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

Abstract

Rationale-Deployment to the Southwest Asia Theater of Military Operations is associated with new-onset respiratory symptoms, yet commonly-used parameters on pulmonary function test (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. Objective-Evaluate the clinical utility of PFT parameters among DEPS and examine associations with baseline respiratory symptoms, functional limitations, healthcare utilization, and longitudinal trajectories. Methods-We identified veterans in the U.S. Department of Veterans Affairs Airborne Hazards and Open Burn Pit Registry who enrolled in the Veterans Health Administration and had at least one PFT after the end of their initial deployment (1990-2019) and before completion of the Registry self-assessment questionnaire (2014-2024). We defined DEPS as having no airflow obstruction (forced expiratory volume in 1 second-to-forced vital capacity ratio≥lower-limit-of-normal or LLN) or restriction (total lung capacity≥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's 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 or mMRC≥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 years-old, 86% male, 15% current and 19% former smoker, 64% mMRC≥1), several PFT parameters were linked to outcomes, but diffusing capacity (DL_CO) was the strongest predictor, showing significant relationships with many outcomes (Odds ratios ranging from 0.46 to 0.89, all P<0.05). Among the 289 DEPS with follow-up PFT 6±4 years later, those with baseline isolated reduction in DL_CO (CO (33% vs. 19%, P=0.048). Conclusion-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.