Novel Virtual Reality Technique Improves Pain, Motor Function

Batya Swift Yasgur MA, LSW

July 25, 2018

Heartbeat-enhanced virtual reality (HEVR) can reduce pain and improve motor limb function in patients with complex regional pain syndrome (CRPS), new research suggests.

HEVR improved symptoms of pain and motor limb function and modulated heart rate variability (HRV), a physiologic pain marker — effects that were absent in healthy control patients or individuals with CRPS who received a sham virtual reality (VR) condition.

"Integrating online cardiac physiology and multisensory stimulation with immersive VR technology, we designed a novel digital therapy for patients with CRPS that reduces pain, improves limb function, and modulates a physiological pain marker without applying any touch or movement to the patient's limb," lead author Marco Solcá, MD, from the Department of Mental Health and Psychiatry, University Hospital, and the Laboratory of Cognitive Neuroscience, University of Geneva, told Medscape Medical News.

HEVR "reduces pain without any need for tactile stimulation or movement, avoiding the risk of allodynia, and thus it can be used in most...patients with chronic pain, including those with allodynia or somatosensory deficit," he said.

The study was published online July 6 in Neurology.

Novel Rehabilitative Tool

"Pain is inextricably linked to the body and, in the case of chronic pain…often associated with abnormalities in the central representation of painful body parts," the authors write.

Recent research in cognitive neuroscience suggests that "altering the central representation of the body through multisensory bodily inputs, such as visuotactile in the rubber hand illusion...may be of relevance for the understanding or treatment of pain," they add.

Typical multisensory stimulation procedures are often not feasible in patients with chronic pain because movement of the affected limb, or even gentle touch, may increase pain.

However, "[m]odulation of bodily experience can be also be induced without any tactile stimulation by coupling visual information about the seen hand with cardiac signals," the authors note.

In addition, there may be direct central interactions between pain processing and heart-related processing.

The researchers combined the benefits of cardiovisual stimulation with those of immersive VR technology to "create a new, fully automated analgesic solution for [CRPS]."

"Because it remains extremely challenging to alleviate chronic pain, patients frequently go from doctor to doctor, desperately seeking help for relief," Solcá said.

"Recent advances in neuroscience and engineering have motivated new technology-based interventions to override this major health problem, but because of partially limited success rates and the inherent invasiveness of many of these latter treatments, novel rehabilitation technology for chronic pain [is] still needed," he continued.

"The present study describes, tests, and proves the efficacy of this novel rehabilitative tool — HEVR — in a group of patients suffering from CRPS," he added.

Virtual Hand

The researchers exposed 24 patients with upper limb CRPS after upper limb trauma or stroke and 24 age- and sex-matched healthy control patients (14 women; mean ± SD age, 50.3 ± 13.5 years; range, 27 - 80 years) to a virtual environment, during which they were presented with a realistic three-dimensional depiction of their affected hand, flashing synchronously with their own online-detected heartbeat.

The rubber hand illusion setup was adapted for HEVR design.

Patients received a clinical assessment consisting of medical interview and measures of hand edema and pain severity.

Pain ratings were measured using the vertical visual continuous analog scale (VAS), grip strength was measured through the Jamar test, and HRV was calculated using specific HRV analysis software.

Of the patients, 19 presented with spontaneous pain; 18 were physically able to perform the force strength test, and 14 performed both (ie, included in correlation analysis between pain rating and Jamar).

Participants were studied under synchronous and asynchronous conditions that were repeated 3 times consecutively (ie, 3 blocks of the same condition).

Baseline measurements of grip strength and subjective pain were taken, and then participants sat at a table, where they were assisted in putting on the VR headset, individually adjusted and calibrated for stereoscopic vision.

Participants were instructed to place both of their "real" hands in a lateral position and to avoid hand movements.

At the beginning of each block, a "virtual hand" appeared at the center of the screen and the experimenter moved it toward the real hand until the participant reported that the virtual and real positions of the hands matched.

Each block started with 3 proprioceptive measurements, followed by HEVR stimulation, during which participants were requested to fixate the virtual hand that was flashing in synchrony (or, in the case of control conditions, in asynchrony) with their own heartbeat.

Drift measurements were recorded for 3 times, and then, after the conclusions of each block, the VR headset was removed and the participant indicated the subjective pain level.

"Sounds Like Magic"

Across the 3 experimental blocks, there was a decrease in pain ratings in synchronous vs asynchronous control stimulation (linear mixed model; F 1,94.09 = 4.63; P = .033; βvisual feedback: synchronous = −0.93; standard error of the mean, 0.14).

The researchers found a visual feedback × session interaction (F 1,17 = 5.35; P = .034; d = 0.54) for grip strength, with a further analysis revealing that grip strength increased after synchronous stimulation compared with baseline, whereas no significant change was observed after asynchronous control stimulation.

In the patient group, HRV was higher during the blocks of synchronous vs asynchronous control stimulation, and when the researchers conducted a correlation analysis, they found that the more subjective pain was reduced, the more patients' HRV increased (t[17] = −2.43; r = −0.53; P = .03).

Patients who were receiving pharmacotherapy for CRPS had a stronger response to HEVR than did those who were pharmacologically untreated.

The researchers found no difference in either force strength or HRV between the conditions in healthy control patients. None of the healthy control patients reported pain during either stimulation condition.

"At first sight, it may appear surprising that such 'cardiovisual touches' can function as therapy for pain, and sounds a bit like magic," said Solcá. "But it is based on basic research in cognitive science and neuroscience pathways that guided our research approach."

He said he was surprised that "pain and pain markers increased already after such short sessions of a few minutes. Future therapies will apply this for longer periods."

A Big Step

Commenting on the study for Medscape Medical News, Michael Villiger, PhD, from the Spinal Cord Injury Center Research, Balgrist University Hospital, Zurich, Switzerland, who was not involved with the study, said the authors "presented a well-written and prepared paper on a study on a relevant topic."

The researchers "combined the well-known rubber hand illusion technique, used already to treat pain in subjects with spinal cord injury or phantom limbs, with online-detected heartbeats," which is a "pretty nice way to avoid application or painful bodily cues," he said.

The findings of the study "can be seen as a big step towards a better understanding of analgesic effects in subjects with CRPS and other chronic pain conditions and their treatment."

Solcá added, "We are at the beginning of VR therapies for pain. VR and related media will probably be in every household in the very near future, further underscoring the potential future impact of our results."

Support for this work was provided by grants from the Swiss National Science Foundation, the International Research Foundation for Paraplegia, and the Bertarelli Foundation. Solcá and coauthors and Villiger have disclosed no relevant financial relationships.

Neurology. Published online July 6, 2018. Abstract

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