Drug induced sleep endoscopy (DISE) has become the mainstay in determining the site of anatomical obstruction in patients with obstructive sleep apnea. However, due to the dynamic nature of the airway, a single site of obstruction can cause a negative pressure effect downstream causing collapse in other areas as well.. This lecture will discuss the fundamentals of DISE along with the addition of an intervention that can assist in defining if the downstream collapse is real or influenced by the upstream primary collapse.