Jennifer M. Yentes

Postural control strategy during standing is altered in patients with multiple sclerosis

Disturbances in balance are one of the first reported symptoms of Multiple Sclerosis (MS), yet limited research has been performed to classify the postural control deficits in this population. This study investigated the variability present in the sway patterns during quiet standing in patients with MS (PwMS) and healthy controls. Subjects were assessed (eyes open, closed) standing on a force platform. Variability of the sway patterns was quantified using a measure of amount of variability (root mean square; RMS) and two measures of temporal structure of variability (Lyapunov Exponent - LyE; Approximate Entropy - ApEn). RMS results revealed significantly higher amount of variability in the sway patterns of PwMS. PwMS also exhibit increased regularity (decreased ApEn) and decreased divergence (decreased LyE) during standing compared to healthy controls. Removing vision resulted in significantly decreased divergence (decreased LyE) in the MS subject group. These changes in the temporal structure correspond well with the theoretical model of the optimal movement variability hypothesis and the results support using variability measures to understand the mechanisms that underline postural control in PwMS and possibly other neurodegenerative disease pathologies.

Walking abnormalities are associated with COPD: An investigation of the NHANES III dataset

Research on the peripheral effects of COPD has focused on physiological and structural changes. However, different from muscular weakness or decreased physical activity, mechanical abnormalities of the muscular system, e.g. walking, have yet to be investigated. Our purpose was to utilize the National Health and Nutritional Examination Survey (NHANES) dataset to determine whether walking abnormalities are associated with COPD severity. To determine if walking abnormalities were independently associated with COPD severity, our analysis aimed to investigate the association of physical activity levels with COPD severity and with walking abnormalities. The NHANES III dataset that contains data for 31,000 persons that were collected from 1988 to 1994, was used to explore the association of COPD severity on gross walking abnormalities, i.e. limp, shuffle, etc. Logistic regression models were created using FEV(1)/FVC ratio, age, gender, BMI, and smoking status as predictors of walking abnormalities and physical activity in persons aged 40 to 90 years old. Results demonstrated a significant correlation between the presence of walking abnormalities and severe COPD (odds ratio: 1.97; 95% CI: 1.1 to 3.5). This suggests that disease severity can contribute to mechanical outcomes of patients with COPD. In addition, decreased physical activity levels were significantly associated with all COPD severity levels with the exception of mild COPD. The association between altered gait and COPD status may be due to the presence of physical inactivity that is present in patients with COPD. Future research directions should include investigating more closely the mechanical outcomes of persons with COPD.

Frontal joint dynamics when initiating stair ascent from a walk versus a stand

Ascending stairs is a challenging activity of daily living for many populations. Frontal plane joint dynamics are critical to understand the mechanisms involved in stair ascension as they contribute to both propulsion and medio-lateral stability. However, previous research is limited to understanding these dynamics while initiating stair ascent from a stand. We investigated if initiating stair ascent from a walk with a comfortable self-selected speed could affect the frontal plane lower-extremity joint moments and powers as compared to initiating stair ascent from a stand and if this difference would exist at consecutive ipsilateral steps on the stairs. Kinematics data using a 3-D motion capture system and kinetics data using two force platforms on the first and third stair treads were recorded simultaneously as ten healthy young adults ascended a custom-built staircase. Data were collected from two starting conditions of stair ascent, from a walk (speed: 1.42 ± 0.21 m/s) and from a stand. Results showed that subjects generated greater peak knee abductor moment and greater peak hip abductor moment when initiating stair ascent from a walk. Greater peak joint moments and powers at all joints were also seen while ascending the second ipsilateral step. Particularly, greater peak hip abductor moment was needed to avoid contact of the contralateral limb with the intermediate step by counteracting the pelvic drop on the contralateral side. This could be important for therapists using stair climbing as a testing/training tool to evaluate hip strength in individuals with documented frontal plane abnormalities (i.e. knee and hip osteoarthritis, ACL injury).

