Effects of caloric vestibular stimulation on head and trunk movements during walking

Instrumented insoles for assessment of gait in patients with vestibular schwannoma

Background

Imbalance and gait disturbances are common in patients with vestibular schwannoma (VS) and can result in significant morbidity. Current methods for quantitative gait analysis are cumbersome and difficult to implement. Here, we use custom-engineered instrumented insoles to evaluate the gait of patients diagnosed with VS.

Methods

Twenty patients with VS were recruited from otology, neurosurgery, and radiation oncology clinics at a tertiary referral center. Functional gait assessment (FGA), 2-minute walk test (2MWT), and uneven surface walk test (USWT) were performed. Custom-engineered instrumented insoles, equipped with an 8-cell force sensitive resistor (FSR) and a 9-degree-of-freedom inertial measurement unit (IMU), were used to collect stride-by-stride spatiotemporal gait parameters, from which mean values and coefficients of variation (CV) were determined for each patient.

Results

FGA scores were significantly correlated with gait metrics obtained from the 2MWT and USWT, including stride length, stride velocity, normalized stride length, normalized stride velocity, stride length CV, and stride velocity CV. Tumor diameter was negatively associated with stride time and swing time on the 2MWT; no such association existed between tumor diameter and FGA or DHI.

Conclusions

Instrumented insoles may unveil associations between VS tumor size and gait dysfunction that cannot be captured by standardized clinical assessments and self-reported questionnaires.

Truncal ataxia and the vestibulo spinal reflex. A historical review

The vestibulospinal pathway was described many years ago. Along with it, the vestibulospinal signs that are used for the diagnosis of vestibular disorders were described. In this work we summarize the history of the vestibulospinal pathway, the classic signs and the new signs that can be used in the diagnosis of vestibular disorders, paying special attention to truncal ataxia as a useful element to differentiate central from peripheral pathology.

Change of gait after unilateral vestibular neuritis: a prospective longitudinal observation study

Although symptoms of unilateral vestibular neuritis (uVN) resolve spontaneously within several weeks, recovery of gait function has unclearness in gait parameter changes and mediolateral stability improvements. In addition, prospective longitudinal studies on gait parameters after uVN are lacking. This study was conducted to reveal longitudinal change of gait function after acute uVN and to help the precise rehabilitation planning. Twenty three participants with uVN and 20 controls were included. 3D gait analyses were conducted three times after uVN onset at monthly intervals. From the gait analysis data, spatio-temporal parameters, inclination angle (IA) representing the relationship between center of mass (CoM) and center of pressure (CoP) in the frontal plane, and IA variability were obtained. Time effects on gait metrics were tested. Walking speed of participants with uVN improved significantly between the 1st and 3rd tests, but they were not significantly different to that of control, even in the 1st test. The step width of participants with uVN was significantly larger than that of control in the 1st test and improved significantly in the 2nd test. Variability of IA in affected side was significantly larger than that in controls in the 1st test and improved significantly in the 3rd test compared to the 1st test. Improvement of overall gait function and mediolateral stability during gait continued after acute stage of uVN (two months from onset in this study). Rehabilitation intervention should be continued after the acute stage of uVN to enhance appropriate adaptation in gait.

Development of a Computerized Device for Evaluating Vestibular Function in Locomotion: A New Evaluation Tool of Vestibular Hypofunction

To evaluate vestibular function in the clinic, current assessments are applied under static conditions, such as with the subject in a sitting or supine position. Considering the complexities of daily activities, the combination of dynamic activities, dynamic visual acuity (DVA) and postural control could produce an evaluation that better reflects vestibular function in daily activities.

Objective: To develop a novel sensor-based system to investigate DVA, walking trajectory, head and trunk movements and the chest-pelvis rotation ratio during forward and backward overground walking in both healthy individuals and patients with vestibular hypofunction.

Methods: Fifteen healthy subjects and 7 patients with bilateral vestibular hypofunction (BVH) were recruited for this study. Inertial measurement units were placed on each subject's head and torso. Each subject walked forward and backward for 5 m twice with 2 Hz head yaw. Our experiment comprised 2 stages. In stage 1, we measured forward (FW), backward (BW), and medial-lateral (MLW) walking trajectories; head and trunk movements; and the chest-pelvis rotation ratio. In stage 2, we measured standing and locomotion DVA (loDVA). Using Mann–Whitney U-test, we compared the abovementioned parameters between the 2 groups.

