Functional assessment of chronic obstructive pulmonary disease

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Correspondence
Charles A. Downs, PhD Candidate, ACNP-BC, CCRN, 1305 N. Martin, P.O. Box 210203, Tucson, AZ 85721-0203. Tel: 520-626-7523; Fax: 520-344-9076; E-mail: cdowns@nursing.arizona.edu

Abstract

Purpose: To describe available methods for assessing functional capacity in persons with chronic obstructive pulmonary disease (COPD).

Data sources: An extensive literature review is used to provide pertinent information.

Conclusions: COPD disease affects millions of Americans and is physically and psychologically distressing. The hallmark of chronic obstructive pulmonary disease is irreversible airflow limitation and dyspnea. Dyspnea is a major contributor to decreased exercise capacity and functional status in this population. Understanding the methods to complete a functional assessment is important for all practitioners caring for this population.

Implications for practice: This paper provides an overview of current methods used to assess functional status, including pulmonary function testing, exercise testing, and anthropomorphic and self-report measurements. In addition, there is discussion of the indications and contraindications for exercise testing in chronic obstructive pulmonary disease and the clinical significance of performing a global composite of functional ability.

Chronic obstructive pulmonary disease (COPD) affects millions of Americans and is physically and psychologically distressing. The hallmark of COPD is irreversible airflow limitation—typically caused by cigarette smoking, although there are other causes (Pauwels, Buist, Calverley, Jenkins, & Hurd, 2001). Currently, COPD is the fourth leading cause of death; however, it is under diagnosed, and efforts are being made to improve clinician diagnosis (Eisner et al., 2008). Early diagnosis is essential to decreasing morbidity and mortality. Patients who suffer with COPD frequently complain of dyspnea that is exacerbated by exercise. Limited or impaired exercise capacity—for example, from dyspnea—results in a reduced ability to perform routine activities such as bathing, shopping, and household chores.

It is important for practitioners to qualitatively and quantitatively describe the functional status of the patient with COPD. A functional assessment provides pertinent information related to disease severity, management effectiveness, and the patient's ability to cope with COPD. This article will provide an overview of tools available to perform a functional assessment in persons who suffer from COPD and conclude with a discussion of clinical applications.

Functional assessment

A functional assessment is the use of subjective and objective data, often from diagnostic tools, to obtain a description of an individual's functional status or ability to participate in everyday activities by quantifying the effects of disease severity on physical and psychological function. Indications for performing a functional assessment include the following: to determine the root cause of changes in functional status, to document physical disability, to determine the need for long-term care, to certify for assistance with healthcare or home care needs, to perform a preoperative evaluation, and to evaluate for lung transplantation referral. The methods used to perform a functional assessment include activities of daily living (ADL) and instrumental ADL tools, pulmonary function testing (PFT), exercise testing, and anthropomorphic and self-report measurements. As a result of the heterogeneity of COPD, functional assessment is a complex task as no one method provides an accurate reflection of functional status. For this reason, several functional assessment tools are needed to obtain a composite profile that reflects the functional status of the individual.

Numerous tools are available, leading to the need to clarify their role in assessing functional status. The American Thoracic Society (ATS) guidelines suggest the use of functional assessment tools, such as exercise testing, be performed when less physically rigorous tools (PFT, history, and physical) do not adequately explain the functional changes. Moreover, ATS has specific guidelines for PFT and walk-based tests, but guidelines do not exist for other measurement tools. Determining functional status with more physically rigorous tools may also help assess that treatments are most effective in specific patient populations, where less physically rigorous tools, such as spirometric parameters, provide insufficient determination. In addition, new methods are being investigated. For example, radiographic studies demonstrate promise in quantifying functional ability, although availability, expense, and radiation exposure are limitations (Hasegawa et al., 2006).

Activities of daily living

An individual's functional status may remain stable, gradually decline over time, or acutely change. Consequently, the patient with COPD may attribute subtle changes in functional status to advancing age or other health conditions—that is, compensating or justifying changes in physical limitations. Baseline testing and subsequent testing are vital for determining changes in functional status. When performing a functional assessment the initial measures should attempt to ascertain the ability to participate in ADL. There are numerous ADL tools available, and many can be accessed at http://endoflifecare.tripod.com/imbeddedlinks/id17.html. Instrumental ADL scales, such as Lawton-Brody Instrumental ADL Scale, are useful in quantifying an individual's ability to function independently (Lawton & Brody, 1969). The advantage of these tools is that they are easy to use, free to the public, and provide quick, objective, and quantifiable data that can be followed over time. These advantages make them appealing for initial and subsequent screening for impaired ADL in the COPD population.

