Effect of obstructive sleep apnea on cardiopulmonary function in patients with chronic obstructive pulmonary disease

Objective: To study the characteristics of cardiopulmonary function in patients with chronic obstructive pulmonary disease (COPD) and obstructive sleep apnea (OSA) overlapping syndrome (OS). Methods: A total of 149 COPD patients, who were on stable treatment, were enrolled from the Second Affiliated Hospital of Soochow University from December 2017 to December 2019. The patients were divided into the OS group (n=56) and the COPD only group (n=93) according to their apnea hypopnea index (AHI) measured by the Apnealink device. Data were gathered from polysomnograph (PSG), spirometry, arterial blood gas and N-terminal pro-brain natriuretic peptide (NT-proBNP) assay to assess the cardiopulmonary function of patients. Partial correlation analysis was used to analyze the correlation between AHI and various factors, to study the characteristic changes in the cardiopulmonary function of these OS patients. Results: There were no significant cross-group differences in age and gender (all P>0.05). In the OS group, the forced expiratory volume in one second to forced vital capacity ratio (FEV1/FVC), the forced expiratory volume in the first second expressed as percent predicted (FEV1%pred), pH[M (Q1, Q3)], partial pressure of oxygen (PaO2) and oxygen saturation (SaO2) were lower than those in the COPD group [(49.46±12.98)% vs (54.38±11.72)%, (47.86±14.78)% vs (57.78±15.81)%, 7.37(7.34, 7.39) vs 7.40(7.39, 7.41), (80.75±10.20) vs (84.28±8.43) mmHg (1 mmHg=0.133 kPa), (94.46±2.52)% vs (95.74±2.28)%], whereas partial pressure of carbon dioxide (PaCO2) [M (Q1, Q3)] was higher than that in the COPD group [55.00 (45.50, 60.00) vs 44.00(40.00, 48.00)mmHg] (all P<0.05). Pulmonary arterial pressure and plasma NT-proBNP levels [M (Q1, Q3)] in the OS group were significantly higher than those in the COPD group [38.90 (28.60, 49.05) vs 28.60 (24.95, 32.60) mmHg, 434.00 (273.75, 631.00) vs 136.00 (86.00, 205.00) pg/ml] (P<0.05). Partial correlation analysis showed that AHI was positively correlated with PaCO2, pulmonary artery pressure, NT-proBNP, and acute exacerbation events (r values: 0.496, 0.544, 0.628, 0.446), and negatively correlated with FEV1/FVC, FEV1%pred, pH, PaO2, and SaO2 (r values:-0.309, -0.346, -0.410, -0.289, -0.267) (all P<0.05). Conclusion: Patients with OS suffer from more severe hypoxemia, hypercapnia and pulmonary function damage, and their pulmonary arterial pressure and NT-proBNP are significantly higher than those with COPD only.