Clin Chest Med 23 (2002) 841 – 851

Pulmonary impairment and disability

Oyebode A. Taiwo, MD, MPHa,b,*, Hilary C. Cain, MDc,d
a
Occupational and Environmental Medicine Program, Department of Medicine, Yale University School of Medicine,
135 College Street, Third Floor, New Haven, CT 06510, USA
b
Yale New Haven Hospital, 20 York Street, New Haven, CT 06510, USA
c
Section of Critical Care and Pulmonary Medicine, Department of Medicine, Yale University School of Medicine,
333 Cedar Street, New Haven, CT 06520, USA
d
Pulmonary Function Laboratory, VA Connecticut Healthcare System – West Haven Campus, 950 Campbell Avenue,
West Haven, CT 06516, USA

Chronic respiratory diseases of occupational or Definitions

environmental origin, and those associated with ciga-
rette smoking are the leading causes of respiratory Impairment is defined as any loss or abnormality
disability in the United States and throughout the of psychological, physiological, or anatomical struc-
world [1]. The interplay between occupational and en- ture or function that is objectively measured; it may
vironmental exposures and concomitant tobacco expo- be temporary or permanent, and may be variable in
sure, genetic susceptibility, and comorbid diseases severity. Impairment assessment is a medical evalu-
complicates diagnosis, prevention, and the response ation and the physician’s role is to determine the
to illness [2]. As a consequence, the physician is fre- presence and severity of a pulmonary disorder using
quently called upon to assist in the assessment of the objective criteria. Disability is defined as any restric-
impact of these diseases on the well-being and live- tion or lack of ability to perform an activity in the
lihood of the affected individuals. Impairment and manner or within the range considered normal for a
disability evaluation of the respiratory system is fre- human being [3]. An impairment or a disability can
quently done in the context of a patient’s application be temporary or permanent, depending on whether it
for benefits under a disability or entitlement program is expected to improve with time or treatment. To aid
or for legal proceedings. Therefore, along with the in the determination of impairment, several profes-
medical system, legal and administrative systems also sional organizations such as the American Thoracic
have important roles in this determination. society (ATS), the American Medical Association
This article reviews the evaluation of impairment (AMA), and the European Society for Clinical Res-
and disability caused by respiratory diseases, includ- piratory Physiology have developed detailed guide-
ing common occupational and environmental respira- lines for the evaluation of impairment [4 – 6].
tory diseases. It is intended to provide a framework by
which practicing physicians may understand their role
and responsibilities in the determination of disability. Clinical approach to evaluating
The respiratory system differs from many other organ pulmonary impairment
systems; objective measures of pulmonary function
exist and are readily applicable to the evaluation. The evaluation of patients for impairment caused
by respiratory diseases requires a comprehensive
history and physical examination, followed by appro-
* Corresponding author. 135 College Street, 3rd floor, priate standardized testing such as spirometry, diffus-
New Haven, CT 06510. ing capacity, and often, chest radiography to establish
E-mail address: oyebode.taiwo@yale.edu (O.A. Taiwo). a diagnosis and determine the severity of the disease.

0272-5231/02/$ – see front matter D 2002, Elsevier Science (USA). All rights reserved.
PII: S 0 2 7 2 - 5 2 3 1 ( 0 2 ) 0 0 0 3 6 - 9
842 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851

