Poster D8 - Arm Swing Responses to Walking Perturbations in People with Vestibular Hypofunction.

Thursday, October 24, 2024

10:00 AM - 11:00 AM EST

Location: Exhibit Hall E, F & G

Presenting Author(s)

Colby M. V Shores

Undergraduate Research Assistant
University of Pittsburgh
Penfield, New York, United States

Co-Author(s)

MK

Michelle Karabin

PhD Candidate
University of Pittsburgh, United States

Last Author(s)

MR

Mark Redfern, PhD

Professor
University of Pittsburgh, United States

Introduction: Walking is naturally unstable and 50% of falls occur during gait [1]. To maintain balance, the body integrates sensory signals from the visual, somatosensory, and vestibular systems. Thus, sensory impairments, such as vestibular hypofunction, can impair walking balance [2]. People with vestibular hypofunction (PwVH) have poor stability during steady state walking and in response to perturbations, where PwVH take longer to recover compared to healthy adults [3].

In response to perturbations, arm movements contribute directly to the recovery of stability in gait [4]. Moreover, corrective arm swing during the reactive phase of a perturbation allows for more favorable foot placement [5]. These findings suggest that arm swings have an impact on global gait stability; however, research detailing PwVH’s use of arm swings during walking has not been studied.

The purpose of this work is to identify differences in arm swing between healthy adults and PwVH in response to mechanical disturbances during walking. We hypothesized that in comparison to healthy adults, PwVH would (1) exhibit larger arm swing responses and (2) have slower arm swing reactions to perturbations. These findings can impact rehabilitation efforts aimed at improving dynamic and reactive stability in this population.

Materials and

Methods: This study is a secondary analysis of earlier work [6]. Fourteen healthy control (HC) participants and nine PwVH walked with and without perturbations. Arm swing kinematics were recorded using a fourteen-camera motion capture system (Vicon) and a full body Plug-In Gait marker set. Participants first completed three trials of unperturbed walking. For subsequent trials, on the third right heel strike, participants were subject to a perturbation, where the floor was shifted 6.5 cm in the medial or lateral direction (See [6] for details on device used to deliver perturbation). Participants were exposed to each perturbation three times and the order was randomized.

Arm swing responses were compared across HCs, well-compensated PwVH (wPwVH) and poorly compensated PwVH (pPwVH). PwVH were divided into wPwVH (n=6) and pPwVH (n=3) using a clinical gait test (Functional Gait Assessment [7]). Arm swing responses to perturbations were evaluated by looking at the deviation of the wrist marker from the participant’s center of mass (CoM) following a perturbation, with the trajectory from unperturbed walking subtracted off. We examined responses in the vertical and mediolateral directions for both arms. The magnitude of the arm responses were evaluated by looking at the maximum displacement of the wrist from the CoM. The response timing was quantified by the time the maximum displacement occurred post-perturbation.

Differences were identified across the three groups using an ANOVA or the non-parametric equivalent for not normally distributed variables. Statistical analysis was performed using MATLAB.

Results, Conclusions, and Discussions: HCs and wPwVH had similar magnitude and timing of arm responses following both perturbation types. Therefore, we focus on comparing HCs and pPwVH. Following lateral perturbations, HCs and pPwVH displaced both arms in a lateral superior direction (Fig 1a, 1b). pPwVH tended to have larger vertical wrist displacement compared to HCs, but this trend was influenced by one participant. Following medial perturbations, HCs moved both arms in a medial superior direction (Fig 1e). pPwVH again moved the arms in a lateral superior direction (Fig 1f), with greater vertical displacement of the contralateral arm (p = 0.08, Fig 1h) and greater lateral displacement of the ipsilateral arm (p = 0.03, Fig 1g) compared to HCs. There were no group differences in the timing of the maximum arm displacement for either perturbation type.

The larger arm displacement post-perturbation is consistent with exaggerated, or hypermetric, postural responses previously seen in PwVH [8]. The similar response timing between HCs and PwVH also echoes previous work, reinforcing that therapists should focus on calibrating postural responses as opposed to addressing delayed responses [8].

Beyond differences in response magnitude, there were differences in response movement patterns. Following lateral perturbations, HCs and pPwVH raised their arms laterally and superiorly, thus increasing their moment of inertia and slowing the angular momentum generated by the perturbation. Following medial perturbations, HCs moved their arms medially and superiorly, generating angular momentum to counteract the perturbation, which has been described as a preventative strategy (i.e. actions aimed at preventing a fall) [9]. In contrast, pPwVH adopted a protective strategy, whereby the lateral superior arm response prepares to protect the body in case of a fall [9]. This may indicate a lack of balance confidence in pPwVH that should be addressed in physical therapy interventions.

In addition to the small number of patients, one limitation was that this study did not investigate how differences in arm swing impact balance recovery. Future studies should investigate how arm swing strategies affect stability in order to design interventions using arm swing to improve balance in this population.

Acknowledgements (Optional): This work was supported by the National Institute On Deafness And Other Communication Disorders of the National Institutes of Health under Award Number F31DC020110.

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