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The periods of silence can last 20 seconds or longer and can happen many times each hour, resulting in poor sleep and reduced levels of oxygen in the blood. Other symptoms of hypopnea may include depression, forgetfulness, mood or behaviour changes, trouble concentrating, loss of energy, nervousness, and morning headaches.
Normal: AHI<5; Mild sleep apnea: 5≤AHI<15; Moderate sleep apnea: 15≤AHI<30; Severe sleep apnea: AHI≥30; For children, because of their different physiology, an AHI in excess of 1 is considered abnormal. Underage pediatric patients presenting with AHI of 2 or greater will often be referred for treatment. [3]
For adults, an AHI of less than 5 is considered normal, an AHI of [5–15) is mild, [15–30) is moderate, and ≥30 events per hour characterizes severe sleep apnea. For pediatrics, an AHI of less than 1 is considered normal, an AHI of [1–5) is mild, [5–10) is moderate, and ≥10 events per hour characterizes severe sleep apnea.
The respiratory disturbance index (RDI)—or respiratory distress Index—is a formula used in reporting polysomnography (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). [1]
If the pause in breathing is long enough, the percentage of oxygen in the circulation can drop to a lower than normal level and the concentration of carbon dioxide can build to a higher than normal level (hypercapnia). [16]
Hypopneas in adults are defined as a 30% reduction in air flow for more than ten seconds, followed by oxygen-saturation declines of at least 3% or 4% per the AASM standards. [clarification needed] and/or EEG arousal. The Apnea-Hypopnea Index (AHI) is expressed as the number of apneas or hypopneas per hour of sleep. [10]
In adults, it is typical to have up to 4.9 events per hour. In obstructive sleep apnea, affected individuals are categorized based on how many apneas or hypopneas (apnea-hypopnea index or AHI) or events they have per hour. Normal: <5 events per hour; Mild: 5 to <15 events per hour; Moderate: 15 to 30 events per hour; Severe: >30 events per hour
Causes may include heart failure, kidney failure, narcotic poisoning, intracranial pressure, and hypoperfusion of the brain (particularly of the respiratory center). The pathophysiology of Cheyne–Stokes breathing can be summarized as apnea leading to increased CO 2 which causes excessive compensatory hyperventilation, in turn causing decreased CO 2 which causes apnea, restarting the cycle.