In the minority of cases, more comprehensive cardio- respiratory disease. Most dyspnea seems to be caused
pulmonary exercise testing may be indicated to define by five major etiologies including cardiac disease,
the extent of impairment. pulmonary disorders, psychogenic/hyperventilation,
gastroesophageal reflux disease, and deconditioning
History disorders. The majority of patients can be categorized
into one of four conditions; chronic obstructive lung
The primary symptoms of respiratory disorders disease, asthma, interstitial lung disease, or cardiomy-
are cough, dyspnea, wheezing, and chest tightness or opathy [17 – 19].
pain. These symptoms need to be correlated with A detailed occupational and environmental expo-
physical findings and objective testing to assess their sure history is required to establish a diagnosis of an
importance and implication. occupational or environmental lung disease. This his-
Cough is an important defense mechanism that tory should include all employments in chronological
helps to clear excessive secretions, irritants, and for- order, including part-time jobs and hobbies. History of
eign materials from the airway. Cough is a nonspecific exposure to specific respiratory agents in the work-
symptom that can be caused by a multiplicity of dis- place like dusts, fumes, and vapors should prompt
orders in various locations. Virtually any condition further questioning to clarify the timing, duration, and
that stimulates cough receptors or afferent nervous dose of exposure when possible, and the use of res-
pathways is capable of producing cough [7]. Cough piratory protection. Presence of similar complaints or
can be categorized as acute or chronic based on the diseases in coworkers also is helpful in establishing
duration of symptoms. Acute cough is generally con- an occupational etiology. An environmental exposure
sidered as less than 3 weeks’ duration and typically of history should include a discussion of potential envi-
minor consequence (eg, viral syndrome, acute ex- ronmental triggers that include pets in the household,
posure to airway irritants). Rarely, acute cough may exposures to birds or other organic antigens, such
signal a potentially life-threatening condition (eg., as molds, as well as seasonal or temporal variability
pulmonary embolism, congestive heart failure). Cough of symptoms.
is considered chronic if it lasts longer than 3 weeks. Smoking can be the primary cause or a major
The most common causes of chronic cough are asth- contributing factor to many respiratory diseases, there-
ma, chronic bronchitis, bronchiectasis, postinfectious fore a detailed smoking history should be obtained.
cough, postnasal drip syndrome, and gastroesophageal This should include types of tobacco smoked, quantity,
reflux disease. These conditions account for more than and duration of smoking, estimated in pack-years, as
95% of the cases of chronic cough [8 – 10]. Other less well as second-hand smoke exposure.
common conditions associated with cough include
bronchogenic carcinoma, chronic interstitial pneumo- Physical examination
nia, sarcoidosis, left ventricular failure, and aspiration
caused by pharyngeal dysfunction [10,11]. A physical examination, that is primarily focused
A wheeze is a continuous, musical sound that is on the cardiopulmonary system, should be per-
produced by a large number of conditions associated formed. This should include the height, weight, and
with obstruction at various levels of the airway vital signs at rest. A description of the patient’s
[12,13]. Wheezing originates in airways of any size, breathing pattern, and presence or absence of labored
from the large extrathoracic upper airway to intra- breathing at rest should be recorded. The timing and
thoracic small airways. The pathophysiologic mecha- quality of breath sounds suggest various processes.
nisms that generate wheezing are not fully understood. For example, early coarse inspiratory crackles may be
An appropriate history should include questions heard in diseases of airflow obstruction with excess
related to the frequency of duration, triggers producing mucus production or airway collapse, whereas late
symptoms, and the response of symptoms to interven- inspiratory crackles or fine end inspiratory crackles
tion including trigger avoidance or medication. For may be present in patients with chronic interstitial
example, asthma should be considered likely when diseases or congestive heart failure [12].
patients present with episodic wheezing triggered by An important extra pulmonary manifestation of
exposure to cold, infection, irritants, allergens, or other pulmonary diseases is digital clubbing. Clubbing is
workplace sensitizing agents such as latex, isocyanates believed to be a consequence of chronic hypoxia, but
or organic antigens [14 – 16]. other unidentified factors likely play a role, as well
Dyspnea, or shortness of breath, is a distressing [20,21]. Respiratory diseases associated with clubbing
sensation of difficult, labored, or unpleasant breathing. include pulmonary fibrosis, bronchiectasis, broncho-
Dyspnea is a sensitive, but not specific, symptom of genic carcinoma, and pleural tumors [22 – 24].
 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851 843

The patient also should be evaluated for clinical question to be answered (see later discussion). The
evidence of right heart failure associated with largest value, either pre- or postbronchodilator, should
advanced and chronic respiratory disease (cor pulmo- be used to quantify impairment. The values obtained
nale). Typical findings include distended neck veins, for FVC and FEV1 may be compared with normative
dependent edema, enlarged liver, which may be ac- data described by various investigators, that provide
companied by ascites, a right ventricular early dia- predicted values on the basis of age, gender, and height
stolic gallop rhythm along the left sternal border or [30]. The ATS and AMA guidelines suggest the use of
epigastrium that increases with inspiration, or a right normal values of Crapo [4,31]. Racial differences in
ventricular heave [25 – 27]. normal values were reported. Adjustments for race are
available for blacks, but no reliable data yet exist for
Pulmonary function tests other racial groups. Although some controversy exists
regarding race corrections, the AMA guide suggests
Spirometry multiplication of predicted normal FVC and FEV1
Spirometry is the most commonly used objective values by 0.88 for blacks, before calculation of the
measure of respiratory limitation. Forced vital capa- value as a percent of predicted. Measurements should
city and forced expiratory volume in the first second always be compared with the patient’s previous test-
are effort-dependent, expiratory maneuvers that re- ing, especially if tests were performed before a specific
quire patient cooperation, but no specific training of injury or exposure.
the patient. These tests may be performed reliably and Spirometry can distinguish obstructive from
reproducibly on relatively simple equipment, at low restrictive lung physiology and provide quantification
cost, and spirometry is available in many physicians’ of the degree of pulmonary dysfunction. On the basis
offices. Portable equipment allows for workplace eval- of FVC, FEV1, and diffusing capacity, classification
uation of pulmonary function. of degree of respiratory impairment can be made
Valid pulmonary function testing requires that the using the AMA recommended guidelines (Table 1)
tests be performed by trained technicians in strict [4]. The AMA classes of respiratory impairment refer
accordance with standardized techniques [28,29]. to values as percent of predicted for spirometry and
The AMA guidelines for disability evaluation recom- diffusing capacity, but do not differentiate whether
mend obtaining three spirometric tracings with rea- the values are reflective of obstructive or restrictive
sonable uniformity of flow pattern and exhibiting lung disease.
concordance of at least two values within 5% [4]. Measurements that are readily available from
Tests may either be performed off medication or after routine spirometry, but not recommended for use in
administration of a bronchodilator, dependent on the evaluation of impairment, include the midflow rates

