Design and Evaluation of a Bilateral Semi-Rigid Exoskeleton to Assist Hip Motion.

This study focused on designing and evaluating a bilateral semi-rigid hip exoskeleton. The exoskeleton assisted the hip joint, capitalizing on its proximity to the body's center of mass. Unlike its rigid counterparts, the semi-rigid design permitted greater freedom of movement. A temporal force-tracking controller allowed us to prescribe torque profiles during walking. We ensured high accuracy by tuning control parameters and series elasticity. The evaluation involved experiments with ten participants across ten force profile conditions with different end-timings and peak magnitudes. Our findings revealed a trend of greater reductions in metabolic cost with assistance provided at later timings in stride and at greater magnitudes. Compared to walking with the exoskeleton powered off, the largest reduction in metabolic cost was 9.1%. This was achieved when providing assistance using an end-timing at 44.6% of the stride cycle and a peak magnitude of 0.11 Nm kg-1. None of the tested conditions reduced the metabolic cost compared to walking without the exoskeleton, highlighting the necessity for further enhancements, such as a lighter and more form-fitting design. The optimal end-timing aligns with findings from other soft hip exosuit devices, indicating a comparable interaction with this prototype to that observed in entirely soft exosuit prototypes.

Enhancing walking performance in patients with peripheral arterial disease: An intervention with ankle-foot orthosis.

Lower extremity peripheral artery disease (PAD) is a cardiovascular condition manifesting from narrowed or blocked arteries supplying the legs. Gait is impaired in patients with PAD. Recent evidence suggests that walking with carbon fiber ankle foot orthoses (AFOs) can improve patient mobility and delay claudication time. This study aimed to employ advanced biomechanical gait analysis to evaluate the impact of AFO intervention on gait performance among patients with PAD. Patients with claudication had hip, knee, and ankle joint kinetics and kinematics assessed using a cross-over intervention design. Participants walked over the force platforms with and without AFOs while kinematic data was recorded with motion analysis cameras. Kinetics and kinematics were combined to quantify torques and powers during the stance period of the gait cycle. The AFOs effectively reduced the excessive ankle plantar flexion and knee extension angles, bringing the patients' joint motions closer to those observed in healthy individuals. After 3 months of the AFO intervention, the hip range of motion decreased, likely due to changes occurring within the ankle chain. With the assistance of the AFOs, the biological power generation required from the ankle and hip during the push-off phase of walking decreased. Wearing AFOs resulted in increased knee flexor torque during the loading response phase of the gait. Based on this study, AFOs may allow patients with PAD to maintain or improve gait performance. More investigation is needed to fully understand and improve the potential benefits of ankle assistive devices.

Peripheral artery disease causes consistent gait irregularities regardless of the location of leg claudication pain.

BACKGROUND: The most common symptom of peripheral artery disease (PAD) is intermittent claudication that involves the calf, thigh, and/or buttock muscles. How the specific location of this leg pain is related to altered gait, however, is unknown. OBJECTIVES: We hypothesized that because the location of claudication symptoms uniquely affects different leg muscle groups in people with PAD, this would produce distinctive walking patterns. METHODS: A total of 105 participants with PAD and 35 age-matched older volunteers without PAD (CTRL) were recruited. Participants completed walking impairment questionnaires (WIQ), Gardner-Skinner progressive treadmill tests, the six-minute walk test, and we performed an advanced evaluation of the biomechanics of their overground walking. Participants with PAD were categorized into 4 groups according to their stated pain location(s): calf only (C, n = 43); thigh and calf (TC, n = 18); buttock and calf (BC, n = 15); or buttock, thigh, and calf (BTC, n = 29). Outcomes were compared between CTRL, C, TC, BC and BTC groups using a one-way ANOVA with post-hoc comparisons to identify and assess statistically significant differences. RESULTS: There were no significant differences between CTRL, C, TC, BC and BTC groups in distances walked or walking speed when either pain-free or experiencing claudication pain. Each participant with PAD had significantly dysfunctional biomechanical gait parameters, even when pain-free, when compared to CTRL (pain-free) walking data. During pain-free walking, out of the 18 gait parameters evaluated, we only identified significant differences in hip power generation during push-off (in C and TC groups) and in knee power absorption during weight acceptance (in TC and BC groups). There were no between-group differences in gait parameters while people with PAD were walking with claudication pain. CONCLUSIONS: Our data demonstrate that PAD affects the ischemic lower extremities in a diffuse manner irrespective of the location of claudication symptoms. DATABASE REGISTRATION: ClinicalTrials.gov NCT01970332.

