Analysis of airway resistance and hypoxemia in overlap syndrome

OBJECTIVES To characterize overlap syndrome, investigate its impact on airflow limitation and blood oxygen condition, and detect the risk factors that affect its airway resistance.  METHODS We reviewed retrospectively the clinical data of 158 patients with overlap syndrome (OS), chronic obstructive pulmonary disease (COPD), and obstructive sleep  apnea (OSA), treated in the Critical Care Medicine Department of the People's Hospital of Liaocheng, Liaocheng, China from May 2014 to March 2015. The lowest and average oxyhemoglobin saturation were measured using polysomnography. The pulmonary functions were tested using the cardiopulmonary measuring instruments, and the viscous resistance at oscillation frequencies of 5, 10, 15, 20 Hz was measured using the impulse oscillation system for all the patients.  RESULTS The values of forced expiratory volume (FEV)1/FVC, FEV1% predicted, and the lowest SaO2 in the OS group were significantly lower than those in the OSA (p less than 0.01, p less than 0.01, p=0.01), or the COPD group (p=0.03, p=0.02, p=0.03, but the value of viscous resistance at 5 Hz was significantly higher than that in the 2 groups (p less than 0.01). Old age, body mass index, and smoking history were significantly correlated with the viscous resistance in OS patients, at an oscillation frequency of 5Hz (p=0.03, p=0.04).  CONCLUSION The OS patients present with higher viscous resistance and more severe oxygen deficit, when compared with OSA and COPD patients, and weight decrease and smoking cessation are necessary for these patients.