Evaluation of pulmonary disability

INTRODUCTION — Chronic respiratory disease is a major cause of disability worldwide, and workplace exposures contribute to the burden of non-malignant lung disorders such as asthma, chronic obstructive lung disease, pulmonary fibrosis, hypersensitivity pneumonitis, and other granulomatous disorders such as sarcoidosis and pulmonary alveolar proteinosis, tuberculosis, and community acquired pneumonia in adults [1]. Evaluation of pulmonary disability for social security or workers' compensation assessments is an important aspect of clinical care. Examples include the cigarette smoker with severe emphysema who is no longer able to do his or her job, the auto body worker with isocyanate-induced asthma, the retired coal miner with pneumoconiosis, the business executive with severe sleep apnea, or the plumber or ship builder with lung cancer or asbestosis.

An approach to the evaluation of pulmonary disability that largely reflects the recommendations in the American Medical Association Guides to the Evaluation of Permanent Impairment, 6th Edition, will be reviewed here [2]. The routine clinical evaluation and management of the specific conditions noted above are reviewed separately. (See "Disability assessment and determination in the United States".)

DEFINITIONS

WHO model of disablement — The World Health Organization (WHO) has developed the International Classification of Functioning, Disability, and Health, known more commonly as the ICF [3]. The ICF is WHO's framework for measuring health and disability at both the individual and population levels. Unlike its predecessor, which was endorsed for field trial purposes only, the ICF was endorsed for use as the international standard to describe and measure health and disability. This model is composed of health and health-related domains that reflect body, individual, and societal perspectives (figure 1) [4]. The components of functioning and disability include body function and structure and also activities and participation. Consideration of environmental factors takes into account that an individual's functioning and disability occur in a context that may be influenced by their immediate and general environment.

The American Medical Association Guides to the Evaluation of Permanent Impairment, 6th Edition, has embraced this classification system because it incorporates the complex and dynamic interactions between an individual's medical condition, the environment, and personal factors [2]. Further, it recognizes that the relationships between impairment, activity limitations, and participation are fluid and multidirectional. For instance, an individual may have measurable impairment without significant impact on activity level, either in work or recreation, or conversely, they may report major activity limitation without significant demonstrable objective impairment.

Impairment ratings — Physicians are typically asked to provide an impairment rating based upon quantitative objective measurements. This rating is generally submitted to a Social Security Board, Workers' Compensation carrier, or other administrative body that will determine the final degree of disability. Physicians' impairment ratings are usually given heavy weighting in determining the degree of disability. Other socioeconomic factors are given varying degrees of import in the final evaluation.

In the United States, the most common system of pulmonary impairment rating is based upon the American Medical Association (AMA) Guides to the Evaluation of Permanent Impairment [2], which in turn incorporate many of the recommendations found in the American Thoracic Society (ATS) official statements on assessing impairment for respiratory diseases [5] and the various ATS\European Respiratory Society (ERS) statement standards for performance of spirometry [6,7], interpretation of pulmonary function tests [8], diffusing capacity for carbon monoxide [9], exercise testing, and methacholine challenge testing [10-12]. Additionally, the ATS has published an official statement for a standard format for reporting pulmonary function tests [13].

The AMA guides have also drawn on the recommendations from the ATS guidelines for the assessment of disability and impairment secondary to asthma [14]. In addition, certain occupational groups with specific occupational exposures well-known to cause lung disease have their own standards for evaluating disability. Examples of these groups include the United States Department of Veterans' Affairs [15], coal miners (the Black Lung Benefits Act) [16,17], cotton workers (Cotton Dust Standard) [18], and longshore workers involved in ship building (Longshore and Harbor Workers' Compensation Act) [19].

Despite the attempts of guidelines to provide objective criteria to judge impairment and disability, there still remain numerous circumstances in which strict adherence to such formulations is problematic. The latest iteration of the guidelines attempts to address some of these issues but challenges remain in certain cases to decide on the most objective yet comprehensive approach to determining the degree of impairment [2]. Assessment of disability necessitates a thorough knowledge of the demands of different types of work, as well as the patient's motivation and capacity for retraining.

