As a major feature of population-based studies, a sleek classification system of impairments would simplify the process of clinically projecting functional limitations associated with specific impairments. With a more operationally friendly system, we would expect to provide clinicians with tools for determining patients’ likely functional needs as they attempt to remain living in their communities.
The Perceived Causative Impairment Classification system has implications for understanding likely types of activity limitation (ADL vs. IADL) as well as the nature of assistance required for elderly people living in the community with particular types of conditions. Consistent with the findings of others, we found that chronic illnesses affecting the musculoskeletal, brain or behavioral, or cardiovascular systems represent the major perceived causes of functional loss in elderly populations.25, 26
All persons in this study by definition had health conditions of sufficient severity to cause activity limitations, yet patterns of activity limitation, the severity and the types of assistance needed differed across the impairment categories in clinically logical ways.
Although musculoskeletal impairments were the most common cause of activity limitations in the US population, those involving brain or behavioral impairments were the most disabling, highlighting the importance of PM&R to maintaining and building future professional capacity in the area of managing impairments associated with brain disorders. After adjusting for age, gender and race, elderly persons with perceived causative impairments involving the brain or behavior and those who could not identify a single causative condition were approximately 3 times more likely than those with cardiopulmonary or hematological impairments to have ADL limitations. Since ADLs depend on the more fundamental body movements, balance and cognitive sequencing (executive function), it is not surprising that those with brain or behavioral, and multiple impairments were more likely than those with other types of impairments to experience ADL problems. Conversely, IADLs are more dependent on endurance, energy and the ability to interact intellectually at higher levels with others and with the environment. Thus, impairments that limit energy such as those involving the cardiopulmonary or hematological systems or impairments that limit the capacity of the person to obtain important sensory information from the environment such as vision or hearing would logically tend to primarily interfere with IADL functioning.
The associations between impairment and the need for physical help or supervision with ADLs were also clinically intuitive. As expected, respondents whose limitations were attributed to health conditions classified in the brain or behavioral impairment category were also the most likely to need supervision or physical help when performing ADLs. This strong association is consistent with our hypothesis that people with these types of impairments would be more likely than those with other types of impairments to be seen as requiring help and/or supervision in carrying out ADLs. Brain or behavioral impairment can be associated with any combination of mental disturbances, paralysis, movement disorders, or sensory loss. These manifestations logically translate into the most severe activity limitations, i.e., those needing a second person to be available when performing ADL. In contrast, elderly people whose activity limitations are attributed to impairments of the cardiopulmonary or hematological systems, because they experience fatigue, will logically have difficulties performing the most energy-demanding IADL, but will be less likely to require a second person to help them perform the simpler and less energy-demanding ADLs.
Those with musculoskeletal conditions, the most common perceived causative impairment, were more likely than those with cardiopulmonary or hematological conditions to require a second person when performing ADL, but they were less likely than those with brain or behavioral impairments to require a second person. People with musculoskeletal conditions likely experience pain or difficulty with performance, rather than complete loss of physical strength or cognitive impairment, where help or supervision would be required.
Because earlier research has shown that functional limitations are more prevalent in women27,28
and the elderly,29,30
we controlled for gender and age in our models. The association between perceived causative impairment and activity limitations remained statistically significant after removing the effects of these demographic differences. Only a very advanced age of 85 years and older remained independently associated with an increased likelihood of needing a second person in performing ADL after adjustment for causative impairment.31
Findings from this study have implications for understanding patient and caregiver participation in the experiences of disability, as well as for research, clinical practice, and healthcare policy. The perceived causative impairment classification may give clinicians a quick picture of the patient’s or close proxy’s perceptions of the conditions underlying activity limitations, and facilitate the planning of appropriate interventions. ADL and/or IADL limitation may be considered a final common pathway resulting from clinically significant impairments as caused by myriad types of illnesses and injuries. Yet the pharmacological treatments, physical or occupational therapies, environmental modifications, as well as the caregiver infrastructure and support systems required will all depend on the impairment and its prognosis.
The implications of activity limitation will depend on the type and nature of limitation. IADL limitations suggest early or more mild disability compared to ADL limitations. IADL activities, unlike ADL activities, are often routinely performed by others such as a spouse and, if not, can be more easily taken over by others. Conversely, once an individual needs ADL assistance from a second person s/he loses the ability to participate autonomously in managing intimate personal care. Once supervision is necessary, privacy is lost. Whether physical help is needed or supervision is necessary shapes the individual’s participatory experiences. The need to wait for physical help reduces spontaneity. From the caregiver’s perspective, the nature of assistance required by the individual will bear on opportunities to participate in other desired life occupations and activities. The nature of assistance needed also has bearing on the capacity or willingness of the caregiver to provide essential care. Need for physical help may require physical lifting, while need for supervision may require less physical strength but a greater time commitment, sometimes around the clock.
There were a number of study limitations. First, the study was based on the survey of respondents’ perceptions regarding the health conditions they believed were causing their activity limitations. Their perceptions may or may not concur with a clinician’s impression based on an objective medical evaluation. It is important to recognize such potential disparities when communicating with patients and formulating treatment plans. Future studies are needed to examine concordance between the causes of activity limitation as identified by respondents versus health care professionals. Our perceived causative impairment classification is in line with and builds on the general movement towards the patient reporting of disability concepts as reflected in the major NIH-funded patient-reported outcomes measurement information system (PROMIS) initiative.32
That initiative focuses on patient-reported outcomes such as pain, fatigue and function. It does not include patient-reported diagnoses or impairments. Second, this cross-sectional survey study is foundational to our ongoing efforts. The predictive power of the causative impairment and activity limitation will need further assessment in longitudinal studies, part of these ongoing efforts. Age of the 1994–1995 NHIS-D data may be of the greatest concern. We selected these data because we could find no other source of population-level data that characterized the type of medical conditions people believed to be causing their activity limitations. It would not have been possible to address the basic question about linkages between perceived causative impairment and activity limitation at the population-level without using these data. There is no reason to believe that linkages between perceived causative impairment and activity limitation would change greatly over time. This assumption will need to be tested as data become available.
This study advances our understanding of linkages between impairments and activity limitations. While brain or behavior impairments and multiple impairments were shown to be associated with the most severe activity limitations, other types of impairments such as cardiopulmonary or hematology, or musculoskeletal conditions, may prove relatively more important in distinguishing among respondents with regard to other subjective constructs, such as the perceptions of poor health. Future studies will be necessary to explore additional clinical implications. Also, such research needs to incorporate a broader biopsycho-ecological paradigm acknowledging that surrounding structures in the built and human-made physical environments as well as expectations and supports from social environments can limit activity and restrict participation as much as impairment.33,34
Finally, future work will be essential to determine prognostic differences with regard to risks of mortality or further functional decline among elderly persons, whose activity limitations are caused by different types of impairments.