diagnostic methods in occupational allergie lung disease

CLIN REV ALLERGY 289 4:289-302, 1986

Diagnostic Methods in Lung Disease

Occupational Allergic

Manuel Lopez and John E. Salvaggio

Occupational factors are important in an ever increasing number of respiratory diseases. These include obstructive airway diseases such as asthma and a wide array of interstitial fibrotic and granulomatous diseases. It is becoming increasingly apparent that immunologic mechanisms are involved in the pathogenesis of many of these diseases. For example, IgE-mediated reactions are frequently involved in the pathogenesis of many forms of occupational asthma, and both immune complex-mediated and delayed cell-mediated reactions have proved to be important in the production of hypersensitivity pneumonitis. Considerably less is known about involvement of such mechanisms in chronic bronchitis or pulmonary fibrosis induced by various inorganic occupational agents. The evaluation of patients suspected of an occupational allergic lung disease usually includes several of the following: 1) a good history and physical examination, 2) pulmonary function tests, 3) immunologic studies, 4) cellular assays, 5) pulmonary lavage analysis, and 6) inhalation challenge tests.

History and Physical Examination A careful history is of utmost importance in the evaluation of patients with symptoms suggestive of occupational lung disease. The work environment must be carefully evaluated for exposure to allergens, gases, vapors, and organic and inorganic dusts and irritants. Clues that an occupational agent may be responsible for the symptoms include onset of symptoms within months of starting a job, the use of a new industrial agent or process, and improvement during weekends and vacations. Although the respiratory symptoms must be correlated with exposure, this correlation may not be apparent in cases with delayed onset symptoms (several hours after exposure), repetitive patterns of response, or intermittent antigen exposure. In the case of asthma, it is necessary to consider whether the suspected agent acts as a specific sensitizing agent or as a nonspecific irritant that causes a worsening of airway obstruction in a patient with preexisting bronchial hyperreactivity. A history of atopy may be important because atopic individuals

From Tulane University School of Medicine, New Orleans, Louisiana. Address correspondence and requests for reprints to Dr. M. Lopez, Department of Medicine,

Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, LA 70112.

© 1986 Elsevier Science" Publishing Co., Inc. 0731-8235/86/$03.50 52 Vanderbilt Ave., New York, NY 10017

290 M. Lopez and J. E. Salvaggio

may be more prone to develop occupational asthma than nonatopic individuals. However, the same relationship is not seen in hypersensitivity pneumonitis. Physical findings may vary with the type of pulmonary problem, severity of the reaction, and relationship to exposure. A normal physical examination does not exclude the possibility of occupational lung disease. Once the history suggests an occupational triggering cause for the symptoms, an immunologic evaluation is usually indicated. Further evaluation may include immunologic studies, determination of airway hyperreactivity, and inhalation challenge using suspected offending agents.

Immunologic Studies Immunologic studies helpful in establishing a diagnosis of occupational respiratory allergy include skin tests, immunoassays for specific serum IgE antibody such as the radioallergosorbant test (RAST), serum precipitin tests, and, in some cases, studies of bronchoalveolar lavage and peripheral blood or lavage lymphocyte functions.

Skin Testing Immediate wheal and flare (IgE-mediated) skin tests can be used to determine the atopic status of the worker by testing with common environmental allergens such as pollen, animal danders, molds, and house dust. Skin tests with extracts prepared from suspected substances in the work environment may detect specific IgE antibodies and suggest a cause and effect relationship. The suspected occupational antigens are usually prepared in aqueous solution. In the case of a low molecular weight compound, it is frequently necesssary to attach the material to a carrier protein such as h u man serum albumin. The usual method for extract preparation includes an initial extraction into pyr- ogen-free water,' filtration, centrifugation to remove particulates, and lyoph- ilization.

Before testing, samples are reconstituted in physiologic buffered saline sterilized by filtration, cultured to confirm sterility, and tested in animals for pyrogenicity, toxicity, and mutagenicity (Ames test). Extracts should first be evaluated by skin testing a nonatopic control group to determine a nonirri- tative dose before use in patients. Wheal and flare skin tests have been of particular use in evaluating occupational asthma. IgE-mediated allergic reactions have been implicated in asthma due to a wide variety of inhaled industrial proteins, enzymes, and simple chemicals acting as haptens (Table 1).