Trunk Velocity Changes in Response to Physical Perturbations Are Potential Indicators of Gait Stability.

Response to challenging situations is important to avoid falls, especially after medial perturbations, which require active control. There is a lack of evidence on the relationship between the trunk's motion in response to perturbations and gait stability. Eighteen healthy adults walked on a treadmill at three speeds while receiving perturbations of three magnitudes. Medial perturbations were applied by translating the walking platform to the right at left heel contact. Trunk velocity changes in response to the perturbation were calculated and divided into the initial and the recovery phases. Gait stability after a perturbation was assessed using the margin of stability (MOS) at the first heel contact, MOS mean, and standard deviation for the first five strides after the perturbation onset. Faster speed and smaller perturbations led to a lower deviation of trunk velocity from the steady state, which can be interpreted as an improvement in response to the perturbation. Recovery was quicker after small perturbations. The MOS mean was associated with the trunk's motion in response to perturbations during the initial phase. Increasing walking speed may increase resistance to perturbations, while increasing the magnitude of perturbation leads to greater trunk motions. MOS is a useful marker of resistance to perturbations.

A biomechanical perspective on walking in patients with peripheral artery disease.

The most common symptom of peripheral artery disease (PAD) is intermittent claudication, which consists of debilitating leg pain during walking. In clinical settings, the presence of PAD is often noninvasively evaluated using the ankle-brachial index and imaging of the arterial supply. Furthermore, various questionnaires and functional tests are commonly used to measure the severity and negative effect of PAD on quality of life. However, these evaluations only provide information on vascular insufficiency and severity of the disease, but not regarding the complex mechanisms underlying walking impairments in patients with PAD. Biomechanical analyses using motion capture and ground reaction force measurements can provide insight into the underlying mechanisms to walking impairments in PAD. This review analyzes the application of biomechanics tools to identify gait impairments and their clinical implications on rehabilitation of patients with PAD. A total of 18 published journal articles focused on gait biomechanics in patients with PAD were studied. This narriative review shows that the gait of patients with PAD is impaired from the first steps that a patient takes and deteriorates further after the onset of claudication leg pain. These results point toward impaired muscle function across the ankle, knee, and hip joints during walking. Gait analysis helps understand the mechanisms operating in PAD and could also facilitate earlier diagnosis, better treatment, and slower progression of PAD.

Long-term use of an ankle-foot orthosis intervention in patients with peripheral artery disease using the integrated promoting action on research implementation in health services (i-PARIHS) framework.

BACKGROUND: Peripheral artery disease (PAD) is a cardiovascular disease that limits patients' walking ability. Persistent ankle-foot orthosis (AFO) use may increase the distance patients can walk as well as physical activity. PURPOSE: The purpose of the study was to determine the implementation and patients' perspectives related to the use or disuse of the AFO intervention six months post-intervention. This study was guided by a semi-structured interview and survey based on the integrated Promoting Action on Research Implementation in Health Services (i-PARIHS) constructs. DESIGN: A convergent mixed methods design was used to evaluate participants' perceptions six months following a three-month AFO intervention. A survey and semi-structured questionnaire based on the i-PARIHS constructs were administered and analyzed. SETTING: Vascular surgery clinic and biomechanics research laboratory. PARTICIPANTS: Patients (N = 7; male, 100%; age, 71.9 ± 0.6.7y; body mass index, 29.0 ± 0.5.5; ankle brachial index 0.50 ± 0.17) with claudication completed the study. INTERVENTIONS: A certified orthotist fit participants with an AFO that was worn for 3 months. MAIN OUTCOME MEASURES: Qualitative analysis of semi-structured interviews and quantitative analysis of the survey. RESULTS: The highest positive ratings were seen in the dimensions of usability and cost-effectiveness. The patients found the AFO device and instructions to wear, easy when starting the intervention and there were no out-of-pocket costs. The lower scores and challenges faced with observability and relative advantage domains indicated issues related to motivation for sustained use of the AFO. CONCLUSIONS: Barriers associated with AFO function that prevent common activities and poor health seem to be the biggest issue for not wanting to wear the AFO after the 3-month intervention. Addressing patients' perceptions and challenges to wearing the AFO is essential to increasing compliance and physical activity. Future research should concentrate on understanding the compatibility of orthotic device interventions with the subject's lifestyle. CLINICAL TRIAL REGISTRATION NO: NCT02902211.

