deviation of head movement across gait cycles for along each of the three dimensions of rotation and translation Fore-aft (translation) Interaural (translation) Vertical (translation) Roll (rotation) Pitch (rotation) Yaw (rotation) Average of the range of head movement across gait cycles along each of the three dimensions of rotation and translation: Fore-aft (translation) Interaural (translation) Vertical (translation) Roll (rotation) Pitch (rotation) Yaw (rotation) The peak of yaw angular velocity during the pivot Post-pivot head motion sway, calculated as the root mean square of linear accelerations in the horizontal plane within two seconds after the end of the turn The distance divided by the time of completion of the task Root mean square of linear accelerations in the horizontals plane during the task
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