Table 1
Impairment classification for respiratory disorders
Pulmonary Class 1 Class 2 Class 3 Class 4
function 0% – 9% Impairment 10% – 25% Impairment 26% – 50% Impairment 51% – 100% Impairment
measurement of the whole person of the whole person of the whole person of the whole person
FVC  lower limit  60% of predicted and 51% – 59% of  50% of predicted, or
of normal, and < lower limit predicted, or
of normal, or
FEV1  lower limit  60% of predicted and 41% – 59% of  40% of predicted, or
of normal, and < lower limit predicted, or
of normal, or
FEV1/FVC  lower limit
of normal, and
DLCOsb  lower limit  60% of predicted and 41% – 59% of  40% of predicted, or
of normal, or < lower limit of predicted, or
normal, or
VO2max  25 ml/kg/min, 20 – 25ml/kg/min, 15 – 20 mL/kg/min, < 15 mL/kg/min, or
or 7.1 METS or 5.7 – 7.1 METS or 4.3 – 5.7 METS < 4.3 METS
Adapted from: American Medical Association Guides to the Evaluation of Permanent Disability, 5th edition, 2000;
with permission.
Abbreviations: METS, metabolic units.
844 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851

(ie, flow measured at the mid-portion of the expi- carboxyhemoglobin (COHb) may decrease the dif-
ratory loop [FEF25 – 75% and FEF50%]). These mea- fusing capacity by reducing the availability of hemo-
surements are relatively effort-independent, and are globin binding sites and creating back pressure of CO
believed by some, to reflect small airways disease. in the plasma. Venous COHb may be measured if
The measurements are highly sensitive, but correlate smoking abstinence is in doubt. Apart from forming
poorly with maximal achievable oxygen consumption a firm seal around the mouthpiece, the test does not
or dyspnea, among subjects with normal FEV1 and require particular training or cooperation on the part
FVC [32]. In smokers, the midflow rates are directly of the patient. Normative reference values based on
related to the FEV1 and diffusing capacity, but they age, height, and gender are well-established for
add no additional information when the conventional diffusing capacity [4]. It is recommended that pre-
forced expiratory measures are abnormal [33]. The dicted normal values be multiplied by 0.93 for
usefulness of midflow rate measurement is debated . blacks, but no adjustments are recommended for
It was suggested that abnormality of the small air- other racial groups [4].
ways, as reflected by FEF25 – 75%,precedes the devel- The diffusing capacity is routinely used in con-
opment of clinically significant obstructive airways junction with spirometry to classify impairment for
disease. Thus, abnormality of the midflow rates may respiratory disorders (see Table 1). It has particular
reflect a ‘‘probabilistic estimate of future risk’’ [32]; usefulness in evaluation of restrictive ventilatory
without other predictors for development of func- defects and is more sensitive than lung volume
tional impairment, it is problematic to use midflow measurement as a screening tool for patients at risk
rate abnormality to assign disability of the basis of an for pneumoconiosis [35].
unknown probability of future risk.
Cardiopulmonary exercise tests
Diffusing capacity
The measurement of the diffusing capacity for Standard pulmonary function testing with mea-
carbon monoxide (CO) is routinely performed as a surement of FVC, FEV1,and DLCOsb is sufficient for
single breathhold maneuver, (DLCOsb), and is mea- assessment of the majority of patients who are under-
sured as mL/min/mmHg at standard temperature pres- going disability evaluation [4]. Certain subgroups of
sure dry conditions. The diffusing capacity for CO patients, however, may require more extensive and
reflects the ease with which oxygen moves from the sophisticated evaluation. Relationships between sim-
alveolus into the red blood cells in the pulmonary ple spirometric measurements and DLCOsb, and dysp-
capillaries. In actuality, the usefulness and the lim- nea on exertion, oxygen consumption and work
itation of the diffusing capacity measurement derive capacity have been established [36 – 39]. On the basis
from the fact that the measurement integrates a num- of these studies, the AMA, ATS, and the American
ber of variables into a single value; it is dependent College of Occupational and Environmental Medi-
on the surface area available for gas exchange, the cine recommended the use of spirometry and diffus-
thickness of the interstitium, as well as the diffusivity ing capacity as the key objective elements of
of CO through each of the epithelial and endothelial assessment of respiratory impairment.
interfaces from alveolus to red blood cell. In addition, The relationship between simple pulmonary func-
lung volume, distribution of ventilation, volume of tion testing and exercise limitation, however, is not
plasma, and hemoglobin concentration all have an strong. For example, Cotes and colleagues [40] tested
impact on the measured diffusing capacity. As a the hypothesis that exercise limitation associated with
consequence of these variables, the measurement is respiratory dysfunction may be accurately predicted
highly nonspecific, but can be sensitive to a variety of by measurement of dynamic lung volumes and dif-
factors. For a full discussion of diffusing capacity see fusing capacity. Using the maximal oxygen uptake on
a recent review by Crapo and colleagues [34]. exertion (VO2 max) as the ‘‘gold standard’’ of exer-
Performance of the diffusing capacity test requires cise limitation of respiratory origin, they found that
careful attention to standards such as those published the predictive value of the individual spirometric
by the American Thoracic Society [28]. Accurate indices (FVC, FEV1, and FEV1/FVC) or diffusing
instrument calibration and precise execution of the capacity was poor, accounting for only 15% to 25%
diffusing capacity test is critical, and the test should of the variance in VO2 max. The predictive power of
be performed by experienced pulmonary function these values was improved by using them in com-
technicians. Patients should be instructed to refrain bination and further enhanced by incorporating the
from smoking for at least 8 hours before testing to ventilatory capacity during submaximal exercise into
minimize blood content of CO [4]. Elevated levels of the analysis. Similarly, not everyone who has gas
 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851 845