Machine Learning-Based Peripheral Artery Disease Identification Using Laboratory-Based Gait Data.

Peripheral artery disease (PAD) manifests from atherosclerosis, which limits blood flow to the legs and causes changes in muscle structure and function, and in gait performance. PAD is underdiagnosed, which delays treatment and worsens clinical outcomes. To overcome this challenge, the purpose of this study is to develop machine learning (ML) models that distinguish individuals with and without PAD. This is the first step to using ML to identify those with PAD risk early. We built ML models based on previously acquired overground walking biomechanics data from patients with PAD and healthy controls. Gait signatures were characterized using ankle, knee, and hip joint angles, torques, and powers, as well as ground reaction forces (GRF). ML was able to classify those with and without PAD using Neural Networks or Random Forest algorithms with 89% accuracy (0.64 Matthew's Correlation Coefficient) using all laboratory-based gait variables. Moreover, models using only GRF variables provided up to 87% accuracy (0.64 Matthew's Correlation Coefficient). These results indicate that ML models can classify those with and without PAD using gait signatures with acceptable performance. Results also show that an ML gait signature model that uses GRF features delivers the most informative data for PAD classification.

Peripheral artery disease affects the function of the legs of claudicating patients in a diffuse manner irrespective of the segment of the arterial tree primarily involved.

Different levels of arterial occlusive disease (aortoiliac, femoropopliteal, multi-level disease) can produce claudication symptoms in different leg muscle groups (buttocks, thighs, calves) in patients with peripheral artery disease (PAD). We tested the hypothesis that different locations of occlusive disease uniquely affect the muscles of PAD legs and produce distinctive patterns in the way claudicating patients walk. Ninety-seven PAD patients and 35 healthy controls were recruited. PAD patients were categorized to aortoiliac, femoropopliteal and multi-level disease groups using computerized tomographic angiography. Subjects performed walking trials both pain-free and during claudication pain and joint kinematics, kinetics, and spatiotemporal parameters were calculated to evaluate the net contribution of the calf, thigh and buttock muscles. PAD patients with occlusive disease affecting different segments of the arterial tree (aortoiliac, femoropopliteal, multi-level disease) presented with symptoms affecting different muscle groups of the lower extremity (calves, thighs and buttocks alone or in combination). However, no significant biomechanical differences were found between PAD groups during the pain-free conditions with minimal differences between PAD groups in the claudicating state. All statistical differences in the pain-free condition occurred between healthy controls and one or more PAD groups. A discriminant analysis function was able to adequately predict if a subject was a control with over 70% accuracy, but the function was unable to differentiate between PAD groups. In-depth gait analyses of claudicating PAD patients indicate that different locations of arterial disease produce claudication symptoms that affect different muscle groups across the lower extremity but impact the function of the leg muscles in a diffuse manner generating similar walking impairments.

Patient Compliance With Wearing Lower Limb Assistive Devices: A Scoping Review.

