5
Functional Limitations Research in Rehabilitation Science and Engineering

Although rehabilitation interventions can effectively target impairments that can be remediated, little is known about the relationship between impairment and functional limitations (Jette, 1995). This chapter reviews knowledge and research in the area of functional limitation in the context of the enabling-disabling model (see Chapter 3). In this conceptual framework, the functional limitations result from impairment, and functional limitation may result in a disability. Reduction of functional limitation from arthritis alone by only 0.5 percent per year over 50 years could reduce disability by 4 million person-years, a savings of nearly $100 billion in 1993 dollars (Boult et al., 1996). Proper measurement of functional limitations is difficult and expensive, and many clinicians are not aware of the extraordinary deficiencies that exist in the functional limitations literature. For example, the functional benefits of strengthening exercises for older people with one or more weakness-producing impairments are essentially unknown, despite the obvious appeal of such a commonsensical notion. Although intervention strategies may be offered by the clinician, valid treatment outcomes have not been reported. Strength may have a nonlinear relationship to functional locomotion, because strength changes beyond some threshold may not engender further gait improvement (Buchner and deLateur, 1991).

At the opposite extreme, however, is the obvious and well-documented relationship between impairment from a lower limb amputation and the functional restoration provided by a leg prosthesis. Just as clearly, however, impairment does not always lead to functional limitation; in-



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--> 5 Functional Limitations Research in Rehabilitation Science and Engineering Although rehabilitation interventions can effectively target impairments that can be remediated, little is known about the relationship between impairment and functional limitations (Jette, 1995). This chapter reviews knowledge and research in the area of functional limitation in the context of the enabling-disabling model (see Chapter 3). In this conceptual framework, the functional limitations result from impairment, and functional limitation may result in a disability. Reduction of functional limitation from arthritis alone by only 0.5 percent per year over 50 years could reduce disability by 4 million person-years, a savings of nearly $100 billion in 1993 dollars (Boult et al., 1996). Proper measurement of functional limitations is difficult and expensive, and many clinicians are not aware of the extraordinary deficiencies that exist in the functional limitations literature. For example, the functional benefits of strengthening exercises for older people with one or more weakness-producing impairments are essentially unknown, despite the obvious appeal of such a commonsensical notion. Although intervention strategies may be offered by the clinician, valid treatment outcomes have not been reported. Strength may have a nonlinear relationship to functional locomotion, because strength changes beyond some threshold may not engender further gait improvement (Buchner and deLateur, 1991). At the opposite extreme, however, is the obvious and well-documented relationship between impairment from a lower limb amputation and the functional restoration provided by a leg prosthesis. Just as clearly, however, impairment does not always lead to functional limitation; in-

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--> deed, disfiguring dermatological impairments may cause societal disability but engender no functional limitations. Background The term impairment, for example, describes abnormalities in specific organs or organ systems (see Chapter 4). Pain* and decrements in strength, range of motion, balance, and endurance are examples of impairments. Functional limitations are restrictions or lack of abilities in performance of the whole organism or individual, assessed in a manner to eliminate external environmental barriers to performance. An individual's gait and other locomotor activities as assessed in a gait laboratory are examples of functional limitations measures. As such, functional limitations reflect an attribute of the capacity of an individual. In this report functional limitation is used as defined and discussed by Nagi (1965) and further developed in Disability in America (Institute of Medicine, 1991). Disability, in contrast to functional limitation, is a relational concept that describes any restriction or lack of ability to perform an activity in the manner or within the range considered normal for a human being. As a relational concept, disability reflects the individual's capacity to perform a task or activity necessary to achieve a role such as homemaker, worker, parent, or spouse, as well as the environmental conditions in which they are to be performed. These activities can be organized and assessed across different spheres of life. Thus, a subject's report of self-care performance (as reflected in the Sickness Impact Profile, Functional Independence Measure [FIM], Barthel, and other traditional activities of daily living [ADL] measures) is an activity, and measures of such are indicators of disability. The link between changes in impairment and changes in functional limitation has long been assumed, but it has rarely been documented scientifically. New impairments have been shown to engender locomotor compensatory mechanisms; to date, however, no data are available to link impairments to such compensatory mechanisms in individuals with specific functional limitations or disabilities. Until this link is established, it will be impossible to discern compensatory mechanisms such as Trendelenburg gait resulting from primary disabling and functionally limiting mechanisms such as hip abductor muscle weakness or range of motion limitation. *   Most often, pain is considered an impairment, a result of a pathology or impairment, and a cause for functional limitation. Chronic pain, pain that persists for 3 months or longer, has implications across the enabling-disabling process, with most significant impact at the level of disability and quality of life. Thus, pain may be identified at multiple areas of the model and may be modified through a variety of interventions.