exchange abnormalities during exercise testing will monary function testing does not accurately reflect
have a reduced DLCOsb; the diffusing capacity is, in the degree of ventilatory impairment of an individual,
some cases, an insensitive predictor of gas exchange consideration may be given to CPET; VO2 max can
abnormality, although its specificity is good [41]. be used to assess the degree of impairment under
As a result of limitations inherent to simple pul- certain guidelines (see Table 1). The ATS statement
monary function testing, there has been increased on evaluation of impairment and disability in patients
interest in the role of cardiopulmonary exercise testing with respiratory disorders suggested that considera-
(CPET) in disability evaluations. The measurement of tion should be given to CPET in persons whose work
oxygen consumption during CPET is considered to be necessitates sustained moderate exertion or frequent
the ‘‘gold standard’’ assessment of the subject’s ability heavy exertion, and is accompanied by significant
to perform work. When performed properly, the CPET dyspnea [31].
can provide a quantifiable measure of exercise capa-
city, as well as offer the examiner a means of differ- Chest radiograph
entiating respiratory impairment from deconditioning
or cardiac dysfunction. The chest radiograph is a standard element of the
An advantage of measuring oxygen consumption clinical evaluation of patients with respiratory dis-
in a particular subject, is that the individual’s max- ease. In most cases, the assessment of respiratory
imal work capacity may be quantified and compared impairment and disability does not rely on the chest
with the established oxygen requirements of his or radiograph, because the correlation between radio-
her job. This comparison relies on the assumption graphic abnormality of the chest and physiologic
that, if appropriately conditioned, a worker is gen- dysfunction is imperfect. For example, among pa-
erally able to sustain 40% to 60% of his or her tients with obstructive lung disease, chest radiog-
maximal oxygen consumption over the majority of raphy may correlate poorly with the degree of
a work day. Near maximal oxygen consumption may abnormality of lung mechanics. An asthmatic patient
only be sustained for shorter times, at intervals with severe, partially irreversible airflow obstruction
throughout the day. Oxygen consumption and energy may have only minimal abnormality of the chest
expenditure were determined for work of various radiograph. Conversely, patients with a significant
intensities and data exist for the typical energy amount of bullous emphysema may not have a
expenditure imposed by specific employment cat- comparable degree of airflow limitation. Nonetheless,
egories. Such data can be a useful reference tool, a subject with a chest radiograph that shows hyper-
but energy expenditure during the performance of inflation, diaphragmatic flattening, bullae, and prom-
work is dependent on a variety of factors; specific inence of the pulmonary arteries (suggesting cor
comparisons of an individual with normative values pulmonale) is very likely to have significant ventila-
are limited by the nature of the data. For example, tory impairment and disability. Thus, chest imaging,
jobs of the same title may vary considerably from one whether by simple chest radiograph or CT scan, may
work site to another. Workers will have different be an ancillary tool in the evaluation of pulmonary
oxygen consumption depending on their physiologic diseases, despite the absence of specific guidelines
characteristics such as body size, obesity, age, mus- about how to incorporate the findings into the assess-
cular energetics, and muscle length – tension relation- ment of impairment.
ships. Workers are unlikely to perform tasks in a Abnormalities of the chest radiograph may be
stereotypical fashion throughout the workday and used to assign disability in selected cases. Among
considerable interworker variability likely exists that patients with pneumoconioses (inorganic dust-related
depends on work experience, efficiency, and organi- pulmonary interstitial diseases such as asbestosis,
zation. Additionally, tolerance of dyspnea likely dif- silicosis, and coal workers’ pneumoconioses), the
fers from one person to another. In one study, general importance of the radiographic findings is height-
attitude explained more of the variance in dyspnea ened. In an attempt to objectively characterize and
and oxygen consumption than did FEV1 [42]. A more communicate the extent of radiographic abnormal-
detailed discussion of the complexities of oxygen ities in the pneumoconioses, the International Labor
consumption and disability is available in an excel- Organization (ILO) devised a classification scheme
lent review by Harber [32]. for the standardized interpretation of chest radio-
The addition of cardiopulmonary exercise testing graphs [43]. The National Institute for Occupational
to routine evaluation of impairment is appropriately Safety and Health (NIOSH) trains and certifies
left to the discretion of the examining physician. If physicians as ‘‘B readers’’ who are deemed proficient