OBJECTIVE: The aim of this scoping review was to identify information on compliance with wearing orthoses and other supportive devices, to discuss the barriers to adherence, and to suggest strategies for improvement based on these findings. METHODS: Online databases of PubMed, Web of Science, and the Cochrane Library were searched for articles about patients' compliance with regard to lower limb assistive devices. In addition, a methodological quality control process was conducted. Studies were included if in the English language and related to compliance and adherence to the lower limb assistive device. Exclusion was based on first reading the abstract and then the full manuscript confirming content was not related to orthotic devices and compliance. RESULTS: Twelve studies were included. The data revealed between 6% and 80% of patients were not using a prescribed device. Barriers to the use of the orthotic device included medical, functional, device properties and lack of proper fit. Strategies for improved compliance included better communication between patient and clinician, patient education, and improved comfort and device esthetics. CONCLUSIONS: Individualized orthotic adjustments, rehabilitation, and patient education were promising for increasing adherence. Despite positive aspects of improvements in gait, balance in elderly, and a sense of security produced by using assistive devices, compliance remains less than ideal due to barriers. As compliance in recent studies has not improved, continued work in this area is essential to realize the benefits of technological advances in orthotic and assistive devices.

Metabolically efficient walking assistance using optimized timed forces at the waist.

The metabolic rate of walking can be reduced by applying a constant forward force at the center of mass. It has been shown that the metabolically optimal constant force magnitude minimizes propulsion ground reaction force at the expense of increased braking. This led to the hypothesis that selectively assisting propulsion could lead to greater benefits. We used a robotic waist tether to evaluate the effects of forward forces with different timings and magnitudes. Here, we show that it is possible to reduce the metabolic rate of healthy participants by 48% with a greater efficiency ratio of metabolic cost reduction per unit of net aiding work compared with other assistive robots. This result was obtained using a sinusoidal force profile with peak timing during the middle of the double support. The same timing could also reduce the metabolic rate in patients with peripheral artery disease. A model explains that the optimal force profile accelerates the center of mass into the inverted pendulum movement during single support. Contrary to the hypothesis, the optimal force timing did not entirely coincide with propulsion. Within the field of wearable robotics, there is a trend to use devices to mimic biological torque or force profiles. Such bioinspired actuation can have relevant benefits; however, our results demonstrate that this is not necessarily optimal for reducing metabolic rate.

Muscle forces and power are significantly reduced during walking in patients with peripheral artery disease.

Patients with peripheral artery disease (PAD) have significantly reduced lower extremity muscle strength compared with healthy individuals as measured during isolated, single plane joint motion by isometric and isokinetic strength dynamometers. Alterations to the force contribution of muscles during walking caused by PAD are not well understood. Therefore, this study used simulations with PAD biomechanics data to understand lower extremity muscle functions in patients with PAD during walking and to compare that with healthy older individuals. A total of 12 patients with PAD and 10 age-matched healthy older controls walked across a 10-meter pathway with reflective markers on their lower limbs. Marker coordinates and ground reaction forces were recorded and exported to OpenSim software to perform gait simulations. Walking velocity, joint angles, muscle force, muscle power, and metabolic rate were calculated and compared between patients with PAD and healthy older controls. Our results suggest that patients with PAD walked slower with less hip extension during propulsion. Significant force and power reductions were observed in knee extensors during weight acceptance and in plantar flexors and hip flexors during propulsion in patients with PAD. The estimated metabolic rate of walking during stance was not different between patients with PAD and controls. This study is the first to analyze lower limb muscular responses during walking in patients with PAD using the OpenSim simulation software. The simulation results of this study identified important information about alterations to muscle force and power during walking in those with PAD.

A robust technique for optimal fitting of roll-over shapes of human locomotor systems.

