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Minisymposium 3

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Assessing occupational respiratory disease in epidemiology

M3.1 UTILITY OF PULMONARY FUNCTION AND EXERCISE TESTING FOR INTERSTITIAL LUNG DISEASE IN FIELD SETTINGS

M. B. Schenker, M. Stoecklin, R. Lupercio, H. Black, L. Beckett.Department of Public Health Sciences, University of California, Davis, CA, USA

Introduction: Previous studies have found no effect of chronic low level paraquat exposure on spirometry; however, paraquat is known to cause interstitial fibrosis with acute high dose exposure. In addition, chest x rays are insensitive for early interstitial lung disease.

Objective: To assess the utility of measures of restrictive lung disease in a field study of agricultural workers.

Methods: Paraquat exposure and respiratory health was assessed in 340 farm workers (mean (SD) age 37 (10.5) years). We measured single breath diffusion capacity (DLCO), cardiopulmonary exercise testing (CPET), and spirometry. Data collection was done at farms by technicians following American Thoracic Society guidelines. CPET participants were screened for cardiovascular disease according to American Association of Sports Medicine criteria. Eligible participants were ⩽40 years of age. Results were graded for acceptability according to previously published criteria. Correlations and regression modeling assessed relationships between measures of interstitial lung disease.

Results: The percentage of unacceptable spirometry and DLCO tests was low. The biggest limitation to CPET was the exclusion of 113 people (33.2%) because of age. The largest correlation was between percentage predicted FVC and alveolar volume (VASB). After dichotomising the scales into the lowest fifth percentile, 91% was normal for both measures of restriction and 2% was abnormal on both measures. Comparisons with VO2 identified no subjects with abnormal results on both VO2 and FVC or on VO2 and VASB.

Conclusions: Exercise testing in field studies is limited by logistical issues, cost and participation rates. Spirometry and DLCO may not be adequate to detect subclinical interstitial disease in healthy, working populations, and longitudinal data may be required to detect indicators of disease. General issues regarding screening tests for occupational restrictive lung disease in epidemiological studies will be discussed.

M3.2 ASSESSMENT OF OCCUPATIONAL AIRWAYS DISEASES

M. Abramson.Department of Epidemiology & Preventive Medicine, Monash University, Melbourne, Victoria, Australia

The effects of occupational exposures upon the airways include asthma, reactive airways dysfunction syndrome, and acute and chronic bronchitis. Spirometry remains the mainstay of early detection and diagnosis. Careful attention needs to be paid to calibration of equipment, quality control (satisfying American Thoracic Society criteria) and selection of appropriate predicted values. Cross shift changes in forced expiratory volume in 1 second (FEV1) have been used to detect asthma, but are not always convenient for workers or researchers. Acute responsiveness to bronchodilator can distinguish between asthma and chronic bronchitis. However, there is no consensus on what constitutes significant reversibility of bronchoconstriction. Frequent peak flow monitoring at work has long been used to detect patterns consistent with occupational asthma. Modern portable electronic spirometers and analytical software (such as OASYS) have made this task easier. Nonspecific airways hyperresponsiveness to histamine or methacholine has been measured in many occupational health studies. New challenge tests with hypertonic saline or mannitol are more specific for asthma, but have not yet been evaluated in occupational settings. Specific occupational challenges remain the gold standard for clinical diagnosis. However, logistic difficulties mean that these are rarely performed outside specialist units and almost never used in epidemiological studies. Non-invasive measures of airway inflammation such as exhaled nitric oxide, induced sputum or breath condensate solutes offer promise for the future.

M3.3 HOW USEFUL ARE INDUCED SPUTUM AND EXHALED BREATH CONDENSATE METHODS IN EPIDEMIOLOGICAL STUDIES OF OCCUPATIONAL ASTHMA?

J. Douwes, N. Pearce.Centre for Public Health Research, Massey University, Wellington, New Zealand

Pathophysiological mechanisms involved in occupational asthma are not completely understood. Asthma is often treated as a single condition based on “typical” asthma symptoms such as wheezing and cough, and has almost universally been regarded as an atopic disease involving allergen exposure, allergic (IgE mediated) sensitisation with a TH2 CD4+ lymphocyte response and subsequent interleukin-5 mediated eosinophilic airways inflammation, resulting in enhanced bronchial reactivity and eventually in reversible airflow obstruction (asthma). However, there is now increasing evidence that, in addition to atopy, other non-TH2 mediated inflammatory mechanisms may be involved. Non-atopic occupational asthma is frequently referred to as “asthma-like syndrome” or “irritant induced asthma” and is relatively common in occupational settings such as farming and textile fibre processing. Neutrophilic inflammation appears to play a major role in these types of asthma. Non-atopic mechanisms are also suspected in Western red cedar and di-isocyanate induced asthma, but the underlying mechanisms have not conclusively been identified. Thus, objective monitoring of airway inflammation is essential to differentiate between asthma phenotypes. In addition, it furthers our understanding of the underlying pathophysiology. Several methods have been used, including sputum induction and exhaled breath condensate (EBC) testing. Sputum induction is relatively safe and non-invasive, but rather laborious, complicating its use in large population studies. Measurement of inflammatory markers in EBC is safe, non-invasive, rapid, simple to perform, and effort independent. However, there is very limited experience with this method and results obtained with EBC are mixed. Improved phenotyping of asthma using sputum induction and/or EBC is essential to: (a) identify causal exposures and (b) accurately assess dose–response relationships (particularly in case of mixed exposures). These methods are therefore expected to be of great use in future studies of occupational asthma, but, further validation studies (particularly for EBC) are required.

M3.4 METHODS OF ASSESSING OCCUPATIONAL RESPIRATORY DISEASES: RADIOLOGICAL ASSESSMENT

A. W. Musk.Department of Respiratory Medicine, Sir Charles Gairdner Hospital and School of Population Health, University of Western Australia, Nedlands, WA, Australia

Background: Chest radiography is a most important tool for detecting the effects of particle deposition in the lungs and in measuring disease progression, especially for the understanding of inorganic dust diseases, but also for organic dust diseases and airway diseases (including emphysema).It is the classic tool for surveillance of chronic respiratory infections, particularly tuberculosis (TB). Screening for lung cancer will not be discussed.

Inorganic dust diseases (the pneumoconioses): The plain chest x ray (CXR) has been the standard method for detecting the presence of dust disease in the mining industry since the early 20th century when mass screening became feasible. For use in epidemiological studies, the International Labour Office classification has been developed since 1930 to codify the radiographic changes in a simple, reproducible manner. It provides a simple, semi-quantitative method of reporting the type and extent of disease which is comparable internationally. Computerised tomography (CT) of the chest has not yet been refined to a stage where it can be used in large epidemiological studies although it is valuable clinically.

Organic dust diseases (extrinsic allergic alveolitis; EAA): While the plain chest radiographic and the CT appearances in the acute and chronic forms of EAA are well described, the variability of the disease process makes chest radiography less useful for epidemiological studies, which rely on lung function and immunological tests. In the clinical setting, high resolution CT scans are diagnostically valuable.

Airway diseases: Although not used primarily for determining the presence of airway diseases, radiography can be useful for determining the presence of hyperinflation, parenchymal destruction (for example, emphysema), bronchial wall thickening (for example, asthma) and increased peripheral lung markings (as in bronchiolitis) to supplement the information provided by lung function tests (particularly the forced expiratory volume in 1 second) in studies of the obstructive lung diseases. The CT provides much more information than the plain CXR.

Chronic respiratory infections: Surveillance of populations (especially miners) for TB in the past has been an important means of TB control (and incidentally pneumoconiosis).

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