APPROACH TO ASSESSMENT — The American Medical Association (AMA) Guidelines [2], which are similar to the American Thoracic Society (ATS) 1986 statement [5], provide an approach to the assessment and rating of pulmonary impairment and disability. Many jurisdictions, including most State Workers' Compensation programs and programs in other countries, use similar criteria to varying degrees. A comprehensive review of different state and international systems is beyond the scope of this chapter. Physicians should check with the pertinent jurisdiction as to the specific criteria used for assessment of pulmonary impairment and disability.

The AMA guidelines categorize dysfunction into five classes that are based upon different percentages of impairment of the whole person (table 1) [2]:

●Class 0 – minimal to no impairment

●Class 1 – 2 to 10 percent impairment

●Class 2 – 11 to 23 percent impairment

●Class 3 – 24 to 40 percent impairment

●Class 4 – 45 to 65 percent impairment

History and physical examination — The history and physical examination are critical on two important fronts: first, the diagnosis and evaluation of a possible causal relationship between the pulmonary diagnosis and workplace or other exposures, and second, assessing the severity of symptoms and physical findings (so called non-key factors) to further refine the impairment rating that is established on the basis of "key" objective factors such as results of pulmonary function tests and cardiopulmonary exercise tests.

The basic components of a pulmonary evaluation include the following:

●A complete medical history outlining the onset and pattern of symptoms and, in particular, a description and quantification of the patient's respiratory symptoms, including shortness of breath, cough, chest tightness, and wheezing. The medical history should also document coexisting medical conditions, medications, and allergies. An impairment classification scheme has been developed to classify dyspnea on a qualitative scale from mild to very severe (table 1) [20].

●A comprehensive employment history outlining all jobs, specific toxic exposures, intensity, duration, frequency of exposure, the nature of ventilation and use of personal protective equipment, and prevalence of disease in fellow employees.

●A description of the temporal relationship between exposures and the onset and duration of symptoms. Particular attention should be given to whether symptoms are markedly improved during periods away from work (eg, days off, weekends, vacations).

●Identification of nonoccupational exposures that may contribute to the patient's clinical presentation, such as smoking, pets, hobbies.  

●Documentation of any previous evaluation and treatment.

●Performance of a thorough physical examination, with concentration on the respiratory, cardiovascular, musculoskeletal, and central nervous systems and also identification of physical signs of impairment and dysfunction (eg, tachypnea, use of accessory muscles, crackles or wheezing, signs of cor pulmonale).

The history and physical examination do not always contribute to the quantification of the degree of impairment. However, they provide supportive evidence for establishing the correct diagnosis and defining possible work-related and non-work-related factors. In addition, clinical signs of cor pulmonale or pulmonary hypertension are sufficient criteria for a severe impairment rating according to the AMA guidelines [2].

Pulmonary function testing — The following pulmonary function tests (PFTs) are considered the "key" measures of pulmonary impairment:

●Forced expiratory volume in one second (FEV₁)

●Forced vital capacity (FVC)

●FEV₁/FVC ratio

●Diffusing capacity for carbon monoxide (DLCO)

The spirometry and diffusing capacity studies should be performed in accordance with the ATS/European Respiratory Society (ERS) standards [7,9]. Normal values for spirometry and single breath carbon monoxide diffusing capacity (also known as carbon monoxide transfer factor [TLCO] in Europe and elsewhere) are based upon height, age, and sex [7,9,21,22]. Spirometry also incorporates adjustments in predicted values according to race and ethnicity given that correlations between social class, race and ethnicity, and spirometry have also been observed [23,24]. More recently, with the increased awareness about the ways in which such adjustments may perpetuate health disparities and structural racism, their use has come into question, particularly when it comes to such issues as adjudication of impairment ratings in workers compensation and employability for certain jobs [25-33]. Indeed, based on a statistical re-examination of the NHANES III (1988 to 1994) data, investigators found no statistical justification (evidence of effect modification), for race/ethnic-specific reference equations [34]. Hence, with the current reference standards for the United States population, several studies have suggested that no adjustments are necessary among individuals of European, Mexican, or African descent living in the United States [21,34,35]. These findings have further fueled the point of view that removing racial/ethnic adjustments (that typically have found lower reference values in certain racial/ethnic groups), reduces the potential for underestimating the severity of disease and impairment for these individuals. As stated above, using the same reference values potentially has both treatment and compensation consequences (see "Overview of pulmonary function testing in adults" and "Selecting reference values for pulmonary function tests"). Nonetheless, at the current time, many jurisdictions continue to incorporate some adjustment factor for race and ethnicity either using equations or a simple correction factor; for example, the state of Colorado Disability Board suggests multiplying the standard predicted values by 0.9 [36]. The ATS/ERS guidelines have recommended that in any case a statement should be made as to whether or not a correction factor was applied [37].