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--> It is therefore not known at present whether rehabilitation interventions should focus on the impairment, the primary functional limitation, or the compensatory functional limitations level. Rehabilitation demands that all levels of disability be addressed. Until more functional limitations research is done, however, it will be impossible to know how much activity limitation is imposed by the environment and how much is imposed by the whole person's functional capacity. Virtually all rehabilitation texts suggest that strength, restriction of movement, and other impairments be measured during assessments of people with disabling conditions, but the current emphasis of health maintenance organizations and preferred provider organizations on rapidly returning patients to premorbid functional status is beginning to cause this paradigm to shift. Assessments of the level of home care support available and barriers to returning to work are causing disability and functional limitations to be measured first. Once established, the clinician can work to obviate the functional limitation by addressing it directly or, in the traditional way by fixing the impairment. Little research, however, supports either approach, and many more data are needed before such methods can be proven to be scientifically sound. Cross-Cutting Issues Two particular issues relative to functional limitations research must be addressed: (1) measurement of functional limitations and (2) time of onset or duration of impairment and functional limitation. Both of these issues affect the research and science in this area. Measurement in functional limitations research is essential, but it is poorly developed and often costly to complete. Measurement must be standardized for the age of the person with a disabling condition. It must also be recognized that people with disabling conditions age with their disabling conditions, and aging and secondary conditions affect the functional limitation and disability of those people. Measurement Measuring the effects of interventions has traditionally been at the impairment level. For example, clinicians frequently measure the levels of certain substances in blood, range of motion, and change in range of motion or strength in the laboratory. As well, burden of care or disability measures of performance are often confused as representing functional capacity measures. Typical examples of these measures are the FIM, Barthel, and other traditional measures. More recently, the FIM has been more consistently utilized to determine aggregate outcomes of a program

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--> rather than individual measurement. Measuring functional capacity outcomes requires determination of the performance of the whole person. Standardized measures of functional outcomes for use in evaluation or diagnosis are being developed, but they are not routinely used to obtain outcomes measurements for specific interventions. Contextual and environmental factors, however, must be noted and controlled: frequently, there is a difference between capability (the ability to complete a task in an ideal situation) and real-life performance (the ability to complete a task in a typical situation). Such standardized measures would be important for monitoring individuals and for determination of the costs-benefits of rehabilitation programs and interventions to society. Care must be taken in using existing outcomes measures accurately, because measurement at the functional limitation level is expensive and difficult. Functional limitations measures—obtained, for example, through gait studies and gait analysis—are few and incompletely validated. Although computerized locomotion analysis laboratories have been widely available for many years, few data support the need for gait analysis in clinical decision making, with the possible exception of presurgical decisions for children with cerebral palsy (Krebs, 1995). More studies of locomotor activities of daily living (ADL) are needed to assess functional performance pre- and postintervention and to provide descriptions of the nature of functional limitations. For example, it is known that people with balance disorders may have ataxic gait, but there is no quantitative clinical, bedside, or laboratory measure of ataxia. As a result, treatment for ataxia resulting from cerebellar lesions is entirely empiric. Measurement at the level of functional limitation requires at least whole-body, person-level measurements of performance of ADL. Such measures should include not only the gait on smooth, level surfaces but also sit-to-stand, stair ascent and descent, turning, reaching, and other locomotor ADL. Basic ADL include locomotor ADL and bowel, bladder, and sexual functions; that is, those ADL that are usually performed without aids or instrumentation. Instrumented ADL (IADL), by contrast, include some device such as a telephone or toothbrush in the performance of a task. Thus, the adaptation (or lack thereof) of the device will affect performance capacity. For example, a child may write or brush her teeth much better with a large-diameter pencil or toothbrush than with regular devices designed for use by adults. Elderly people with impaired vision will perform as well as subjects without impaired vision if the numbers on an instrument are large and have high contrast. Functional limitations research usually attempts to obviate such IADL differences, but in practice, some standardization is required even in basic ADL. For example, stair or chair height contributes substantially to performance variation (Krebs et al., 1992). Burden-of-care measures such as the Functional Independence

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--> Measurement usually attempt to estimate the impact of functional limitations on care providers, but they often ignore differences among IADL. As noted, these measures are disability-level measures. Aging and Secondary Conditions The age of onset of an impairment and the duration of impairment are recognized as important aspects of functional limitations knowledge and research. Aging must be considered in evaluating the functional status of a person with a disabling condition over time and in evaluating the appropriate interventions. Aging is a conception-to-death series of events that includes attaining, maintaining, and losing skills. Therefore, functional capacity changes with age. Growth and development affect the functional outcomes of interventions for infants and children with disabling conditions. No validated methods of discriminating between development and interventions in children with developmental disabling conditions exist. The process of aging discriminates against no person. Everyone is a participant in the process of growing older—including people with disabilities. ''Nondisabled Americans are getting older; they're living longer, there are vastly more of them, and they're getting old nonfatally. In short, they're becoming more disabled.... All at once, it seems, there are a lot of formerly nondisabled people around." (Corbet, 1990) In the last two decades increasing attention has been directed toward disability and aging. In people with disabling conditions, depending on the compensatory strategies used, secondary conditions and comorbidities, can affect functional status throughout a person's life. Secondary conditions are impairments, functional limitations, disabilities, diseases, injuries or other conditions that occur during the life of a person with a disability, where the primary disabling condition is a risk factor for that secondary condition, or may alter the management of health and medical conditions. This of course is based on the new paradigm that people with disabilities are healthy, that is a disabling condition does not imply illness and disease. Each factor in the interaction of disability and aging has the capability to become a "negative feedback loop" (Guralnick, 1994) which may lead to further disability or a new medical condition. In recent years, a body of literature regarding the effects of aging and secondary conditions has been developing. Spinal cord injury and aging is the best developed, with information available in the areas of quality of life (Evans et al., 1994), functional changes over time (Gerhart et al., 1993; Pentland and Twomey, 1994), premature and interactive effects of disability and aging (Ohry et al., 1983; Lammertse and Yarkony, 1991; Bauman and Spungen, 1994), aging and secondary conditions (Charlifue,

