Common Sleep Apnea Terms

I thought I would spend some time listing some of the most common acronyms and terminology used in the world of sleep apnea to give you a basic understanding of what these terms mean.  For those of you newly diagnosed and even some of you long term CPAP users it can sometimes feel as though you are trying to maneuver through a foreign language.  The following definitions are very basic and if you need a more detailed definition you can use a dictionary, especially a medical dictionary to obtain a more detailed definition of the terms below.

Obstructive Sleep Apnea (OSA)- This is the most common form of sleep apnea  which occurs when air cannot flow into the lungs as a result of closure of the upper airway (the back of the throat) despite continuing efforts to breath. In obstructive sleep apnea, the throat collapses during sleep causing the individual to snort and gasp for breath. Hundreds of these episodes can occur every night causing daytime sleepiness, fatigue, inattentiveness or mood disturbances.  Untreated sleep apnea is also thought to increase the risk of hypertension (high blood pressure) and heart problems.

Central Sleep Apnea (CSA)- a person’s respiratory effort temporarily stops even though the airway remains open.  CSA occurs when the brain does not send the signal to breathe to the muscles of breathing. This usually occurs in infants or in adults with heart disease, cerebrovascular disease, or congenital diseases, but it also can be caused by some medications and high altitudes

Complex Sleep Apnea (Comp SA)- A form of central sleep apnea, Comp SA exhibits primarily obstructive or mixed apneas during the diagnostic study.

Apnea – 90% or more reduction in airflow for greater than 10 seconds.  Apnea is Greek  for “without breath”. An estimate of the severity of apnea is calculated by dividing the number of apneas by the number of hours of sleep, giving an apnea index (AI in apneas per hour); the greater the AI, the more severe the apnea.

Hypopnea-A hypopnea is a decrease in breathing that is not as severe as an apnea. Decrease in airflow by 30% for greater than 10 seconds with a 4% drop in oxygen saturation. Like apneas, hypopneas usually disrupt the level of sleep. A hypopnea index (HI) can be calculated by dividing the number of hypopneas by the number of hours of sleep.  Greek roots hypo- (meaning low, under, beneath, down, below normal) and pnoe (meaning breathing).  From a medical standpoint, hypopneas are equivalent to apneas in importance and severity.

AHI– Apnea-Hypopnea index (AHI) is an index of severity that combines apneas and hypopneas. Combining them gives an overall severity of sleep apnea including sleep disruptions and desaturations (a low level of oxygen in the blood). The apnea-hypopnea index, like the apnea index and hypopnea index, is calculated by dividing the number of apneas and hypopneas by the number of hours of sleep

RDI–  Respiratory Disturbance Index is another index that is used to measure sleep apnea is the respiratory disturbance index (RDI). The respiratory disturbance index is similar to the apnea-hypopnea index; however, it also includes respiratory events that do not technically meet the definitions of apneas or hypopneas, but do disrupt sleep.

CPAP– Continuous Positive Airway Pressure therapy provides one constant air pressure all through the night

APAP– Automatic Positive Airway Pressure therapy automatically varies the pressure all through the night and from night to night.  It actively responds to the continuous changes in your upper airway

Bilevel– Bilevel therapy provides a higher pressure when you breathe in and a lower pressure when you breathe out.  This therapy is most often used for patients that have a hard time tolerating CPAP or APAP therapy for a variety of reasons

REM– Rapid Eye Movement- Most dreams take place during this stage of sleep.  Occurs roughly every 90 minutes and progressively increases in duration over the course of the night.  About 25% of an adult’s total sleep time is spent in REM sleep.

Snore– Vibration that occurs when your upper airway narrows and limits airflow as you breathe

Gasping– Instance of difficulty in breathing; a laborious effort to breath