Pulmonary function testing

PFT is widely used to quantify lung function, evaluate regimen effectiveness, diagnose lung disease, and to determine disability. PFT is divided into four components: spirometry, lung volumes, gas diffusion, and arterial blood gases. Participants are asked to perform multiple breathing maneuvers to provide the components of pulmonary function data. PFT is used to categorize abnormalities into two categories: obstructive and restrictive. COPD is an obstructive disorder with specific PFT criteria. The PFT criteria used to diagnose and stage COPD are included in Table 1.

Table 1.  Pulmonary function testing criteria for staging of COPD
StagePulmonary function parameters
  1. FEV1, forced expiratory volume in 1 s, the volume of air exhaled during the first second of the forced vital capacity (FVC) maneuver.

  2. FEV1/FVC, the ratio of the forced expiratory volume in 1 s to the forced vital capacity.

Mild COPDFEV1 > 80% predicted; FEV1/FVC < 70%
Moderate COPD50% < FEV1 < 80%; FEV1/FVC < 70%
Severe COPD30% < FEV1 < 50%; FEV1/FVC < 70%
Very severe COPDFEV1 < 30%; FEV1/FVC < 70%

Data from multiple studies illustrate the importance of PFT data in quantifying lung disease and assessing functional status. PFT measurements include spirometry (forced expiratory volume in 1 s [FEV1], forced vital capacity [FVC], the FEV1/FVC ratio, and maximum voluntary ventilation [MVV]), lung volumes (vital capacity [VC], residual volume [RV], total lung volume [TLC]), and gas diffusion studies (diffusing capacity of carbon monoxide [DLCO]). The components of PFT are used to quantify lung function. Spirometry neither predicts survival nor clinical status; however, spirometry is one component of PFT (Domingo-Salvany et al., 2002; Oga, Nishimura, Tsukino, Sato, & Hajiro, 2003). A more detailed description of lung function can be achieved through complete PFT than from simple spirometry. Table 2 provides an overview of the various components of PFT and their relevance to predicting functional status in the patient with COPD.

Table 2.  The relationship of pulmonary function components to functional assessment
ComponentDescriptionRelationship to functional assessment
  1. FVC = forced vital capacity; FEV1= forced expiratory volume in 1 s; MVV = maximal voluntary ventilation; VC = vital capacity; RV = residual volume; TLC = total lung capacity; DLCO= diffusion capacity for carbon monoxide.

SpirometryUsed to measure changes in lung volume with forced maneuversReliable and valid measure of lung function parameters
 FVCPatient inhales maximally then exhales rapidly and completely as possibleProvides the most important data related to lung function; used to classify lung disease
 FEV1Air exhaled during first second of FVC maneuverLower values correlate with more severe disease
 FEV1/FVCRatio of FEV1 to FVCUsed to classify disorders as obstructive or restrictive
 MVVPatient breaths as hard and as fast as possible for 10–15 sLower MVV values correlate with decreased exercise capacity and increased dyspnea
Lung volumesProvides information related to static lung volumesUseful in assessing for over or under inflated lungs
 VCPatient inhales maximally and then exhales slowly and completelyCompare with FVC to determine the presence of air trapping
 RVAir that remains after maximal exhalationAssesses air trapping; add to VC to obtain TLC
 TLCTotal amount of air theUseful in classifying disorders
  patient can inhale and exhale plus RV as obstructive or restrictive
Diffusion studiesEstimates the transfer of oxygen from the alveolus to the red blood cellUseful in monitoring parenchymal lung disease
 DLCODiffusion of carbon monoxideUseful in determining the presence of parenchymal lung disease such as emphysema
Blood gasesAssess gas exchange and metabolic functionUseful for monitoring and provides rapid information related to gas exchange and metabolic state
 pHAcid-base balanceExtremes, especially those associated with marked changes in PaCO2, indicate respiratory failure
 PaCO2Reflects the transfer of carbon dioxide from the blood to the lungsUseful in assessing ventilation
 PaO2Reflects the transfer of oxygen from ambient air to bloodUseful in assessing oxygenation

PFT provides pertinent information that can be used with other tests to provide a composite of functional status. Spirometry measurements are typically used as a result of their high degree of reproducibility and ease of interpretation (Enright, Johnson, Connett, Voelker, & Buist, 1991). The most common measures include the FVC, FEV1, and their ratio. The FVC maneuver is integral to useful spirometric data. It is performed by having the patient inhale maximally and then exhale as rapidly and completely as possible. The FEV1 is a measure of the first second of the FVC. The FEV1/FVC ratio is expressed as a percentage and is useful for: (a) identifying persons with airway obstruction, and (b) identifying the cause of a low FEV1.