The roll-over shape (ROS) effectively characterizes the lower limb's ability to roll forward during the single-limb support phase of human walking. ROS is modelled as an optimally fitted circular arc to the center of pressure (CoP) data transformed in the shank/leg-based local coordinate system. The commonly used method for optimal fitting of ROS is complex to implement and eliminates inherent individual variability in the ROS parameters during walking. We propose and validate a novel computerized method for optimal fitting of roll-over shapes of the lower limb during walking. Gait data of a healthy individual from Winter's book was used to generate ankle-foot and knee-ankle-foot roll-over shapes using the proposed method. The goodness of fit and form of both the roll-over shapes were validated with the literature. To test the robustness of the proposed technique, small random perturbations were introduced to the transformed CoP data and the effect of these small changes in the data on the ROS parameters was studied. The ROS parameters such as radius, arc length, subtended arc angle, and horizontal and vertical shift in the arc center did not change substantially with small changes in the CoP data. The proposed method is computationally efficient, and easy to implement for optimal fitting and characterization of ROS.

Joint Angle Variability Is Altered in Patients with Peripheral Artery Disease after Six Months of Exercise Intervention.

Supervised exercise therapy (SET) is a conservative non-operative treatment strategy for improving walking performance in patients with peripheral artery disease (PAD). Gait variability is altered in patients with PAD, but the effect of SET on gait variability is unknown. Forty-three claudicating patients with PAD underwent gait analysis before and immediately after a 6-month SET program. Nonlinear gait variability was assessed using sample entropy, and the largest Lyapunov exponent of the ankle, knee, and hip joint angle time series. Linear mean and variability of the range of motion time series for these three joint angles were also calculated. Two-factor repeated measure analysis of variance determined the effect of the intervention and joint location on linear and nonlinear dependent variables. After SET, walking regularity decreased, while the stability remained unaffected. Ankle nonlinear variability had increased values compared with the knee and hip joints. Linear measures did not change following SET, except for knee angle, in which the magnitude of variations increased after the intervention. A six-month SET program produced changes in gait variability toward the direction of healthy controls, which indicates that in general, SET improved walking performance in individuals with PAD.

Claudicating patients with peripheral artery disease have meaningful improvement in walking speed after supervised exercise therapy.

OBJECTIVE: Supervised exercise therapy (SET) is a first-line treatment for patients with peripheral artery disease (PAD). The efficacy of SET is most commonly expressed by significant statistical improvement of parameters that do not clarify how each individual patient will benefit from SET. This study examined the minimal clinically important difference (MCID) in walking speed in claudicating patients with PAD after SET. METHODS: A total of 63 patients with PAD-related claudication (Fontaine stage II PAD) participated in a 6-month SET program. Self-selected walking speed was measured before and after SET. Distribution and anchor-based approaches were used to estimate the MCID for small and substantial improvement. The ability to walk one block and the ability to climb one flight of stairs questions were chosen as anchor questions from the Medical Outcomes Study 36-item Short Form questionnaire. Receiver operating characteristics curve analyses were performed to detect the threshold for MCID in walking speed after treatment. RESULTS: The distribution-based method estimated 0.03 m/s as a small improvement and 0.08 m/s as a substantial improvement after SET. Small and substantial improvements according to the anchor question walking one block were 0.05 m/s and 0.15 m/s, respectively. For the climbing one flight of stairs anchor question, 0.10 m/s was a small improvement. Receiver operating characteristics curve analyses identified an increase of 0.04 m/s and 0.03 m/s for improvement based on walking one block and climbing one flight of stairs, respectively. CONCLUSIONS: We report our findings for the MCID for walking speed among claudicating patients receiving SET. Claudicating patients who increase walking speed of 0.03 m/s or greater are more likely to experience a meaningful improvement in walking impairment than those who do not. The MCID reported in this study can serve as a benchmark for clinicians to develop goals and interpret clinically meaningful progress in the care of claudicating patients with PAD.

Considerations for Implementation of an Ankle-Foot Orthosis to Improve Mobility in Peripheral Artery Disease.

