To investigate the relationship between eosinophil (EOS) count and alveolar damage in patients with chronic obstructive pulmonary disease (COPD) complicated with emphysema.

A total of 186 patients with COPD and emphysema admitted to our hospital from January 2021 to June 2025 were selected. EOS counts were measured, and patients underwent chest computerized tomography (CT) scans, pulmonary function tests, and cardiopulmonary exercise testing (CPET). Spearman analysis was used to analyze the correlations between EOS count and CT parameters, pulmonary function, and CPET parameters. Multiple linear regression was employed to adjust for confounding factors.

Among the 186 patients, 82 were identified as the EOS phenotype (EOS ≥300/μl) and 104 as the non-EOS phenotype (EOS<300/μl). The use of bronchodilators was higher in the EOS phenotype group 63 cases( 76.83%) compared to the non-EOS phenotype group 56 cases(53.85%) (P=0.001), and the neutrophil count was lower in the EOS phenotype group (P=0.027). Spearman correlation analysis showed that in the EOS phenotype group, EOS count was positively correlated with the expiratory to inspiratory ratio of mean lung density (E/I) (r_s=0.484, P=0.000), the wall area percentage of the 5th generation apical segment bronchus (B¹ 5th WA%) (r_s=0.396, P=0.000), and the wall thickness of the 5th generation apical segment airway (B¹ 5th WT) (r_s=0.245, P=0.041). It was negatively correlated with the peak of minute ventilation (VE_peak) (r_s=-0.239, P=0.030), maximum voluntary ventilation (MVV) (r_s=-0.442, P=0.000), peak heart rate (HR_peak) (r_s=-0.336, P=0.002), oxygen saturation (SpO₂) (r_s=-0.230, P=0.037), Z score of forced expiratory volume in one second (FEV_{1 Z-score}) (r_s=-0.484, P=0.000), Z score of FEV₁ to forced vital capacity ratio (FEV₁/FVC_Z-score) (r_s=-0.488, P=0.000), Z score of diffusion capacity for carbon monoxide of the lung (DL_{CO Z-score}) (r_s=-0.230, P=0.038), and Z score of alveolar ventilation (VA_Z-score) (r_s=-0.231, P=0.037). In the non-EOS phenotype group, EOS count was negatively correlated with diffusion capacity for carbon monoxide per liter of alveolar volume (K_CO) (r_s=-0.200, P=0.042). Multiple linear regression showed that in the EOS phenotype group, EOS count was associated with E/I (P=0.000), B¹ 5th WA% (P=0.000), B₁ 5th WT (P=0.041), VE_peak (P=0.008), MVV (P=0.000), VR (P=0.004), FEV_{1 Z-score} (P=0.000), FEV₁/FVC_Z-score (P=0.000), and VA_Z-score(P=0.029). No such associations were found in non-EOS patients.

Alveolar damage in patients with COPD and emphysema is associated with airway eosinophilic inflammation. The EOS phenotype is associated with more severe emphysema and alveolar damage.