The results of FEV₁ and FVC form the basis of the objective assessment of pulmonary disability. As an example, an FVC between 45 and 50 percent of predicted or an FEV₁ below 45 percent of predicted correspond with severe impairment. The FEV₁ and FVC values associated with milder degrees of impairment are listed in the table (table 1).

DLCO is a noninvasive measurement of gas exchange and is particularly useful when considering possible interstitial lung disease or emphysema. It is relatively insensitive compared with more direct measurements of gas exchange, such as arterial blood gases. A DLCO below 45 percent of predicted correlates with severe impairment in the AMA classification (table 1). (See "Diffusing capacity for carbon monoxide".)

In addition to FVC, FEV₁, and DLCO, other pulmonary function tests that are not required by the AMA guidelines may be helpful to the examining clinician's understanding of the patient's disability. Lung volume measurement can provide information beyond simple spirometry for patients with a suspected restrictive pattern, hyperinflation, or a mixed restrictive/obstructive pattern, while bronchodilator and bronchial hyperresponsiveness testing help inform the evaluation of suspected asthma. Diseases for which lung volume measurement often provides information beyond spirometry include sarcoidosis, hypersensitivity pneumonitis, interstitial lung diseases, pneumoconiosis, and emphysema. As examples:

●The pattern of a low FVC and low DLCO with relative preservation or increase in the FEV₁/FVC ratio is suggestive of a restrictive pattern. However, further evaluation with lung volumes, such as residual volume (RV), functional residual capacity (FRC), and/or total lung capacity (TLC), is necessary to confirm the diagnosis.

●Significant hyperinflation, as seen with emphysema, will not be detected with simple spirometry, so measurement of lung volumes (eg, TLC, RV, FRC) and calculation of RV/TLC are needed to identify and confirm hyperinflation.

●Mixed obstructive and restrictive patterns, as sometimes seen with lung disorders such as sarcoidosis, hypersensitivity pneumonitis, and pneumoconiosis, are difficult to determine on the basis of spirometry alone. Full PFTs, including lung volume measurements, are important to evaluate the relative contributions of obstructive and non-obstructive components.

Bronchodilator reversibility testing is an essential component of the evaluation and diagnosis of asthma and COPD, and the postbronchodilator FEV₁ is a key objective parameter in the impairment rating for asthma (table 2) [2]. Thus, for patients with a prebronchodilator FEV₁ <80 percent of predicted, the effect of administration of inhaled bronchodilator should be assessed with postbronchodilator spirometry.

Tests of nonspecific bronchial hyperresponsiveness (as measured with methacholine, histamine, or mannitol challenge tests) are reserved for evaluation of impairment in individuals with normal baseline spirometry and a suspicion of asthma or reactive airways dysfunction syndrome (RADS) [38]. (See "Bronchoprovocation testing" and "Occupational asthma: Clinical features, evaluation, and diagnosis" and "Irritant-induced asthma".)

Exercise tests — Exercise testing is not part of the routine evaluation of pulmonary impairment. There are special circumstances, however, in which exercise testing is helpful [2]:

●The patient's symptoms of dyspnea are greater than abnormalities on spirometry or the diffusing capacity would indicate

●The patient reports inability to perform specific job duties due to breathlessness

●Submaximal or incorrect performance of spirometry or diffusing capacity is suspected

●Impairment due to interstitial lung disease (at the discretion of the evaluator)

On the other hand, exercise testing is not necessary when severe impairment is found on the basis of spirometry and DLCO. In addition, there are medical contraindications to exercise testing, such as severe heart disease or arrhythmias, and physical limitations that may preclude accurate testing. (See "Exercise physiology" and "Cardiopulmonary exercise testing in cardiovascular disease".)

Results from exercise testing are expressed as the maximal oxygen consumption (VO₂ max) or as metabolic equivalents (METs), which reflect the maximum workload achievable by the patient. Data obtained from exercise capacity testing should be interpreted by a clinician with expertise in exercise physiology, because the results will be affected by a patient's effort, metabolic state, level of conditioning, and also underlying cardiac, pulmonary, neurologic, neuromuscular, or orthopedic disorders.