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--> 1993), and psychological adjustment (Krause and Crewe, 1991), among other issues. Cerebral palsy (Turk et al., 1996), spina bifida (Lollar, 1994), and polio (Maynard et al., 1991), among other disabling conditions, have also been studied. Identification of age-related changes and secondary conditions and their risk factors has been better developed (Whiteneck et al., 1992; Charlifue, 1993; Turk et al., 1995, 1996; White, Seekins, and Gutierrez, 1996) than prevention or intervention strategies. To illustrate, Table 5-1 provides some examples in various body systems of age-related changes, potential secondary conditions, and prevention strategies for people with mobility limitations such as spinal cord injury. This provides a heuristic and practical guide for examining the interactive effects among disabling conditions, aging, and secondary conditions. The issue of disability and aging is one more dimension that should be considered with the enabling-disabling model. As a person with a disability ages, a series of new pathologies, impairments, and functional limitations become placed over the previous pathologies, impairments, and functional limitations. Thus, the model is a snapshot in time of an individual's status in the disabling process. Relationship Between Functional Limitations and Impairments The committee searched Medline files to determine the quantity of peer-reviewed publications from 1966 to November 1996 addressing functional limitations. Of the 31,612 publications that used the term rehabilitation anywhere in the Medline file, only 34 used the term functional limitations. There were 4,980 publications that included the term "function," which might better represent "functional limitations" in rehabilitation research. Yet most of these articles focused on cell or organ function rather than whole-person function. Of the 34 publications that used the term "functional limitations," only a few examined changes in functional limitation. Therefore, it can be said that there is a paucity of published reports that truly represents research in functional limitations. This is in contrast to the relatively good support for functional limitations research by federal agencies as noted in Appendix A. This apparent mismatch of publications and funded research is likely related to confusion in terminology, difficulty in tracking systems, and unknowingly mixed impairment-functional limitations identifications, interventions, and measures. Funding agencies are increasingly supporting research intending to measure functional limitations, but few reports have emanated in part because functional limitations research is expensive and difficult to conduct.

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--> TABLE 5-1 Lifelong Motor Disabilities, Aging, and Secondary Conditions Body System Pathology, Impairment, or Other Conditions Leading to Potential Secondary Conditions Potential Prevention Strategies Skin and Subcutaneous Tissues Insensate skin; increased areas of pressure due to poor positioning, obesity, or limited weight shifts because of cognitive, behavioral, or personal care issues; decreased elasticity or turgor in aging with top layer thinning resulting in increased susceptibility to shearing and tearing; urinary or bowel incontinence. Regular weight shift routine; appropriate seating systems and surfaces; good nutrition and hygiene habits; social or cognitive support to follow through with prevention. Musculoskeletal System Decreased strength and endurance; decreased range of motion; pain; osteoporosis (must recognize hereditary and all acquired forms); asymmetric motor performance; overuse or repetitive activities on unprepared system; aging issues of decreased flexibility, strength, endurance, and balance; risk of falls; obesity. Maintenance of exercise programs (endurance, strength, flexibility); falls avoidance practices; osteoporosis prevention or management—must determine type of osteoporosis and state of clinical/ scientific information; use of proper body mechanics and posture; appropriate assistive devices utilization; environmental accessibility; consideration of ergonomically correct work and activity surroundings; use of energy conservation and joint protection techniques. Cardiovascular System Hypertension; atherosclerosis (similar risk factors as in nondisabled individuals); limited activity and exercise; deep venous thrombosis and resulting pulmonary emboli—more often an early complication; obesity; age-related changes of slower responsiveness to position or heart rate change. Health practices to identify risk factors for atherosclerosis (hypertension, smoking, hypercholesterolemia or hyperlipidemia, diabetes, menopause, etc.) and initiation of prevention or management strategies; good nutrition; maintenance of exercise or activity programs.

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--> Genitourinary System Urinary retention or incontinence; change in urinary function from existing underlying condition (expected or unexpected progressive changes); progressive and chronic kidney filtration changes from poor or unchanged bladder management techniques; chronic urinary tract infections; kidney stones; prostate enlargement; urinary continence changes with menstrual cycle; changing urinary function from aging (e.g., reduced bladder capacity, decreased tissue compliance, reduced flow rate). Monitoring of fluid intake and output; maintaining regular voiding schedule (e.g., intermittent cath program, use of medication, timed voiding program); achieving acceptable hygiene program; participation in regular evaluation of urinary management (e.g., urodynamics, renal scans, postvoid residual checks); reporting of urinary habit changes; consideration of surgical options when appropriate; education in the consequences of urinary management, pros and cons of suggested interventions. Respiratory System Compromised breathing or cough due to underlying weakness; aspiration; existing obstructive or restrictive pulmonary disease or progression; breathing changes associated with aging (e.g., loss of reserve capacity, decreased tissue compliance); obesity; progressive weakness due to underlying condition; recurrent pneumonia. Monitoring pulmonary function as appropriate and reporting changes; cessation of smoking or contact with secondary smoke; use of assistive coughing; maintaining exercise or activity program and health diet; education of management strategies in progressive conditions; use of vaccinations when appropriate. Gastrointestinal System Decreased bowel motility with increased transit time; esophageal reflux; peptic ulcer disease; constipation or obstipation; megacolon; abnormal swallow function; hemorrhoids or risk for hemorrhoids with bowel program; malabsorption. Good nutrition with diet modification (e.g., consistencies, textures, tastes); maintaining and monitoring routine bowel evacuation with consideration of fiber, fluid, and medication; review of routine medications which could contribute to decreased bowel motility; avoiding overuse of bowel medications; monitoring diet history and weights; reporting changes in bowel evacuation. NOTE: This is not an inclusive table and serves as a practical guide only. SOURCE: Adapted from S. W. Charlifue (1993)

