Mary D. Slavin

Aging, muscle activity, and balance control : physiologic changes associated with balance impairment.

Older adults demonstrate increased amounts of postural sway, which may ultimately lead to falls. The mechanisms contributing to age-related increases in postural sway and falls in the elderly remain unclear. In an effort to understand age-related changes in posture control, we assessed foot center-of-pressure (COP) displacements and electromyographic data from the tibialis anterior, soleus, vastus lateralis, and biceps femoris collected simultaneously during quiet-standing trials from elderly fallers, elderly non-fallers, and healthy young subjects. Both traditional measures of COP displacements and stabilogram-diffusion analysis were used to characterize the postural sway of each group. Regression analyses were used to assess the relationship between the COP measures and muscle activity. Elderly fallers demonstrated significantly greater amounts of sway in the anteroposterior (AP) direction and greater muscle activity during quiet standing compared with the young subjects, while elderly non-fallers demonstrated significantly greater muscle activation and co-activation compared with the young subjects. No significant differences were found between elderly fallers and elderly non-fallers in measures of postural sway or muscle activity. However, greater postural sway in both the AP and mediolateral (ML) directions and trends of greater muscle activity were found in those older adults who demonstrated lower scores on clinical measures of balance. In addition, short-term postural sway was found to be significantly correlated with muscle activity in each of these groups. This work suggests that high levels of muscle activity are a characteristic of age-related declines in postural stability and that such activity is correlated with short-term postural sway. It is unclear whether increases in muscle activity preclude greater postural instability or if increased muscle activity is a compensatory response to increases in postural sway.

Sensitivity to Change and Responsiveness of Four Balance Measures for Community-Dwelling Older Adults

Background Impaired balance has a significant negative impact on mobility, functional independence, and fall risk in older adults. Although several, well-respected balance measures are currently in use, there is limited evidence regarding the most appropriate measure to assess change in community-dwelling older adults. Objective The aim of this study was to compare floor and ceiling effects, sensitivity to change, and responsiveness across the following balance measures in community-dwelling elderly people with functional limitations: Berg Balance Scale (BBS), Performance-Oriented Mobility Assessment total scale (POMA-T), POMA balance subscale (POMA-B), and Dynamic Gait Index (DGI). Design Retrospective data from a 16-week exercise trial were used. Secondary analyses were conducted on the total sample and by subgroups of baseline functional limitation or baseline balance scores. Methods Participants were 111 community-dwelling older adults 65 years of age or older, with functional limitations. Sensitivity to change was assessed using effect size, standardized response mean, and paired t tests. Responsiveness was assessed using minimally important difference (MID) estimates. Results No floor effects were noted. Ceiling effects were observed on all measures, including in people with moderate to severe functional limitations. The POMA-T, POMA-B, and DGI showed significantly larger ceiling effects compared with the BBS. All measures had low sensitivity to change in total sample analyses. Subgroup analyses revealed significantly better sensitivity to change in people with lower compared with higher baseline balance scores. Although both the total sample and lower baseline balance subgroups showed statistically significant improvement from baseline to 16 weeks on all measures, only the lower balance subgroup showed change scores that consistently exceeded corresponding MID estimates. Limitations This study was limited to comparing 4 measures of balance, and anchor-based methods for assessing MID could not be reported. Conclusions Important limitations, including ceiling effects and relatively low sensitivity to change and responsiveness, were noted across all balance measures, highlighting their limited utility across the full spectrum of the community-dwelling elderly population. New, more challenging measures are needed for better discrimination of balance ability in community-dwelling elderly people at higher functional levels.

Spinal cord injury-functional index: item banks to measure physical functioning in individuals with spinal cord injury.

OBJECTIVES To develop a comprehensive set of patient-reported items to assess multiple aspects of physical functioning relevant to the lives of people with spinal cord injury (SCI), and to evaluate the underlying structure of physical functioning. DESIGN Cross-sectional. SETTING Inpatient and community. PARTICIPANTS Item pools of physical functioning were developed, refined, and field tested in a large sample of individuals (N=855) with traumatic SCI stratified by diagnosis, severity, and time since injury. INTERVENTIONS None. MAIN OUTCOME MEASURE Spinal Cord Injury-Functional Index (SCI-FI) measurement system. RESULTS Confirmatory factor analysis (CFA) indicated that a 5-factor model, including basic mobility, ambulation, wheelchair mobility, self-care, and fine motor function, had the best model fit and was most closely aligned conceptually with feedback received from individuals with SCI and SCI clinicians. When just the items making up basic mobility were tested in CFA, the fit statistics indicated strong support for a unidimensional model. Similar results were demonstrated for each of the other 4 factors, indicating unidimensional models. CONCLUSIONS Though unidimensional or 2-factor (mobility and upper extremity) models of physical functioning make up outcomes measures in the general population, the underlying structure of physical function in SCI is more complex. A 5-factor solution allows for comprehensive assessment of key domain areas of physical functioning. These results informed the structure and development of the SCI-FI measurement system of physical functioning.

