Functional Tests in Chronic Obstructive Pulmonary Disease Part 1 : Clinical Relevance and Links to the International Classification of Functioning , Disability and Health

Chronic obstructive pulmonary disease is a major cause of morbidity and mortality worldwide and an important cause of disability. A thorough patient-centered outcome assessment, including not only measures of lung function, exercise capacity and health-related quality of life, but also of functional capacity and performance in activities of daily life, is imperative for a comprehensive management of chronic obstructive pulmonary disease. This American Thoracic Society Seminar Series is devoted to help clinicians substantiate their choice of functional outcome measures in this population. In Part 1 of this two-part Seminar Series, we aim to describe the various domains of functional status, to elucidate terms and key concepts intertwined with functioning, and to demonstrate the clinical relevance of assessing functional capacity in the context of activities of daily living, in agreement with the International Classification of Functioning, Disability and Health. We hope that a better understanding of the various defining components of functional status will be instrumental to healthcare providers to optimize chronic obstructive pulmonary disease evaluation and management, ultimately leading to improved quality of life of patients afflicted by this condition. This first paper also serves as an introduction to Part 2 of this Seminar Series, where the main functional tests available to assess upper and lower body functional capacity of these patients will be discussed. Abstract Word Count: 215 Page 2 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733ASWord Count: 215 Page 2 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733AS Copyright © 2017 by the American Thoracic Society With 210 million individuals affected worldwide, chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death. For people living with severe COPD, the disease imposed an enormous burden of disability and impaired quality of life (1). Even though COPD is primarily a disease of the respiratory system, impaired respiratory function is only one aspect of the disability experienced by individuals with COPD. In addition to expiratory flow limitation and dyspnea, patients with COPD often have comorbidities such as cardiovascular diseases, osteoporosis, limb muscle dysfunction, and psychological disorders, all of which contribute to limited capacity and restricted participation in physical and emotional activities of daily life(2, 3), and as a consequence, to a poor health-related quality of life(4-8). Pulmonary rehabilitation relieves dyspnea and fatigue, improves exercise capacity and emotional function, and enhances the sense of control that individuals have over their health condition(7, 9). Thus, pulmonary rehabilitation is now recognized as a core component for the management of chronic respiratory diseases (7). Because this intervention also aims to improve patients’ ability to carry out daily tasks and to fulfill their social roles, measuring patientcentered outcomes such as activities of daily life and participation beyond the sole assessment of body structures and functions such as expiratory flows, and maximal oxygen consumption based on cardiorespiratory exercise testingis crucial. Clinicians should thus be aware of existing and validated evaluation tools that are representative of patients’ global functioning, and not only of their exercise tolerance. The World Health Organization recommends the use of the International Classification of Functioning, Disability and Health (ICF) to comprehensively assess the health experience of patients living with specific health conditions(10, 11). This classification uses a globally agreedPage 3 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733AS Copyright © 2017 by the American Thoracic Society on language and reflects the biopsychosocial model in a unified view of various dimensions of health(11). In the first part of this two-part AnnalsATS Seminar Series, we aim to demonstrate the clinical relevance of globally assessing function in patients with COPD. In agreement with the ICF framework, the approach we advocate includes evaluation of the three distinct dimensions of bodily function:, exercise capacity; functional capacity; and functional performance, in. This first paper serves as an introduction to the second part of this Seminar Series in which the main functional tests available to assess upper and lower body functional capacity and their clinical relevance in different contexts of COPD management will be discussed to help health care professionals substantiate their choice of functional tests in clinical practice or in laboratory settings. International Classification of Functioning, Disability and Health (ICF) Based on the work of Nagi(12, 13), the ICF was developed by the World