Abstract Rationale Patients with CPFE tend to have normal spirometry and lung volumes despite marked parenchymal disease on imaging. The pseudo-normalization of lung volumes in CPFE results from the counterbalancing effects of restrictive fibrosis and emphysematous hyperinflation. Elastic recoil from fibrotic tissue helps preserve expiratory flow despite alveolar destruction from emphysema. In this study, IOS was used to examine differences in respiratory physiology in CPFE versus COPD. Methods Retrospective single-center cohort study in the Veteran patient population undergoing clinical pulmonary function testing including IOS. CPFE patients were defined as those with upper lobe-predominant emphysema and lower lobe-predominant pulmonary fibrosis on chest CT. Each CPFE patient was matched to two COPD controls for age (± 2 years), biological sex, and smoking status. The predicted values for IOS were based on the equations of Oostveen et al. (Eur Respir J 2013;42:1513-1523), while spirometry was performed using GLI-Global equations. CPFE and control groups were compared using the Wilcoxon rank-sum (continuous variables) and Fisher’s exact test (categorical variables). Results CPFE patients (n = 21) and COPD controls (n = 42) were well-matched in age (median 76 versus 75.5 years, respectively) and smoking status, and were all male (Table 1). Pulmonary function testing, including IOS parameters, are detailed in Table 1. As anticipated, FEV1 (absolute/liters or % predicted) and FEV1/FVC ratio were higher in CPFE compared with COPD, as was FEF25%-75% (p 0.001 for all). Total lung capacity and residual volume were higher in COPD, while diffusion capacity for carbon monoxide was significantly lower in CPFE. Respiratory system resistance at 5Hz (R5) and the difference between resistance at 5Hz and 20Hz (R5-R20) were significantly lower in CPFE. CPFE patients showed less negative reactance at 5Hz (X5, a measure of the elastic and inertial properties of the respiratory system), with a lower area under the reactance curve (AX) and a lower resonant frequency than COPD controls. Conclusions CPFE patients demonstrated lower respiratory system resistance at 5 Hz and less frequency dependence of resistance (i.e., lower R5-R20) than COPD controls, indicating better preservation of small airway patency. Reactance values were less negative, and the area under the reactance curve was reduced in CPFE, suggesting greater overall respiratory system compliance in CPFE despite lung fibrosis. In contrast, higher lung volumes and greater air trapping in COPD likely contribute to increased respiratory system stiffness. Together, IOS and conventional pulmonary function testing provide complementary insights into the complex physiology of CPFE. This abstract is funded by: None
Vakharia et al. (Fri,) studied this question.