Results: Patients exhibited an in-phase chest/pelvis reciprocal rotation ratio only in FW. The walking trajectory deviation, calculated by normalizing the summation of medial-lateral swaying with 1/2 body height (%), was significantly larger (FW mean ± standard deviation: 20.4 ± 7.1% (median (M)/interquartile range (IQR): 19.3/14.4–25.2)in healthy vs. 43.9 ± 27. 3% (M/IQR: 36.9/21.3–56.9) in patients, p = 0.020)/(BW mean ± standard deviation: 19.2 ± 11.5% (M/IQR: 13.6/10.4–25.3) in healthy vs. 29.3 ± 6.4% (M/IQR: 27.7/26.5–34.4) in patients, p = 0.026), and the walking DVA was also significantly higher (LogMAR score in the patient group [FW LogMAR: rightDVA: mean ± standard deviation:0.127 ± 0.081 (M/IQR: 0.127/0.036–0.159) in healthy vs. 0.243 ± 0.101 (M/IQR: 0.247/0.143–0.337) in patients (p = 0.013) and leftDVA: 0.136 ± 0.096 (M/IQR: 0.127/0.036–0.176) in healthy vs. 0.258 ± 0.092 (M/IQR: 0.247/0.176–0.301) in patients (p = 0.016); BW LogMAR: rightDVA: mean ± standard deviation: 0.162 ± 0.097 (M/IQR: 0.159/0.097–0.273) in healthy vs. 0.281 ± 0.130 (M/IQR: 0.273/0.176–0.418) in patients(p = 0.047) and leftDVA: 0.156 ± 0.101 (M/IQR: 0.159/0.097–0.198) in healthy vs. 0.298 ± 0.153 (M/IQR: 0.2730/0.159–0.484) in patients (p = 0.038)].

Conclusions: Our sensor-based vestibular evaluation system provided a more functionally relevant assessment for the identification of BVH patients.

An Oculus Rift Assessment of Dynamic Balance by Head Mobility in a Virtual Park Scene: A Pilot Study

Postural sway does not differentiate between balance disorders. Head kinematics within a salient, immersive environment could potentially help identifying movement patterns that are unique to vestibular dysfunction. We describe a virtual park scene, where participants are asked to avoid a virtual ball approaching their head, to target dynamic balance and quantify head movement strategy. Sixteen patients with vestibular dysfunction and 16 healthy controls were wearing the Oculus Rift and performed the "park" scene on floor and stability trainers. Significant between-group differences emerged in head path (patients rotated their head sideways more), head acceleration (controls had higher acceleration, especially on translation movements), and peak frequency (controls peaked around the frequency of the ball whereas patients were variable). Those findings demonstrated good to excellent test-retest reliability. There were no significant between-group differences in postural sway parameters. Future studies should establish norms across different levels of balance dysfunction and investigate the underlying mechanism leading to the movement strategy observed.

Reduced vestibular function is associated with longer, slower steps in healthy adults during normal speed walking

BACKGROUND

Vestibular signals contribute to balance and walking. With aging, vestibular function declines and gait speed decreases. Vestibular loss contributes to decreasing gait speed, but this influence could be linked to spatial and/or temporal aspects of gait. We investigated the relationship between vestibular function (semicircular canal and otolith function) and spatial and temporal gait parameters in a cohort of adults.

METHODS

113 community-dwelling healthy adults (mean age 72.2 (14.6) years) participating in the Baltimore Longitudinal Study of Aging were tested. Horizontal semicircular canal (SCC) function was evaluated using quantitative vestibulo-ocular reflex gain. Otolith function was measured with cervical and ocular vestibular evoked myogenic potentials. Gait kinematics were collected during normal speed walking. Multiple linear regressions examined the association between spatial and temporal gait parameters and SCC and otolith function separately, controlling for age, gender, height, and either cadence (for spatial gait outcomes) or stride length (for temporal gait outcomes) to account for gait speed effects.

RESULTS

Vestibular SCC function was significantly associated with both spatial and temporal gait parameters. Every 0.1 decrease in SCC function resulted in longer stride length (β = -.04 m, p = 0.004), longer stance time (β = 15.8 ms, p < 0.003), and a slower cadence (β = -2.1 steps/minute, p < 0.001). Otolith function was not associated with any gait parameter.

CONCLUSIONS

Reduced horizontal SCC function was associated with longer, slower steps in a cohort of healthy adults. These results indicate that vestibular signals contribute to specific spatial and temporal aspects of gait thought to contribute to upright balance.