the examining physician believes that standard pul- in the use of this classification system. The ILO
846 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851

classification system is designed as a tool for prisingly variable within the individual. No validated
description rather than diagnosis of a disease; find- relationship has been defined between resting arterial
ings are to be reported as ‘‘consistent with’’ rather oxygenation and physiologic impairment, although
than ‘‘diagnostic of’’ a specific pneumoconiosis. The extremely low oxygen tensions and oxygen desatura-
reporting scheme rates small opacities by shape, size, tion with exertion are undoubtedly significant. These
and profusion on posteroanterior view of the chest caveats, along with the invasive nature of the test,
radiograph (ie, rounded opacities are designated as p, limit the usefulness of routine arterial blood gas
q, or r and linear opacities are designated as s, t, or u measurement in assessing pulmonary impairment.
by size, and the extent of the opacities is rated as 0,
1, 2, or 3 with intermediate scores such as 1/2
assigned to images with profusion of opacities Disease specific impairment assessment
greater than 1, but less than 2). The system also
allows for characterization of the sites, extent, and Obstructive lung disease
calcification of pleural thickening and plaques. The
clinical significance of the chest radiograph may Asthma
follow from the detailed description. Evaluation of impairment in the setting of asthma
The AMA Guide to the Evaluation of Permanent is one of the more problematic aspects of disability
Impairment recommends that those who develop assessment in respiratory disease. Asthma is defined
pneumoconiosis should limit further exposure to the as an inflammatory disorder of the airways accom-
offending agent, ‘‘particularly if radiographic changes panied by variable airflow limitation, which is at least
have occurred at a relatively young age or if there is partially reversible, and airways hyperresponsiveness.
associated physiologic impairment’’ [4]. It follows Asthma may be categorized as allergic (extrinsic),
that an older patient who is nearing retirement, with intrinsic, and occupational. Each of these subtypes
minimal radiographic change after a long history of poses a specific challenge to the physician who per-
exposure, could elect to continue in the workplace, forms the evaluation of impairment and potential dis-
under the assumption of a lower risk of development ability. Because of the complexities involved with
of disabling disease. Such discretionary decisions asthmatic patients, the ATS developed specific guide-
should be made with informed discussion between lines for the evaluation of impairment and disability
the patient and physician. for the asthmatic population [44].
The variable nature of asthma is the most evident
Computed tomography problem that impedes disability assessment. As a
result of the variability, a patient’s lung function on
Specific guidelines for the use of computed to- the day of evaluation may not be an accurate reflection
mography in disability assessment have not been of the patient’s usual condition, but may be atypically
established. Computed tomography (CT) scans offer bad or atypically good. Additionally, the impact of
considerable insight into the precise anatomic medical treatment of asthma may be substantial, and
changes that accompany a disease state, but offer what is considered as adequate treatment may vary
little to the evaluation of physiologic impairment. The from one practitioner to another. In addition to these
greater resolution of high resolution CT compared with treatment goals, nonpharmacologic interventions
simple chest radiography, allows for identification of must be addressed, such as control of environment
more subtle interstitial changes. The argument may be triggers, patient and family education, and compli-
made that earlier identification of subtle disease could ance. Efforts must be made to ensure that evaluation
prompt removal of the individual from exposure, thus of impairment is performed, with the patient as well-
decreasing the risk of disease progression. There are treated and clinically stable as possible [4].
no recommendations at present for CT-screening As with all evaluations of respiratory impairment,
of populations at risk for occupational interstitial spirometry is the key objective measurement of
lung disease. function. The initial goal of evaluation is to document
the presence of asthma. It is recommended that
Arterial blood gas measurement spirometry be performed after withholding inhaled,
short-acting bronchodilators for at least 6 hours
Arterial blood gas measurement of oxygen and before testing and long-acting agents (including theo-
carbon dioxide tension is considered to be an adjunc- phylline) for 24 hours. A notation should be made if
tive tool in the assessment of impairment [4]. The the patient is unable to withhold medication use as
results of arterial blood gas measurements are sur- directed. Anti-inflammatory agents should not be
 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851 847