Specific values for VO₂ max and METs are correlated with levels of impairment in the AMA guide for permanent impairment due to pulmonary dysfunction (table 1) [2]. A VO₂ max of less than 15 mL/kg per min is suggestive of severe impairment. However, this classification is not absolute and should be considered in the context of additional information, such as the patient's level of general conditioning and other possible contributing diseases. A guide to oxygen consumption and energy expenditure for different levels of work intensity is provided in the table (table 3).

A general empiric rule has been that a person should be able to work eight hours a day at his or her job if it does not require more than 40 percent of the VO₂ max achieved during exercise capacity testing. In other words, one needs to have some knowledge of what the actual energy or metabolic requirements are for specific jobs to assess whether an individual is capable of performing that job based on the VO₂ max (table 3). Again, this should only be considered as a general guideline, since there are often extenuating circumstances that may make direct application of this rule inappropriate.

Arterial blood gases — Arterial blood gases, aside from being invasive, are also difficult to standardize and interpret, since they may be affected by such factors as altitude. Nonetheless, in individuals whose degree of breathlessness is not explainable on the basis of spirometry or when the DLCO is between 40 and 60 percent predicted and in whom exercise testing is contraindicated or not available, documentation of the resting arterial oxygen tension (PaO₂) is recommended. According to the AMA guidelines [2], hypoxemia must be documented on two separate occasions at least four weeks apart. (See "Arterial blood gases" and "Measures of oxygenation and mechanisms of hypoxemia".)

With regard to arterial blood gas analysis, severe impairment is considered present in the following circumstances:

●Resting PaO₂ less than 50 mmHg

●A PaO₂ less than 55 mmHg on room air obtained in the presence of pulmonary hypertension, cor pulmonale, erythrocytosis, or increasing hypoxemia on exercise

While the guidelines do not require that adjustments be made for altitude, it is probably appropriate that the clinician report the normal PaO₂ range for the altitude at which the test was performed (table 4).

CALCULATING THE PERMANENT IMPAIRMENT RATING — The approach to determining impairment ratings that is used by the AMA is illustrated in the figure (algorithm 1) [2]. The "Key Factors" for determining impairment are considered to be the objective assessments obtained by pulmonary function testing at a time of clinical stability. The patient's percent predicted values for forced vital capacity (FVC), forced expiratory volume in one second (FEV₁), FEV₁/FVC ratio, and diffusing capacity for carbon monoxide (DLCO) are used to determine the initial impairment classification (table 1). As needed, the values for maximal oxygen consumption (VO₂ max) or metabolic equivalents (METs) obtained from exercise testing are used. (See "Selecting reference values for pulmonary function tests", section on 'Pulmonary function reference equations' and 'Exercise tests' above.)

The following steps show an example of the process for determining the impairment rating for a given set of specific pulmonary function results (algorithm 1):

●The most severely affected parameter determines the impairment rating (table 1). As an example, if the FVC is 65 percent predicted and the FEV₁ is 52 percent predicted, the latter parameter places the patient in Class 3, rather than the Class 2 category associated with the FVC percent predicted.

●Once the impairment class is determined, the default impairment grade within that class is "C." The impairment grade is further refined by taking into account the non-key factor scores according to history and physical findings; the default C grade is adjusted according to the algebraic sum of the difference of the rating class for each non-key factor (history and physical examination) compared to the key factor class rating.

●If the impairment rating from the spirometry "key factor" yields an impairment rating of Class 3, then the initial impairment rating given would be 3C which equals 32 percent impairment of the whole person (table 1).

●If the "history score" from table 2 leads to a class rating of 1, when this is combined with the key factor class rating of 3, the score is: 1 - 3 = -2. If the "physical finding score" is 4, when this is combined with the key factor class rating of 3, the score is: 4 – 3 = 1. The algebraic sum of the non-key factor ratings would be (-2) + 1 = -1. The final impairment rating would then be 3C + (-1) = 3B, and the numeric value assigned to this is 28 percent.

●Regardless of the final non-key factor score the final impairment rating must stay inside the range for the class determined by the key factor. Hence if the algebraic sum of non-key factors was -3, the final score would be "A" within the class (rather than moving down a class). Similarly, if it is 3 or greater the final score would be "E", staying within the class (rather than moving up a class).

