Arian Vistamehr - Academia.edu (original) (raw)

Papers by Arian Vistamehr

An instrumented walker is an assistive device designed to assess the effects of upper-limb loadin... more An instrumented walker is an assistive device designed to assess the effects of upper-limb loading on gait characteristics. Such a device is used in conjunction with a motion analysis system, and electromyography (EMG) (i.e., muscle electrical activity) to gain a complete assessment of the patient's gait patterns during clinical interventions. In this work we developed an instrumented wireless walker using Commercial-Off-The-Shelf components aiming to determine a patient's weight dependency by measuring upper-limb loading at its handle bars during clinical rehabilitation studies. The device consists of a transmitter/receiver, force sensors, rechargeable 9V Nickel-Metal Hydride battery, microcontroller, 16×2 LCD screen, and a Hugo assistive walker. All components are housed in a 71/2” X 4” X 11/4” plastic enclosure and secured in an unobtrusive manner on the walker. The device was tested for accuracy and ease of use during real-time simultaneous data acquisition along with motion capture kinematics, EMG activity and overground force plate data recordings. Successful data acquisitions from these tests along with the advantages over the traditional wired walkers show the feasibility and benefit of using this novel device in future gait studies and in rehabilitation settings.

Topics in Stroke Rehabilitation, May 12, 2019

Background: While over half of stroke survivors recover the ability to walk without assistance, d... more Background: While over half of stroke survivors recover the ability to walk without assistance, deficits persist in the performance of walking adaptations necessary for safe home and community mobility. One such adaptation is the ability to walk or step backward. Post-stroke rehabilitation rarely includes backward walking (BW) assessment and BW deficits have not been quantified in post-stroke community ambulators. Objective: To quantify spatiotemporal and kinematic BW characteristics in post-stroke community ambulators and compare their performance to controls. Methods: Individuals post-stroke (n = 15, 60.1 ± 12.9 years, forward speed: 1.13 ± 0.23 m/s) and healthy adults (n = 12, 61.2 ± 16.2 years, forward speed: 1.40 ± 0.13 m/s) performed forward walking (FW) and BW during a single session. Step characteristics and peak lower extremity joint angles were extracted using 3D motion analysis and analyzed with mixed-method ANOVAs (group, walking condition). Results: The stroke group demonstrated greater reductions in speed, step length and cadence and a greater increase in double-support time during BW compared to FW (p < .01). Compared to FW, the post-stroke group demonstrated greater reductions in hip extension and knee flexion during BW (p < .05). The control group demonstrated decreased plantarflexion and increased dorsiflexion during BW, but these increases were attenuated in the post-stroke group (p < .05). Conclusions: Assessment of BW can unmask post-stroke walking impairments not detected during typical FW. BW impairments may contribute to the mobility difficulties reported by adults poststroke. Therefore, BW should be assessed when determining readiness for home and community ambulation.

Journal of Biomechanics, Jun 1, 2018

Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Communi... more Maintaining dynamic balance during community ambulation is a major challenge post-stroke. Community ambulation requires performance of steady-state level walking as well as tasks that require walking adaptability. Prior studies on balance control post-stroke have mainly focused on steady-state walking, but walking adaptability tasks have received little attention. The purpose of this study was to quantify and compare dynamic balance requirements during common walking adaptability tasks post-stroke and in healthy adults and identify differences in underlying mechanisms used for maintaining dynamic balance. Kinematic data were collected from fifteen individuals with post-stroke hemiparesis during steady-state forward and backward walking, obstacle negotiation, and step-up tasks. In addition, data from ten healthy adults provided the basis for comparison. Dynamic balance was quantified using the peak-to-peak range of whole-body angular-momentum in each anatomical plane during the paretic, nonparetic and healthy control single-leg-stance phase of the gait cycle. To understand differences in some of the key underlying mechanisms for maintaining dynamic balance, foot placement and plantarflexor muscle activation were examined. Individuals post-stroke had significant dynamic balance deficits in the frontal plane across most tasks, particularly during the paretic single-leg-stance. Frontal plane balance deficits were associated with wider paretic foot placement, elevated body center-of-mass, and lower soleus activity. Further, the obstacle negotiation task imposed a higher balance requirement, particularly during the trailing leg single-stance. Thus, improving paretic foot placement and ankle plantarflexor activity, particularly during obstacle negotiation, may be important rehabilitation targets to enhance dynamic balance during post-stroke community ambulation.