Exercise testing

Exercise capacity is the maximal ability of the body to take up oxygen and perform work (ATS/American College of Chest Physician [ACCP] statement on cardiopulmonary exercise testing, 2003). The gold standard for the measurement of exercise capacity is exercise testing with progressive, incremental tests using a treadmill or cycle ergometry with cardiopulmonary monitoring. However, exercise testing is of questionable benefit when predicting physical functioning for daily living. Moreover, frail elderly, or those with severe cardiac or pulmonary disease, are easily fatigued when performing these rigorous tests (ATS/ACCP, 2003). Subsequently, their exercise capacity may be underestimated as a result of the intensity of the exercise testing—that is, maximal effort is exerted over a short period of time (exercise testing) compared to submaximal effort over a longer period of time (daily exercise capacity).

Exercise testing determines peak oxygen consumption (VO2). VO2 is a measure of cellular uptake of oxygen, a relationship that is strongly influenced by work (ATS/ACCP, 2003). As oxygen demand increases, there is a need to increase oxygen delivery. Factors that influence oxygen availability and utilization can hinder VO2 data results (see Table 3). Typically, the higher the VO2 the more fit the participant (values about 15 times resting indicate fitness; athletes may achieve values about 20 times resting) (ATS/ACCP, 2003). VO2 data from exercise testing are reported as absolute values and percentage predicted. Thus, VO2 values are referenced to body weight, height, age, and gender. Several studies have evaluated the use of VO2 in assessing physical function and conclude that the use of spirometry measurements (FEV1) with peak VO2 improves the ability to predict physical function in COPD patients (Berry, Adair, & Rejeski, 2006; Rejeski, Foley, Woodard, Zaccaro, & Berry, 2000).

Table 3.  Factors influencing oxygen availability and utilization
Oxygen availabilityOxygen utilization
AnemiaProcesses affecting metabolic efficiency of muscles
Arterial oxygen saturation 
Arterial carbon dioxideMitochondrial myopathy
TemperatureCystic fibrosis
Cardiac functionCachexia
 Heart rateMalnourishment
 Stroke volume 
Shunting 
 Redistribution of blood flow 
Factors affecting oxygen diffusion into tissue 

Exercise testing is contraindicated in certain populations. Table 4 outlines the contraindications for exercise testing, while Table 5 outlines the indications for exercise testing in persons with COPD. Less rigorous but reliable and valid exercise tools are available to assist in the quantification of functional ability especially in those who cannot perform the more demanding cardiopulmonary testing. Furthermore, there is minimal cost in implementing these exercise tests, and some can be performed within the clinic setting. The simplicity of these tests makes them suitable for rapid incorporation into routine assessment of lung disease severity and the physical limitations imposed by COPD. The tests include (in order of physical rigor): stair climb, timed walk tests, and the shuttle walk test.

Table 4.  Contraindications and relative contraindications for exercise testing
Absolute contraindicationsRelative contraindications
Heart diseaseHeart disease
 Myocardial infarction in past 3–5 daysHypertrophic cardiomyopathy
Arrhythmias
Tachyarrhythmia
Bradyarrhythmia
High-degree atrioventricular block
Coronary artery disease
Left main coronary stenosis or dominant artery stenosis
Valvular heart disease
Moderate valvular stenosis
Hypertension
Severe untreated hypertension
Significant pulmonary hypertension
Advanced or complicated pregnancy
Orthopedic impairment
Electrolyte abnormalities
 Acute endocarditis, myocarditis, or pericarditis 
 Uncontrolled congestive heart failure 
 Unstable angina 
 Unstable arrhythmias 
 Valvular heart disease 
   Symptomatic severe aortic stenosis 
   Syncope 
 Suspected dissecting aneurysm 
Pulmonary/pulmonary vascular disease 
 Uncontrolled asthma 
 Acute pulmonary embolus, pulmonary infarction, or deep vein thrombosis 
 Pulmonary edema 
 Respiratory failure 
 Room air desaturation at rest ≤ 85% 
Acute illness affecting exercise tolerance 
Inability to cooperate 
Table 5.  Indications for cardiopulmonary exercise testing in COPD
Functional assessment
Establishing exercise limitations
Assessing for contributing causes of functional impairment or dyspnea
Assessing for hypoxemia and oxygen prescription
Pulmonary function testing fails to provide adequate information of therapeutic intervention

