Abstract Rationale Air trapping is recognized as one of the earliest pathophysiologic abnormalities in individuals at risk for COPD from direct or secondhand tobacco smoke exposure. Several physiologic and radiologic indices have been proposed to quantify air trapping; however, their relative performances in discriminating respiratory symptoms and exercise intolerance remain incompletely characterized. Objective To determine which air trapping index performs most accurately in identifying dyspnea and exercise intolerance. Methods This post-hoc analysis included 441 never-smoking flight attendants with a history of heavy occupational exposure to secondhand tobacco smoke and at risk for COPD. Static air-trapping indices from pulmonary function tests included FRC/TLC and RV/TLC (representing lung volume plethysmographic abnormality), and (TLC-VA)/TLC (representing gas diffusion abnormality). Outcomes were dyspnea (mMRC ≥1) and reduced exercise tolerance (peak VO2 86% predicted) from cardiopulmonary exercise testing. Receiver operating characteristic (ROC) analyses evaluated each index’s discriminative ability. A baseline model adjusted for covariates (age, sex, height, and weight) was first established and each air trapping index was then added individually and in combination to assess incremental performance. Furthermore, a subset of 44 participants underwent quantitative CT imaging to generate % low-attenuation voxels between -860 and -950 HU on expiratory images (LAAexp-860to-950) (representing radiographic gas distribution abnormality), which was incorporated into static models, to determine the added predictive contribution of radiologic measures. Results Data were available for 441 participants (mean age=55±11 years, 85% female, BMI=24±4 kg/m²). For dyspnea, the covariate-only model achieved an AUC of 0.70 95% CI: 0.62-0.78. Adding physiologic air trapping indices incrementally improved model performance (AUCs ranging from 0.70 to 0.79) with FRC/TLC providing the highest discrimination (AUC=0.79 0.70-0.87). Combining multiple indices did not further enhance accuracy beyond FRC/TLC alone (Table 1). For exercise tolerance, the covariate-only model demonstrated an AUC of 0.69 0.62-0.76. Only the addition of FRC/TLC meaningfully improved discrimination (AUC=0.73 0.65-0.81). The final model including all physiologic indices was the best overall predictor (AUC=0.76 0.66-0.81). In the CT-imaged subset (n = 44, mean age=60±8 years, 100% female, BMI=24±3 kg/m²), incorporating CT-derived air trapping index (LAAexp-860to-950) produced minimal improvement for dyspnea (AUC=0.84; covariate-only model=0.83) but substantially enhanced prediction of exercise intolerance (AUC=0.75; covariate-only model=0.62). Conclusion Among the evaluated air trapping indices measured by plethysmography, gas dilution, and CT imaging, FRC/TLC and LAAexp-860to-950 demonstrated the strongest performance in discriminating dyspnea and exercise limitation, respectively. Integrating physiologic and radiologic measures of air trapping may improve detection of early airway dysfunction in populations at risk for COPD. This abstract is funded by: The Flight Attendant Medical Research Institute (FAMRI)
Kaboudan et al. (Fri,) studied this question.