Virtual reality detects early impairment in walking balance

By Christine Kilgore

Researchers seeking simple and sensitive ways to detect walking balance impairments early on – before such impairments become clinically apparent in patients with multiple sclerosis (MS) – have reported success in the lab with the use of a virtual reality–based system that assesses one’s responses to subtle visual perturbations while walking.

The system uncovered “preclinical walking balance deficits” in a small group of patients with relapsing remitting MS. The researchers are planning further research and hope to develop a simplified version that could provide clinicians with an objective – and actionable – assessment of walking balance impairment in a single test.

“We’re hoping that we can detect small, subtle impairments earlier and then intervene earlier, so that we can minimize any deficits that might crop up,” said Jacob J. Sosnoff, PhD, a kinesiologist in the department of kinesiology and community health at the University of Illinois at Urbana-Champaign and a coinvestigator of the study, in an interview. The study was reported in March 2020 in PLoS One (2020 Mar 10;15[3]:e0230202).

A total of 14 individuals with MS and 14 age-matched controls walked several times on a treadmill while viewing a virtual hallway that was projected onto a semicircular curved screen positioned in front of the treadmill. On two of the three walking trials, the researchers applied optical flow perturbations to the foreground of the virtual hallway (in the mediolateral direction in one trial and in the anterior-posterior direction in the other).

Dr. Jacob J. Sosnoff

A biomedical engineering student stands in the floor-to-ceiling virtual hallway environment that was used to detect balance impairments that went undetected during normal unperturbed walking.
Image credit: Joint Department of Biomedical Engineering, UNC Chapel Hill and NC State University

Without any visual disturbances – during the normal walking trial – there were no significant differences between individuals with and without MS in step width, step length, variabilities in step width and length, and other traditional markers of gait and walking balance integrity.

But when walking in the presence of visual perturbations – especially those perturbations that flowed in the mediolateral direction – those with MS had significantly higher variability in foot placement, in sacrum position (reflecting trunk motion), and in another biomechanical measure of gait known as the margin of stability at heel-strike.

By using virtual reality, “we’re leveraging” the fact that visual feedback becomes more important for walking balance control as “proprioceptive sensors become more unreliable,” said Jason R. Franz, PhD, the study’s principal investigator, in an interview. Just as many older adults do, “individuals [with MS] rely a lot on vision to compensate [for impaired proprioceptive acuity] and tell their brains what kinds of corrections they should make from one step to the next.” Vision also can compensate for potentially balance-impairing vestibulopathies, which have been shown to affect both older adults and many patients with MS.

The visual-reality system “tricks the brain into thinking that [one is] experiencing a fall so that we can bring to the surface all of the underlying things that might eventually percolate up and cause a fall,” said Dr. Franz, of the joint department of biomedical engineering at the University of North Carolina at Chapel Hill and North Carolina State University.

Dr. Jason R. Franz

A 2015 meta-analysis of individual data from studies in the United States and three other countries concluded that approximately 56% of people with MS fell over the course of 3 months, and that 37% reported frequent falls. Even those who exhibit minimal or no disability on the Expanded Disability Status Scale are over twice as likely to fall as the general population, the study showed (Mult Scler. 2015;21[1]:92-100).

The study participants with MS “all had normal gait on traditional clinical gait measures – no obvious impairments,” said Dr. Sosnoff, who is also director of the Illinois Multiple Sclerosis Research Collaborative. “But with subtle visual perturbations, especially with stars going across the screen side to side at differing speeds, people start to sway more left to right. And the important thing is they don’t know they’re doing it.”

Dr. Franz, who developed the virtual reality–based system used in the study, plans to adapt it for use with consumer-grade virtual reality headsets so that it can be used in a neurologist’s or therapist’s practice as a detection tool – and, hopefully, as a training tool for corrective motor adjustment and balance improvement. “The work we’ve done so far is all about detection – to be able to say to someone with MS, you may be at [higher] risk of falls,” he said. “But you really want to be able to do something about it.”

Dr. Franz, whose research focuses largely on walking balance in older adults and age-related fall risk, said he’s encouraged by the findings from a similarly small study on optical flow perturbation training in older adults (J Neuroeng Rehabil. 2019;16[1]:81). With aging, there is a tendency to rely more on vision for balance and movement control, he added.

Using a similar virtual reality–based system of treadmill walking, the older adults “walked with prolonged exposure to these visual flow oscillations,” Dr. Franz said. “We just let them practice. We looked at their balance when they came into the lab. We looked at their immediate response to the onset of the visual perturbations. And then we looked at their balance at the end, after we turned off the perturbations.”

At the end, most outcomes returned to values observed during normal, unperturbed walking. The study offered proof of concept that there’s clinical benefit to using optical flow perturbations as a training tool. “We’re giving people the opportunity to practice the exact type of neuromuscular correction they’d need to use if something unexpected happened [while walking] in the community,” he said.

Image credit: Joint Department of Biomedical Engineering, UNC Chapel Hill and NC State University

With respect to MS, larger studies are needed to assess the technology in individuals with a wider range of ages, disease progression, and balance impairments, Dr. Franz and coinvestigators wrote in their paper.

“The presentation and progression of the disease can be so varied,” Dr. Franz said in the interview, and it may be that not everyone with MS will benefit from visual perturbation training. “With this pilot testing [completed], we need to do dose-response testing, for instance, and we need to look at different types of individuals with MS.”

The MS study was supported by a pilot grant from the National MS Society to Dr. Franz. Dr. Sosnoff and coinvestigators reported to PLoS One that they had no competing interests.