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--> Functional Capacity Index and the 10 Dimensions of Function As mentioned above, one of the current issues within functional limitations research is measurement and quantification of functional limitation in an individual. One proposed method of classification is embodied in the recently developed Functional Capacity Index (FCI). As a way to map out anatomic descriptions of the nature and extent of functional limitations, the FCI first defines 10 dimensions of function in which scientists can describe physical capacity (MacKenzie et al., 1996). Using the FCI as a guide to describing the different areas of research in functional limitation, this chapter reviews 10 dimensions of function: (1) locomotion, (2) hand and arm manipulation, (3) bending and lifting, (4) eating, (5) elimination, (6) sexual function, (7) visual function, (8) auditory function, (9) speech, and (10) cognitive function. The category of pain is excluded because it does not describe function but rather determines function. Thus, only to the extent that pain affects function in each of the dimensions will it be reflected in this schema. Pain can be considered an impairment, and intervention for pain is often at the organ system level. Cardiopulmonary function is not identified individually, but is felt to be included for performance of most of the functions. It should however be noted that rehabilitation science and engineering has had direct involvement in research and intervention in this area (e.g. cardiac rehabilitation, pulmonary rehabilitation, mechanical ventilation [noninvasive and invasive]). Psychosocial function is also excluded, consistent with the entire committee report. It should be noted that much of what is reported in this section is a combination of impairment and functional limitations research, and at times consideration or recognition of disability and quality of life measures. This points out the difficulty in identification of this research realm, but as in rehabilitation science and practice, recognizes the often blurred and necessary distinctions. Locomotion Functional Limitations Strength Impairment Relationships to Locomotor Functional Limitations Scant data exist on strength training among people with impairments, still fewer studies include people with functional limitations, and to date no reports relate strength changes to disability measures and locomotor activities among people with disabling conditions. "Although high-intensity training increases force-generating capacity, little is known about its effects on functional performance. Unless investigations are conducted in which different measures of functional performance are made prior to

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--> and following resistance training, the validity of this approach to improving the quality of life of older persons cannot be established" (Hopp, 1993, p. 371). Studying only outcomes and not the mechanisms by which strength contributes to function has produced limited and contradictory results. For example, Fiatarone et al. (1990) found that frail institutionalized subjects with a mean age of 90 ± 1 years experienced highly significant strength gains (mean strength gain, 174 ± 31 percent) following an 8-week high-resistance exercise training program, but they did not measure functional locomotor benefits or the real-life role changes, if any, that resulted. Using cardiopulmonary and musculoskeletal outcomes measures, Morey et al. (1989) reported significant improvements in endurance, strength, and flexibility following regular exercise for 49 elderly people with chronic diseases including arthritis, heart or lung disease, and diabetes. By contrast, Thompson et al. (1988) reported that 16 weeks of exercise among 22 elderly people with hypertension, chronic obstructive pulmonary disease, or osteoarthritis resulted in no changes in cardiopulmonary performance, timed tasks, balance tests, and extremity muscle performance. One of the few extant studies showing a clear relationship between isokinetic strength and objectively tested gait and locomotion variables was limited primarily to young subjects following knee arthrotomy (Krebs, 1989). Lord and colleagues (1993) used retrospective data to suggest that strength exercises engender better balance and gait in women ages 57 and older. Gehlsen and Whaley (1990), however, reported a low correlation between balance and strength outcomes in elderly subjects divided into fallers and nonfallers. Judge et al. (1993b) reported that gait measures improved insignificantly among 31 exercising elderly subjects (mean age, 82.1 years); self-selected gait velocity improved 8 percent, but maximal gait speed increased only 4 percent. Judge and colleagues (1993a) did find that combined exercise training (resistance exercise, brisk walking, postural control, and flexibility exercises) produced improved balance outcomes compared with those from flexibility exercise training among 21 women with a mean age of 67.8 years. No study has examined the extent to which potentially destabilizing postural compensations for weakness, such as excess abductor lurch or forward trunk rotations, are ameliorated following strength gains. Balance Impairment Relationships to Locomotor Functional Limitations Rehabilitation scientists have begun to study whether exercise improves impairments and performance of ADL; the important missing component that should be addressed includes the relationship of impairments