Journal of Biomechanics, Nov 1, 2021

Each year approximately one third of older adults fall and experience extensive musculoskeletal i... more Each year approximately one third of older adults fall and experience extensive musculoskeletal injuries and functional disabilities. An important element in maintaining dynamic balance is the regulation of whole-body angular momentum, which is achieved by proper foot placement with respect to the body center-of-mass as well as generation of appropriate ground reaction forces. Analyzing these quantities in younger and older adults may provide insight into differences in their underlying mechanics for maintaining dynamic balance. This study examined three-dimensional whole-body angular momentum in 13 healthy older (71.8 ± 8.3 years) and 9 younger (23.2 ± 2.8 years) adults walking at their self-selected and fastest-comfortable speeds. The older adults had a significantly higher range of frontal-plane angular momentum compared to the younger adults at both speeds, suggesting poorer mediolateral balance control. This difference was related to the older adults having a wider foot placement with respect to the body center-of-mass, which when combined with the vertical ground reaction force, created a higher destabilizing external moment during single-limb stance that acts to rotate the body towards the contralateral swing leg. To counteract this destabilizing moment, the older adults generated a higher hip abduction moment. There were no differences in the range of sagittal-and transverse-plane angular momentum between age groups at either speed. These results suggest that control of dynamic balance in the frontal-plane is more challenging than in the sagittal-plane for older adults and highlight the importance of proper weight transfer mechanisms and hip abductor force production for maintaining mediolateral balance during walking.

Journal of Biomechanics, May 1, 2019

Slow walking speed and lack of balance control are common impairments post-stroke. While locomoto... more Slow walking speed and lack of balance control are common impairments post-stroke. While locomotor training often improves walking speed, its influence on dynamic balance is unclear. The goal of this study was to assess the influence of a locomotor training program on dynamic balance in individuals post-stroke during steady-state walking and determine if improvements in walking speed are associated with improved balance control. Kinematic and kinetic data were collected pre-and post-training from seventeen participants who completed a 12-week locomotor training program. Dynamic balance was quantified biomechanically (peak-to-peak range of frontal plane whole-body angular-momentum) and clinically (Berg-Balance-Scale and Dynamic-Gait-Index). To understand the underlying biomechanical mechanisms associated with changes in angularmomentum, foot placement and ground-reaction-forces were quantified. As a group, biomechanical assessments of dynamic balance did not reveal any improvements after locomotor training. However, improved dynamic balance post-training, observed in a subgroup of 10 participants (i.e., Responders), was associated with a narrowed paretic foot placement and higher paretic leg vertical ground-reaction-force impulse during late stance. Dynamic balance was not improved post-training in the remaining seven participants (i.e., Non-responders), who did not alter their foot placement and had an increased reliance on their nonparetic leg during weightbearing. As a group, increased walking speed was not correlated with improved dynamic balance. However, a higher pre-training walking speed was associated with higher gains in dynamic balance post-training. These findings highlight the importance of the paretic leg weight bearing and mediolateral foot placement in improving frontal plane dynamic balance post-stroke.

Journal of Biomechanics, Jun 1, 2023

textMaintaining dynamic balance during walking is a major challenge in many patient populations i... more textMaintaining dynamic balance during walking is a major challenge in many patient populations including older adults and post-stroke hemiparetic subjects. To maintain dynamic balance, whole-body angular-momentum has to be regulated through proper foot placement and generation of the ground-reaction-forces. Thus, the overall goal of this research was to understand the mechanisms and adaptations used to maintain dynamic balance during walking by analyzing whole-body angular-momentum, foot placement and ground-reaction-forces in older adults and post-stroke subjects. The analysis of healthy older adults showed that they regulated their frontal-plane angular-momentum poorly compared to the younger adults. This was mainly related to the increased step width, which when combined with the dominant vertical ground-reaction-force, created a higher destabilizing external moment during single-leg stance. The results also suggested that exercise programs targeting appropriate foot placement and lower extremity muscle strengthening, particularly of the ankle plantarflexors and hip abductors, may enhance balance control in older adults. During post-stroke hemiparetic walking, ankle-foot-orthosis and locomotor therapy are used in an effort to improve the overall mobility. However, the analyses of healthy subjects walking with and without a solid ankle-foot-orthosis showed that they can restrict ankle plantarflexor output and limit the successful regulation of angular-momentum and generation of forward propulsion. Thus, the prescription of solid ankle-foot-orthosis should be carefully considered. The analysis of hemiparetic subjects walking pre- and post-therapy showed that locomotor training did not improve dynamic balance. However, for those subjects who achieved a clinically meaningful improvement in their self-selected walking speed, their change in speed was correlated with improved dynamic balance. Also, improved balance was associated with narrower mediolateral paretic foot placement, longer anterior nonparetic steps, higher braking ground-reaction-force peaks and impulses, higher (lower) propulsive ground-reaction-force peaks and impulses from the paretic (nonparetic) leg, and higher vertical ground-reaction-force impulses from both legs during the late stance. Further, simulation analyses of hemiparetic walking highlighted the importance of ankle plantarflexors, knee extensors and hip abductors in maintaining balance and revealed the existence of compensatory mechanisms due to the paretic leg muscle weakness. Collectively, these studies showed the importance of ankle plantarflexors and hip abductors in maintaining dynamic balance.Mechanical Engineerin

45th AIAA Aerospace Sciences Meeting and Exhibit, Jan 8, 2007

In this study it was determined whether or not a reduction was realized for thermal joint resista... more In this study it was determined whether or not a reduction was realized for thermal joint resistance a s a result of applying a TIM (Thermal Interface Material) , in particularly eGraf , at an interface formed between metals of various thermal conductivities. The level of this reduction was measured . In addition, the experimental data was compared against an existing analytical model. Experimental data was obtained in vacuum condition for Al 7075, Steel 1018, and Inconel samples with applied interface pressure s ranging from 0.15 -2.7 MPa. The experimental data showed that thermal joint resistance was reduced fo r all metals with application of eGraf TIM . However, the experimental data indicated that eGraf was more effective i n reducing the joint resistance of materials with low thermal conductivities, and can reduce this value by as much 95% when compared to bare contacting surfaces . The analytical model predicted well the trend of the experimental data, but not the actual magnitudes . This could be due to the uncertainty associated with the eGraf Young’ s modulus measured under compressive load ing . The agreement be tween the model and the experimental data improved at high interface pressures (i.e., above 2,000 kPa ).