ASSESSMENT OF MAXIMUM MEDICAL IMPROVEMENT — Maximum medical improvement (MMI) refers to the point in time when the patient's condition is clinically stable and that no further treatment is likely to improve the condition. The guidelines specify that a patient must be deemed to have reached their MMI before a final impairment rating is calculated [2]. In occupational asthma related to a sensitizer, this can require up to two years after removal from exposure [38]. Improvement may occur simply with the passage of time after there is evidence of a plateau in the patient's clinical condition, but this should not influence determination of MMI. Clearly, there are differences in the duration of time it takes a patient to reach MMI that are influenced by the nature of the condition and by individual variation.

SPECIFIC CONDITIONS — The American Medical Association (AMA) guidelines contain a series of pulmonary disorders that require special consideration.

Asthma — Asthma is a common cause of pulmonary disability. It is estimated that 38 percent of patients with asthma who are currently employed have partial work disability, while 14 percent of working-age adults with severe asthma have complete work disability [38-40]. (See "Asthma in adolescents and adults: Evaluation and diagnosis".)

In asthma, spirometry results can be highly variable and dependent upon the adequacy of treatment with anti-inflammatory and bronchodilator medications. Thus, the AMA has developed criteria for the assessment of asthma that incorporate the postbronchodilator forced expiratory volume in one second (FEV₁) and the degree of airway hyperresponsiveness (methacholine/histamine PC20) (table 2) [2]. Impairment classes (0 to 4) for asthma are based upon total score values. Total impairment/disability (class 4) is defined as asthma that is uncontrolled despite maximum treatment with inhaled glucocorticoids and/or oral prednisone and typically characterized by a postbronchodilator FEV₁ below 50 percent predicted. It is important to note that there will be individuals who will meet criteria on the basis of medication requirement but have an FEV₁ better than 50 percent of predicted on medication.

Minimum medication requirements provide another criterion for assessment of patients with asthma. These requirements should be evaluated during a patient's period of clinical stability with minimum symptoms and optimum lung function. It should also be documented that reduction in medications below this level leads to exacerbations of symptoms and reduced lung function.

The clinician has some discretion in deciding whether the impairment rating may overestimate or underestimate impairment. Individual confounding factors include compliance with treatment, environmental control measures, and coexisting diseases (eg, gastroesophageal reflux disease or rhinosinusitis) or habits (eg, cigarette smoking).

In the case of occupational asthma, it is important to state whether the disease is felt to be an immunologic or non-immunologic (irritant) type of asthma, since management may be somewhat different. A workshop report from the American Thoracic Society highlighted that certain compounds such as quaternary ammonia compounds can act as sensitizers and/or irritants or simply aggravate underlying asthma. It provides a robust discussion of ways to distinguish the nature of the bronchial reactions by physiological and immunological assessments [41]. The workshop also discussed occupational COPD due to exposure to vapors, gases, dusts and fumes (VGDF) as an underrecognized and undercompensated condition.

●Individuals with immune-mediated occupational asthma (with latency) due to a recognized sensitizer in the workplace should be removed from all further exposure, since even trivial level exposures can lead to significant morbidity and even death. (See "Occupational asthma: Management, prognosis, and prevention".)

●Irritant-induced asthma, reactive airways dysfunction syndrome (RADS), and workplace aggravation of underlying asthma can often be managed by adequate pharmacotherapy and maintenance of exposure levels below irritant thresholds. Unfortunately, a number of individuals with irritant-induced asthma secondary to inadvertent high-level exposures find that subsequent exposures to irritants below typical threshold levels still exacerbate symptoms. (See "Irritant-induced asthma".)

As mentioned above, it is appropriate to wait up to two years after the time of last exposure before assessing maximum medical improvement in patients with occupational asthma due to a sensitizer (also called occupational asthma with latency). Improvement will typically have reached a plateau by that time [34]. (See 'Assessment of maximum medical improvement' above.)

Other disorders — The following disorders also deserve special consideration:

●Individuals with hypersensitivity pneumonitis or pneumoconiosis should be removed from further exposure even if they have relatively well-preserved pulmonary function at the time of assessment. (See "Hypersensitivity pneumonitis (extrinsic allergic alveolitis): Treatment, prognosis, and prevention" and "Asbestos-related pleuropulmonary disease", section on 'Management' and "Chronic beryllium disease (berylliosis)", section on 'Supportive therapy' and "Flock worker's lung", section on 'Treatment and prevention' and "Silicosis", section on 'Treatment'.)