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--> and disabling conditions to compensatory mechanisms and functional limitations. Whole-body locomotor studies provide insight into postures substituted for or compensatory mechanisms for lower-limb weakness or other impairments. One third to one half of all people over age 65 experience a fall, many of which are injurious, and most occur during locomotion (Overstall et al., 1977; Baker and Harvey, 1985; Pentland et al., 1986; Tinetti and Ginter, 1988). To date, most investigations of "balance" have investigated standing-still activities alone. Although compensating for an internal or external perturbation while trying to stand is still important, most exercise treatments have been developed in part because standing still is easily measured by timed tests or with force plates (Heitmann et al., 1989). Few facilities are capable of measuring whole-body posture and momentum during locomotor studies. No studies have described objective changes in gait, balance, or locomotor function from exercise interventions among patients with cerebellar disorders (CbD). Rehabilitation of individuals with acute CbD has included the use of Frenkel's exercises, rhythmic stabilization (Littell, 1989), and walking aids and weights (Urbscheit, 1990; Morgan, 1975). Frenkel's exercises were the earliest exercises used to reduce lower-limb dysmetria. Frenkel's exercises can be performed in the supine, sitting, or standing position and can involve performance of slow active movements by the subject while the subject is carefully watching the extremity. Kabat described proprioceptive neuromuscular facilitation in 1955, including resistive exercises that were used to develop strength, endurance, balance, and gait (Littell, 1989). However, no systematic research studies of the efficacy of proprioceptive neuromuscular facilitation for patients with CbD have been reported. There is sparse evidence of successful treatment of chronic CbD, and it has been regarded as a condition refractive to treatment (Sage, 1984). Generally, rehabilitation intervention in individuals with chronic CbD has been restricted to substitution strategies and conservative management, such as recommending that affected individuals increase their base of support or use assistive devices (such as canes and wheelchairs) to improve stability and maintain their range of motion. Most treatment-related publications lack adequate intervention descriptions. Balliet et al. (1987) were among the first investigators to propose neuromuscular retraining methods. They described five patients with chronic CbD and gait disorders who reacquired "proper motor control and associated balance through slow, successive adaptation to increasingly demanding conditions" (Balliet et al., 1987). All 5 individuals improved on all variables measured; however, the overall treatment duration varied from 3 months to 2 years. Brandt and colleagues (1981)

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--> or companion telecommunication devices for people who are deaf. Interpreters for both oral and manual communication can be provided in other situations. Strategies for enhancing visual communication, including lighting and seating positions, may be used. An auditory impairment can greatly complicate assessment and rehabilitation of other physical impairments. Assessments of cognitive or receptive language ability following a stroke may be based on hearing-based tasks that usually assume that the auditory system is healthy. This is a tenuous assumption because of possible preexisting peripheral auditory pathology. Incorrect responses to certain questions by an individual who has experienced a stroke may be interpreted as a cognitive deficit when in fact the responses may be the result of misperceptions due to a preexisting, mild peripheral hearing impairment, a common condition in people who are elderly. Hearing: Engineering Advances Hearing loss, after having normal hearing, is common, particularly among elderly people. Engineering advances have made hearing aids much smaller and more effective than earlier versions. Although hearing aids are useful they have many shortcomings that signal processing theory, technology (e.g., digital processors), and better understanding of the auditory system and its pathologies should be able to improve. The ability to place computers within hearing aids opens up a whole new world for hearing assistance. These new technical opportunities may produce changes in hearing aid performance that are as dramatic in nature as the changes that computers have brought about in society in general. Future Needs All of the technological devices mentioned above can be improved. Furthermore, as the technology is improved, behavior-based rehabilitation procedures need to be modified accordingly. Therefore, research projects need to center on both improvements to the devices themselves and improvements related to rehabilitation strategies, particularly as they interact with various technologies. Research projects can be at the cellular level (e.g., development of improved electrodes for cochlear implants), the signal processing level (e.g., development of improved digital processing software for enhancing speech perception with computer-based hearing aids), the assessment level (developing physiologically based techniques for detecting and quantifying hearing impairments in neonates), and the environmental level (developing strategies for supporting the communications abilities of all people).

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--> Speech Limitations of speech include difficulties in voice production and articulation, not in language, content, or structure of communication. The latter group are determined by cognition and are noted in the "Cognitive Function" section. Speech function is characterized by articulation and audibility and ability to produce and sustain a reasonably fast rate of speech. Impairment Relationship to Functional Limitation The normal process of human speech is accomplished through controlled and sequenced respiration, phonation, and articulation, with adequate resonance from the cavities of mouth, nose, and pharynx. Voice production through the vocal mechanism is accomplished through active inspiration (through activity of thoracic and neck muscles and intrathoracic pressure changes), and expiration through the larynx that is both passive (muscle relaxation and gravity) and supported (abdominal and intercostal muscle activity) for prolonged exhalation for speech. Phonation and articulation require steady maintenance of air pressures, balanced vocal cords, and coordinated actions of tongue, lips, jaw, and soft palate. Resonance in the pharyngeal, oral, and nasal cavities are modified by changing the shape of the vocal tract, again requiring intact musculature and intra vocal tract pressure control. The coordination, sequencing, and programming of these activities is directed by the brain, most specifically, the left frontal cortex. An impairment at any organ level involved in the process will influence speech production, and lead to a functional limitation in speech. Assessment of the impairment focuses on the speech production process. Impairments often occur at varying levels of severity and at numerous points in the process, all of which are interdependent. The speech functional limitation is focused most on intelligibility, and measures have been used to determine intelligibility in the clinic setting (functional limitation). It is recognized that intelligibility scores can be influenced by the speakers' task, the transmission system, and the judges' task (disability) (Yorkston et al., 1984; Yorkston and Beukelman, 1981) Current Status of Science and Research There are a variety of conditions that describe limitations in speech. Etiologies for speech limitations can be at a central or peripheral area, can involve motor control, and can be mechanically related. Dysarthrias are characterized by slow, weak, imprecise, or uncoordinated movements of