Health Organization to provide a comprehensive framework of definitions and structures for rehabilitation(14), allowing a patient-centered outcome assessment, including not only body structures and functions but also patient functioning in activities and participation. In this model, the whole health experience of the individual is considered, rather than a limited focus on pathophysiological aspects of diseases. Page 4 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733AS Copyright © 2017 by the American Thoracic Society The Five Domains of Function and Disability As illustrated in Figure 1, the ICF framework presents functioning and disability of an individual with a given health condition as the interaction between five different domains: body functions and structures, activities, participation, environmental and personal factors. Body function and structure domain refers to the anatomical and physiological functions of the different body systems. Deficits in this domain are called “impairments” (e.g. airflow obstruction, muscle weakness, poor cardiorespiratory fitness). The activity domain describes the ability of an individual to perform specific and isolated tasks. Decrements in this domain are called “limitations” and describe the difficulty that an individual experiences when performing a particular task in a controlled environment (e.g. walking up a sloping surface, putting down objects, raising up objects to a higher level) (11). The participation domain describes one’s ability to be involved in life situations. Participation restrictions describe the reduced ability of a person to maintain normal role functions and interact with society (e.g. performing different tasks in a given time for a remunerated employment, engaging in recreational or leisure activities, taking care of plants inor outdoors) (11). Finally the contextual factors, which include the environmental (e.g. air quality, products or substances for personal consumption) and personal (e.g. age, psychosocial status, ethnicity) factors are directly linked to the first three domains and complete this framework. Unlike other existing classifications, ICF sets the ground for a standard language when describing disability (15). This language standardization is relevant and important to describe the functioning of patients with COPD and improve communication between all individuals who could potentially Page 5 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733AS Copyright © 2017 by the American Thoracic Society be involved (e.g. patients, families, health and social professionals, researchers, and policymakers) in the development of a comprehensive interdisciplinary rehabilitation plan of care (15). Therefore, guidelines in COPD management and rehabilitation could appropriately be designed and put into action based on this ICF framework. The Comprehensive Core Set In 2004, 17 experts from eight countries with various professional backgrounds developed an ICF Comprehensive Core Set for multidisciplinary assessment in patients with obstructive lung diseases (under which COPD is the most representative worldwide) (16). This Core Set has been developed from a formal decision-making and consensus process integrating evidence gathered from preliminary studies including a Delphi exercise, a systematic review and an empirical data collection using the ICF checklist(16). It includes 19 categories from the domain “body functions”, five from “body structures”, 24 from “activities and participation”, and 23 from “environmental factors”. Personal factors were not classified by this initiative (16). According to the Comprehensive ICF Core Set, the most frequent impairments in body structures and functions in patients with COPD are the structure and function of respiratory system (100%), exercise tolerance (100%), structure of cardiovascular system (83%), sensations associated with cardiovascular and respiratory functions (92%), limb muscle function (50%) and structure of the trunk (50%) (16). The most frequent limitations in activities and participation were walking (100%), moving around (100%), carrying out daily routine (58%), doing housework (58%) and dressing (50%)(16). In line with the focus of this paper, relevant ICF components adapted from this Core Set and that are commonly assessed in COPD are presented in Figure 2. Page 6 of 26 ANNALSATS Articles in Press. Published on 28-February-2017 as 10.1513/AnnalsATS.201609-733AS Copyright © 2017 by the American Thoracic Society Assessment of Physical Components of Functional Status in Patients with COPD While recognizing that environmental and personal factors (which includes psychosocial factors) associated with chronic respiratory diseases have an impact on functional status and participation in daily activities, this Seminar Series puts the emphasis on the physical dimension of functional status. Regarding the physical components of functioning, the ICF framework 

