Head impulses reveal loss of individual semicircular canal function
We studied individual semicircular canal responses in three dimensions to high-acceleration head rotations ("head impulses") in subjects with known surgical lesions of the semicircular canals, and compared their results to those of normal subjects. We found that vestibular-ocular reflex (VOR) gains at close to peak head velocity in response to yaw, pitch and roll impulses were reliable indicators of semicircular canal function. When compared to normals, lateral canal function showed a 70-80% decrease in VOR gain at peak of yaw head velocity during ipsilesional yaw impulses. After the loss of one vertical canal function there was a 30-50% decrease in vertical and torsional VOR gain in response to ipsilesional pitch and roll impulses respectively. Bilateral deficits in anterior or posterior canal function resulted in a 80-90% decrease in vertical VOR gain during ipsilesional pitch impulses, while the loss of ipsilateral anterior and posterior canal functions will result in a 80-90% decrease in torsional VOR gain in response to ipsilesional roll impulses. Three-dimensional vector analysis and animation of the VOR responses in a unilateral vestibular deafferented subject to yaw, pitch and roll impulses further demonstrated the deficits in magnitude and direction of the VOR responses following the loss of unilateral lateral, anterior and posterior canal functions.
Available from: Zdenek Svoboda
- "These angles are used to study the orientation of the body segments in a complex kinematic chain. Therefore, the pitch, roll and yaw angles are used in the field of medicine (Aw et al., 1999; Allum et al., 2008; Findling et al., 2011; Osler and Reynolds, 2010). Generally, the pitch is a rotational motion of the segment around the medialelateral axis, the roll is a rotational motion around the anterioreposterior axis and the yaw is a rotational motion around the vertical axis. "
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ABSTRACT: This study examines a relatively new method of studying and quantifying human postural stability in patients with degenerative cerebellar disease. Trunk sway and feet sway were measured during quiet stance. To test the method, ten patients and eleven healthy subjects performed two different stance tasks: standing with eyes open on a firm surface and standing with eyes closed on a foam support surface. Data were recorded using three body-worn gyroscopes (Xsens Technologies B.V.) to measure roll and pitch angular movements of the lower trunk, and left and right foot. The pitch versus roll plots of the trunk and feet were created, and the areas of the convex hull shapes were calculated. It was found that the area of the convex hull of the pitch versus roll plots is suitable for the identification of postural instability disorders caused by degenerative cerebellar disease.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Journal of Bodywork and Movement Therapies 06/2015; 19(3):421-428. DOI:10.1016/j.jbmt.2014.09.005
Available from: John Allum
- "Such an imbalance would make the detection of the low velocity head sway deviations involved with two-legged stance more difficult and lead to increased trunk sway. Once the static imbalance due to UVN has been compensated for, a dynamic imbalance will still be prevalent in the VOR causing saturated responses for head movements toward the deficit side in all three planes (Allum et al., 1988a; Halmagyi et al., 1990; Aw et al., 1996, 1999; Allum and Ledin, 1999). Linking these changes to the changes in gait stability observed in UVN patients is difficult for a number of reasons. "
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ABSTRACT: This review describes the effect of unilateral peripheral vestibular deficit (UPVD) on balance control as observed in stance and gait tests. Normally, a UPVD is defined based on vestibular ocular reflex (VOR) function. Therefore, we compare recovery observed in balance control over time with similar patterns of recovery or lack thereof in VOR function. Three types of UPVD are considered; acute vestibular neuritis, vestibular loss prior to and after cerebellar pontine angle tumor (CPAT) surgery during which a vestibular neurectomy was performed, and vestibular loss following neurectomy to eliminate disabling Ménière’s disease. To measure balance control, body-worn gyroscopes, mounted near the body’s centre of mass, were used for stance and gait tests. Measurement variables were the pitch (anterior-posterior) and roll (lateral) sway angles and angular velocities of the lower trunk-pelvis. All three groups showed balance deficits during stance tasks on foam, especially with eyes closed when stable control is highly dependent on vestibular inputs. Deficits in balance control during gait were present but were more profound for complex gait tasks such as tandem gait. Differences emerged between the groups concerning the severity of the deficit and its recovery. Generally, the effects of acute neuritis were more severe but recovered rapidly, deficits due to vestibular neurectomy were less severe but longer lasting. These results paralleled deficits in VOR function and raise questions about two modes of neural plasticity occurring in the vestibular system following vestibular loss: one mode being the limited central compensation for the loss, and the second mode being some restoration of peripheral vestibular function. Future work will need to correlate deficits in balance control during stance and gait more exactly with VOR deficits and carefully consider the differences between insufficient central compensation compared to inadequate peripheral restoration of function.
Frontiers in Neurology 05/2012; 3:83. DOI:10.3389/fneur.2012.00083
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ABSTRACT: Sudden complete loss of input from one labyrinth results in a massive change in behaviour. A vigorous horizontal ocular nystagmus occurs together with postural changes. These dramatic changes are short-lived and within about a week they have almost disappeared. This very rapid recovery has been the basis for the postulation that vestibular compensation is a textbook model for the study of neural plasticity in the central nervous system. Whilst the behavioural recovery is dramatic, quantitative testing reveals the loss and the permanent asymmetry of the system (Table 1). Recordings from single neurones show that many neurones in the ipsilesional VN are silenced by the unilateral loss, but as they start to fire again, so the spontaneous nystagmus declines. The major question which is still unanswered is the cause of the return of the firing of neurones in the ipsilesional VN. The answer may be found by studies of the neurochemistry of the VN using brain slice preparations. This review shows some of the errors which have been made by attempting to infer purely vestibular function from measurements of eye movements when other sources of ocular motor control may operate.
Baillière's clinical neurology 09/1992; 1(2):345-72.
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