OBJECTIVE: To explore the perceptions of wearing an ankle-foot orthosis (AFO) in patients with peripheral artery disease (PAD) who did and did not adopt the AFO intervention. This follows a clinical trial of the effectiveness of an AFO in improving walking distances for patients with PAD-related claudication. DESIGN: A randomized crossover trial of standard of care and an AFO for 3 months. Semistructured interviews were conducted 1.5 months into the AFO intervention to understand acceptability, demand, implementation, and practicality. Data were analyzed using a summative content analysis approach. SETTING: Vascular surgery clinic and biomechanics research laboratory. PARTICIPANTS: Patients (N=15; male, 100%; age, 71.9±.6.7y; body mass index [calculated as weight in kilograms divided by height in meters squared], 29.0±.5.5; ankle brachial index: AFO intervention withdrawal, 0.543; AFO intervention completion, 0.740) with claudication completed the study, and 6 withdrew prior to intervention completion. INTERVENTIONS: A certified orthotist fit participants with an AFO that was worn for 3 months. MAIN OUTCOME MEASURES: Qualitative analysis of the semistructured interviews. RESULTS: Key differences were reported between AFO intervention completion and AFO intervention withdrawal. Six of 14 of AFO intervention completion participants described their initial reactions to the AFO as negative vs 3 of 6 AFO intervention withdrawal participants. Only 5 of 15 AFO intervention completion participants reported minimal use of the AFO compared with 5 of 6 AFO intervention withdrawal participants. The AFO intervention withdrawal group reported higher levels of physical discomfort with the use of the AFO (4/6 vs 7/15) and preexisting health issues becoming a barrier to the use of the AFO (3/6 vs 5/15). Positive aspects reported included ease in standing and walking for AFO intervention withdrawal (4/6) and AFO intervention completion groups (13/15) as well as walking straighter and longer with less pain for AFO intervention withdrawal (3/6) and AFO intervention completion groups (9/15). CONCLUSIONS: Patients withdrawing prior to completion of AFO intervention tended to have more negative perceptions, more comorbidities, and more physical discomfort than those completing the intervention. Both groups reported positive aspects of the AFO. Implementation studies are needed to address barriers to AFO adoption.

Gait variability is affected more by peripheral artery disease than by vascular occlusion.

BACKGROUND: Patients with peripheral artery disease with intermittent claudication (PAD-IC) have altered gait variability from the first step they take, well before the onset of claudication pain. The mechanisms underlying these gait alterations are poorly understood. AIMS: To determine the effect of reduced blood flow on gait variability by comparing healthy older controls and patients with PAD-IC. We also determined the diagnostic value of gait variability parameters to identify the presence of PAD. METHODS: A cross-sectional cohort design was used. Thirty healthy older controls and thirty patients with PAD-IC walked on a treadmill at their self-selected speed in pain free walking (normal walking for healthy older controls; prior to claudication onset for PAD) and reduced blood flow (post vascular occlusion with thigh tourniquet for healthy older controls; pain for PAD) conditions. Gait variability was assessed using the largest Lyapunov exponent, approximate entropy, standard deviation, and coefficient of variation of ankle, knee, and hip joints range of motion. Receiver operating characteristics curve analyses of the pain free walking condition were performed to determine the optimal cut-off values for separating individuals with PAD-IC from those without PAD-IC. RESULTS AND DISCUSSION: Patients with PAD-IC have increased amount of variability for knee and hip ranges of motion compared with the healthy older control group. Regarding the main effect of condition, reduced blood flow demonstrated increased amount of variability compared with pain free walking. Significant interactions between group and condition at the ankle show increased values for temporal structure of variability, but a similar amount of variability in the reduced blood flow condition. This demonstrates subtle interactions in the movement patterns remain distinct between PAD-IC versus healthy older controls during the reduced blood flow condition. A combination of gait variability parameters correctly identifies PAD-IC disease 70% of the time or more. CONCLUSIONS: Gait variability is affected both by PAD and by the mechanical induction of reduced blood flow. Gait variability parameters have potential diagnostic ability, as some measures had 90.0% probability of correctly identifying patients with PAD-IC.

Cytokine signature of inflammation mediated by autoreactive Th-cells, in calf muscle of claudicating patients with Fontaine stage II peripheral artery disease.