●Individuals with sleep disorders may have impairment secondary to hypersomnolence, hypoxia, hemodynamic changes, or personality disorders. The AMA guidelines have a series of combined values charts, which allow the assessor to combine impairment values for different systems such as pulmonary, cardiac, mental, and behavioral [2]. (See "Classification of sleep disorders".)

●Individuals with lung cancer are considered to be severely impaired at the time of diagnosis (table 5). If the patient is disease-free after one year following surgical resection or other treatment, then the impairment is assessed according to physiologic parameters. If there is ever any evidence of recurrence, the patient is again considered to be severely impaired.

●Respiratory impairment due to neurologic disorders is covered in the nervous system section of the AMA guidelines. Discussion of this topic is beyond the scope of this topic review.

Apportionment — In certain jurisdictions, physicians may be asked to judge apportionment (eg, attributing the relative importance of cigarette smoking versus occupational exposures in patients with chronic bronchitis or emphysema). There are no guidelines to assist in making this decision, and it remains a relatively arbitrary distinction left to the discretion of the clinician.

OTHER SYSTEMS — Other systems exist to evaluate patients for impairment and disability.

Social Security Administration — The United States Social Security Administration (SSA) disability system defines two categories: "disabled" and "not disabled" [42,43]. Disability may be on the basis of one or a combination of anatomic, physiologic, and psychological abnormalities including psychiatric diseases and/or substance abuse. It is the clinician's responsibility to document and support evidence from the physical exam and laboratory findings. (See "Disability assessment and determination in the United States", section on 'Social Security Administration'.)

In the instance of Social Security, physicians are not required or expected to determine whether the patient is disabled. Instead, they provide a written medical report giving an impairment rating based upon the patient's forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), and gas transfer and the SSA makes the determination of disability. Information about the evaluation of disability under the SSA is available at SSA Respiratory System Disability Evaluation.

●Pulmonary function tests are to be expressed at standardized body temperature, pressure, and saturation (BTPS), and given in relation to the patient's measured height without shoes. Patients falling below specified values meet the criteria for Social Security disability (table 6). These values do not take age, race, or sex into consideration.

●Resting arterial blood gas (ABG) determination is usually obtained when the diffusing capacity for carbon monoxide (DLCO) is less than 60 percent of predicted and greater than 40 percent of predicted. Criteria from the SSA for impaired gas exchange based on ABGs obtained at rest, in a clinically stable condition, and on at least two occasions three or more weeks apart but within a six month period are provided in the table (table 4).

●Asthma is considered disabling if severe attacks occur at least once every two months or an average of at least six times a year. This criterion is limited because it does not incorporate objective measures or adequacy of therapy.

●There are also criteria for evaluating the disability secondary to lung cancer depending upon cell type and evidence for metastases (SSA evaluation for disability due to cancer).

Department of Veterans' Affairs — The Department of Veterans' Affairs in the United States bases determination of disability on the Code of Federal Regulations (CFR) Book C Schedule for Rating Disabilities (Web Automated Reference Material system [WARMS]) with the requirement that the disability stem from injuries or diseases that were incurred in or aggravated during active duty, active duty for training, or inactive duty training [15,44]. The main tests recommended for disability evaluation include spirometry and maximal voluntary ventilation. Other tests such as blood gases, diffusing capacity, and exercise testing are only to be used in special circumstances.

Black lung evaluations — The United States Department of Labor oversees the occupational health of miners [45]. The Black Lung Act outlines several specific criteria that must be considered in this population [16,17]. The central question for the clinician in these evaluations is to determine whether the miner could presently perform the usual tasks they performed when last employed as a miner.

The evaluation involves recording the symptoms and findings on physical examination as well as a B-reading of the chest radiograph according to the International Labor Organization classification scheme. Coal workers with radiographically identified pneumoconiosis have the legal right (under Title 30 Code of Federal Regulations part 90) to work under reduced dust exposure, including through job reassignment [46]. (See "Evaluation of diffuse lung disease by conventional chest radiography", section on 'Classification'.)

