 However, esophageal manometry is uncomfortable for patients and impractical to use in most sleep centers.Some research studies have found that a high RDI was significantly correlated with excessive daytime sleepiness, and that this correlation was stronger than that for the frequency of oxygen saturation decreases below 85%, but other studies have found only a weak correlation.More recent studies have found more impressive outcomes in treating patients with RERA and respiratory events that satisfy the definition of hypopneas in all aspects other than reduction of oxygen saturation levels.