Objective  To investigate the relationships of cognitive impairment (CI) with levels of endothelin-1 (ET-1) and neutrophil gelatinase-associated lipocalin (NGAL) in patients with overlap syndrome of chronic obstructive pulmonary disease complicated with obstructive sleep apnea hypopnea syndrome (COPD-OSAHS).

Methods  A total of 87 patients with overlap syndrome of COPD-OSAHS in the Zhangjiakou City First Hospital of Hebei Province from January 2021 to January 2022 were selected as COPD-OSAHS group, and these patients were divided into CI group with 41 cases and non-CI group with 46 cases according to the condition of CI; another 62 COPD patients were selected as COPD group. Serum ET-1 and NGAL levels were detected by enzyme-linked immunosorbent assay. Scores of the Montreal Cognitive Assessment (MoCA) and the levels of serum ET-1 and NGAL were compared between COPD-OSAHS group and COPD group. Pearson correlation coefficient was used to analyze the correlations of the MoCA score with serum ET-1 and NGAL levels in patients with overlap syndrome of COPD-OSAHS; the multivariate Logistic regression model was used to analyze the influencing factors of CI in patients with overlap syndrome of COPD-OSAHS; the receiver operating characteristic (ROC) curve was used to analyze the predictive value of serum ET-1 and NGAL levels for CI in patients with overlap syndrome of COPD-OSAHS.

Results  The score of each item in MoCA and total score in the COPD-OSAHS group were significantly lower than those in the COPD group (P < 0.01). The levels of serum ET-1 and NGAL in the COPD-OSAHS group were (52.81±9.95) pg/mL and (7.63±1.62) ng/mL respectively, which were significantly higher than (27.84±6.98) pg/mL and (3.13±1.19) ng/mL in the COPD group (P < 0.01). Pearson correlation coefficient showed that the levels of serum ET-1 and NGAL in patients with overlap syndrome of COPD-OSAHS were negatively correlated with the MoCA score (r=-0.622, -0.613, P < 0.001). Compared with the patients in the non-CI group, the patients in the CI group were older, the ratios of patients with body mass index (BMI) ≥ 28 kg/m², smoking, COPD duration ≥ 5 years, severe COPD, OSAHS duration≥ 5 years, and severe OSAHS were significantly higher, and the levels of ET-1 and NGAL were significantly higher in the CI group (P < 0.05). Multivariate Logistic regression model analysis showed that age, BMI≥ 28 kg/m², severe COPD, OSAHS duration≥ 5 years, severe OSAHS, ET-1 and NGAL were the independent risk factors for CI in patients with overlap syndrome of COPD-OSAHS (P < 0.05). ROC curve showed that the area under curve (AUC) of CI predicted by serum ET-1 and NGAL in patients with overlap syndrome of COPD-OSAHS was significantly greater than that predicted by one indicator alone (Z=2.039, 2.347, P=0.041, 0.019).

Conclusion  Patients with overlap syndrome of COPD-OSAHS have obvious CI, the increased levels of serum ET-1 and NGAL are closely associated with CI, which is also helpful for CI prediction.