restricted before testing. When the FEV1/FVC ratio of time. After an individual is sensitized, re-exposure,
is below the lower limit of normal, a short-acting even to very low levels, can result in asthma (eg,
b-adrenergic agonist should be acutely administered, isocyanate and latex-induced asthma). Early diagnosis
in an effort to identify reversible airflow obstruction. and elimination of exposure will decrease the risk of
Presence of reversibility (defined as a 12% increase in progressive pulmonary dysfunction [46]; thus, com-
FEV1 and an increase of  200 mL) suggests the plete removal from the sensitizing agent is recom-
diagnosis of asthma. Patients without reversibility mended. It is important to distinguish immunologic
should be trialed with inhaled or oral steroids in an occupational asthma from irritant-induced asthma,
attempt to achieve a 20% increase in FEV1, and thus, where continued work may be possible if irritant
a diagnosis of asthma. Patients with a history that is exposures are reasonably controlled.
suggestive of asthma and who have normal spirome- Evaluation of impairment in patients with occu-
try in the absence of medication for asthma, may be pational asthma is similar to that for patients with
tested for airway hyperresponsiveness with nonspe- atopic asthma. If impairment is identified, temporary
cific bronchodilator challenge [45]. The usefulness of disability may be assigned. Reassessment should be
diffusing capacity measurement is to exclude con- made 2 years after cessation of exposure, when the
ditions other than asthma that exhibit airflow obstruc- anticipated improvement is likely to have plateaued
tion (eg, emphysema, or combined obstructive and [47]. It is estimated that between 60% and 90% of
restrictive ventilatory defects). subjects will fail to completely resolve their asthma
After a diagnosis of asthma is established with after exposure is eliminated. Many of these patients
reasonable certainty, evaluation of the degree of will continue to have nonspecific airways hyperres-
impairment may follow. If current treatment is ponsiveness in the absence of the agent to which they
optimal, as outlined by the guidelines for the treat- were originally exposed. A given individual’s dis-
ment of asthma discussed earlier, then the classifica- ability that is related to occupational asthma can vary
tion of impairment may be made as dictated by the greatly depending on the patient’s occupation and
scoring scheme in Tables 2 and 3. Patients who have work exposures (see later discussion).
not yet achieved optimal control may be rated on a
temporary basis and then re-evaluated for long-term Chronic obstructive pulmonary disease
impairment and disability. Patients with chronic obstructive pulmonary dis-
The current ATS impairment classification scheme ease constitute a specific subset of patients with
differs from the previous recommendation [31,44]. In airflow obstruction. The AMA guidelines suggest
the older recommendations, the frequency of acute the use of the impairment classification (see Table
exacerbations and treatment in emergency depart- 1) for the rating of impairment in patients with COPD
ments and hospitals were incorporated into the evalu- [4]. The guidelines provide no specific recommenda-
ation of impairment. Most physicians now agree that tions for the evaluation of patients with COPD;
frequent exacerbations do not necessarily suggest however, some recent data suggested that work-
more severe disease, but may imply inadequate related exercise capacity may not be adequately
control, and potentially the need for more aggressive predicted by standard pulmonary function tests alone.
management of inflammation and bronchospasm (eg, Among a cohort of 216 workers with COPD, tested
increased use of inhaled corticosteroids or addition of with routine spirometry and CPET, only 30% of
long-acting bronchodilators). subjects were similarly classified by the two techni-
Occupational asthma narrows the definition of ques. Cardiopulmonary exercise testing suggested
asthma to disease that is attributable to a specific less impairment than spirometry in 61% of the sub-
workplace exposure(s). It is now the most frequently jects and more impairment in 9% [48]. Cardiopulmo-
reported occupational lung disease in the industrial- nary exercise testing is not routinely available, is not
ized world. Occupational asthma caused by workplace easily performed, and is costly. Currently, recommen-
exposures should be distinguished from work-aggra- dations for evaluation of impairment in patients
vated asthma (ie, pre-existing asthma which is aggra- with COPD include routine testing with spirometry
vated by workplace exposures). Occupational asthma and diffusing capacity alone, with exceptions as
may be either immunologic or nonimmunologic in noted earlier.
origin. Nonimmunologic, or irritant-induced, asthma
occurs following high-concentration occupational Upper airway obstruction
exposures to a variety of particulate or toxic irritants. Upper airway obstruction is also associated with
Immunologically-mediated occupational asthma is airflow limitation that leads to respiratory impair-
characterized by immune sensitization over a period ment. Such obstruction may be caused by upper
848 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851

