Imaging Phenotype of Occupational Endotoxin-Related Lung Function Decline

Abstract

Background: Although occupational exposures contribute to a significant proportion of obstructive lung disease, the phenotype of obstructive lung disease associated with work-related organic dust exposure independent of smoking remains poorly defined.

Objective: We identified the relative contributions of smoking and occupational endotoxin exposure to parenchymal and airway remodeling as defined by quantitative computed tomography (CT).

Methods: The Shanghai Textile Worker Study is a longitudinal study of endotoxin-exposed cotton workers and endotoxin-unexposed silk workers that was initiated in 1981. Spirometry, occupational endotoxin exposure, and smoking habits were assessed at 5-year intervals. High-resolution computed tomography (CT) was performed in 464 retired workers in 2011, along with quantitative lung densitometric and airway analysis.

Results: Significant differences in all CT measures were noted across exposure groups. Occupational endotoxin exposure was associated with a decrease (-1.3%) in percent emphysema (LAAI-950), a 3.3-Hounsfield unit increase in 15th percentile density, an 18.1-g increase in lung mass, and a 2.3% increase in wall area percent. Current but not former smoking was associated with a similar CT phenotype. Changes in LAAI-950 were highly correlated with 15th percentile density (correlation -1.0). Lung mass was the only measure associated with forced expiratory volume in 1 sec (FEV1) decline, with each 10-g increase in lung mass associated with an additional loss (-6.1 mL) of FEV1 (p = 0.001) between 1981 and 2011.

Conclusions: There are many similarities between the effects of occupational endotoxin exposure and those of tobacco smoke exposure on lung parenchyma and airway remodeling. The effects of occupational endotoxin exposure appear to persist even after the cessation of exposure. LAAI-950 may not be a reliable indicator of emphysema in subjects without spirometric impairment. Lung mass is a CT-based biomarker of accelerated lung function decline.

Citation: Lai PS, Hang J, Zhang F, Sun J, Zheng BY, Su L, Washko GR, Christiani DC. 2016. Imaging phenotype of occupational endotoxin-related lung function decline. Environ Health Perspect 124:1436-1442; http://dx.doi.org/10.1289/EHP195.

Figure 1

Overview of Shanghai Textile Worker Study. Most of the workers retired between 1992 and 2001. Of the 587 subjects in the 2011 follow-up survey, 464 consented to and received high-resolution computed tomography of the chest. Abbreviations: ATS, American Thoracic Society; CT, computed tomography.

Figure 2

Correlation between CT measure of percent emphysema (using cutoff of –950 Hounsfield units, LAA_I-950) and 15th percentile density across all exposure subgroups. Correlation was high (Pearson correlation –0.87, Spearman correlation –1.00) and suggested that the percent emphysema measure may actually be reflecting changes in lung density, and not a true measure of emphysema.