The respiratory disturbance index (RDI)—or respiratory distress Index—is a formula used in reporting

polysomnography Polysomnography (PSG), a type of sleep study, is a multi-parameter study of sleep and a diagnostic tool in sleep medicine. The test result is called a polysomnogram, also abbreviated PSG. The name is derived from Greek and Latin roots: the Gr ...

(sleep study) findings. Like the apnea-hypopnea index (AHI), it reports on respiratory distress events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs). RERAs are arousals from

sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited Perception, sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefuln ...

that do not technically meet the definitions of

apnea Apnea, BrE: apnoea, is the temporal cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the airways are (patency), there may ...

s or

hypopnea Hypopnea is overly shallow breathing or an abnormally low respiratory rate. Hypopnea is defined by some to be less severe than apnea (the complete cessation of breathing), while other researchers have discovered hypopnea to have a "similar if no ...

s, but do in some way disrupt breathing during sleep and cause respiratory symptoms that may cause a arousal. A RERA is characterized by increasing respiratory effort such as dyspneas (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.

Diagnosis

The gold standard method for measuring RERAs is esophageal manometry, as recommended by the

American Academy of Sleep Medicine The American Academy of Sleep Medicine (AASM) is a United States professional society for the medical subspecialty of sleep medicine which includes disorders of circadian rhythms. It was established in 1975. The organization's functions include ...

(AASM). However, esophageal manometry is uncomfortable for patients, may disrupt sleep and is impractical to use in most

sleep center Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a d ...

s. Some research studies have found that a high RDI was significantly

correlated In statistics, correlation or dependence is any statistical relationship, whether causal or not, between two random variables or bivariate data. Although in the broadest sense, "correlation" may indicate any type of association, in statisti ...

with

excessive daytime sleepiness Excessive daytime sleepiness (EDS) is characterized by persistent sleepiness and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. EDS can be considered as a broad condition encompass ...

, and that this correlation was stronger than that for the frequency of

oxygen saturation Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...

decreases below 85%, but other studies have found only a weak and unreliable correlation. More recent studies have found more impressive outcomes of methods in treating patients with RERAs and respiratory events that satisfy the definition of hypopneas in all aspects other than reduction of oxygen saturation levels. The

uses RDI to determine the severity of

Obstructive Sleep Apnea Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder and is characterized by recurrent episodes of complete or partial obstruction of the upper airway leading to reduced or absent breathing during sleep. These episo ...

according to the following range: 5–14.9 for mild, 15–29.9 for moderate, and 30+ for severe, similar to the one used in the AHI.

Formula

The formula to assessing the RDI is = (RERAs + Hypopneas + Apneas) X 60 / TST (in minutes). That is, RDI means the average number of episodes of obstructive apnea, hypopnea, and respiratory event-related arousal per hour of sleep. (TST is "total sleep time".)

References

Pulmonology {{med-diagnostic-stub

Diagnosis

Formula

See also

References