The relationship between sleep respiratory disorder and daytime PaO2 in OSAS and in overlap syndrome

OSAS and COPD are often associated with daytime hypoxiemia. Overlap Syndrome (OS) increases the risk of daytime hypoxiemia. The aimof this study was to investigate the mechanisms which could justify the low oxygen9s levelin these patients and the effect of CPAP therapy. 563 consecutive OSAS patients were enrolled. According to pulmonary function test they were divided in 2 groups. Group 1: 473 OSAS/COPD +/-; Group 2: 90 patients OSAS/COPD +/+. All patients underwent blood gases, nocturnal polisomnography, postbronchodilator spirometry. A multivariate analysis was performed to evaluate which were the factors that determining the diurnal PaO2 The groups were matched for BMI, for age and AHI. OS group showed lower level of daytime PaO2 compared with OSAS patients (71.6±9.7 vs 79.3±11 mmHg, p In both groups, patients with good compliance (>4H/night) of CPAP improve daytime PaO2 (p Our data suggest that daytime hypoxemia in OSAS patients is largely determinated by the increased of body weight. In the overlap patients daytime hypoxiemia has a more complex origin. However CPAP therapy has been shown to improve daytime PaO2 values both in OSAS than in OS patients with good compliance