Skin tests not only can be used in the evaluation of individual patients, but also may be of importance in s tudying the pathogenesis of certain types of occupational airway diseases and in performing large epidemiologic sur- veys designed to detect susceptible populations or diagnose overt occupational airway disease. Immediate skin tests are not useful in the evaluation of hypersensitivity pneumonit is . The majority of currently available ther- mophylic actinomycete antigens have nonspecific irritant properties and, thus,

Allergic Lung Disease 291

Table 1. Types of Occupational Asthma in Which Skin Tests Have Been Used to Determine Probable Etiology

Industry Industrial Material Reference

Metals Metal refining

Chemical and pharmaceutical agents Dyers Pharmaceutical Pharmaceutical

Platinum salts 1 Nickel salts 2

Reactive dyes 3 Cephalosporins 4 Phenylglycine acid 5

chloride Biological materials

Veterinarians, animal and Animal serum, dander, 6 poultry breeders, and secreatum laboratory workers Food industry Castor beans 7 Food industry Soy beans 8 Food industry Green coffee beans 17 Millers, bakers Flour 9 Grain elevator operators Grain 10 Sawmills, carpenters Wood dust 11 Printers Vegetable gums 12 Plastic, rubber and resin Hog trypsin 13 industry Food industry Papain 14 Pharmaceutical Pancreatic extracts 15 Detergent industry Bacillus subtilis 16

should not be used as skin test reagents. Positive skin tests have been reported in patients with farmer's lung, probably associated with so called "short-term skin sensitizing" IgG rather than IgE antibodies. TM Pigeon antigens can produce both immediate and late edematous reactions at 4 to 6 hours in patients with pigeon breeder's disease. Many asymptomatic pigeon breeders also have a positive skin test reactivity. 19

There are, however, limitations to the usefulness of the immediate skin tests for presumptive diagnosis of occupational allergic lung disease. For example, in studies involving sensitization of individuals to previously unen- countered antigens via the respiratory route, positive wheal and flare skin tests develop initially, followed within weeks or months by symptoms, and finally by demonstrable circulatory IgE antibody. After cessation of exposure, the level of circulating IgE antibody decreases rapidly, but skin reactivity persists. Thus, a positive immediate wheal and flare skin test may be noted in: 1) past allergic disease, 2) currently active allergic disease, or 3) the absence of an overt disease, but with potential to develop clinically manifest disease.

Delayed (48 hours) skin tests are commonly used in the assessment of intact cell-mediated (delayed) hypersensitivity or its absence (anergy). The most common panel of "recall" antigens used in the evaluation of cell-mediated immunity includes Candida, Trychophyton, mumps, streptokinase- streptodornase (SK-SD), and tuberculin. More than 90% of the general pop-


ulation will show a positive response to 2 or more antigens with this antigen panel. Thus, delayed skin testing is a useful screening procedure in evaluating a study population for a possible defect in the cellular immune system (anergy). Delayed hypersensitivity has been implicated in a variety of occupational lung diseases including hypersensitivity pneumonitis and berylliosis. Anergy has been reported in asbestosis and the active phase of hypersensitivity pneumonitis. 2°'21 In berylliosis, in vitro tests for delayed hypersensitivity correlated well with skin reactivity. 17 However, skin testing with beryllium salts is con- traindicated because the testing may cause exacerbation of preexisting lesions or induce primary sensitization. Positive delayed skin tests (using pigeon serum or pigeon-dropping extracts) have been reported in pigeon breeder's disease as has in vitro lymphokine production using sensitized bronchoalveolar cells from affected patients. 22 In general, however, delayed skin tests are of little diagnostic use in the evaluation of patients with suspected occupational respiratory allergy.

Radioallergosorbent Test (RAST) Specific IgE antibodies can also be studied in vitro by the RAST. Some advantages of the RAST compared with skin tests are that it is rapid, many tests can be processed in 1 day, it does not require the presence of the patient, and it is less subject to false-positive results.

