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Modulation of walking speed by changing optic flow in persons with stroke.

Lamontagne A, Fung J, McFadyen BJ, Faubert J - J Neuroeng Rehabil (2007)

Bottom Line: Two experiments were carried out on the same day.In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes.In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Physical and Occupational Therapy, McGill University and Jewish Rehabilitation Hospital Research Center (CRIR), Montreal, Canada. anouk.lamontagne@mcgill.ca

ABSTRACT

Background: Walking speed, which is often reduced after stroke, can be influenced by the perception of optic flow (OF) speed. The present study aims to: 1) compare the modulation of walking speed in response to OF speed changes between persons with stroke and healthy controls and 2) investigate whether virtual environments (VE) manipulating OF speed can be used to promote volitional changes in walking speed post stroke.

Methods: Twelve persons with stroke and 12 healthy individuals walked on a self-paced treadmill while viewing a virtual corridor in a helmet-mounted display. Two experiments were carried out on the same day. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes. In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed. Each test trial was paired with a control trial performed at comfortable speed with matching OF. For each of the test trials, subjects were instructed to walk the distance within the same time as during the immediately preceding control trial. VEs were controlled by the CAREN-2 system (Motek). Instantaneous changes in gait speed (experiment 1) and the ratio of speed changes in the test trial over the control trial (experiment 2) were contrasted between the two groups of subjects.

Results: When OF speed was changing continuously (experiment 1), an out-of-phase modulation was observed in the gait speed of healthy subjects, such that slower OFs induced faster walking speeds, and vice versa. Persons with stroke displayed weaker (p < 0.05, T-test) correlation coefficients between gait speed and OF speed, due to less pronounced changes and an altered phasing of gait speed modulation. When OF speed was manipulated discretely (experiment 2), a negative linear relationship was generally observed between the test-control ratio of gait speed and OF speed in healthy and stroke individuals. The slope of this relationship was similar between the stroke and healthy groups (p > 0.05, T-test).

Conclusion: Stroke affects the modulation of gait speed in response to changes in the perception of movement through different OF speeds. Nevertheless, the preservation of even a modest modulation enabled the persons with stroke to increase walking speed when presented with slower OFs. Manipulation of OF speed using virtual reality technology could be implemented in a gait rehabilitation intervention to promote faster walking speeds after stroke.

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Related in: MedlinePlus

Changes in gait speed as a function of changes in optic flow speed in a healthy subject (A) and subjects with stroke presenting with a slow (B) and fast (C) walking speed. Both gait speed and optic flow speed were expressed as ratios of the actual speed observed in the test trial as compared to control trial with matching gait and OF speeds.
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Figure 4: Changes in gait speed as a function of changes in optic flow speed in a healthy subject (A) and subjects with stroke presenting with a slow (B) and fast (C) walking speed. Both gait speed and optic flow speed were expressed as ratios of the actual speed observed in the test trial as compared to control trial with matching gait and OF speeds.

Mentions: Figure 4 represents examples of changes in walking speed as a function of changes in OF speed, as measured during Experiment 2. In healthy subjects and subjects with stroke, a negative linear relationship was generally observed between gait speed and OF speed, such that subjects walked faster at slower OFs. The gain of this relationship, as quantified by the slope between gait speed ratio vs. OF speed ratio, was similar between subjects with stroke and healthy controls (p > 0.05) (Figure 5). On average, the highest increments in speed observed at slow OFs reached 1.32 ± 0.25 and 1.44 ± 0.38 times comfortable gait speed values, respectively, in the healthy and stroke groups. Subjects with stroke who walked at slower comfortable speeds displayed steeper modulation slopes (R2 = 0.53, p < 0.05) and higher ratios of speed increment (R2 = 0.78, p < 0.05) than those who walked at faster initial speeds.


Modulation of walking speed by changing optic flow in persons with stroke.

