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

Full-body kinematics and head stabilisation strategies during walking in patients with chronic unilateral and bilateral vestibulopathy

Chronic imbalance is a frequent and limiting symptom of patients with chronic unilateral and bilateral vestibulopathy. A full-body kinematic analysis of the movement of patients with vestibulopathy would provide a better understanding of the impact of the pathology on dynamic tasks such as walking. Therefore, this study aimed to investigate the global body movement during walking, its variability (assessed with the GaitSD), and the strategies to stabilise the head (assessed with the head Anchoring Index). The full-body motion capture data of 10 patients with bilateral vestibulopathy (BV), 10 patients with unilateral vestibulopathy (UV), and 10 healthy subjects (HS) walking at several speeds (slow, comfortable, and fast) were analysed in this prospective cohort study. We observed only a few significant differences between groups in parts of the gait cycle (shoulder abduction-adduction, pelvis rotation, and hip flexion-extension) during the analysis of kinematic curves. Only BV patients had significantly higher gait variability (GaitSD) for all three walking speeds. Head stabilisation strategies depended on the plan of motion and walking speed condition, but BV and UV patients tended to stabilise their head in relation to the trunk and HS tended to stabilise their head in space. These results suggest that GaitSD could be a relevant biomarker of chronic instability in BV and that the head Anchoring Index tends to confirm clinical observations of abnormal head-trunk dynamics in patients with vestibulopathy while walking.

The minimal clinically important difference for gait speed in significant unilateral vestibular hypofunction after vestibular rehabilitation

Gait speed is a valid measure of both physical function and vestibular health. Vestibular rehabilitation is useful to improve gait speed for patients with vestibular hypofunction, yet there is little data to indicate how changes in gait speed reflect changes in patient-reported health outcomes. We determined the minimal clinically important difference in the gait speed of patients with unilateral vestibular hypofunction, mostly due to deafferentation surgery, as anchored to the Dizziness Handicap Index and the Activities Balance Confidence scale, validated using regression analysis, change difference, receiver-operator characteristic curve, and average change methods. After six weeks of vestibular rehabilitation, a change in gait speed from 0.20 to 0.34 m/s with 95% confidence was required for the patients to perceive a significant reduction in perception of dizziness and improved balance confidence.

Characterizing stroke-induced changes in the variability of lower limb kinematics using multifractal detrended fluctuation analysis

Movement variability reflects the adaptation of the neuromuscular control system to internal or external perturbations, but its relationship to stroke-induced injury is still unclear. In this study, the multifractal detrended fluctuation analysis was used to explore the stroke-induced changes in movement variability by analyzing the joint angles in a treadmill-walking task. Eight healthy subjects and ten patients after stroke participated in the experiment, performing a treadmill-walking task at a comfortable speed. The kinematics data of the lower limbs were collected by the motion-capture system, and two indicators, the degree of multifractality (α) and degree of correlation [h(2)], were used to investigate the mechanisms underlying neuromuscular control. The results showed that the knee and ankle joint angles were multifractal and persistent at various scales, and there was a significant difference in the degree of multifractality and the degree of correlation at the knee and ankle joint angles among the three groups, with the values being ranked in the following order: healthy subjects < non-paretic limb < paretic limb. These observations highlighted increased movement variability and multifractal strength in patients after stroke due to neuromotor defects. This study provided evidence that multifractal detrended analysis of the angles of the knee and ankle joints is useful to investigate the changes in movement variability and multifractal after stroke. Further research is needed to verify and promote the clinical applications.

Stabilization demands of walking modulate the vestibular contributions to gait

Stable walking relies critically on motor responses to signals of head motion provided by the vestibular system, which are phase-dependent and modulated differently within each muscle. It is unclear, however, whether these vestibular contributions also vary according to the stability of the walking task. Here we investigate how vestibular signals influence muscles relevant for gait stability (medial gastrocnemius, gluteus medius and erector spinae)-as well as their net effect on ground reaction forces-while humans walked normally, with mediolateral stabilization, wide and narrow steps. We estimated local dynamic stability of trunk kinematics together with coherence of electrical vestibular stimulation (EVS) with muscle activity and mediolateral ground reaction forces. Walking with external stabilization increased local dynamic stability and decreased coherence between EVS and all muscles/forces compared to normal walking. Wide-base walking also decreased vestibulomotor coherence, though local dynamic stability did not differ. Conversely, narrow-base walking increased local dynamic stability, but produced muscle-specific increases and decreases in coherence that resulted in a net increase in vestibulomotor coherence with ground reaction forces. Overall, our results show that while vestibular contributions may vary with gait stability, they more critically depend on the stabilization demands (i.e. control effort) needed to maintain a stable walking pattern.

Relations between gait characteristics and subjective visual vertical results in young adults

OBJECTIVE

Subjective visual vertical (SVV) deviation can indicate impairments of motion perception and spatial orientation in individuals with vestibular disorders. This study investigated the influence of SVV on tandem gait ability by assessing differences between temporal, spatial, and kinematic characteristics in young adults.

METHODS

We recruited sixteen young adults with increased SVV and 17 age-matched control subjects. All subjects recruited for this study were with no history of neurological or musculoskeletal diseases. Knee and hip-joint kinematic data, spatio-temporal parameters, and gait variability were measured during tandem gait.

RESULTS

Stride time variability and stride velocity variability were significantly greater in the experimental group than the control group (p < 0.05). In addition, a significant correlation was observed between stride time variability and SVV results (r = 0.345, p < 0.05). However, hip and knee joint angles were non-significantly different in the experimental and control groups (p > 0.05) and spatio-temporal parameters were similar between the two groups (p > 0.05).

CONCLUSION

Stride time variability and stride velocity variability during tandem gait were significantly different in the experimental and control groups. We presume that increased SVV deviation is related to greater gait variability during tandem gait.

Impact of visual signals on axial segmental control during walking in patients with vestibular disorder and healthy persons

Head and trunk control during standing in patients with vestibular disorder may depend on intact visual signal to override vestibular disturbance. It is unknown if such process during walking would change. Therefore, the aims of this study were to quantify (1) head and trunk control in healthy participants (HPs) and patients with unilateral vestibular hypofunction (UVH) during walking with and without visual manipulation; and (2) the correlation/association between vestibular function and head/trunk control during walking with visual manipulation in patients. Seventeen UVH patients and 15 HPs completed all the tests. They participated in the caloric test, which was used to examine vestibular function, and walked on a treadmill with and without visual manipulation. Head and trunk angular displacement and velocity were primary outcome measures, deviation of center of mass and step variability were secondary. Head roll angular displacement (7.38° ± 1.38 [mean ± SE] v.s. 12.95° ± 1.48, p = 0.004) and head-trunk correlation (in the pitch/sagittal plane: 0.22 ± 0.05 v.s. 0.38 ± 0.05, roll/frontal plane: 0.35 ± 0.06 v.s. 0.55 ± 0.06, p < 0.05) were significantly lower in patients compared to HPs. Head pitch angular velocity (8.58°/s ± 2.17 v.s. 14.23°/s ± 1.22, p = 0.026) and step width variability (0.075 ± 0.010 v.s. 0.083 ± 0.009, p = 0.04) increased with visual manipulation only in patients. No significant correlation/association was found between vestibular function and head/trunk control. Lower head-trunk correlation in patients suggests an independent head-trunk control strategy in response to vestibular impairment. Visual input could be used by patients to compensate for vestibular disturbance for head control and foot placement. Severe UVH may not lead to worse postural control compared to mild disorder.