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Purpose: It is known that obstructive sleep apnea syndrome (OSAS) can affect right ventricular (RV) performance even in the absence of systemic hypertension and other known cardiac or obstructive pulmonary disease. We assessed changes in ventricular parameters determined by three-dimensional echocardiography (3DE) and speckle tracking imaging (STI) before and after continuous positive airway pressure (CPAP) treatment.Methods: We recruited 31 patients with OSAS and 31 healthy subjects without signs of cardiopulmonary dysfunction. OSAS was defined as apnea hypopnea index (AHI) ≥5 events per hour. Twelve patients with severe OSAS (AHI≥30) underwent chronic nocturnal nasal CPAP therapy. RV end-diastolic and end-systolic volumes were measured from three-dimensional echocardiographic datasets and right ventricular ejection fraction (3D-RVEF) was calculated. Pulmonary arterial systolic pressure was obtained by standard Doppler methods. Pulmonary hypertension was defined as a pulmonary artery systolic pressure of 40 mmHg or greater. To assess regional and global RV systolic function in the longitudinal direction using STI, we adopted a 6-segment RV model (basal RV lateral wall, mid RV lateral wall, apical RV wall, apical septum, mid septum, and basal septum). RV peak systolic strain and time to peak-systolic strain from the onset of QRS were recorded for the 6 RV myocardial segments and for the entire RV myocardium (EchoPAC BT09, GE Ultrasound). Global longitudinal strain was calculated by averaging local strains along the entire right ventricle using machine software. RV dyssynchrony (RV-SD6) was defined as the standard deviation of the six time to peak systolic strain values.Results: 3D-RVEF was lower in patients with OSAS and pulmonary hypertension compared to the control group (p<0.001) and compared to patients with OSAS and normal pulmonary pressure (p<0.05). A significant correlation was found between RV-SD6 and pulmonary artery systolic pressure (r = 0.74, p <0.005) and between RV-SD6 and AHI (r = 0.77, p <0.001). The group treated with CPAP had a significant decrease in pulmonary artery systolic pressure, total pulmonary vascular resistance and RV-SD6 as well as significant increase in 3D-RVEF. By multivariate analysis, RV-SD6 (p=0.006) and 3D-RVEF (p=0.03) were predictive of AHI.Conclusions: Our data show that OSAS has a significant impact on RV function and synchrony, 3D-RVEF and RV-SD6 correlate with pulmonary hypertension and disease severity, and abnormal values may regress after CPAP therapy.