bstructive sleep apnea (OSA) syndrome is highly associated with cardiovascular morbidities. [1][2][3][4][5] These patients have recurrent inspiratory flow arrest during sleep and regain inspiration after forcefully expanding the thoracic cages, using a Müller-like maneuver. 6 This unique respiratory pattern (cyclic apnea and a hypoxic reaction) causes swings in the heart rate, blood pressure, and cardiac output; finally, grave disorders involving the pulmonary, cardiovascular, hormonal, central nervous system ensue. 2,3,7 Focusing on its effect on the central neural system, it is known that perfusion of the cerebral arteries is decreased either during sleep or while awake, [8][9][10] and OSA syndrome is considered a risk factor for cerebral vascular accidents. 1,4,11,12 Results of several studies have suggested that the more negative intrapulmonary pressure in patients -Yi Chi, MD, Chang-Sheng Lin, MD, Min-hsien Hsu, MD, Po-chi Chan, MD, Han-Hwa Hu, MD Received December 31, 2014, Hsin ORIGINAL RESEARCHObjectives-Evidence reveals a pathophysiologic link between sleep apnea syndrome and cerebrovascular diseases. It is known that obstructive sleep apnea (OSA) may cause serial hemodynamic changes and structural abnormalities in the cerebral and cardiac arterial systems, but its effect on the cerebral venous system has remained unclear. The purpose of this study was to compare internal jugular vein hemodynamics between patients with OSA and healthy individuals.Methods-Patients with OSA and age-, body mass index-, and sex-matched healthy control participants were recruited for a jugular venous duplex study and neurologic examination. The luminal area of the internal jugular vein, jugular venous flow volume, time-averaged mean velocity, and presence of jugular venous reflux were recorded. These flow characteristics were obtained at different respiratory statuses, and we analyzed the differences between patients and controls.Results-In the OSA group, there was an increasing flow volume in total internal jugular veins at rest. The frequency of venous reflux in patients compared with controls was significantly decreased (26.7% versus 53.3%, respectively; P < .05). The internal jugular vein drainage dominance was greater on the left side in the OSA group (right versus left: 48.8% versus 51.2%), whereas it was greater on the right side in the control group (right versus left: 61.7% versus 38.3%).Conclusions-Our data showed peculiar internal jugular vein hemodynamics at baseline and different respiratory statuses in patients with OSA. These characteristics imply that cerebral venous drainage conditions might be involved in the pathophysiologic mechanisms of OSA syndrome.