Journal of biomechanical engineering, May 23, 2019

Walking can be exceedingly complex to analyze due to highly nonlinear multibody dynamics, nonline... more Walking can be exceedingly complex to analyze due to highly nonlinear multibody dynamics, nonlinear relationships between muscle excitations and resulting muscle forces, dynamic coupling that allows muscles to accelerate joints and segments they do not span, and redundant muscle control. Walking requires the successful execution of a number of biomechanical functions such as providing body support, forward propulsion, and balance control, with specific muscle groups contributing to their execution. Thus, muscle injury or neurological impairment that affects muscle output can alter the successful execution of these functions and impair walking performance. The loss of balance control in particular can result in falls and subsequent injuries that lead to the loss of mobility and functional independence. Thus, it is important to assess the mechanisms used to control balance in clinical populations using reliable methods with the ultimate goal of improving rehabilitation outcomes. In this review, we highlight common clinical and laboratory-based measures used to assess balance control and their potential limitations, show how these measures have been used to analyze balance in several clinical populations, and consider the translation of specific laboratory-based measures from the research laboratory to the clinic.

45th AIAA Aerospace Sciences Meeting and Exhibit, 2007

Archives of Physical Medicine and Rehabilitation, 2016

, sex, the presence of lipid metabolism disorders, and cardiovascular comorbidities, statin use w... more , sex, the presence of lipid metabolism disorders, and cardiovascular comorbidities, statin use was not significantly associated with any acute, rehabilitation, or 1 year outcomes assessed (p>0.05). However, sex significantly moderated the association between acute inpatient statin use and days to follow command (pZ0.008). There appeared to be no effect of statin use on days to follow commands among women; however, there may be a beneficial effect among men. Conclusions: Sex differences may exist for neuroprotective effects of statin use based on unique sex-related pathophysiology (e.g. endocrine, immunology, amyloid deposition). This may contribute to differential effects of statins by sex. Future studies should further examine sex differences in statin effects after TBI.

Spinal Cord, Apr 27, 2022

Study Design: Feasibility study, consisting of random-order, cross-over study of a single interve... more Study Design: Feasibility study, consisting of random-order, cross-over study of a single intervention session, followed by a parallel-arm study of 16 sessions Objectives: To investigate the feasibility of a novel combinatorial approach with simultaneous delivery of transcutaneous spinal direct current stimulation (tsDCS) and locomotor training (tsDCS+LT) after spinal cord injury, compared to sham stimulation and locomotor training (sham+LT), and examine preliminary effects on walking function. Setting: Clinical research center in the southeastern United States Methods: Eight individuals with chronic incomplete spinal cord injury (ISCI) completed the two-part protocol. Feasibility was assessed based on safety (adverse responses), tolerability (pain, spasticity, skin integrity), and protocol achievement (session duration, intensity). Walking function was assessed with the 10-meter and 6-minute walk tests. Results: There were no major adverse responses. Minimal reports of skin irritation and musculoskeletal pain were consistent between groups. Average training peak heart rate as percent of maximum (mean(SD); tsDCS+LT: 66(4)%, sham+LT: 69(10)%) and Borg ratings of perceived exertion (tsDCS+LT: 17.5(1.2), sham+LT: 14.4(1.8)) indicate both groups trained at high Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the

Journal of Biomechanics, 2021

Archives of Physical Medicine and Rehabilitation, 2018

Main Outcome Measure(s): All participants performed a maximal oxygen consumption test (VO2 max) w... more Main Outcome Measure(s): All participants performed a maximal oxygen consumption test (VO2 max) with a metabolic analyzer and treadmill using a modified Balke test protocol. Other outcomes were; physiological cost index (PCI), 10-meter even and uneven terrain and 20-meter walk tests, 2-minute walk test. Results: Treatment group improved; VO2 max (ml/kg/min) by 22.32%, PCI 13.89%, 10-meter walk tests by 15.25% and 20-meter walk speeds improved 7.25%. Two-minute walk saw minor improvement of 2%. Controls saw no improvements in outcome metrics from baseline to to post-exercise outcomes. Conclusions: This preliminary investigation shows improvement in aerobic capacity and functional outcome measures for transtibial prosthesis wearers. Participating in an evidence based structured exercise training program and using wearable HR monitors and RPE to dictate intensity is recommended.

Topics in Stroke Rehabilitation, 2019

Journal of Biomechanics, 2019

Journal of biomechanics, Jan 24, 2018