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--> the speech musculature, which results in reduced speech intelligibility. A number of diagnoses can be associated with dysarthria, and includes cerebral palsy, stroke, parkinsonism, multiple sclerosis, brain injury, muscle diseases, and amyotrophic lateral sclerosis. All or several speech subsystems may be involved in varying degrees (respiratory, phonatory, pharyngeal, and articulatory) (Miller et al., 1993). The dysarthrias can be described and diagnosed based on a cluster of features. (Darley, 1969a,b; Rosenbek and LaPoint, 1985). There are a variety of assessments that measure speech performance (Netsell, 1973; Netsell et al., 1989; Gerratt et al., 1991), since intelligibility is the hallmark of functional speech. Most tools are perceptual, and rely on a trained observer. However, at an impairment level, respiratory performance can be measured aerodynamically (Netsell, 1973); acoustic analysis can be performed (Keller et al., 1991); and measures of laryngeal resistance can be obtained (Smitheran and Hixon, 1981). Application of these technologies as a measure of intervention assessment could be helpful, but measures only a limited portion of speech function. Standard tools have been developed to measure sentence and single word intelligibility and speaking rate in a more structured fashion (Yorkston et al., 1984). Those with severe limitations in speech may require augmentative or alternative communication devices. Treatment goals are to establish a functional means of communication. Systems range from communication boards and books to computer based speech synthesis systems (Brandenburg and Vanderheiden, 1987; Yorkston and Beukelman, 1991). Simple low tech strategies must also be considered and may be preferred. The selection of the most appropriate intervention requires careful consideration of the individual's capabilities (e.g., cognitive function, vision, hearing, hand and arm manipulation, positioning for function), proposed use in the selected environments, and financial issues. Lifelong use of these devices or staging of interventions need to be investigated more fully. A moderate or mild limitation in intelligibility may require exercises to improve respiratory control (Netsell and Daniel, 1979; Bellaire et al., 1986), change speech rate to improve intelligibility (Yorkston et al., 1990), or focusing on phonation (Ramig, 1992). Effectiveness of speech interventions for individuals with spastic dysarthrias has been documented through case reports, single-subject design studies, and uncontrolled group treatments (Aten, 1988). Study outcomes measure changes in muscle strength and control, reduction in consonant imprecision, and improved intelligibility and speaking rate (Yorkston, 1995). A prosthetic lift at the nasopharyngeal area may improve dysarthria by controlling oral air pressures (Gonzalez and Aronson, 1970). Interventions for per-

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--> sons with progressive disorders require changing interventions, based on function (Hillel et al., 1989). Articulation and phonologic disorders comprise a large portion of speech limitations. Disruptions in speech, or stuttering, vary greatly in frequency, duration, type, and severity. Stuttering is characterized by hesitations, prolongations, and repetitions of speech. Treatment effectiveness studies in school aged children show about a 61% reduction (Conture and Guitar, 1993). In adults, 60 to 80% improve with treatment (Bloodstein, 1987). Treatment approaches are determined by a variety of factors, and may be intensive or extensive (Conture, 1995). Articulation and phonologic disorders are among the most prevalent speech limitation in preschool and school aged children, affecting 10% of this population (Geirut, 1995). Interventions in this age group have been long-standing (Sommers, 1992). Hearing impairments must be considered in the pediatric group in particular when speech delays are noted. Laryngeal-based voice disorders are characterized by abnormal pitch, loudness, or vocal quality and ranges from mild hoarseness to complete voice loss. Voice therapy can improve the characteristics of voice and reduce laryngeal pathology (Ramig, 1995). Voice treatment has been found to improve vocal nodules and to reduce recurrence if instituted after surgery (Lancer et al., 1988). Speech options after laryngectomies include external prosthetic devices (electrolarynxes and pneumatic reeds) (Miller et al., 1993), tracheal-esophageal puncture (one-way valved voice prosthesis) (Singer and Blom, 1980), and esophageal speech (Gates et al., 1982). Outcome studies have shown both difficulties (Schaefer and Johns, 1982; Miller et al., 1993) and success (Singer et al., 1981; Wetmore et al., 1985; Miller et al., 1993). Technology has assisted speech production for persons with chronic tracheostomies. In particular, the Passy-Muir tracheostomy speaking valve allows speech production through a one-way valve which opens with inspiration, and closes with expiration, redirecting air into the trachea and vocal cords creating sound through the oral and nasal cavities. Speech: Engineering and Technical Advances Communication aids for people who are unable to speak came into existence about 30 years ago, and the application of the sciences of information theory, computational linguistics, and coding theory, along with new computer technologies, have had a material influence on the ability of people to generate messages through standard alphabetic notation, speech input, or symbolic methods. Nevertheless, not all people who are unable to speak are able to communicate in these novel ways. Engineering and rehabilitation science can make big advances in this area, as well