Characterizing Patients with Unilateral Vestibular Hypofunction Using Kinematic Variability and Local Dynamic Stability during Treadmill Walking

Here, we aimed to compare the unstable gait caused by unilateral vestibular hypofunction (UVH) with the normal gait. Twelve patients with UVH and twelve age-matched control subjects were enrolled in the study. Thirty-four markers were attached to anatomical positions of each participant, and a three-dimensional (3D) motion analysis system was used to capture marker coordinates as the participants walked on a treadmill. The mean standard deviation of the rotation angles was used to represent gait variability. To explore gait stability, local dynamic stability was calculated from the trunk trajectory. The UVH group had wider step width and greater variability of roll rotation at the hip than the control group (P < 0.05). Also, the UVH group had lower local dynamic stability in the medial-lateral (ML) direction than the control group (P < 0.05). By linear regression analysis, we identified a linear relationship between the short-term Lyapunov exponent and vestibular functional asymmetry. The result implies that UVH-induced asymmetry can increase posture variability and gait instability. This study demonstrates the potential for using kinematic parameters to quantitatively evaluate the severity of vestibular functional asymmetry. Further studies will be needed to explore the clinical effectiveness of such approaches.

3D body segment oscillation and gait analysis for vestibular disorders

OBJECTIVE

To investigate the patterns of gait and locomotion in three dimension space in patients with vestibular disorders.

METHODS

A 3D motion analysis system was employed to evaluate locomotor pattern and body's oscillation during gait under different conditions (normal, slow, fast speeds walking with eye open and normal speed walking with eyes closed) of nine patients with vestibular disorders. Twenty-one markers placed on the subject to record kinematics and locomotions of the head, spine and pelvis segments while walking. For each locomotor trial, the walking speed, locomotor patterns as well as the absolute angular dispersions of six segments around the roll, pitch and yaw axes were calculated to assess the equilibrium strategies of head, trunk and pelvis. Data was also recorded in 10 healthy subjects as control.

RESULTS

Patients' cadence is faster, and the stride time at normal walking speed is shorter than that of the controls (p<0.05). The body sway has also been documented some impairment in patients. With respect to the control, patients' oscillation of trunk around yaw axis at fast speed is less (p<0.05), which means the patient seems need less shoulder torsional movement. Moreover, the most prominent changes in patients are the sway of hip in roll, which is significant less than controls at fast (p<0.01), slow speed (p<0.01) and in eye-closed condition (p<0.05).

CONCLUSION

Our investigation corroborates those reports that higher velocities would be helpful for the increased gait stability in patients with vestibular disorders. And the body always try to keep the stability of head during gait, even under vestibular deficit conditions.

Effect of changing visual condition and frequency of horizontal oscillations on postural balance of standing healthy subjects

The goal of this study was to describe the movement pattern of the body-segment rotations of healthy subjects in the horizontal plane while they were standing on a supporting platform that imposed steady sinusoidal horizontal rotations under three visual conditions: (a) eyes closed with no instructions (EC-NI), (b) eyes open with instructions to gaze at a stationary black dot located at eye level on a wall surface about four meters in front of them (EO-WI), and (c) eyes closed with instructions to imagine looking at the same target (EC-WI). The selected input signal was a sinusoid with an amplitude of +/-45 deg at different frequencies equal to 0.25, 0.50 and 0.75 Hz, which were referred to as L, M and H. Bipedal balance measurements were taken in 10 adult subjects (mean age 30+/-9 years; three men and seven women). Subjects' kinematics were analyzed with an optoelectronic system. Under the three visual conditions, the movements of the pelvis, the trunk, and the head decreased and were inversely dependent on platform frequency; specifically, both the head and the trunk decreased their gain rotation of about 1.8-2.9 times from L to H, while the pelvis decreased its by about 1.3 times. However, the arm oscillations showed a gain and phase tendency opposite to that of the other body segments, with the gain rotation having increased of about 1.8-3.7 times from L to H. Comparing the three visual conditions, the finding suggests that the subjects were able to stabilize their head as a reference frame to maintain postural balance in a similar way under the EC-WI and EO-WI conditions. Instead, in the EC-NI trials, the subjects compensated less, in particular at the hip, the external perturbation producing higher absolute body rotations and lower relative body rotations. In fact, the head rotation was about four and three times the one showed in EC-WI and EO-WI, while for the trunk and the pelvis it was always equal to two and 1.5 times the correspondent rotation observed under the WI conditions. These results provide a quantitative assessment of compensatory balance reactions in healthy subjects to periodical horizontal perturbations.