Further disability testing includes spirometry and measurement of maximal voluntary ventilation in addition to arterial blood gases during exercise. The normal values used for spirometry in this legislation have been published [16].

In 2010, the Health Care Reform Bill included reinstatement of provisions for black lung disability payments. For claims filed after 2004, coal miners who cannot work as a result of respiratory impairment will receive total disability benefits if they worked 15 years or more in or around coal mines, and, if their employer cannot prove the disability was caused by something other than black lung disease. Previously, the miner had to prove disability and survivors had to demonstrate black lung disease caused, contributed to, or hastened the miner's death.

Cotton Dust Standard Act — There are similar requirements for the evaluation of patients with work-related byssinosis as outlined in the Cotton Dust Standard of the Occupational Safety and Health Administration regulations [18,47].

Amendments to this act in 1985 and 2000 with regard to washing methods have significantly reduced the exposure levels of cotton dust and led to dramatic reductions in cases of byssinosis [48].

Longshoremen's Act — Impairment rating for longshoremen who may have had asbestos exposure during ship building is outlined in the Longshoremen's Act [19]. This act states that doctors should rate impairment based upon the whole person as outlined in the AMA guidelines. (See "Asbestos-related pleuropulmonary disease".)

The American Thoracic Society (ATS) statement on the diagnosis and initial management of nonmalignant diseases due to asbestos, as well as other ATS guidelines, can be accessed through the ATS web site at www.thoracic.org/statements.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Pulmonary function testing".)

SUMMARY AND RECOMMENDATIONS

●Definitions – The terms "impairment," "disability," and "handicap" have precise and distinct definitions with regard to evaluation of pulmonary disability. Disability is not only assessed by objective quantitative measures of pulmonary function, but also incorporates such diverse factors as age, sex, education, and both economic and social environment. (See 'Definitions' above and "Disability assessment and determination in the United States".)

●AMA guidelines – The American Medical Association provides guidelines for rating pulmonary impairment and disability (table 1 and algorithm 1). Many jurisdictions, including most state Workers' Compensation programs, use these criteria to varying degrees. (See 'Approach to assessment' above.)

●Initial Assessment

•History and Physical – Obtaining a comprehensive history and physical examination does not always contribute to quantifying the degree of impairment. However, this information provides supportive evidence for the correct diagnosis and defines possible work-related and non-work-related factors contributing to the diagnosis. (See 'History and physical examination' above.)

•Spirometry – The main physiologic parameters used in the evaluation of pulmonary impairment include the forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), the FEV₁/FVC ratio, and the diffusing capacity for carbon monoxide (DLCO) (table 1). (See 'Pulmonary function testing' above.)

•Hypoxemia – When a disability determination is based on hypoxemia, the AMA guidelines require documentation of hypoxemia on two separate occasions at least four weeks apart. Criteria from the SSA for impaired gas exchange based on ABGs obtained at rest and in a clinically stable condition are provided in the table (table 4). (See 'Arterial blood gases' above and 'Social Security Administration' above.)

•Exercise testing, in some patients – Cardiopulmonary exercise testing is not part of routine disability assessment but may be helpful when dyspnea is greater than either spirometry or the diffusing capacity would indicate, or the results of these tests are inconclusive. Exercise testing results are expressed as the maximal oxygen consumption (VO₂ max) or as metabolic equivalents (METS), which reflect the maximum workload achievable by the patient (table 1). (See 'Exercise tests' above.)

●Maximum medical improvement – Maximum medical improvement (MMI) refers to the point in time when the clinician feels that the patient's condition is clinically stable and that no further treatment is likely to improve the condition. (See 'Assessment of maximum medical improvement' above.)

●Special considerations for asthma evaluation – In the evaluation of disability from asthma, the preferred test for rating impairment (postbronchodilator FEV₁ or degree of hyperresponsiveness to methacholine) is dependent upon the baseline FEV₁ (table 2). In addition, assessment of the minimal amount of medication needed to control asthma is incorporated into the disability determination. (See 'Asthma' above.)

●Exposure modification – Individuals with immune-mediated occupational asthma due to a recognized sensitizer in the workplace should be removed from all further exposure. Similarly, individuals with hypersensitivity pneumonitis or pneumoconiosis should be removed from further exposure even if they have relatively well-preserved pulmonary function at the time of assessment. (See 'Specific conditions' above.)