Clinical Utility of Pulmonary Function Testing in Assessing Longitudinal Outcomes of Deployed Veterans with Preserved...

Rationale: Deployment to the Southwest Asia theater of military operations is associated with new-onset respiratory symptoms, yet commonly used parameters on pulmonary function testing (PFT) are typically reported to be within the normal range for most deployers, referred to here as deployment-exposed veterans with preserved spirometry (DEPS). The relationship between these normal-range PFT parameters and long-term outcomes has not been thoroughly investigated. Objectives: To evaluate the clinical utility of PFT parameters among DEPS and examine associations with baseline respiratory symptoms, functional limitations, healthcare use, and longitudinal trajectories. Methods: We identified veterans in the U.S. Department of Veterans Affairs AHOBPR (Airborne Hazards and Open Burn Pit Registry) who enrolled in the Veterans Health Administration and underwent at least one pulmonary function test after the end of their initial deployment (1990-2019) and before completion of the AHOBPR self-assessment questionnaire (2014-2024). We defined DEPS as having no airflow obstruction (ratio of forced expiratory volume in 1 second to forced vital capacity greater than or equal to the lower limit of normal [LLN]) or restriction (total lung capacity greater than or equal to the LLN). We applied adjusted mixed-effects regression and machine learning to assess the predictive value of PFT parameters for key outcomes. We also examined the longitudinal trajectories of DEPS' PFT patterns using interval-censored Cox proportional-hazards regression. Results: Among eligible veterans with complete data (n = 3,814), 68% reported respiratory symptoms (modified Medical Research Council dyspnea scale score ≥1), but most had preserved spirometry (DEPS, 49%), followed by obstructive (28%), restrictive (21%), and mixed (2%) PFT patterns. Among DEPS (n = 1,879, 37 ± 10 yr of age, 86% men, 15% current smokers and 19% former smokers, 64% with modified Medical Research Council dyspnea scale scores ≥1), several PFT parameters were linked to outcomes, but diffusing capacity of the lung for carbon monoxide (Dl_CO) was the strongest predictor, showing significant relationships with many outcomes (odds ratios ranging from 0.46 to 0.89; P < 0.05 for all). Among the 289 DEPS with follow-up PFT 6 ± 4 years later, those with baseline isolated reduction in Dl_CO (less than the LLN) were more likely to develop restrictive impairments compared with those with normal Dl_CO (33% vs. 19%; P = 0.048). Conclusions: In a national sample of deployed veterans with military environmental exposures, approximately half had preserved spirometry (DEPS), but many endorsed substantial respiratory symptoms and functional limitation. DEPS with reduced Dl_CO appear to be at increased risk for developing lung parenchymal disease over time.