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--> as in the recognition of speech that is difficult to understand through the translation of utterances into understandable artificial speech. Cellular telephone links (voice and data), fax services, e-mail, and the Internet have opened up wide communication channels for everyone and it is incumbent upon rehabilitation technology to make these links accessible to people with disabling conditions, using universal design where possible. These communications systems can also provide much assistance to people with sensory losses (e.g., hearing or visual losses). Future Needs Currently, the majority of outcome measures in speech rehabilitation are perceptual or observational, and lack standardization. Research into the development of standardized instrumental and observational measures would move evaluation to the functional limitations level. Research regarding the effectiveness of interventions using rigorous descriptions of interventions and outcome measures would provide a basis for duration and frequency of treatments and indications for treatment options. Application of speech intelligibility measures into the disability realm would allow a realistic measure of intervention success. In addition to the specific areas identified above, research along the lifecourse regarding interventions and devices is needed. Issues of patient and family choices should be considered. Cognitive Function Relationship of Impairment and Functional Limitation The performance of everyday activities is supported by a number of physiological and psychological processes. Cognition represents one of these processes that guides individuals as they acquire and use information to support their actions. Cognition at the impairment level involves the mechanisms of language comprehension and production, pattern recognition, task organization, reasoning, attention, and memory (Duchek, 1991). When these mechanisms are intact, they support the person in learning, communicating, moving, and observing. When the mechanisms are deficient, they create functional limitations for individuals who require rehabilitation services to learn strategies to bypass the deficit or compensate for the loss, or both. They also create functional limitations for the families of such individuals. Cognitive problems are common following stroke or head injury in people with Parkinson's and Alzheimer's disease and in some people with multiple sclerosis and other chronic conditions. It is the beginning of

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--> a new era in the study of cognition as ''we understand how experiences generate changes in the nervous system that shape our language, our visual world, our coordinated movements, our cognition" (Merzenich et al., 1993, p. 17). It should be the goal of rehabilitation to minimize the consequences of brain injury in the lives of those who suddenly are impaired by difficulties in living, social interaction, family life, and vocational and educational pursuits. The major cognitive deficits that create functional limitations are described below. Aphasia is the term attributed to difficulties with language comprehension and expression. It is the absence or impairment of the ability to communicate through speech, writing, or signing and may limit the person's ability to comprehend or express language making it very difficult for the person to communicate wants, needs, and ideas to others. Agnosia refers to problems with pattern recognition. Agnosia can impair the recognition of objects, facial discrimination (Allender and Kaszniak, 1989), and the recognition of voice tone (Eslinger and Damasio, 1986), making it very difficult to recognize familiar people and voices and common objects such as a fork, toothbrush, or razor. Agnosia presents a difficult challenge, requiring rehabilitation and education for the affected individual and the family. Apraxia describes the deficit that occurs when an individual has difficulty in organizing and executing purposeful movements. Functional limitations occur when the person cannot perform tasks such as putting an arm in a sleeve, reaching for a glass to take a drink, or even putting one leg in front of the other to take a step. Deficits in reasoning and problem solving are frequently the result of frontal and temporal lobe damage (Mayer et al., 1986; Sullivan et al., 1989). Functional limitations occur because a person cannot put steps together in a sequence to accomplish a goal or may not be able to choose the items or tools necessary to perform even a simple task such as putting on a robe. Such a deficit makes tasks such as driving a car, paying bills, preparing food, and using the telephone problematic without training in compensatory strategies and environmental modifications. Executive function comprises the mental capacities required to formulate goals, plan how to achieve them, and carry out the task effectively (Stuss, 1992). A person with impaired executive function has a functional limitation that results in difficulty beginning an activity, monitoring his or her performance during an activity, inhibiting irrelevant information, and maintaining attention. This configuration of cognitive problems makes independent living and productive work a challenge for a person who has sustained an injury and for the rehabilitation professional who needs to help the person and the family learn how to give the cognitive support that will make performance possible.

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--> Memory plays a very important role in everyday functioning. Different types of memory can be impaired, depending on the location of the brain damage. Deficits in short-term memory, which holds information for further processing, can make new learning difficult. Individuals with memory loss often need rehabilitation to develop strategies to access long-term memory for personal events and general knowledge, to remember future events, and to support the procedures required to perform an activity. Cognitive deficits that impair memory have a profound impact on the performance of people as they recover from physical impairments and move on to try to reestablish independence following injury or illness. Cognitive Issues: Engineering and Technical Advancements Few investigators have examined if or how technical devices might be helpful in cases in which and individual is impaired because of the loss of cognitive ability. Nevertheless, it is known that developments in this area will not occur de novo. Positive action needs to be taken to investigate how assistive technical aids may be useful in this area. Action needs to come through the interaction of scientists, clinicians, and engineers. Memory aids and the use of step-by-step instructions are areas tailor-made for providing technical assistance, and engineering may be able to help make significant advances in this area. However, collaboration with families and caregivers, will be necessary for the problems to be understood and for design iterations to be based on realistic clinical experiences. Future Needs Cognition plays a critical role in the performance of the tasks of living. When any of these deficits occur (and many of these deficits occur simultaneously), the person is disabled until environmental and compensatory strategies are put in place to support him or her. During the past decade, the emphasis on biomedical science has generated new knowledge about brain plasticity and brain structure-function relationships. As this emphasis expands to include issues of functional limitation and disability, it should be possible to test the application of these findings in clinical interventions to determine how individuals with brain injuries can improve their performance of functional, real-world tasks (e.g., self-care, meal preparation, parenting, and employment). Most cognitive research has been performed at the impairment level and has involved the administration of experimental and neuropsychological tests. As more clinical studies have been funded, investigators

