FIG. 4:  OSA is depicted schematically in this Figure.^[1]The top panel depicts normal breathing; the blue arrow shows the airflow into the upper airway and then into the lungs.  On the bottom left depicts what we call a hypopnea, essentially because it represents loss of muscle tone.  Because in this particular case the subject is lying on his back, the tongue is falling backwards into the airway, and that is associated with a partial obstruction, so some airflow gets through and therefore it is called a hypopnea.  On the bottom right panel is a complete occlusion, or an apnea, where the soft palate and the tongue fall backwards into the airway, causing a complete occlusion.