There are, however, variables and limitations that should be considered. It is somewhat less sensitive than skin tests, it is more expensive, the results are not immediately available, and not all antigens can be coupled to a solid phase. The RAST is most suited for protein antigens and less useful for polysaccharide antigens. Complex allergens that may nonspecifically bind to IgE may produce a false-positive RAST. Therefore, it is important to include appropriate controls in each assay.

The RAST has been diagnostically useful in many types of occupational asthma. In a study of coffee- and castor bean-induced asthma, Karr and co- workers 23 demonstrated a positive RAST using crude and partially purified extract of green coffee bean and castor bean. Zeiss and co-workers, 24 using a polystyrene tube assay, reported specific IgE antibodies to a trimellitic anhydride human serum albumin conjugate in workers in the plastic industry. Specific IgE antibodies to western red cedar (Thuja plicata) extract were detected by RAST in 40% of patients proved by inhalation test to have red cedar- induced asthma. 2s Pepys and associates 26 reported specific IgE antibodies to enzymes from Bacillus subtilis in the sera of workers in the detergent industry. RAST technology has been used to investigate many other types of occupational asthma.

The standard RAST inhibition technique (RAST inhibition assay) also may be useful in occupational respiratory allergic disease. In this assay, various quantities of soluble antigen (inhibiting extract) are added to the reactants from the first stage of the RAST. This produces competitive binding between the soluble and the solid phase (RAST) antigens for the available IgE antibodies. The resulting soluble complexes (antigen-IgE antibodies) are removed. Radiolabeled anti-IgE is added in the second stage. The amount of radioac-


tivity is determined, and inhibition curves are established for the various concentrations of the soluble antigen extract. This method is useful in com- paring the allergen content of different crude allergenic extracts. One example of the use of this method is occupational asthma occurring in workers engaged in roasting, processing, and packing green coffee beans. 23 In this study, 5 affected individuals demonstrated a positive RAST with extracts prepared from green coffee beans and castor bean extracts, even though castor beans were not used in this work environment. By RAST inhibition, it was demonstrated that both extracts were antigenically distinct, indicating that these patients had significant levels of specific IgE antibodies against both coffee beans and castor bean allergens. Further studies then showed castor bean dust contamination of the coffee bean sacks used in their transport (ie, the sacks had previously been used elsewhere to carry castor beans).

Gel Double-Diffusion This technique is based on the principle that antigen and antibody form precipitate as they diffuse thorugh a semi-solid media such as agar or aga- rose. 27 This assay has been particularly useful to determine the presence of precipitins in the sera of patients with hypersensitivity pneumonitis. Most patients with hypersensitivity pneumonitis demonstrate precipitating antibodies directed against the offending organic dust or animal protein antigen. For example, precipitins against extracts of the thermophilic actinomycete Thermoactinomyces sacchari have been demonstrated in most patients with active bagassosis. 28,29 Precipitins against pigeon serum and crude pigeon-dropping extracts have been reported in pigeon breeder's disease, 3° and approx- imately 90% of patients with farmer's lung have precipitating antibodies to thermophilic actinomycetes. 31 However a significant percentage of farmers exposed to moldy hay, and of sugar cane processing workers exposed to bagasse, who had no history suggestive of the diseases also demonstrated precipitins to moldy hay and bagasse antigens, respectively. As many as 50% of exposed but asymptomatic pigeon breeders also demonstrated precipitins to pigeon serum. Thus, it is clear that serum "anti-organic dust" precipitins are not diagnostic per se and primarily reflect intense environmental exposure.