Stair climb The stair climb is an inexpensive and objective measurement of functional ability and can be performed in a clinic provided the clinic has multiple floors (at least six). The patient is asked to climb as quickly and as fast as able while pulse oximetry is continuously assessed. Heart rate and oxygen saturation can be automatically recorded with an oximeter or periodically recorded by a member of the healthcare team as the patient climbs. A reduction in oxygen saturation (SpO2) below 90% or marked increase in heart rate (greater than 20% over baseline) suggest deconditioning (Koegelenberg, Diacon, Irani, & Bolliger, 2008). The number of stairs climbed correlates with functional ability—that is, the more stairs the patient climbs without oxygen desaturation or a marked increase in heart rate, the better their functional status.

Timed walk tests There are numerous timed walk test with the most commonly used being the 6-min walk test (6-MWT). The 6-MWT, a supervised measurement of the distance walked on level ground in 6 min, has been extensively studied and found to be a predictor of functional ability (Rosa, Camelier, Mayer, & Jardim, 2006). The distance walked is obtained using a pedometer and compared to standards (576 m for health males and 494 m for healthy females) to determine functional limitation brought on by exercise (Enright & Sherril, 1998). The 6-MWT is a reliable and accurate test in the evaluation of functional capacity in COPD patients, and results from the 6-MWT correlate with cardiopulmonary exercise testing (Baughman, Sparkman, & Lower, 2007; Starobin et al., 2006). Other timed walk tests include the 2- and 12-MWTs. Both have been studied and data suggest that they are reliable measures for functional assessment (Leung, Chan, Sykes, & Chan, 2006; McGavin, Gupta, & McHardy, 1976). The 2- and 12-MWT are performed like the 6-MWT; the only difference is the duration—2 and 12 min, respectively.

Shuttle walk test The shuttle walk test is another exercise test that is useful in predicting functional ability in patients with COPD. The shuttle walk test consists of a standardized walk (10 m between two cones) on level ground with increasing speeds, performed at 12 different levels. Each level lasts 1 min and auditory cues are used to control the pace—for example, faster speeds at higher levels. The patient walks back and forth between the cones at the increasing prescribed pace; the longer the patient performs the better his or her functional status. Data indicate that the shuttle walk test is reliable and correlates with peak VO2 measurements obtained from more rigorous exercise testing (Rosa et al., 2006; Singh, Morgan, Hardman, Rowe, & Bardsley, 1994).

Anthropomorphic and self-report measures

COPD is associated with physical changes, specifically a reduction in skeletal muscle mass and body mass index (BMI). Studies demonstrate that lower BMI is a predictor for COPD severity, although the mechanisms responsible are not fully known (Roth, 2008). It is becoming increasing accepted that COPD is a condition that involves multiple organs and systems (Ran et al., 2007). The major determinant of anthropomorphic and self-report measures include measures of body mass (muscle composition, BMI), dyspnea scales, and quality of life assessment. The data obtained from these measures provide objective and subjective data that can be incorporated with other objective data (PFT and exercise testing) to produce a composite of functional ability in the patient with COPD.

Anthropomorphic measures Peripheral muscle composition is recognized as an important factor in assessing functional ability. With the development of COPD, peripheral muscles may undergo compositional changes—there is a loss of peripheral muscle mass—despite having a normal BMI. These changes are associated with a decrease in exercise capacity (Hamilton, Killian, Summers, & Jones, 1995). In addition, BMI has shown to be a predictor of functional ability in persons with COPD and a reduction in BMI adversely affects clinical outcomes in COPD (American Thoracic Society/European Respiratory Society, 1999). However, no mechanistic connection—that is, physiological cause—has been found between peripheral muscle composition and BMI with severity of COPD (Roth, 2008).

Common anthropomorphic measurements include height, weight, and BMI. There is no agreed upon measure to assess peripheral muscle composition; the current methods require either biopsy for muscle fibers or computerized tomography to assess muscle size and composition (Debigare et al., 2003; de Oca et al., 2006). Graphically recording height, weight, and BMI provides pertinent information that can be used to form a composite of functional ability and is easily performed in a clinical setting.