on language and reflects the biopsychosocial model in a unified view of various dimensions of health (11).
In the first part of this two-part AnnalsATS Seminar Series, we aim to demonstrate the clinical relevance of globally assessing function in patients with COPD. In agreement with the ICF framework, the approach we advocate includes evaluation of the three distinct dimensions of bodily function:, exercise capacity; functional capacity; and functional performance, in. This first paper serves as an introduction to the second part of this Seminar Series in which the main functional tests available to assess upper and lower body functional capacity and their clinical relevance in different contexts of COPD management will be discussed to help health care professionals substantiate their choice of functional tests in clinical practice or in laboratory settings.

International Classification of Functioning, Disability and Health (ICF)
Based on the work of Nagi (12,13), the ICF was developed by the World Health Organization to provide a comprehensive framework of definitions and structures for rehabilitation (14), allowing a patient-centered outcome assessment, including not only body structures and functions but also patient functioning in activities and participation. In this model, the whole health experience of the individual is considered, rather than a limited focus on pathophysiological aspects of diseases.

The Five Domains of Function and Disability
As illustrated in Figure 1, the ICF framework presents functioning and disability of an individual with a given health condition as the interaction between five different domains: body functions and structures, activities, participation, environmental and personal factors.
Body function and structure domain refers to the anatomical and physiological functions of the different body systems. Deficits in this domain are called "impairments" (e.g. airflow obstruction, muscle weakness, poor cardiorespiratory fitness). The activity domain describes the ability of an individual to perform specific and isolated tasks. Decrements in this domain are called "limitations" and describe the difficulty that an individual experiences when performing a particular task in a controlled environment (e.g. walking up a sloping surface, putting down objects, raising up objects to a higher level) (11).
The participation domain describes one's ability to be involved in life situations.
Participation restrictions describe the reduced ability of a person to maintain normal role functions and interact with society (e.g. performing different tasks in a given time for a remunerated employment, engaging in recreational or leisure activities, taking care of plants inor outdoors) (11).
Finally the contextual factors, which include the environmental (e.g. air quality, products or substances for personal consumption) and personal (e.g. age, psychosocial status, ethnicity) factors are directly linked to the first three domains and complete this framework. Unlike other existing classifications, ICF sets the ground for a standard language when describing disability (15). This language standardization is relevant and important to describe the functioning of patients with COPD and improve communication between all individuals who could potentially be involved (e.g. patients, families, health and social professionals, researchers, and policymakers) in the development of a comprehensive interdisciplinary rehabilitation plan of care (15). Therefore, guidelines in COPD management and rehabilitation could appropriately be designed and put into action based on this ICF framework.

The Comprehensive Core Set
In 2004, 17 experts from eight countries with various professional backgrounds developed an ICF Comprehensive Core Set for multidisciplinary assessment in patients with obstructive lung diseases (under which COPD is the most representative worldwide) (16). This Core Set has been developed from a formal decision-making and consensus process integrating evidence gathered from preliminary studies including a Delphi exercise, a systematic review and an empirical data collection using the ICF checklist (16). It includes 19 categories from the domain "body functions", five from "body structures", 24 from "activities and participation", and 23 from "environmental factors". Personal factors were not classified by this initiative (16).
According to the Comprehensive ICF Core Set, the most frequent impairments in body structures and functions in patients with COPD are the structure and function of respiratory system (100%), exercise tolerance (100%), structure of cardiovascular system (83%), sensations associated with cardiovascular and respiratory functions (92%), limb muscle function (50%) and structure of the trunk (50%) (16). The most frequent limitations in activities and participation were walking (100%), moving around (100%), carrying out daily routine (58%), doing housework (58%) and dressing (50%) (16). In line with the focus of this paper, relevant ICF components adapted from this Core Set and that are commonly assessed in COPD are presented in Figure 2.

Assessment of Physical Components of Functional Status in Patients with COPD
While recognizing that environmental and personal factors (which includes psychosocial factors) associated with chronic respiratory diseases have an impact on functional status and participation in daily activities, this Seminar Series puts the emphasis on the physical dimension of functional status. Regarding the physical components of functioning, the ICF framework and Core Sets lead to the evaluation of three closely interrelated but distinct concepts: exercise capacity, functional capacity and functional performance ( Figure 3), each of them referring to a specific domain (body structure and function, activities, and participation, respectively).
Exercise capacity refers to one's physiological maximal response to exercise (e.g.: maximal oxygen consumption or heart rate) or the body structure's maximal ability to fulfill its own function (e.g.: maximal voluntary contraction of a skeletal muscle). Functional capacity is defined as one's maximal potential to realize a functional activity in a standardized environment (e.g.: walking distance during the 6-minute walk test).
Functional performance refers to the ability to complete "the physical, psychological, social, occupational, and spiritual activities that people actually do in the normal course [and context] of their lives to meet basic needs, fulfill usual roles, and maintain their health and wellbeing" (e.g.: ability to get dressed without help) (7,17). Functional performance thus refers to participation in daily life activities and is usually performed at a level that does not require nor meet maximal exercise capacity. Examples of commonly used outcomes and associated tests hinged on the ICF components and categorized according to the different key concepts to which they refer are presented in Table 1. A greater physiological exercise capacity will likely result in a greater maximal potential ability to realize functional activities and thus patients should perform a daily functional task more easily, e.g. in a lesser time, with less dyspnea (better functional performance).

Exercise Capacity
In patients with COPD, exercise tolerance tests include the incremental or constant walking or cycling tests, measurement of voluntary or nonvoluntary maximal muscle contractions, spirometry, and field walking tests. Exercise tolerance tests are often used to assess objectively a patient's exercise capacity and response to, and efficacy of, pulmonary rehabilitation. Table 1 presents examples of exercise capacity tests for various body structures and functions. Field walking tests are, however, primarily considered to assess functional capacity, as explained in the next section. Often used as a surrogate to determine functional capacity, maximal exercise tests-such as incremental and constant cycling and walking tests-are usually performed with comprehensive monitoring of cardiopulmonary variables, providing precise indications of maximal and submaximal exercise capacity and of the physiological responses to exercise, in addition to being useful for prognostication of patients with respiratory diseases (18).
Exercise capacity tests are especially useful for quantifying exercise tolerance, determining mechanisms of and contributors to exercise limitation, and prescribing the exercise training regimen to be used during pulmonary rehabilitation. They can predict coexisting or alternative conditions, as well as patients' prognosis in terms of the likelihood of exacerbations, hospitalizations, and even mortality (4,19,20). However, they do not evaluate limitations (activities domain) or the ability to perform daily activities (participation domain) of the ICF Framework (18). Thus, in addition to maximal exercise tests, activity and participation domains need to be addressed with specific tests as representative as possible of one's functional status.