There are several other limitations to the diagnostic use of this test. Pre- cipitins may be falsely negative if the quantity of antibodies is tow or if the antigen used is not sufficiently potent. If antigen concentration is too high or too low, the precipitin arc may not occur between the wells of a particular gel diffusion template. The usual procedure in cases of hypersensitivity pneumonitis is to check the suspected organic dust for antigen activity by simple gel double-diffusion using the patient's serum, a positive reference serum, and a negative control. If the patient's serum demonstrates precipitins, the crude dust extract can be presumed to contain the offending antigen and further precipitin tests can be performed with purified antigenic components of the dust. Occasionally, it may be useful to prepare cultures from suspected antigen sources to identify possible etiologic microorganisms and develop a source for preparation of antigens to be used for in vitro diagnostic assays. It is important to stress that precipitins may be positive in a significant pro-


portion of individuals exposed to the organic material without overt disease. For this reason, a positive precipitin test must always be interpreted in the light of clinical symptoms.

Among other more sensitive techniques used in attempts to demonstrate antibodies and/or identification of antigens and allergens are enzyme-linked immunoassay (ELISA), counter immunoelectrophoresis, crossed immunoelectrophoresis, complement fixation assays, and isoelectricfocusing. In general, these techniques are more sensitive and have often been used as research tools rather than as practical clinical assays. Their increased sensitivity has also resulted in even lesser degrees of specificity.

Cel lu lar A s s a y s

A number of in vitro tests to demonstrate delayed hypersensitivity have been used diagnostically in occupational respiratory diseases. These include tests for lymphocyte transformation (blastogenic factor production) and other lym- phokines (mainly migration inhibitory factor [MIF]). These assays have been of some use in evaluating the immunologic mechanisms in hypersensitivity pneumonitis. For example, some studies 32 have shown that in patients with pigeon breeder's disease, avian antigens stimulate peripheral blood lymphocytes from symptomatic subjects but not from asymptomatic exposed individuals, while other studies 33 have shown that lymphocytes from some exposed asymptornatic subjects will also undergo blastogenesis in vitro upon exposure to antigen. However, using direct and indirect standard capillary tube assays, MIF production in response to avian antigens has generally been shown in symptomatic patients, but not in asymptomatic exposed subjects. 34 Although these cellular studies have been helpful in understanding the mechanisms of hypersensitivity pneumonitis, they are not used routinely in clinical practice for evaluation of patients suspected of having the disease.

B r o n c h o a l v e o l a r L a v a g e

Studies of bronchoalveolar lavage fluid are becoming very important in the evaluation of patients with inflammatory disorders of the lower, respiratory tract. Several reasons can be given for the recent popularity of this technique. The procedure has very low morbidity, the cellular and protein components of the lavage are considered to be representative of the immune system of the entire lower respiratory tract, the data obtained have provided insight into the pathophysiologic mechanisms of many diseases, particularly those associated with diffuse infiltration of the lung parenchyma.

Components in Bronchoalveolar Lavage of Normal Airways In the normal lung, most of the inflammatory and immune effector cells recovered in lavage fluid are macrophages (Table 2). Typically, in normal nonsmokers, macrophages represent about 90% of the cells; a small percentage (6 to 8%) are lymphocytes and very few polymorphonuclear leukocytes are found. Bs The lymphocyte subpopulation is similar to that seen in periph-


Table 2. Bronchoalveolar Lavage

Total Cells Macrophages Lymphocytes PMN IgG/Alb Ratio

Normal (nonsmokers) 5-10 x 106 93 + 3% 7 + 1% <1% 031 - 003mg/mL Normal (smokers) 1' N N - 1' 1' N - Hypersensitivity pneumoni t is 1' 1' $ ~ 1' N 1' Sarcoidosis 1' 1' ~, N Asbestosis 1' 1' N ~, N T 1' 1' Idiopathic pulmonary fibrosis 1' 1' N $ N '~ 1' '~

IgG/Alb Ratio = IgG to albumin ratio; PMN = polymorphonudear leukocytes.

eral blood, with 60 to 70% T cells and 5 to 10% B cells. The ratio of helper to suppressor T ceils is 1.6. The fluid recovered by pulmonary lavage is a mixture of epithelial fluid and saline. Because fluid recovered varies from lavage to lavage, it is meaningless to report the data in terms of amount of protein per milliliter of fluid recovered. Albumin has been used as a "marker" protein because it is not locally produced and is passively transferred from the serum to the epithelial fluid. For this reason, a comparison of a lavage protein concentration with lavage albumin (protein/albumin ratio) gives a good estimate as to whether that protein is increased or decreased in relation to its concentration in the serum. 36

The bronchoalveolar lavage fluid of normal individuals contains most of the protein components involved in inflammatory and immune processes. IgG, IgA, and IgE are present, but IgM (being primarily in intravascular immunoglobulin) is not commonly demonstrated. Complement components of both the classic and alternate pathways as well as a variety of enzymes have also been indentified in lavage fluid.