Peripheral artery disease (PAD), a severe atherosclerotic condition primarily of the elderly, afflicts 200 million individuals, worldwide, and is associated with lower extremity myopathy. Circulating markers of inflammation have been linked to risk and severity of PAD but the contribution of local inflammation to myopathy remains unknown. We evaluated, by ELISA, calf muscle of PAD patients (N = 23) and control subjects (N = 18) for local expression of inflammatory cytokines including Granulocyte/Monocyte Colony-Stimulating Factor (GM-CSF), Interleukin 17A (IL-17A), Interferon ϒ (IFN-ϒ), tumor necrosis factor α (TNF-α), and Interleukin 6 (IL-6). One or more of these cytokines were expressed in nineteen patients and 2 controls and coordinated expression of GM-CSF, IL-17A, IFN-ϒ, and TNF-α, a signature of activated, MHC Class II dependent autoreactive Th-cells, was unique to 11 patients. GM-CSF is the central driver of tissue-damaging myeloid macrophages. Patients with this cytokine signature had a shorter (P= 0.017) Claudication Onset Distance (17 m) compared with patients lacking the signature (102 m). Transforming Growth Factor ß1 (TGFß1) and Chemokine Ligand 5 (CCL5) were expressed coordinately in all PAD and control muscles, independently of GM-CSF, IL-17A, IFN-ϒ, TNF-α, or IL-6. TGFß1 and CCL5 and their gene transcripts were increased in PAD muscle, consistent with increased age-associated inflammation in these patients. Serum cytokines were not informative of muscle cytokine expression. We have identified a cytokine profile of autoimmune inflammation in calf muscles of a significant proportion of claudicating PAD patients, in association with decreased limb function, and a second independent profile consistent with increased "inflammaging" in all PAD patients.

A low-cost, wireless near-infrared spectroscopy device detects the presence of lower extremity atherosclerosis as measured by computed tomographic angiography and characterizes walking impairment in peripheral artery disease.

BACKGROUND: Patients with peripheral artery disease (PAD) who experience intermittent claudication report a range of symptoms. Patients with symptoms other than classically described intermittent claudication may be at the highest risk for functional decline and mobility loss. Therefore, technologies allowing for characterization of PAD severity are desirable. Near-infrared spectroscopy (NIRS) allows for measurements of muscle heme oxygen saturation (StO2) during exercise. We hypothesized lower extremities affected by PAD would exhibit distinct NIRS profiles as measured by a low-cost, wireless NIRS device and that NIRS during exercise predicts walking limitation. METHODS: We recruited 40 patients with PAD and 10 control participants. All patients with PAD completed a computed tomographic angiography, 6-minute walk test, and a standardized treadmill test. Controls completed a 540-second treadmill test for comparison. StO2 measurements were continuously taken from the gastrocnemius during exercise. Variables were analyzed by Fischer's exact, χ2, Wilcoxon rank-sum, and Kruskal-Wallis tests as appropriate. Correlations were assessed by partial Spearman correlation coefficients adjusted for occlusive disease pattern. RESULTS: Patients with PAD experienced claudication onset at a median of 108 seconds with a median peak walking time of 288 seconds. The baseline StO2 was similar between PAD and control. The StO2 of PAD and control participants dropped below baseline at a median of 1 and 104 seconds of exercise, respectively (P < .0001). Patients with PAD reached minimum StO2 earlier than control participants (119 seconds vs 522 seconds, respectively; P < .001) and experienced a greater change in StO2 at 1 minute of exercise (-73.2% vs 8.3%; P < .0001) and a greater decrease at minimum exercise StO2 (-83.4% vs -16.1%; P < .0001). For patients with PAD, peak walking time, and 6-minute walking distance correlated with percent change in StO2 at 1 minute of exercise (r = -0.76 and -0.67, respectively; P < .001) and time to minimum StO2 (r = 0.79 and 0.70, respectively; P < .0001). CONCLUSIONS: In this initial evaluation of a novel, low-cost NIRS device, lower extremities affected by PAD exhibited characteristic changes in calf muscle StO2, which differentiated them from healthy controls and were strongly correlated with walking impairment. These findings confirm and expand on previous work demonstrating the potential clinical value of NIRS devices and the need for further research investigating the ability of low-cost NIRS technology to evaluate, diagnose, and monitor treatment response in PAD.