Development and initial evaluation of the spinal cord injury-functional index.

OBJECTIVES To describe the calibration of the Spinal Cord Injury-Functional Index (SCI-FI) and report on the initial psychometric evaluation of the SCI-FI scales in each content domain. DESIGN Cross-sectional survey followed by calibration data simulations. SETTING Inpatient and community settings. PARTICIPANTS A sample of participants (N=855) with traumatic spinal cord injury (SCI) recruited from 6 SCI Model Systems and stratified by diagnosis, severity, and time since injury. INTERVENTIONS None. MAIN OUTCOME MEASURE SCI-FI instrument. RESULTS Item response theory analyses confirmed the unidimensionality of 5 SCI-FI scales: basic mobility (54 items), fine motor function (36 items), self-care (90 items), ambulation (39 items), and wheelchair mobility (56 items). All SCI-FI scales revealed strong psychometric properties. High correlations of scores on simulated computer adaptive testing (CAT) with the overall SCI-FI domain scores indicated excellent potential for CAT to accurately characterize functional profiles of adults with SCI. Overall, there was very little loss of measurement reliability or precision using CAT compared with the full item bank; however, there was some loss of reliability and precision at the lower and upper ranges of each scale, corresponding to regions where there were few questions in the item banks. CONCLUSIONS Initial evaluation revealed that the SCI-FI achieved considerable breadth of coverage in each content domain and demonstrated acceptable psychometric properties. The use of CAT to administer the SCI-FI will minimize assessment burden, while allowing for the comprehensive assessment of the functional abilities of adults with SCI.

Developing a contemporary functional outcome measure for spinal cord injury research

Study design:This study used qualitative analysis of focus group discussions.Objective:The primary objective was to select functional activities to include in an item pool, which is the first step in developing a spinal cord injury computer adaptive test (SCI-CAT).Setting:This multisite study was conducted at six US National Spinal Cord Injury Model Systems Programs.Methods:Focus group discussions, which included persons with tetraplegia and paraplegia and clinicians, were conducted. Transcripts were analyzed using a grounded theory approach. Functional activities were identified, binned, winnowed, written as functional items, and cognitively tested.Results:Focus group discussion analysis identified 326 functional activity items that fit into categories outlined in the International Classification of Functioning, Disability and Health (ICF) framework: Mobility (193 items), including assessment of functioning in a manual (44 items) and power wheelchair (19 items); self-care (109 items); and communication (19 items). Items related to sexual function were also identified (5 items).Conclusion:The SCI-CAT item pool includes items that assess functional activities important to persons with SCI. Items cover a wide range of functional ability and reflect most ICF categories. The SCI-CAT pool is currently being field tested to develop a calibrated item bank. Further development will yield a CAT of functional activities appropriate for SCI research.

Conceptual Limitations of Balance Measures for Community-Dwelling Older Adults

Background Psychometric limitations of balance measures for community-dwelling elderly may be related to gaps in task and environmental representation. Objective The purposes of this study were: (1) to conduct item-level content analysis of balance measures for community-dwelling elderly people based on task and environmental factors and (2) to develop profiles of individual measures summarizing their task and environment representation. Design A systematic content analysis was conducted. Methods A literature search was conducted to identify balance measures. Item-level content analysis was based on 7 criteria related to task and environment: (1) task role, (2) environmental variation, (3) object interaction, (4) obstacle negotiation, (5) external forces, (6) dual-tasking, and (7) moving people or objects in the environment. Results Twenty-six measures, containing 167 items, were identified. Task role was fairly evenly distributed, with the majority of items examining gait tasks (32.3%), followed by dynamic body stability (29.9%) and static body stability (25.1%). The majority of items involved no environmental variation (58.1%), followed by variation of support surfaces (20.4%), visual conditions (13.2%), and both support and visual conditions (8.4%). Limited task role variability was seen within measures, with 73.1% of measures examining only one task role. Environmental variation was present in 65.3% of measures, primarily during static body stability tasks. Few measures involved object interaction (23.1%), obstacle negotiation (38.5%), external forces (11.5%), dual-tasking (7.7%), or moving people or objects (0%). Limitations The classification framework was not externally validated. Conclusions Existing measures focus on single-task assessment in static environments, underrepresenting postural control demands in daily-life situations involving dynamic changing environments, person-environment interactions, and multitasking. New items better reflecting postural control demands in daily-life situations are needed for more ecologically valid balance assessment. Individual balance measure profiles provided can help identify the most appropriate measure for a given purpose.

