The<unk>  <unk> —or respiratory distress<unk> —is a formula used in reporting polysomnography (sleep study) findings. Like the apnea-hypopnea<unk>  (AHI), it reports on respiratory events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs). RERAs are arousals from sleep that do not technically meet the definitions of apneas or hypopneas, but do disrupt sleep and cause symptoms. A RERA is characterized by increasing respiratory effort (and thus decreasing esophageal pressures) for 10 seconds or more leading to an arousal from sleep, but one that does not fulfill the criteria for a hypopnea or apnea. The gold standard for measuring RERAs is esophageal manometry, as recommended by the American Academy of Sleep Medicine (AASM). However, esophageal manometry is uncomfortable for patients and impractical to use in most sleep centers. Some research studies have found that a high<unk>  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. The American Academy of Sleep Medicine uses<unk>  to determine the severity of Obstructive Sleep Apnea according to the following range: 5–14.9 for mild, 15–29.9 for moderate, and 30+ for severe.
Respiratory disturbance index
Bispectral index
Oxygenation index
Hyperoxia test
Respiratory pressure meter
Breath analysis
Fraction of inspired oxygen
Plethysmograph