Figure 1.

Firefighters who participated in the chest computed tomography (CT) study. Shown is the source population of male firefighters who were employed by the Fire Department of the City of New York (FDNY) on 11/9/2001, present at the World Trade Center (WTC) site between 11/9/2001 and 24/9/2001, and had at least three monitoring pulmonary function tests (PFTs) between 11/9/2001–10/9/2018 to assess longitudinal forced expiratory volume at one second (FEV₁) and FEV₁/FVC (forced vital capacity). The final study population included those who had received a clinically-indicated chest CT scan between 11/9/2001 and 10/9/2018. A subgroup had a clinically-indicated bronchodilator PFT within one year of the chest CT.