Asbestos-induced pleural fibrosis and impaired exercise physiology

Functional exercise capacity and health-related quality of life in people with asbestos related pleural disease: an observational study

BACKGROUND

Functional exercise capacity in people with asbestos related pleural disease (ARPD) is unknown and there are no data on health-related quality of life (HRQoL). The primary aims were to determine whether functional exercise capacity and HRQoL were reduced in people with ARPD. The secondary aim was to determine whether functional exercise capacity was related to peak exercise capacity, HRQoL, physical activity or respiratory function.

METHODS

In participants with ARPD, exercise capacity was measured by the six-minute walk test (6MWT) and incremental cycle test (ICT); HRQoL by the St George's Respiratory Questionnaire and physical activity by an activity monitor worn for one week. Participants also underwent lung function testing.

RESULTS

25 males completed the study with a mean (SD) age of 71 (6) years, FVC 82 (19)% predicted, FEV1/FVC 66 (11)%, TLC 80 (19)% predicted and DLCO 59 (13)% predicted. Participants had reduced exercise capacity demonstrated by six-minute walk distance (6MWD) of 76 (11)% predicted and peak work rate of 71 (21)% predicted. HRQoL was also reduced. The 6MWD correlated with peak work rate (r=0.58, p=0.002), St George's Respiratory Questionnaire Total score (r=-0.57, p=0.003), metabolic equivalents from the activity monitor (r=0.45, p<0.05), and FVC % predicted (r=0.52, p<0.01).

CONCLUSIONS

People with ARPD have reduced exercise capacity and HRQoL. The 6MWT may be a useful surrogate measure of peak exercise capacity and physical activity levels in the absence of cardiopulmonary exercise testing and activity monitors.

TRIAL REGISTRATION

ANZCTR12608000147381.

Asbestos-related pleuropulmonary diseases: benign and malignant

Asbestos is known for its desirable properties of thermal and heat resistance along with excellent strength and durability. It was widely used in many industries since the late 19th century, until its adverse effects on health were recognized. The occurrence of pleuropulmonary changes from exposure to asbestos often has a latency period of 20 to 30 years. The use of asbestos has been banned, regulated, and minimized in many countries, but in several developing countries, the use of asbestos in industries is still a common practice. In this article, the benign and malignant clinical manifestations of asbestos exposure are discussed.

Occupational lung disease

Despite federally mandated safety standards, occupational lung disease remains one of the most common work-related injuries. Inhaled dust can result in a range of tissue injury in the lung and can lead to significant respiratory insufficiency causing death. Although silicosis and coal worker's pneumoconiosis are becoming less common, hypersensitivity pneumonitis is increasingly recognized as an occupational lung disease with new antigens being introduced annually. Imaging, particularly high-resolution computed tomography, is central to the management of occupational lung disease and is useful in diagnosis, assessment of disease activity, and evaluating response to therapy.

The suction mechanism as a factor in intrathoracic oedema, connective tissue or pleural effusion

In pathological conditions, the negative intrapleural pressures (Ppl) may increase unequally. At some sites they may remain increased. We maintain that at these sites the increased pressures may lead to the production of oedema in the adjacent pleural walls and in adjacent pre-existing connective tissue, which may remain as oedema or may become connective tissue. Occasionally the increased negative Ppl may contribute to the production of pleural effusion. We term all these processes the suction mechanism (SM). This mechanism affords an interpretation of a series of images observed in chest X-rays. According to this view, lung shrinkage, narrowing of the pulmonary vessels and impairment of the lung function are not caused by the diffuse pleural fibrosis, but result from damage to the lung parenchyma. We also interpret the apical cap, the blunting of the costophrenic sulci, the broadening of the mediastinum and the retrosternal stripe in terms of the SM.

Chest pain in asbestos-exposed individuals with benign pleural and parenchymal disease

Many asbestos-exposed individuals complain of chest pain for which there is no clear explanation. To determine whether chest pain is associated with the presence of benign pleural or parenchymal disease on chest radiograph, we studied 1,280 subjects undergoing surveillance because of prior asbestos exposure at Wittenoom, Western Australia. All subjects completed the Rose questionnaire on chest pain and this revealed 556 subjects (43%) who experienced some chest pain. A posterior-anterior chest radiograph was performed at the same clinic visit and was subsequently graded independently by two experienced readers for diffuse parenchymal disease and pleural disease. Logistic regression models adjusted for sex, age, and cumulative asbestos exposure indicated that the presence of chest pain was significantly associated with the presence of both benign pleural disease and diffuse parenchymal disease. Further analysis after stratification of chest pain into nonanginal and anginal pain showed that there was a significant association between anginal pain and the presence of pleural and parenchymal asbestos-induced radiologic abnormalities and an association of nonanginal pain with parenchymal disease. We conclude that radiographic evidence of either parenchymal or pleural disease in subjects exposed to asbestos is significantly related to the presence of chest pain, particularly anginal pain.

Asbestos fibers and interleukin-1 upregulate the formation of reactive nitrogen species in rat pleural mesothelial cells

Nitric oxide radical (.NO) and peroxynitrite anion (ONOO-) have been implicated in lung inflammation and may be important in pleural injury. The present study was undertaken to determine the effects of asbestos exposure and cytokine stimulation on .NO and ONOO- production by rat pleural mesothelial cells. Accordingly, rat parietal pleural mesothelial cells were cultured for 2 to 72 h with or without 50 ng/ml of recombinant interleukin-1beta (IL-1beta) in the presence (1.05 to 8.4 microg/cm2) or absence of crocidolite or chrysotile asbestos fibers. The effects of asbestos were compared with those of carbonyl iron, a nonfibrogenic particulate. Mesothelial cell messenger RNA (mRNA) expression of the inducible form of .NO synthase (iNOS), assessed with the reverse transcription-polymerase chain reaction (RT-PCR), increased progressively from 2 to 12 h in IL-1beta-containing cultures. Nitrite (NO2-), the stable oxidation product of .NO in mesothelial cell conditioned medium, was assayed through the Griess reaction. Both types of asbestos fibers (chrysotile > crocidolite) upregulated the formation of NO2- in mesothelial cells costimulated with IL-1beta in a concentration-dependent and time-dependent fashion. In contrast, carbonyl iron did not upregulate NO2- formation in IL-1beta-stimulated cells. Both types of asbestos fibers also induced iNOS protein expression and the formation of nitrotyrosine in mesothelial cells and greatly induced the formation of nitrate (NO3-), a surrogate marker of ONOO- formation, in IL-1beta-stimulated cells. However, the effects of chrysotile were notably greater than those of crocidolite. These findings may have significance for the induction of pleural injury by asbestos fibers.