Do lower-extremity joint dynamics change when stair negotiation is initiated with a self-selected comfortable gait speed?

Previous research on the biomechanics of stair negotiation has ignored the effect of the approaching speed. We examined if initiating stair ascent with a comfortable self-selected speed can affect the lower-extremity joint moments and powers as compared to initiating stair ascent directly in front of the stairs. Healthy young adults ascended a custom-built staircase instrumented with force platforms. Kinematics and kinetics data were collected simultaneously for two conditions: starting from farther away and starting in front of the stairs and analyzed at the first and second ipsilateral steps. Results showed that for the first step, participants produced greater peak knee extensor moment, peak hip extensor and flexor moments and peak hip positive power while starting from farther away. Also, for both the conditions combined, participants generated lesser peak ankle plantiflexor, greater peak knee flexor moment, lesser peak ankle negative power and greater peak hip negative power while encountering the first step. These results identify the importance of the starting position in experiments dealing with biomechanics of stair negotiation. Further, these findings have important implications for studying stair ascent characteristics of other populations such as older adults.

Clinical and Spatiotemporal Gait Effects of Canes in Hip Osteoarthritis

To investigate the effects of cane use on spatiotemporal gait parameters, pain, and function in adults with hip osteoarthritis (OA).

Immediate Effects of Contralateral and Ipsilateral Cane Use On Normal Adult Gait

To determine the effects of ipsilateral and contralateral cane use on gait kinematics and peak vertical force in young healthy adults.

Patients with Chronic Obstructive Pulmonary Disease Walk with Altered Step Time and Step Width Variability as Compared with Healthy Control Subjects

Rationale: Compared with control subjects, patients with chronic obstructive pulmonary disease (COPD) have an increased incidence of falls and demonstrate balance deficits and alterations in mediolateral trunk acceleration while walking. Measures of gait variability have been implicated as indicators of fall risk, fear of falling, and future falls. Objectives: To investigate whether alterations in gait variability are found in patients with COPD as compared with healthy control subjects. Methods: Twenty patients with COPD (16 males; mean age, 63.6 ± 9.7 yr; FEV1/FVC, 0.52 ± 0.12) and 20 control subjects (9 males; mean age, 62.5 ± 8.2 yr) walked for 3 minutes on a treadmill while their gait was recorded. The amount (SD and coefficient of variation) and structure of variability (sample entropy, a measure of regularity) were quantified for step length, time, and width at three walking speeds (self‐selected and ±20% of self‐selected speed). Generalized linear mixed models were used to compare dependent variables. Results: Patients with COPD demonstrated increased mean and SD step time across all speed conditions as compared with control subjects. They also walked with a narrower step width that increased with increasing speed, whereas the healthy control subjects walked with a wider step width that decreased as speed increased. Further, patients with COPD demonstrated less variability in step width, with decreased SD, compared with control subjects at all three speed conditions. No differences in regularity of gait patterns were found between groups. Conclusions: Patients with COPD walk with increased duration of time between steps, and this timing is more variable than that of control subjects. They also walk with a narrower step width in which the variability of the step widths from step to step is decreased. Changes in these parameters have been related to increased risk of falling in aging research. This provides a mechanism that could explain the increased prevalence of falls in patients with COPD.