Lamontagne A, Fung J, McFadyen BJ, Faubert J - J Neuroeng Rehabil (2007)

Changes in gait speed as a function of changes in optic flow speed in a healthy subject (A) and subjects with stroke presenting with a slow (B) and fast (C) walking speed. Both gait speed and optic flow speed were expressed as ratios of the actual speed observed in the test trial as compared to control trial with matching gait and OF speeds.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1913055&req=5

Figure 4: Changes in gait speed as a function of changes in optic flow speed in a healthy subject (A) and subjects with stroke presenting with a slow (B) and fast (C) walking speed. Both gait speed and optic flow speed were expressed as ratios of the actual speed observed in the test trial as compared to control trial with matching gait and OF speeds.
Mentions: Figure 4 represents examples of changes in walking speed as a function of changes in OF speed, as measured during Experiment 2. In healthy subjects and subjects with stroke, a negative linear relationship was generally observed between gait speed and OF speed, such that subjects walked faster at slower OFs. The gain of this relationship, as quantified by the slope between gait speed ratio vs. OF speed ratio, was similar between subjects with stroke and healthy controls (p > 0.05) (Figure 5). On average, the highest increments in speed observed at slow OFs reached 1.32 ± 0.25 and 1.44 ± 0.38 times comfortable gait speed values, respectively, in the healthy and stroke groups. Subjects with stroke who walked at slower comfortable speeds displayed steeper modulation slopes (R2 = 0.53, p < 0.05) and higher ratios of speed increment (R2 = 0.78, p < 0.05) than those who walked at faster initial speeds.

Bottom Line: Two experiments were carried out on the same day.In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes.In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Physical and Occupational Therapy, McGill University and Jewish Rehabilitation Hospital Research Center (CRIR), Montreal, Canada. anouk.lamontagne@mcgill.ca

ABSTRACT

Background: Walking speed, which is often reduced after stroke, can be influenced by the perception of optic flow (OF) speed. The present study aims to: 1) compare the modulation of walking speed in response to OF speed changes between persons with stroke and healthy controls and 2) investigate whether virtual environments (VE) manipulating OF speed can be used to promote volitional changes in walking speed post stroke.

Methods: Twelve persons with stroke and 12 healthy individuals walked on a self-paced treadmill while viewing a virtual corridor in a helmet-mounted display. Two experiments were carried out on the same day. In experiment 1, the speed of an expanding OF was varied sinusoidally at 0.017 Hz (sine duration = 60 s), from 0 to 2 times the subject's comfortable walking speed, for a total duration of 5 minutes. In experiment 2, subjects were exposed to expanding OFs at discrete speeds that ranged from 0.25 to 2 times their comfortable speed. Each test trial was paired with a control trial performed at comfortable speed with matching OF. For each of the test trials, subjects were instructed to walk the distance within the same time as during the immediately preceding control trial. VEs were controlled by the CAREN-2 system (Motek). Instantaneous changes in gait speed (experiment 1) and the ratio of speed changes in the test trial over the control trial (experiment 2) were contrasted between the two groups of subjects.

Results: When OF speed was changing continuously (experiment 1), an out-of-phase modulation was observed in the gait speed of healthy subjects, such that slower OFs induced faster walking speeds, and vice versa. Persons with stroke displayed weaker (p < 0.05, T-test) correlation coefficients between gait speed and OF speed, due to less pronounced changes and an altered phasing of gait speed modulation. When OF speed was manipulated discretely (experiment 2), a negative linear relationship was generally observed between the test-control ratio of gait speed and OF speed in healthy and stroke individuals. The slope of this relationship was similar between the stroke and healthy groups (p > 0.05, T-test).

Conclusion: Stroke affects the modulation of gait speed in response to changes in the perception of movement through different OF speeds. Nevertheless, the preservation of even a modest modulation enabled the persons with stroke to increase walking speed when presented with slower OFs. Manipulation of OF speed using virtual reality technology could be implemented in a gait rehabilitation intervention to promote faster walking speeds after stroke.

Show MeSH
Related in: MedlinePlus