A sleep mask valve structure for treating a patient suffering from obstructive sleep apnea is provided. The valve structure includes a rigid valve housing comprising an inspiratory valve and an adjustable expiratory valve. The housing defines an outside mask side and an intra-mask side, and further defines an expiratory airflow conduit accommodating airflow from the intra-mask side to the outside mask side and an inspiratory airflow conduit accommodating airflow from the outside mask side to the intra-mask side. The expiratory airflow conduit includes at least two changes of direction, with each direction change greater than or equal to 75 degrees, and the inspiratory airflow conduit includes at least one change of direction greater than or equal to 75 degrees. The two paths share at least one change of direction.