Bronchoalveolar Lavage in Interstitial Lung Disease Bronchoalveolar lavage by itself is not diagnostic of specific disease. However, it may be useful diagnostically in pneumocystis infection, carcinoma, eosin- ophilic granuloma, and alveolar proteinosis. The information most commonly used from lavage studies is the differential count of inflammatory cells recovered. According to the types of cells in the lavage fluid, alveolitis may be classified in two groups: lymphocyte predominant and polymorphonuclear leukocyte predominant.

Lymphocyte-predominant. Increased lymphocytes in lavage fluid have been observed in patients with hypersensitivity pneumonitis, sarcoidosis, berylliosis, and tuberculosis. Lavage fluid from patients with chronic hypersensitivity pneumonitis contains increased numbers of cells, with significant el- evation in the percentage of lymphocytes (average 66%). The IgG/albumin ratio is also significantly elevated, with mean values of 1.5 mg/mg. 37 IgM, not usually found in normal lavage fluid, is present in measurable amounts. In a study of patients with pigeon breeder's disease, 22 lavage fluid contained a large proportion of lymphocytes. However, several pigeon breeders without


clinical manifestations of the disease also had a high percentage of lymphocytes. Lymphocytes from both groups responded well to phytohemagglutinin stimulation, but the bronchoalveolar lavage lymphocytes from most patients with pigeon breeder's disease stimulated with pigeon antigens showed significant responsiveness in contrast to only 2 of 9 asymptomatic pigeon breeders. More recently, Leatherman and co-workers 3s demonstrated a predomi-. nance of a suppressor/cytotoxic subset of T cells in lavage fluid obtained from 6 patients with chronic hypersensitivity pneumonitis (farmer's lung and pigeon breeder's disease). However, other studies 39 have not confirmed these observations.

Lavage fluid from patients with sarcoidosis shows an increase in the total number of cells, mainly due to an increase in the proportion of lymphocytes. The majority of these lymphocytes are T cells, with an increase in the percentage of helper T cells. The helper/suppressor ratio is 4 to 10 times that found in lavage fluid of normal subjects. It has been suggested that lavage studies may be a means of defining disease activity and prognosis. Patients with "high intensity alveolitis" (>28% lymphocytes) presumably have more active disease than those with "low intensity alveolitis" (<28% lymphocytes). However, this association between disease activity and degree of lymphocytes is not absolute and should be correlated with other clinical and laboratory findings.

Polymorphonuclear Leukocyte-Predominant Disorders. The group of diseases with a predominant increase in polymorphonuclear leukocytes in lavage fluid includes idiopathic pulmonary fibrosis, asbestosis, and interstitial fibrosis associated with autoimmune collagen vascular disease. Bronchoalveolar lavage combined with biopsy can provide useful information in establishing the diagnosis of idiopathic pulmonary fibrosis. Several studies have suggested that the proportion of neutrophils can be correlated with disease activity and that high levels of neutrophils are associated with a poor response to therapy. However, lymphocyte counts may also be increased in the disease. At least two studies have shown that an increase in the percentage of lymphocytes in lavage fluid is associated with a favorable response to therapy. Therefore, although the finding of a predominance of neutrophils in lavage fluid adds support to the diagnosis of idiopathic pulmonary fibrosis, by itself it is not diagnostic.

In summary, analysis of lavage fluid, although rarely diagnostic of any particular disease, may permit evaluation of the disease process and the effects of treatment. It may help in characterizing patients with interstitial fibrosis when the specific organic dust is not apparent, and may provide valuable insight into the pathogenesis of the disease process.

