Comparison of Fractional Exhaled Nitric Oxide in Elderly Patients with Asthma-chronic Obstructive Pulmonary Disease Overlap and Other Airway Inflammatory Diseases

The exact role of fractional exhaled nitric oxide (FeNO) in older patients with chronic inflammatory diseases including asthma-chronic obstructive pulmonary disease (COPD) overlap (ACO) remains unclear. This study aimed to investigate the differences in FeNO levels of elderly patients with ACO, asthma, COPD, and chronic cough. We conducted a retrospective study analysing the data of stable outpatients from Pulmonary Department of the Second Clinical College, Jinan University. All participants (Age≥55 years) were divided into the ACO group (n=19), asthma group (n=16), COPD group (n=25), and chronic cough group (n=22). The clinical data such as peripheral eosinophil counts, serum high sensitivity C-reactive protein (hs-CRP), FeNO, and spirometry was collected, and the correlations between FeNO levels and systemic markers or spirometric indices were analyzed. Patients with ACO and asthma had significantly elevated FeNO levels (37.7±16.5, and 36.3±17.7 ppb) compared with COPD, and chronic cough patients (21.9±10.3, and 16.1±8.8 ppb). The FeNO levels were negatively associated with forced expiratory volume in 1 second (FEV1, p=0.003), FEV1% predicted (p=0.012), and FEV1/forced vital capacity (FVC, p=0.002) in all groups. However, there were no significant correlation between FeNO levels and FVC, peripheral eosinophil counts, or serum hs-CRP (p>0.05). Elderly patients with ACO have higher levels of FeNO, when compared with patients with COPD or chronic cough. These findings suggest that FeNO measurement may provide an important implication for the etiological diagnosis of ACO in the elderly patients.