Obstructive sleep apnea syndrome (OSAS) is a common condition affecting up to 2-4 % of the general population. The pathophysiologic consequences of OSA include: excessive daytime sleepiness leading to increased car and work related accidents; and increased incidence of hypertension (HTN), stroke and possibly coronary artery events. In addition, patients with severe and untreated obstructive sleep apnea (OSA) have increased mortality compared to patients with treated severe OSA.The main stay of treatment of OSAS is the application of continuous positive airway pressure (CPAP) during sleep. The main problem with CPAP therapy is compliance. Heliox, a mixture of oxygen and helium has been used for many years in the treatment of upper airway obstruction. In this study, the investigators will evaluate the effectiveness of Heliox in the treatment of OSAS. Adult subjects with the diagnosis of obstructive sleep apnea syndrome who are referred for repeat sleep study for CPAP titration will be evaluated.