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The Effect of Prosthetic Feedback on the Strategies and Synergies Used by Vestibular Loss Subjects to Control Stance

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The Effect of Prosthetic Feedback on the Strategies and Synergies Used by Vestibular Loss Subjects to Control Stance

Flurin Honegger et al. J Neuroeng Rehabil.

Abstract

Background: This study investigated changes in stance movement strategies and muscle synergies when bilateral peripheral vestibular loss (BVL) subjects are provided feedback of pelvis sway angle.

Methods: Six BVL (all male) and 7 age-matched male healthy control (HC) subjects performed 3 stance tasks: standing feet hip width apart, eyes closed, on a firm and foam surface, and eyes open on foam. Pelvis and upper trunk movements were recorded in the roll and pitch planes. Surface EMG was recorded from pairs of antagonistic muscles at the lower leg, trunk and upper arm. Subjects were first assessed without feedback. Then, they received training with vibrotactile, auditory, and fall-warning visual feedback during stance tasks before being reassessed with feedback.

Results: Feedback reduced pelvis sway angle displacements to values of HCs for all tasks. Movement strategies were reduced in amplitude but not otherwise changed by feedback. These strategies were not different from those of HCs before or after use of feedback. Low frequency motion was in-phase and high frequency motion anti-phasic. Feedback reduced amplitudes of EMG, activity ratios (synergies) of antagonistic muscle pairs and slightly reduced baseline muscle activity.

Conclusions: This is the first study demonstrating how vestibular loss subjects achieve a reduction of sway during stance with prosthetic feedback. Unchanged movement strategies with reduced amplitudes are achieved with improved antagonistic muscle synergies. This study suggests that both body movement and muscle measures could be explored when choosing feedback variables, feedback location, and patient groups for prosthetic devices which reduce sway of those with a tendency to fall.

Figures

Figure 1
Figure 1
Schema showing the placement of the trunk and pelvis gyroscopes on the subject’s back.
Figure 2
Figure 2
Improvement in roll sway for a BVL subject when provided feedback of pelvis sway angle. The upper four panels show the sway angles in degrees of the pelvis and upper trunk while standing feet shoulder width apart, eyes closed on foam without feedback, the lower panels with feedback. a. 50 seconds of the original unfiltered traces of upper trunk and pelvis sway with general trend lines. b. The same traces as in a. after removing the general trend and low pass filtering. c. 20 seconds of the same traces as in a. after removing the general trend and band pass filtering. d. 5 seconds of the same traces as in a. after removing the general trend and high pass filtering.
Figure 3
Figure 3
Group angle and angular velocity means of 90% pelvis sway ranges with and without feedback. The column height represents the mean group pelvis angle or angular velocity for each task. Values are shown for stance tasks on foam with eyes open (EOF) or closed (ECF). The vertical lines above each column indicate the standard error of the means. BVL stands for bilateral vestibular loss group, HC for the healthy control group. BVL means with feedback marked with * have a significant decrease compared to means without feedback. If the means of BVL subjects with feedback remained significantly greater than healthy controls the BVL values are marked with #.
Figure 4
Figure 4
Mean regression slopes of trunk angles with respect to pelvis angles. Mean regression slopes are depicted for the two foam tasks, eyes open and closed, without and with biofeedback. The upper panels show the slope angles in pitch, the lower panels in roll. a. slope values for low-pass filtered angle values, b. band-pass filtered angles and c. for high-pass filtered values. The bullet symbol marks the mean value of the slope; the vertical line depicts the 95% confidence intervals of the mean.
Figure 5
Figure 5
Regression slopes of trunk versus pelvis movements of a BVL subject standing eyes closed on foam with and without feedback. Regression slopes after low-pass filtering (LP) and band-pass filtering (BP) of trunk and pelvis sway angle traces are shown. The upper panel shows the slopes without biofeedback, the lower ones with feedback. On the left are the low pass regressions, on the right the band-pass regressions.
Figure 6
Figure 6
EMG activity with and without feedback. a: Mean group PSDs of BVL EMG activity with and without feedback compared to mean activity of controls without feedback for the task of standing eyes closed on foam. The upper grey line is mean BVL activity without feedback, the lower black line is the mean activity with feedback. Triangles indicate those frequency bins where the PSD values were significantly lower with feedback (p < 0.05). The grey dotted lines indicate the mean of healthy control values (without feedback). The mean values of BVL subjects with feedback were not significantly different from controls, except for tibialis anterior. b: Mean group activation ratios of pairs of ankle (tibialis/soleus) and trunk (paraspinals/obliques) muscles compared for BVL subjects with and without feedback and to controls. The ratios at each frequency are of PSD values shown at the same frequency in a. For example, the tibilalis anterior/soleus ratio for BVLs at 1.9 Hz is the ratio of the PSD values of the thick lines in A for tibialis and soleus. The vertical bars mark the 95% confidence intervals. Asterisks (*) mark significant (p < 0.05) differences of BVL subjects with and without feedback, while gate symbols (#) mark trends (p < 0.1).
Figure 7
Figure 7
EMG activity of a BVL subject with and without feedback for the task standing eyes closed on foam. The ankle and trunk muscle activity without feedback is shown in the upper traces of each panel, the activity from the same muscles with feedback is shown inverted in each panel.

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