Functional Capacity
Field walking tests are low-cost, require little equipment, and are considered to be more reflective of daily life than laboratory-based treadmill or cycle ergometer tests. Although these tests were developed to evaluate functional capacity and indicate one's maximal ability to conduct a functional activity (in that case walking), they can also measure exercise capacity by providing physiological measures when cardiopulmonary variables are monitored (body functions).
The most recognized test is the self-paced 6-minute walk test (7,(19)(20)(21), which has been used in many clinical trials of pulmonary rehabilitation in COPD (22). The incremental shuttle walk test and the endurance shuttle walk test are externally paced field walking tests (23,24).
These two tests are considered more standardized than the 6-minute walk test since the walking speed is set and thus less influenced by motivation, self-selected pacing, or variability of instructions provided. The incremental shuttle walk test is a true symptom-limited maximal exercise capacity test since the distance walked relates strongly to peak aerobic capacity (25).
The endurance shuttle walk test is a constant walking speed test performed at a set speed based on performance during the incremental shuttle walk test: it cannot, therefore, be conducted independently from the latter. The outcome of the total distance covered in these two tests is also a good indicator of one's functional capacity since it presents the maximal distance that a person can walk at a given speed.
Because a large variability in individual goals and physical limitations is present in patients with chronic respiratory diseases, walking may not always be a significant functional activity for the individual patient. Indeed, a large study suggested that up to one-third of individuals with COPD do not describe walking as an important goal (8). In this context, there is a growing interest in the use of functional tests that evaluate patient's functional capacity in activities other than walking. These tests were often designed and developed for aging populations, but their use is also gaining popularity in chronic respiratory diseases.
To be reflective of functional performance and to adequately assess functional capacity, functional tests need to be performed in a standardized environment and should include components of the ICF focusing on physical functional activities such as maintaining a standing position, changing basic body position, walking and moving, as well as carrying, moving and handling objects as referred to in the ICF Chapter 4-Mobility (11). The most commonly used or recommended tests to assess upper and lower body functional capacity and functional performance in patients with COPD are listed in Table 2 It is also feasible to quantify physical activity in daily life (defined as the totality of voluntary movements produced by skeletal muscles during every day functioning (30)). activity, in both healthy adults (30,31) and those with chronic obstructive pulmonary diseases (32). As previously detailed(3), various technologies have been developed in recent years, integrating various motion sensors to different devices such as pedometers, watches (e.g. Fitbit(33)), and activity monitors (34)(35)(36) to quantify duration, frequency and intensity of physical activity).
Pedometers are portable devices usually worn at the belt/hips height counting the number of steps taken by an individual during the day.
The main advantages of pedometers are a low cost (37)(38)(39), an ease of use, easy-to-view data and good insight in the patients' daily functional status (40). These devices may however underestimate the level of physical activity in patients walking at low speed where pedometers may be less sensitive to detect movements (41,42). Furthermore, pedometers give only a glimpse of functional performance in daily life situations that involve walking activities and do not capture other significant functional activities for patients. Numerous watches that keep track of the number of steps taken in the day, calories spent, and distance walked for example, were also recently put on the market but validation studies are still lacking. The reader is invited to refer to the recently published European Respiratory Society statement on physical activity(43) which provides a comprehensive review of the topic.

Clinical Relevance of Assessing Activities Limitations Using Functional Tests
The present article highlights the need for understanding the specific utility of functional tests to assess activity limitations as also considered in a recent perspective by Nyberg and colleagues (44). In patients with COPD, exercise capacity during cycling or walking tests is often used as a surrogate for functional performance; however, in agreement with the ICF developed by the World Health Organization, exercise capacity is only one aspect of functioning. Because these laboratory or field tests evaluating exercise capacity do not provide an adequate assessment of the limitations when performing significant daily activities, the use of functional tests is encouraged for a comprehensive management of patients with COPD. By allowing identification of specific limitations in tasks that are relevant to daily living such as standing, carrying or handling objects, functional tests should lead to better individualized rehabilitation interventions that should also be more effective in translating their benefits in daily life, ultimately resulting in optimized health status and quality of life for the patients.