Gait mechanics in patients with chronic obstructive pulmonary disease

BackgroundChronic obstructive pulmonary disease (COPD) is characterized by the frequent association of disease outside the lung. The objective of this study was to determine the presence of biomechanical gait abnormalities in COPD patients compared to healthy controls while well rested and without rest.MethodsPatients with COPD (N = 17) and aged-matched, healthy controls (N = 21) walked at their self-selected pace down a 10-meter walkway while biomechanical gait variables were collected. A one-minute rest was given between each of the five collected trials to prevent tiredness (REST condition). Patients with COPD then walked at a self-selected pace on a treadmill until the onset of self-reported breathlessness or leg tiredness. Subjects immediately underwent gait analysis with no rest between each of the five collected trials (NO REST condition). Statistical models with and without covariates age, gender, and smoking history were used.ResultsAfter adjusting for covariates, COPD patients demonstrated more ankle power absorption in mid-stance (P = 0.006) than controls during both conditions. Both groups during NO REST demonstrated increased gait speed (P = 0.04), stride length (P = 0.03), and peak hip flexion (P = 0.04) with decreased plantarflexion moment (P = 0.04) and increased knee power absorption (P = 0.04) as compared to REST. A significant interaction revealed that peak ankle dorsiflexion moment was maintained from REST to NO REST for COPD but increased for controls (P < 0.01). Stratifying by disease severity did not alter these findings, except that step width decreased in NO REST as compared to REST (P = 0.01). Standardized effect sizes of significant effects varied from 0.5 to 0.98.ConclusionsPatients with COPD appear to demonstrate biomechanical gait changes at the ankle as compared to healthy controls. This was seen not only in increased peak ankle power absorption during no rest but was also demonstrated by a lack of increase in peak ankle dorsiflexion moment from the REST to the NO REST condition as compared to the healthy controls. Furthermore, a wider step width has been associated with fall risk and this could account for the increased incidence of falls in patients with COPD.

Evaluation of two cane instruments in older adults with knee osteoarthritis.

The objectives of this study were to describe the psychometric properties of the Cane Cognitive Mediator Scale (CCMS) and the Psychosocial Impact of Assistive Devices Scale (PIADS) in adults with knee osteoarthritis (OA) and to determine the feasibility of applying these instruments as screening tools to identify patients with the propensity to use a cane. Data from a randomized crossover trial were analyzed for 53 older adults with knee OA. Perceptions on using a cane were measured at baseline using the CCMS and PIADS. The CCMS was repeated 1 wk later. At 6 mo, subjects rated their intention to use a cane. The findings indicated that 1 wk test-retest reliability was acceptable for the CCMS Attitudes and Subjective Norms subscales (r = 0.48 to 0.93) and low for the CCMS Perceived Behavioral Control subscale (r = 0.15). Internal consistency reliability was good for each CCMS and PIADS subscale. The CCMS Subjective Norms subscale demonstrated acceptable predictive validity across all subgroups (r = 0.53 to 0.88). The PIADS Adaptability subscale demonstrated acceptable predictive validity for the 45 to 64 yr-old age group (r = 0.54). The findings indicate that the CCMS Subjective Norms subscale exhibits good psychometric properties and has potential application as a screening tool.

Effect of parameter selection on entropy calculation for long walking trials

It is sometimes difficult to obtain uninterrupted data sets that are long enough to perform nonlinear analysis, especially in pathological populations. It is currently unclear as to how many data points are needed for reliable entropy analysis. The aims of this study were to determine the effect of changing parameter values of m, r, and N on entropy calculations for long gait data sets using two different modes of walking (i.e., overground versus treadmill). Fourteen young adults walked overground and on a treadmill at their preferred walking speed for one-hour while step time was collected via heel switches. Approximate (ApEn) and sample entropy (SampEn) were calculated using multiple parameter combinations of m, N, and r. Further, r was tested under two cases r*standard deviation and r constant. ApEn differed depending on the combination of r, m, and N. ApEn demonstrated relative consistency except when m=2 and the smallest r values used (rSD=0.015*SD, 0.20*SD; rConstant=0 and 0.003). For SampEn, as r increased, SampEn decreased. When r was constant, SampEn demonstrated excellent relative consistency for all combinations of r, m, and N. When r constant was used, overground walking was more regular than treadmill. However, treadmill walking was found to be more regular when using rSD for both ApEn and SampEn. For greatest relative consistency of step time data, it was best to use a constant r value and SampEn. When using entropy, several r values must be examined and reported to ensure that results are not an artifact of parameter choice.