Head control: volitional aspects of rehabilitation training in patients with multiple sclerosis compared with healthy subjects

OBJECTIVE

To investigate the role of voluntary mechanisms and motor learning in head stability and the impact of longitudinal biofeedback training in head control.

DESIGN

Crossover trial and single-subject research design.

SETTING

Neurorehabilitation research institute.

PARTICIPANTS

Head stability during treadmill gait was measured in healthy subjects and patients with multiple sclerosis (MS).

INTERVENTION

The experimental condition in which subjects walked on the treadmill was compared with that in which the head was voluntarily stabilized. In another experimental condition, augmented feedback of head displacement was provided by means of a laser mounted on the head that projected a laser beam on a screen. The motor learning was investigated with biofeedback training sessions. Positional feedback was represented by the laser beam, with subjects having to stabilize the beam while walking on the treadmill.

MAIN OUTCOME MEASURE

Head angular oscillation in the sagittal and frontal planes.

RESULTS

Results showed that on verbal request, healthy subjects and patients further stabilized the head during gait, especially in the sagittal plane. Short-term feedback of head displacement was no better than self-stabilization at improving head control. Conversely, the motor learning was evident in the rehabilitation protocol: after 10 to 15 training sessions, patients with MS showed a clinically relevant decrease of head angular oscillations.

CONCLUSIONS

Voluntary mechanisms play a role in head stabilization during gait. Augmented biofeedback of head displacement may be effective in reducing head oscillations.

Stroke affects the coordination and stabilization of head, thorax and pelvis during voluntary horizontal head motions performed in walking

OBJECTIVE

This study was conducted to investigate and compare the coordination and stabilization of axial segments during walking with and without horizontal voluntary head turns, in healthy (n=5) and hemiparetic (n=10) subjects.

METHODS

Subjects were instructed to turn the head as fast and as soon as possible in the direction indicated by an illuminated arrow signal (right, left or none) that was triggered at initial contact of the right (healthy) or paretic (hemiparetic) foot. Head, thorax, and pelvis motions were obtained from a 9-segment model using retro-reflective markers and a Vicon-512 system with 6 high-resolution cameras. Coordination of axial segments in the horizontal plane was characterized using cyclographs and cross-correlation analyses. Stabilization of the segments was quantified using root mean square (RMS) values of the segment's normalized acceleration profile.

RESULTS

The healthy subjects showed a direction-dependent modulation of axial segment coordination, with head turns toward and away from the stance limb favoring and hindering, respectively, the contra-rotational pattern of the thorax with respect to the pelvis during locomotion. Meanwhile, pelvis motions remained unaltered. This direction-specific modulation pattern was disrupted in the hemiparetic subjects, both in the spatial and temporal domains. Moreover, larger RMS values for head and thorax segments were observed in the hemiparetic groups, both with and without the superimposition of voluntary head motions.

CONCLUSIONS

The findings suggest that: (1) head rotations during walking modify axial segment coordination in a direction-specific manner, (2) the pelvic rotations associated with locomotion remained unaffected by head rotations and (3) stroke alters this coordination behavior, which may contribute to balance dysfunctions during locomotion.

Neck muscle vibration and spatial orientation during stepping in place in humans

Unilateral long-lasting vibration was applied to the sternomastoid muscle to assess the influence of asymmetric neck proprioceptive input on body orientation during stepping-in-place. Blindfolded subjects performed 3 sequences of 3 trials, each lasting 60 s: control, vibration applied during stepping (VDS), and vibration applied before stepping (VBS). VDS caused clear-cut whole body rotation toward the side opposite to vibration. The body rotated around a vertical axis placed at about arm's length from the body. The rotation did not begin immediately on switching on the vibrator. The delay varied from subject to subject from a few seconds to about 10 s. Once initiated, the angular velocity of rotation was remarkably constant (about 1 degrees /s). In VBS, at the beginning of stepping, subjects rotated for a while as if their neck were still vibrated. At a variable delay, the direction of rotation reversed, and the effects were opposite to those observed during VDS. Under no condition did head rotation, head roll, or lateral body tilt accompany rotation. The results confirm and extend the notion that the neck proprioceptive input plays a major role in body orientation during locomotion. The body rotation does not seem to depend on the same mechanisms that modify the erect posture; rather, the asymmetric neck input would seem to modify the egocentric body-centered coordinate system.