Spirometric pattern transitions in a World Trade Center occupational cohort on longitudinal surveillance

Background: Many workers and volunteers who participated in the rescue and recovery of the World Trade Center (WTC) disaster site in 2001–2002 manifest a heterogeneous group of chronic lower airway diseases, with variable spirometric patterns on longitudinal surveillance. We examined systematically the observed transitions among those spirometric patterns and assessed their association with BMI and occupational WTC exposure intensity. Methods: We selected 10,810 Mount Sinai WTC General Responders’ Cohort members with at least three acceptable quality periodic spirometries (n = 56,312) performed between July 2002 and November 2019. We defined three spirometric patterns: (1) normal: prebronchodilator first-second forced expiratory volume (FEV₁), forced vital capacity (FVC), and FEV₁/FVC ratio > lower limit of normal (LLN); (2) obstruction: pre-bronchodilator FEV₁/FVC ratio<LLN; (3) low FVC: FVC < LLN and FEV₁/FVC > LLN. We built a multi-state Markov-like model to analyze probabilities of transition between those three spirometric patterns. Results: Low FVC is the most frequent abnormal spirometric pattern in the WTC workers. Substantial stationary probabilities of stability (0.88) were observed for normal, and less so for low FVC (0.73) and obstructive (0.65) pattern. At least 80 % of the observed transitions involved the normal and low FVC patterns, and both higher WTC exposure intensity (early arrival at the site), and body mass index (BMI) were predictors of transitions to low FVC in this cohort. Conclusion: Low FVC is relatively stable, and both WTC exposure intensity and BMI are independently and significantly associated with transitions to it. Transitions to obstruction are generally infrequent among the WTC workers and have greater instability.