Development and initial evaluation of the SCI-FI/AT

Abstract Objectives To describe the domain structure and calibration of the Spinal Cord Injury Functional Index for samples using Assistive Technology (SCI-FI/AT) and report the initial psychometric properties of each domain. Design Cross sectional survey followed by computerized adaptive test (CAT) simulations. Setting Inpatient and community settings. Participants A sample of 460 adults with traumatic spinal cord injury (SCI) stratified by level of injury, completeness of injury, and time since injury. Interventions None Main outcome measure SCI-FI/AT Results Confirmatory factor analysis (CFA) and Item response theory (IRT) analyses identified 4 unidimensional SCI-FI/AT domains: Basic Mobility (41 items) Self-care (71 items), Fine Motor Function (35 items), and Ambulation (29 items). High correlations of full item banks with 10-item simulated CATs indicated high accuracy of each CAT in estimating a persons function, and there was high measurement reliability for the simulated CAT scales compared with the full item bank. SCI-FI/AT item difficulties in the domains of Self-care, Fine Motor Function, and Ambulation were less difficult than the same items in the original SCI-FI item banks. Conclusion With the development of the SCI-FI/AT, clinicians and investigators have available multidimensional assessment scales that evaluate function for users of AT to complement the scales available in the original SCI-FI.

Lower extremity Muscle force measures and functional ambulation in patients with amyotrophic lateral sclerosis

OBJECTIVE To examine the relation between lower extremity muscle force production and functional ambulation in patients with amyotrophic lateral sclerosis (ALS). DESIGN Retrospective analysis of data collected from 1979 to 1995. PATIENTS Two hundred forty ALS patients referred to the New England Medical Center Neuromuscular Research Unit. MAIN OUTCOME MEASURES Muscle force production during a maximum, voluntary isometric contraction of ankle dorsiflexors, knee flexors, knee extensors, hip flexors, and hip extensors was calculated as percent predicted maximal force (PPMF). Functional ambulation status was classified as unable, home, or community. RESULTS The probability of community ambulation compared with home increased with progressively higher PPMF for all muscle groups. Subjects with knee flexion strength greater than 75% PPMF were 395 times more likely to ambulate in the community. Subjects with hip extension strength over 50% PPMF showed improved chance of ambulation at home. CONCLUSION Lower extremity PPMF is a critical factor determining functional ambulation in patients with ALS. Knee flexors play an important role in community ambulation while the hip extensors are important for home ambulation.

Differential item functioning in the Patient Reported Outcomes Measurement Information System Pediatric Short Forms in a sample of children and adolescents with cerebral palsy

The present study examined the Patient Reported Outcomes Measurement Information System (PROMIS) Mobility, Fatigue, and Pain Interference Short Forms (SFs) in children and adolescents with cerebral palsy (CP) for the presence of differential item functioning (DIF) relative to the original calibration sample.

Measuring activity limitation outcomes in youth with spinal cord injury.

Study design:A cross-sectional study.Objectives:The Pediatric Spinal Cord Injury Activity Measure (PEDI-SCI AM), which includes calibrated item banks (child and parent versions) for general mobility, daily routines, wheeled mobility and ambulation, can be administered using computerized adaptive tests (CATs) or short forms (SFs). The study objectives are as follows: (1) to examine the psychometric properties of the PEDI-SCI AM item banks and 10-item CATs; and (2) to develop and evaluate the psychometric properties of PEDI-SCI AM SFs.Setting:US Shriners Hospitals for Children (California, Illinois and Pennsylvania).Methods:Calibration data from a convenience sample of 381 children and adolescents with SCI and 322 parents or caregivers were used to examine PEDI-SCI AM item banks, 10-item CATs and SF scores. We calculated group reliability, internal consistency (Cronbach’s alpha) and interclass coefficients (ICCs) to assess agreement between 10-item CATs, SFs and item banks. The percent of the sample with highest (ceiling) and lowest (floor) scores was also determined. An expert panel selected items for 14 SFs.Results:PEDI-SCI item banks, 10-item CATs and SFs demonstrate acceptable group reliability (0.73–0.96) and internal consistency (0.77–0.98). ICC values show strong agreement with item banks for 10-item CATs (0.72-0.99) and SFs. Floor effects are minimal (<15%). Ceiling effects are minimal for children with tetraplegia but high in children with paraplegia for general mobility (13.41–26.05%) and daily activities (12.99–32.71%).Conclusions:The PEDI-SCI AM exhibited strong psychometric properties for children with tetraplegia. Replenishment of the general mobility and daily routine item banks is needed to reduce ceiling effects noted for youth with paraplegia.