Dyspnea scales Dyspnea, or shortness of breath, is a major factor limiting functional performance for persons with COPD. There are numerous methods to assess dyspnea with dyspnea scales being the most common. Dyspnea scales such as the Borg scale or the visual analogue scale (VAS) can be used along with exercise testing to determine an individual's perception of dyspnea. The Borg scale ranges from 0 (no dyspnea) to 10 (maximal dyspnea), while the VAS can range from 0 (no dyspnea) to 100 (maximal dyspnea). Both scales are reliable and valid when used to measure dyspnea and higher scores correlate with lower functional ability (Jones, Kareau, & Mahler, 2005; Reishtein, 2005).

Quality of life assessment Improving quality of life is desirable when managing the patient with COPD and can be quickly assessed with a questionnaire. A commonly used questionnaire is the St. George's Respiratory Questionnaire (SGRQ), a 76-item disease-specific questionnaire that provides an overall measure for quality of life. The SQRQ is divided into three sections (symptoms, activity, and impacts). Scores are obtained for each section as well as an overall score. Scores range from 0 to 100 with higher scores indicating poor health. The SGRQ is reliable and valid and correlates with measures of disease severity and functional ability (Jones, Quirk, & Baveystock, 1991; Jones, Quirk, Baveystock, & Littlejohns, 1992). Clinicians may request to use the SGRQ without charge. Contact information can be obtained at http://www.healthstatus.sgul.ac.uk/downloads/sgrq_scoring_sheet.htm

Functional assessment: Obtaining a global composite

As a result of the heterogeneous nature of COPD, no one test provides an accurate assessment of functional status. Methods of assessing functional status are continuously evolving as methods are developed and tested that are applicable and relevant to all persons with COPD while accurately and reliably assessing dyspnea and quality of life. A composite created from multiple functional tests offers a more accurate reflection of functional status of persons with COPD than can be determined from a single physiologic parameter.

A global composite can be achieved through the use of multiple tests. There are no clear guidelines on which group of tests to use, how frequently to use them, or in which subset of COPD patients. However, the reasons for performing the tests should necessitate which test or group of tests to perform. Simple, reliable, and cost-effective measures can be routinely incorporated into the care of the COPD patient to provide a composite of functional status and to anticipate needs. These measures include the following: an ADL survey tool, spirmoetry, and anthropomorphic and self-report measures. A change in functional status, as indicated by significant changes detected with the tools, prompts the use of additional tests. More physically rigorous tools, such as PFT and exercise testing, have established guidelines that describe their appropriate use. However, research is needed to establish that functional assessment tools are accurate and cost-effective measures that reflect functional status for persons with COPD. This is particularly relevant as the incidence of COPD, for which there is no cure, is increasing.

Clinical application

Although guidelines for performing global composites of functional assessment are lacking, the clinical importance of these data remain. Functional assessment, specifically obtained from a global composite, allows for a richer understanding of how the disease process is affecting the individual. Also, a functional assessment can be completed in a longitudinal fashion (annually for several years) and a composite that reflects changes in functional abilities over time is obtained. These data can be used to assist the nurse practitioner (NP) in managing the disease process and preparing for the individual's potential needs (e.g., supplemental oxygen, pulmonary rehabilitation, ambulatory assistive devices, hospice). To illustrate, suppose a patient has several annual global composites (PFT, stair climb, and VAS data) of functional ability. The latest data indicate a 10% drop in FEV1 accompanied by a SpO2 of 88% and a 25% increase in heart rate during a stair climb with a two point increase in VAS. These data indicate a change in functional ability. This should prompt further investigation for potential causes and may necessitate new interventions or referral. However, if longitudinal data reflect minimal or no change in functional status, the NP may conclude that the current treatment plan is adequate.

Data obtained from a functional assessment may provide insight into developing or subclinical disease. The onset of chest pain, a reduction in exercise performance, and marked changes in quality of life that are disproportionate to expected findings or marked acute changes suggest the potential emergence of a new problem. This should prompt further investigation to uncover the cause of these changes that may not be pulmonary in nature. Consequently, a global composite of functional ability provides useful data to assist the NP in the assessment, diagnosis, and treatment of disease.

Conclusion

COPD is a devastating disease for which there is no cure. COPD is characterized by irreversible airflow limitation and dyspnea that limits functional ability. As COPD progresses functional ability declines and the NP must assess functional status to determine the extent of disease severity—that is, a composite of the physiologic, psychological, and behavioral limitations. This article has provided a review of commonly used functional assessment methods that can be used by the NP in the clinic setting to assess functional ability.

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