Supervised walking exercise therapy improves gait biomechanics in patients with peripheral artery disease.

OBJECTIVE: In patients with peripheral artery disease (PAD), supervised exercise therapy is a first line of treatment because it increases maximum walking distances comparable with surgical revascularization therapy. Little is known regarding gait biomechanics after supervised exercise therapy. This study characterized the effects of supervised exercise therapy on gait biomechanics and walking distances in claudicating patients with PAD. METHODS: Forty-seven claudicating patients with PAD underwent gait analysis before and immediately after 6 months of supervised exercise therapy. Exercise sessions consisted of a 5-minute warmup of mild walking and stretching of upper and lower leg muscles, 50 minutes of intermittent treadmill walking, and 5 minutes of cooldown (similar to warmup) three times per week. Measurements included self-perceived ambulatory limitations measured by questionnaire, the ankle-brachial index (ABI), walking distance measures, maximal plantar flexor strength measured by isometric dynamometry, and overground gait biomechanics trials performed before and after the onset of claudication pain. Paired t-tests were used to test for differences in quality of life, walking distances, ABI, and maximal strength. A two-factor repeated measures analysis of variance determined differences for intervention and condition for gait biomechanics dependent variables. RESULTS: After supervised exercise therapy, quality of life, walking distances, and maximal plantar flexor strength improved, although the ABI did not significantly change. Several gait biomechanics parameters improved after the intervention, including torque and power generation at the ankle and hip. Similar to previous studies, the onset of claudication pain led to a worsening gait or a gait that was less like healthy individuals with a pain-free gait. CONCLUSIONS: Six months of supervised exercise therapy produced increases in walking distances and quality of life that are consistent with concurrent improvements in muscle strength and gait biomechanics. These improvements occurred even though the ABI did not improve. Future work should examine the benefits of supervised exercise therapy used in combination with other available treatments for PAD.

Strength of Plantar- and Dorsiflexors Mediates Step Regularity During a High Cognitive Load Situation in a Cross-sectional Cohort of Older and Younger Adults.

BACKGROUND AND PURPOSE: Completing simultaneous tasks while standing or walking (ie, a high cognitive load situation [HCLS]) is inevitable in daily activities and can lead to interference in task performances. Age-related physical and cognitive changes may confound performance variability during HCLS in older and younger adults. Identification of these confounding effects may reveal therapy targets to maintain optimal physical function later in life. The aim of this study was to investigate the effect of increasing the difficulty levels of an additional motor task and restricting visual information, on gait parameters in younger and older adults while considering the effect of cognitive and physical covariates. METHODS: Fifteen healthy younger and 14 healthy older adults were asked to complete assessments of cognitive function, balance, and strength. They were then asked to walk on a self-paced treadmill with or without carrying a plastic tray. Opaqueness of the tray (vision) and the presence of water in glasses placed on the tray (increasing task difficulty) were varied. Mean, standard deviation, and regularity (sample entropy) of step width and length were compared across conditions and groups using repeated-measures analyses of variance with and without covariate analysis. Only significantly correlated covariates of cognition, balance, and strength were entered into each model. RESULTS AND DISCUSSION: Older adults had greater step width irregularity compared with younger adults across all conditions when controlling for concentric plantar- and dorsiflexion strength. A decline in strength may likely alter neuromuscular control of gait, specifically control of step width, which has been associated with fall risk in older adults. Adjusting for the same covariates revealed increased regularity of step length, as visual feedback from the feet was restricted. Specifically, step length was more regular while carrying an opaque tray compared with not carrying a tray. Visual restriction was a contributing factor, which led to more predictable gait kinematics, indicating the role of sensory information to enhance the adaptability during walking under HCLS. CONCLUSION: The knowledge of the regularity behavior of human movement can expand physical therapists' treatment approaches to promote further interactivity and coordination across body systems that model behavior of healthy young individuals. Targeting strength during therapy may provide additional benefits for gait performance under HCLS.