High-intensity dust exposure linked to airway abnormalities in World Trade Center firefighters

DALLAS — In firefighters who responded to the World Trade Center on 9/11, high-intensity dust exposure and early symptoms were associated with an increased likelihood of evidence of emphysema, bronchial wall thickening and air trapping on CT scan, according to data presented at the American Thoracic Society International Conference.

“The collapse of the World Trade Center on the morning of 9/11 produced an immense more than 10,000,000 tons of irritating alkaline dust with a pH greater than 10,” Charles L. Liu, MD, fellow in the division of pulmonary, critical care and sleep medicine at NYU School of Medicine, said during a presentation.

This first-responder population has served as an important model for studying lung disease after irritant-induced lung function, he added, noting that he and his colleagues have collected about 17 years of longitudinal data on World Trade Center firefighters.

“We already know that first responders develop new and persistent lung function abnormalities, including obstruction, airway-hypersensitivity and accelerated FEV₁ (forced expiratory volume in 1 second) decline,” Liu said. “Our hypothesis for this study was that high-intensity dust exposure is associated with World Trade Center-related airway CT abnormalities.”

For this study, Liu and colleagues categorized firefighters who responded to the World Trade Center before noon on 9/11 as having high-intensity exposure and those who responded after noon as having low-intensity exposure. This allowed researchers to differentiate between World Trade Center-related CT abnormalities and those associated with the occupational hazards of being a firefighter in general, he noted.

Factors related to CT abnormalities

The study cohort was composed of 9,638 firefighters, of whom 4,277 had at least one chest CT scan between Sept. 11, 2001, and Sept. 10, 2018, with a median time to scan of about 6 years. Of those who had a CT scan, 1,226 had a pulmonary function test with a bronchodilator within 1 year of chest CT.

Among those who had CT scans vs. those who did not, there were more ever smokers, firefighters who experienced wheezing or shortness of breath within the first 6 months after 9/11 and firefighters who responded on the morning of 9/11. Other factors were comparable between the two groups, Liu noted.

A number of abnormalities on CT scans were found among World Trade Center responders, including air trapping (20%), bronchial wall thickening (19.6%), nodules of at least 5 mm (14.6%), ground glass opacities (12.2%), emphysema (5.9%), bronchiectasis (3.6%), pleural thickening (3%) and lung fibrosis (0.4%)

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Upon further analysis, the researchers found that high-intensity dust exposure, as compared with low-intensity exposure, was associated with significantly higher risks for emphysema (HR = 1.6; 95% 1.15-2.2), bronchial wall thickening (HR = 2.2;95% CI, 1.8-2.6) and air trapping (HR = 2.2; 95% CI, 1.9-2.6) in the years after 9/11.

Notably, Liu said, the separation between curves indicating higher risk for CT abnormalities increased even 16 to 17 years after 9/11.

In an analysis evaluating potential associations between early symptoms and airway abnormalities, results showed that either shortness of breath or wheeze was associated with an increased risk for emphysema (HR = 1.43; 95% CI, 1.04-1.97), bronchial wall thickening (HR = 1.38; 95% CI, 1.16-1.63) and air trapping (HR = 1.27; 95% CI, 1.08-1.49). Similar results were observed when they evaluated both shortness of breath and wheeze and risk for emphysema (HR = 1.62; 95% CI, 1.12-2.33), bronchial wall thickening (HR = 1.49; 95% CI, 1.22-1.83) and air trapping (HR = 1.41; 95% CI, 1.16-1.7).

Airway abnormalities and lung function

The researchers also investigated the potential association between CT abnormalities and decline in lung function. A multivariable regression model showed that accelerated FEV₁ decline was more likely in firefighters with emphysema (OR = 1.89; 95% CI, 1.37-2.6) and bronchial wall thickening (HR = 1.55; 95% CI, 1.25-1.92). However, the same was not true for air trapping (OR = 0.77; 95% CI, 0.61-0.97).

“Interestingly, even though air trapping is an airway disease and is closely related to bronchial wall thickening, if you look at the numbers, it may be slightly protective,” Liu said.

In looking at longitudinal lung function according to CT abnormality, the emphysema and bronchial wall thickening groups, as compared with firefighters who had no CT abnormalities, had worse lung function almost immediately after exposure — a difference that continued through 17 years without ever quite recovering, according to Liu. Lung function over time in patients with air trapping, however, did not differ significantly from those who had no CT abnormality and was even slightly better at some points.

Final thoughts

The study had several limitations, Liu noted, of which the greatest were the potential for “healthy worker effect” bias and a lack of generalizability, as the cohort was overwhelmingly white and mostly men.

He also added that CT reads were abstracted from clinical reports and that selection bias could be a factor, as CT scans were clinically indicated and the timing of scans was not standardized.

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“Our study showed that in World Trade Center-exposed firefighters, high-intensity dust exposure was associated with subsequent CT evidence of bronchial wall thickening, air trapping and emphysema. We also found that CT evidence of emphysema and bronchial wall thickening were associated with airflow obstruction and an accelerated rate of longitudinal FEV₁ loss and air trapping on CT is associated with symptoms but not with lung function decline,” Liu said. – by Melissa Foster

Reference:

Liu CL. Abstract 4258. Presented at: American Thoracic Society International Conference; May 17-22, 2019; Dallas.

Disclosure: Liu reports no relevant financial disclosures.