Table 2
Impairment classification of asthma severity
Degree of airway
Post bronchodilator FEV1, % change Hyper-responsiveness, Minimal
Score % of predicted in FEV1 PC20 (mg/mL) medication needs
0  80% <10% >8 None
1 70% – 80% 10% – 19% 8 – > 0.6 Occasional bronchodilator
or cromolyn
2 60% – 69% 20% – 29% 0.6 – > 0.125 Daily bronchodilator or
daily cromolyn or daily
corticosteroid (CS)a
3 50% – 59% > 30%  0.125 Bronchodilator prn and
daily high-dose CSb, or
1 – 3 courses of oral
CS per year
4 < 50% Bronchodilator prn and
daily high-dose CSc, and
daily or QOD oral CS
PC20 (mg/mL): provocation concentration which causes a 20% fall in FEV1. QOD, alternate day.
Adapted from American Medical Association Guides to the Evaluation of Permanent Disability, 5th edition. 2000;
with permission.
a
 800 mcg beclomethasone or equivalent
b
> 800 mcg beclomethasone or equivalent
c
>1000 mcg beclomethasone or equivalent

airway tumors, compression of the airway by ex- Restrictive lung disease

trinsic masses, narrowing of the airway by laryngeal
or tracheal sarcoidosis, or vocal cord dysfunction that Many conditions produce restrictive lung physi-
leads to airway obstruction. Spirometry, with particu- ology, including idiopathic pulmonary fibrosis and
lar attention to the shape of the flow volume loop, can interstitial lung disorders associated with collagen
elucidate whether large airway obstruction is intra- or vascular disease, sarcoidosis, or drug-induced con-
extrathoracic, fixed or variable. Truncation of the ditions [49]. Occupational and environmental expo-
expiratory limb suggests intrathoracic large airway sures are notorious causes of interstitial disease and
obstruction, whereas truncation of the inspiratory its associated restrictive ventilatory defect. Inorganic
limb is associated with extrathoracic obstructing dust exposure produces the pneumoconioses, which
lesions. There are no specific guidelines for evalu- include asbestosis, silicosis, and coal workers’ pneu-
ating the degree of impairment in these cases, al- moconiosis, each with fairly characteristic radio-
though the disability may be substantial because of graphic appearances. Exposure to beryllium or hard
airflow limitation and the impact of irritants on the metals also is associated with pulmonary fibrosis.
large airway lesions. Organic dust exposures (eg, among bird breeders and