Inhalation Challenge In many instances, it is important to reproduce the clinical features of the pulmonary reaction induced by an occupationally associated allergen or irritant. This can be accomplished by inhalation challenge and careful observation of the patient. There are two methods of challenge.


"Natural" or "Biologic" Challenge This is accomplished by returning the patient to the suspected environment. The reaction is evaluated by preexposure and postexposure pulmonary function tests compared with those obtained on nonworking days. A simple method is to monitor the patient at work by keeping a record of symptoms and monitoring airflow obstruction using frequent (every 2 hours) peak expiratory flow readings. For this purpose, one of the simple portable peak flow meters can be used. 4°'4~ Results should be compared with those obtained on control days spent outside of the work environment. Significant symptoms accom- panied by changes in peak expiratory flow at work suggest that asthma is associated with the workplace. For more accurate readings, pulmonary function tests, including simple spirometry (FEV1, FVC, and EF25--75), can be performed in the workplace at different intervals through the working day. It also may be necessary to continue the testing for 24 hours because late asthmatic and restrictive reactions may be manifested only after the worker has left the workplace. There is minimal danger because the degree of exposure has been encountered safely many times previously in this "natural" setting. This reduces the need and expense of hospital admission and close medical supervision. On the other hand, symptoms induced at work could result from factors that are not strictly occupational. Among these factors are irritants (ie, smoke, dusts, or pungent fumes) or, in atopic subjects, natural allergens unrelated to occupation (ie, ragweed or grass pollen).

Repeated observations of symptoms and changes in pulmonary function during working periods will likely produce evidence of respiratory symptoms associated with the working environment. However, this method does not help in identifying the specific agent responsible for symptoms. For this purpose a more specialized laboratory is required.

Controlled Provocation Challenge This is carried out in a specialized laboratory. After the patient undergoes measurement of baseline pulmonary function, he or she is exposed to phar- macologic agents by inhalation (ie, methacholine to demonstrate airway hyperreactivity, and the suspected environmental agents to demonstrate a cause and effect relationship). Several measurements of lung function are carried out throughout the challenge, usually using more sophisticated and sensitive measurements of pulmonary function. Guidelines for inhalation challenge techniques have been published. 42

Methacholine Inhalation Challenge Methacholine challenge is very useful in demonstrating the presence or absence of airway hyperreactivity. Asthmatics are 100- to 1000-fold more sensitive to methacholine 42 than normal subjects. The demonstration of airway hyperreactivity involves the administration of methacholine aerosol in increasing concentrations while keeping the number of breaths and volume constant, measuring pulmonary function, and determining a dose-response curve. The test is performed by obtaining baseline simple spirometry (FEV1 and FVC), followed by inhalation of 5 breaths of a solution of methacholine


(0.1 mg/ml). Spirometry is performed 5 minutes after completion of inhalation. The procedure is repeated with increasing concentrations of methacholine (0.5, 1,2,5,10, and 25 mg) until a 20% decrease in FEV1 is demonstrated or a concentration of 25 mg/ml of methacholine has been reached. The provocation dose needed for a 20% decrease in FEV1 is referred to as the PD20. The patient with a positive test demonstrates a PD20 with a concentration of methacholine less than 25 mg/ml. Determination of airway response to methacholine can be helpful in selecting those patients in whom hypersensitivity to an agent in the work environment has developed.

Antigen Inhalation Challenge

When patients are exposed to antigens to which they have become sensitized, they may demonstrate 1 of 4 patterns of response (Fig. 1):

1. Immediate response. The immediate response is the most common reaction observed. It consists of an acute bronchospasm, which occurs within minutes of exposure, characterized clinically by dyspnea and wheezing. Spirometry shows a rapid decrease in FEV1 that is readily reversible with inhaled bronchodilators.

2. Late response. The late response usually occurs 4 to 10 hours after exposure. It can last for 36 hours or longer, and often involves small

Figure 1. Patterns of inhalation challenge response by patients exposed to antigens to which they have become sensitized.