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--> have learned that patterns of behavior in the real-life context differ from those that would have been predicted from neuropsychological tests (Prigatano and Altman, 1990). When a cognitive deficit occurs, the person also experiences changes in emotion, social interaction, and communication; these changes can range from subtle to severe changes and can create complex difficulties for the individual and his or her family, coworkers, and friends. Rehabilitation strategies to overcome problems presented by aphasia, agnosia, and apraxia require further development and testing and will be understood more fully when scientists and engineers interact with clinicians and patients to understand the impact of these conditions on people's lives. The research needed to understand the impact of cognition on the individual and society and the potential of environmental and learning strategies on recovery and functioning is yet to be done. It will require research of issues beyond the current biomedical mechanisms that exist today and involve interdisciplinary teams of professionals from fields that span education, philosophy, cognitive psychology, and neuroscience, including neurobiology and neuroradiology. The research must also include rehabilitation professionals such as occupational therapists, speech language pathologists, physicians, and neuropsychologists. Such teams working together may begin to obtain an understanding of the mechanisms that underlie the recovery and preservation of cognitive functions after brain damage. It will be important to determine if there are aspects of affective disorders that can be distinguished from the cognitive sequelae of acquired brain injury and determine if the brain has different processing pathways for different types of information after brain injury (Buckner et al., 1996). For example, it would be possible to explore whether the cerebellum's contributions to motor learning generalize beyond the purely motor domain and whether the preserved function demonstrated by some people with disabling conditions is mediated by sparing of critical tissue or by compensatory neural pathways. It would be important to know how a deficit in inhibitory control affects everyday function; that is, can different aspects of attentional processing (e.g., divided attention, visual search, and vigilance) predict everyday functioning, including a complex task like driving or work. Not all disability comes from within the individual. Each person needs a supportive environment to perform at his or her best. A study of cognition prompts investigators to ask new questions. How does cognitive activity relate to specific environmental contexts? What is the role of mediated action in the actual performance of cognitive and functional tasks in people with acquired brain injury and those with no cognitive loss? What role does the environment play in the internal representation and

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--> processing of visual information? Also, how is it possible to prepare spouses and families for the multitude of tasks required for life with a person who is severely disabled because of an acquired head injury? Such questions can only be addressed when there is a level of analysis and method of measurement that allows for the description of cognitive deficits in real-life activities. Functional means of measuring intellect, motivation, mood, judgment, visual perception, auditory perception, motor control, visual attention, vigilance and arousal, working memory, procedural memory, declarative memory, and motion in context must be developed. The challenge of preventing disabilities in those with cognitive loss cannot be left at the level of functional limitation. New means of addressing the cognitive needs of individuals must come to the forefront in science to reduce the devastation of a cognitive impairment on the lives of the people and their families who must live with the consequences of the functional limitations brought on by injury and disease. Conclusions Although there is little published research on functional limitations' responsiveness to rehabilitation, this is only partially traceable to the limited funded research in this domain. Functional limitations research requires whole-person studies, which are costly and difficult to perform. Only clinical research that involves the whole person is, by definition, relevant to functional limitations research. Until functional limitations are properly studied, the role of the environment in preventing the physical expression of the person's capacity (i.e., disability) cannot be understood. The process of rehabilitation has heretofore focused on impairment-level interventions, but the economics of rehabilitation, especially in the managed health care sphere, is requiring that people be discharged home as soon as possible. In turn, functional limitations become paramount concerns because they alone prevent the person from returning to the premorbid environment after rehabilitation. Altering the environment to accommodate functional limitations, such as by adding a raised toilet seat following hip replacement or providing durable medical equipment following major amputation or spinal cord injury, are time-honored rehabilitation approaches. The historic reluctance of insurers to pay for such environmental modifications is understandable if one appreciates that society, not the insurer, benefits from improved functional capacity and thus decreased need for "external" support. If the functional capacity of a person, for example, a person with chronic back pain, increases as a result of rehabilitation and the person is able to return to work, society obtains an income tax-paying and less healthcare resource-consuming, member. The insurer benefits directly only inasmuch as the person consumes fewer

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--> health care resources. More functional limitations research is urgently needed to determine the optimal role of rehabilitation for individuals with disabling conditions compared with interventions at the societal or environmental level. Recommendations Recommendation 5.1 The National Institutes of Health (NIH) should ensure that rehabilitation scientists in general, and functional limitation researchers in particular, are well represented on study sections. NIH also should expand the research capacity of its Institutes to include functional limitations and rehabilitation research as important aspects of their missions. Recommendation 5.2 A mechanism should be established, possibly through consensus panels, to frame the questions about functional limitations that would help to draw the link between impairments and functional limitations for the purpose of building the science of rehabilitation. Recommendation 5.3 The Computer Retrieval of Information on Scientific Projects system and other databases used to track research funded by federal agencies should use a government-wide code or coding mechanism to describe rehabilitation research that includes the concepts and definitions of pathology, impairment, functional limitation, and disability presented in this report. This would allow for the more appropriate classification of functional limitations and rehabilitation research. Recommendation 5.4 A commonly used terminology and taxonomy* should be developed and used that would allow scientists and professionals to communicate more effectively with each other across disciplines. This would include terminology regarding methodologies, measures, the enabling-disabling process, and other descriptors of performance and functional limitations. Recommendation 5.5 More research is needed to obtain an understanding of the factors that determine the changes in and causal relationships among impairments, functional limitations, and disabilities, and move- *   Appendix C contains a preliminary draft of an outline of a taxonomy.

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--> ment among these states. Such research should be clearly focused on improving public health from a lifelong perspective. Recommendation 5.6 More research is needed to improve the understanding of the impact of aging and other lifelong disabling conditions on functional limitations and secondary conditions. Recommendation 5.7 The science supporting functional limitations depends on integrative studies of the whole person. Behavioral measurement and the development of valid functional limitation measures, should be high priorities in rehabilitation research.