Restrictions of VC and DLCO in relation to asbestos-related computed tomographic findings quantified by ICOERD-based parameters.

Background
Even almost 30 years after the ban on the use of asbestos in Germany, the effects of asbestos are still highly relevant in everyday clinical practice in occupational medicine. The aim of this study was to further investigate the significance of essential parameters of both pulmonary function diagnostics and imaging techniques (low-dose HR-TCT) for the prevention and early detection of asbestos-related morphological and functional lung changes.

Methods
Data from spirometry, body plethysmography and diffusion capacity, as well as CT images of the thorax, were retrospectively studied from 72 patients examined between 2017 and 2019 at the Institute for Occupational and Maritime Medicine (ZfAM), Hamburg, Germany. The subjects were divided into four subgroups according to the presence of comorbidities (concomitant cardiac diseases, obstructive ventilatory disorder, pulmonary function pattern consistent with emphysema, and no other pulmonary or cardiac diseases). These subgroups were analysed in addition to the overall collective. The CT images were evaluated according to the International Classification of Occupational and Environmental Respiratory Diseases (ICOERD) with radiological expertise. In addition, some asbestos-related parameters were newly quantified, and corresponding scores were defined based on ICOERD. Statistical analysis included the use of correlations and fourfold tables with calculation of Spearman's rho (ρ), Cohen’s κ, and accuracy.

Results
Vital capacity (VC) is slightly reduced in the total collective compared to the normal population (mean 92% of predicted value), while diffusion capacity for CO (DLCO) shows predominantly pathological values, mean 70% of the respective predicted value. The CO transfer coefficient (DLCO/VA), which refers to alveolar volume (VA), also shows slightly decreased values (mean 87% pred.). Seventy-nine percent of patients (n = 57) had signs of pulmonary fibrosis on CT scans, and pleural plaques appeared in 58 of 72 patients (81%). Of the newly quantified additional parameters, particularly frequently described findings are subpleural curvilinear lines (SC, n = 39) and parenchymal bands (PB, n = 29). VC correlates well with the expression of pleural plaques (ρ = − 0.273, P < 0.05), and DLCO measures show a better correlation with fibrosis score (ρ = − 0.315, P < 0.01). A third, newly developed score, which includes the extent of pleural plaques and additional subpleural parameters instead of fibrosis parameters, shows significant correlations for both VC and DLCO (ρ = − 0.283, − 0.274, resp.; both P < 0.05).

Discussion
The importance of spirometry (VC) and diffusion capacity measurement (DLCO) as essential diagnostic procedures for the early detection of asbestos-related changes ‒ also including patients with relevant concomitant cardiac or pulmonary diseases ‒ was confirmed. Significant and better correlations between lung function changes (VC and DLCO) and abnormal CT findings are seen when parenchymal bands (PB), subpleural curvilinear lines (SC), and rounded atelectasis (RA) are quantitatively included into the evaluation, in addition to assessing the extent of pleural plaques alone. Therefore, when assessing CT images according to ICOERD, these parameters should also be quantified.