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airways. The decrease in FEV1 is less reversible with conventional bronchodilators (ie, isoproterenol), and can be prevented by previous administration of steroids or cromolyn sodium. In addition to the smooth muscle contraction, the mechanism may involve inflammatory changes and intraluminal mucus accumulation in the bronchi. Dual response. In this type of response, there is an immediate bron- chospastic reaction that resolves spontaneously and rapidly, followed 6 to 8 hours later by a recurrence of bronchospasm and perceptible symptoms. Restrictive response. This reaction is more commonly seen in patients with acute forms of hypersensitivity pneumonifis. It occurs 4 to 6 hours after challenge and is characterized clinically by chills, fever, dyspnea, and crepitant or subcrepitant rales on auscultation. Pulmonary function tests show a restrictive defect, with a reduction in forced vital capacity and diffusion capacity. This reaction can be blocked by corticosteroids.

Laboratory Challenge with Dusts Workplace exposures can be simulated in the laboratory as described by Pepys and Hutchcroft. 43 Briefly, appropriate quantifies of the test dust may be added to a given amount of lactose so that the occupational exposure is simulated when the subject transfers the dust from one container to another. Lactose alone can be used for the control test; the challenge can be carried out in a single- or double-blind fashion, providing that the agent cannot be detected by its color, taste, or texture at the concentrations used in the test. This technique has been used in the investigation of occupational asthma in workers in a variety of industries. 43'44 The allergenic material can also be extracted from the dust to obtain extracts for challenge by the nebulized aerosol method.

Laboratory Challenge with Nebulized Aerosols This method is most applicable to challenge with common environmental allergens that may be present in the working place. It may be equally suitable for soluble agents and substances that are themselves in a natural liquid state. The advantages of this method are that control and antigen challenges are indistinguishable, providing that the antigen has no characteristic odor or taste. The chief difficulty lies in choosing an appropriate concentration for the initial challenge and the level at which negative results exclude hypersensitivity. In general, initial doses should simulate minimum exposures encountered naturally, while maximum doses should just exceed the maximum likely to have been experienced in the workplace.

Laboratory Challenge with Vapors and Gases With specialized equipment, 45,46 controlled challenge exposures to vapors and gases can be generated to study patients with suspected asthma thought to be caused by agents present in vapor or aerosol form. We employ a specially designed chamber 4-foot wide, 6.2-foot high, and 7.2-foot long, with a special


B-" 72_

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Icl} E .

SECTION

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IH G

X-X

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Figure 2. Schematic drawing of the Tu- lane inhalation challenge chamber. A = intake filter; B = agent injection port; C = ,splitter vane; D = plenum; E = observation window; F = ports; G = door; H = airlock; I = blower; and J = exhaust. Reprinted with permis- sion.

observation window through which the subject can be observed dur ing the test procedure (Fig. 2).

Air entering the chamber through high efficiency particulate and charcoal filters is mixed with the test agent, enters the chamber through air splitter vanes to ensure even distribution, and sweeps the entire chamber. The air mixture is also exhausted through air splitter vanes by a blower capable of suction flow rates up to 250 cfm. The chamber is maintained at a slight negative pressure to prevent leakage of the agents. Access points in the chamber allow monitoring of vital signs, measurements of pu lmonary function, and blood sampling while the subject is in the chamber undergoing exposure. We have used this chamber to s tudy the respiratory response to a variety of chemicals, vapors, and gases, among which are toluene diisocyanate, formaldehyde, crude cigarette smoke, certain amines, and anhydrides. 4s

In summary, a great deal of experience has been accumulated from the use of specific and nonspecific inhalation challenge tests. However, these tests may be t ime-consuming, expensive, and are not without risk. These tools are currently limited for the most part to specialized laboratories wi th special interests in occupational lung diseases.

R e f e r e n c e s

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30. Barboriak JJ, Sosman AJ, Reed CE: Serological studies in pigeon breeder's disease. J Lab Clin Med 65:600, 1965

31. Pepys J, Jenkins PA: Precipitins (F.L.H.) test in farmer's lung. Thorax 20:21, 1965


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