By Allison Proffitt
March 26, 2020 | Researchers at the University of North Carolina, Chapel Hill, have built a virtual reality system that simulates falling while subjects walk on a stable treadmill. By measuring how different subjects respond, they have uncovered clear differences that could have lasting impacts on how we treat and rehabilitate balance issues. The research was published earlier this month in PLoS One (DOI: 10.1371/journal.pone.0230202).
Jason Franz, PhD, assistant professor in the UNC/NC State Joint Department of Biomedical Engineering, has been studying age-related falls for several years. His work has focused on how the elderly might be able stay steady and rehabilitate from falls that have already happened. But with collaborator Jacob J. Sosnoff, Department of Kinesiology and Community Health, University of Illinois at Urbana-Champaign, Franz wondered if similar research might help predict balance issues for patients with the neurodegenerative disease multiple sclerosis.
Balance and gait problems are common symptoms of multiple sclerosis (MS), and even patients with little or no apparent disability may already be at twice the risk of falling, on average, compared to people who don't have MS. Generally our brain relies on many sensors when we walk including force sensors in our feet. In people with MS, force sensors can become less reliable, so people need to rely more on other channels, especially vision. People who have an MS diagnosis fall at least once per year on average.
Virtual Hallway, Real Balance Issues
To see if they could predict balance issues before serious falls, the team built a semi-circular theatre screen that subjects watch while walking on a treadmill wearing a safety harness. The VR scene depicted a hallway down which the subject seemed to be walking. Researchers could turn on side-to-side wobbles in the scene, creating the illusion for each subject that he or she was becoming unstable, triggering a corrective reaction that could be measured as a change in gait and foot placement.
“If you’re an otherwise healthy young person, you aren’t really susceptible to those sorts of simulated falls, or simulated instability,” Franz told Diagnostics World. “But in our research in older adults with a history of falls—and in this most recent paper in people with multiple sclerosis—the susceptibility is much, much higher.”
The team tested 14 people with MS that had not experienced any balance issues yet, and 14 age-matched non-MS volunteers. All the participants walked on the treadmill both with and without the falling simulations playing, and researchers gathered data on their step placement, frequency, and other differences in gait.
“We measured the differences in the response to these virtual reality perturbations,” Franz explained. “We were only really able to distinguish which group of our subjects had the disease and which did not when the virtual reality oscillations were turned on.”
But when the hallway oscillations were on, there was a marked difference.
“If you were standing behind a person [without MS] and we turned on the balance challenge with the virtual reality, you wouldn’t really be able to distinguish any differences in their walking pattern. Then imagine standing behind a person that does have the disease, and what you’d start to notice is their step placement would become incredibly variable as they’re trying to correct the sense of falling from one step to the next. There might be some crossover steps; they would sort of move from one side of the treadmill to the other side of the treadmill. Their balance is very disrupted,” Franz explained.
The platform isn’t appropriate for initial diagnosis of multiple sclerosis, but Franz believes that a VR-based test like this, after further study and development, could be incorporated into consumer-grade VR headsets and used widely in neurology clinics to alert existing MS patients earlier to their balance impairments.
The group has used the same hallway perturbations as balance therapy in its work with older adults. “They give people the opportunity to practice balancing. From one step to the next you’re needing to make those corrections that you’d have to make if there was a threat to your balance in the community as you were walking around.”
This is their first study leveraging what they’ve learned for patients with more acute clinical pathology.
“I think it might be sort of opening the door and showing other people in the research and clinical communities opportunities in which virtual reality might help in what they do, for example with their patients with balance disorders.”