Effect of lung volume on the apnea hypopnea index in patients with overlap syndrome: a single center study.

PURPOSE: This study aimed to evaluate the relationship between lung volume and apnea-hypopnea index (AHI) in patients with overlap syndrome (OVS). METHODS: Chronic obstructive pulmonary disease (COPD) patients diagnosed by spirometry were recruited from Renmin Hospital of Wuhan University. They were asked to take an overnight polysomnography (PSG). Multiple regression analyses were used to assess the relationships between lung volume measures and AHI in OVS patients. RESULTS: Finally, 354 OVS patients and 229 patients with only COPD met the study's entry criteria. After adjusting for age, sex, BMI, neck size, economic status, smoking, alcohol use, and hypertension, residual volume (RV), total lung capacity (TLC), and the RV/TLC ratio each had a negative link with the AHI in OVS patients (RV: exp(β) = 0.903; 95% CI, 0.852 to 0.957; P < 0.05; TLC: exp(β) = 0.947; 95% CI, 0.899 to 0.998; P < 0.05; RV/TLC: exp(β) = 0.898; 95% CI, 0.846 to 0.954; P < 0.01). However, when RV was added as a covariate in the model, forced expiratory volume in one second (FEV1) had no association with the AHI in OVS patients (P > 0.05). Also, when dividing OVS patients by lung function severity, RV had a negative correlation with the AHI in those with Global Initiative for Chronic Obstructive Lung Disease (GOLD) 3-4 grade (exp(β) = 0.905; 95% CI, 0.835 to 0.980; P < 0.05), but in GOLD 1-2 grade patients, there was no link between RV and AHI (P > 0.05). CONCLUSION: The higher residual volume was independently associated with lower AHI in patients with overlap syndrome, particularly among patients with GOLD 3-4 airflow limitation.