Table 3
Impairment rating for asthma
Class 1 Class 2 Class 3 Class 4
Impairment of the 0% 10% – 25% 26% – 50% 51% – 100%
whole person
Total asthma score 0 1–5 6–9 10 – 11, or asthma not
controlled despite
maximal treatment a
Adapted from: American Medical Association Guides to the Evaluation of Permanent Disability, 5th edition, 2000;
with permission.
a
FEV1 < 50% of predicted despite use of  20 mg/day of prednisone or equivalent
 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851 849

farmers) may precipitate hypersensitivity pneumo- without reference to a specific occupation. Impairment
nitis and interstitial disease on that basis. does not necessarily imply disability. For example,
High resolution CT imaging may allow for iden- although two individuals with asthma caused by sen-
tification of subtle degrees of interstitial disease sitization to a specific agent (eg, animals) may have the
among exposed workers who do not yet exhibit same impairment, the individual who is an animal
restrictive patterns on pulmonary function testing; it handler by trade may be completely disabled from his
is not used to assess impairment. Patients with or her own occupation, whereas the other individual
restrictive lung disease are classified by the same (an office worker) may have no disability.
schema used for those who have obstructive lung Information provided by the clinician on a pa-
disease, relying primarily on spirometry and diffusing tient’s impairment due to respiratory disorders is used
capacity reduction (see Table 1). The limitations of by administrators to determine the extent of disability
routine spirometry and diffusing capacity apply to and is translated into financial reimbursements. [50]
subjects with restrictive lung disease, as well as to The process by which disability is assigned varies
those with obstructive physiology. according to the criteria of eligibility and entitlement
for the specific program under which the evaluation
Obstructive sleep apnea is been performed. Examples of entitlement programs
include social security insurance, workers’ compen-
Obstructive sleep apnea is a disorder that is sation, state and federal based eligibility programs
characterized by intermittent, repetitive occlusion of including the Department of Veteran’s Affairs and per-
the large airway during sleep and resultant nocturnal sonal or employer offered disability insurance. [51,52]
desaturation. Obstructive sleep apnea may result in Benefits are provided to individuals who meet the
impairment caused by daytime hypersomnolence and program- specific criteria for disability given the
in some cases, cor pulmonale. Although polysom- severity of impairment, and in the case of workers’
nography can identify the severity of obstructive compensation, criteria for attributing the cause of
events, there is no recommendation for impairment impairment to a workplace exposure.
classification based on polysomnographic findings;
the assessment of impairment is left to the physician’s Physician’s report
judgement. Hypersomnolence is of particular concern
in patients for whom constant workplace vigilance is Evaluations of impairment require a comprehen-
essential (eg, vehicle and machine operators). Ob- sive report of the patient’s history, physical examina-
structive sleep apnea is a treatable disorder. The ulti- tion, and objective tests. The assessment should
mate management strategy is weight loss, but use of include a summary of the questions being addressed,
continuous positive airway pressure mask ventilation the diagnosis, and the degree of impairment referenc-
is effective in eradicating the apneas and the resultant ing the impairment scheme used (eg, AMA or ATS
hypersomnolence. Re-evaluation of impairment after guidelines). Work-related respiratory disorders sel-
treatment is, therefore, essential. dom present as a clinically distinct respiratory disease
(ie, lung cancer or asthma). Attribution of causality is
a complex process in which a physician attempts to
Disability evaluation determine whether a disorder was caused or made
worse by the patient’s workplace exposures.
Disability evaluation is the determination of the Causality in worker compensation cases is usually
impact of impairment on an individual’s ability to meet determined using the legal standard of ‘‘more prob-
the demands of his or her own life. This can be able than not’’, or greater than 50% probability of a
assessed in terms of compromised work capacity (ie, disorder being attributable to work-place exposure
evaluating the impact of respiratory impairment on a [50]. This process requires identification of one or
specific occupation or trade or any reasonable occu- more of the known etiologic factors for a specific
pation). Disability evaluation has a broader focus than disease, an understanding of the natural history of the
impairment because factors like the essential require- disease as it relates to exposure, and an assessment of
ment of a job, specific tasks, reasonable accommoda- the extent of the patient’s relevant work exposures
tion, educational level of the individual, transferable and other host factors. Establishing a temporal rela-
skills, and potential for retraining must be taken into tionship between a specific exposure and onset of the
consideration in determining a specific individual’s disease is critical (eg, exposure to western red cedar
disability. Disability can also be assessed in terms of in a carpenter and the development of asthma).
impact of impairment on activities of daily living Appropriate latency between initial exposure to an
850 O.A. Taiwo, H.C. Cain / Clin Chest Med 23 (2002) 841–851

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