Correlation of fractional exhaled nitric oxide levels with inflammation and lung function in patients with chronic obstructive pulmonary disease at different stages: A retrospective study

Abstract

This study aims to evaluate the levels of fractional exhaled nitric oxide (FeNO) in patients with chronic obstructive pulmonary disease (COPD) at different stages, analyze its correlation with inflammatory markers and lung function indices, and explore the feasibility of FeNO as a potential biomarker for airway inflammation in COPD patients. A retrospective analysis was conducted on 146 COPD patients covering the period from January 2021 to June 2023. Among them, 87 patients in the acute exacerbation phase were designated as group B, 59 patients in the stable phase as group C, and 30 healthy controls were selected as group A. Lung function was assessed by measuring predicted forced expiratory volume in the first second (FEV1)%pred and the FEV1/forced vital capacity ratio, while FeNO levels and various inflammatory markers (C-reactive protein, d-dimer, interleukin [IL]-2, IL-6) were also measured. Pearson correlation analysis was conducted to explore the correlation of FeNO with lung function and inflammatory markers. Patients with COPD at the acute exacerbation phase had significantly higher FeNO levels than the other 2 groups (P < .001), and these levels were negatively correlated with FEV1%pred and the FEV1/forced vital capacity ratio. FeNO levels were positively correlated with inflammatory markers C-reactive protein, d-dimer, and IL-6 (P < .01). Eosinophil counts in peripheral blood and induced sputum showed a significant positive correlation with FeNO levels. FeNO levels significantly increased during acute exacerbation phase of COPD and were associated with declines in lung function and elevated levels of inflammatory markers. FeNO could serve as a potential monitoring indicator for airway inflammation in COPD, aiding in the assessment and management of the condition.

Keywords: COPD; FeNO; airway inflammation; inflammatory markers; lung function.

Figure 1.

Flowchart of patient selection for the study.

Figure 2.

Comparison of lung function levels in patients with COPD at different stages. (A) FEV1pred; (B) FEV1/FVC. Compared with group A, ^***P < .001; compared with group B, ^###P < .001. FEV1pred = predicted forced expiratory volume in the first second, FEV1/FVC = the ratio of forced expiratory volume in the first second and forced vital capacity, Group A = healthy controls, Group B = patients in the acute exacerbation phase, Group C = patients in the stable phase.

Figure 3.

Comparison of FeNO levels in patients with COPD at different stages. (A) Eos; (B) N; (C) FeNO. Compared with group A, ^***P < .001; compared with group B, ^###P < .001. Eos = eosinophils, N = neutrophils, FeNO = fractional exhaled nitric oxide’ Group A = healthy controls, Group B = patients in the acute exacerbation phase, Group C = patients in the stable phase.

Figure 4.

Comparison of CRP, d-dimer, IL-2, and IL-6 levels. (A) CRP; (B) d-dimer; (C) IL-2; (D) IL-6. Compared with group A, ^***P < .001; compared with group B, ^###P < .001. CRP = C-reactive protein, Group A = healthy controls, Group B = patients in the acute exacerbation phase, Group C = patients in the stable phase, IL-2 = interleukin-2, IL-6 = interleukin-6.

Figure 5.

Correlation of serum FeNO levels with lung function and inflammatory markers. (A) FEV1pred; (B) CRP; (C) d-dimer; (D) IL-2; (E) IL-6. CRP = C-reactive protein, FeNO = fractional exhaled nitric oxide, FEV1pred = predicted forced expiratory volume in the first second, IL-2 = interleukin-2.

Figure 6.

Diagnostic value of FeNO in severe COPD during the stable phase.