Sleep Disordered Breathing (SDB) is very complex breathing condition that destroys your slumber and endangers your health by two very prominent physiological processes: 

•  Sleep Fragmentation:  SDB is so disruptive because it constantly interferes with your brain waves as you attempt to sleep.  Instead of remaining in deeper, restorative stages of sleep for much of the night, SDB forces you into lighter sleep stages and in the most cases, it triggers hundreds of little awakenings during the night that literally rob you of sleep.  In fact, if you sleep 8 hours and suffer from moderate to severe SDB, chances are high you are only getting 4 to 6 hours of solid sleep.
• Oxygen Fluctuations:  SDB dramatically alters stabily of the oxygen your body receiveds into the body and transfers into your bloodstream.  In a normal sleeper, oxygen levels are maintained in a surprisingly stable pattern.  For, if the level were 94% (90 to 100% being the standard normal range), then this value could be maintained for minutes on end with minor or no fluctuations whatsoever.  In most SDB cases, oxygen fluctuates all night long, often within a time span as short as a few seconds.  In a 30 second interval (the standard interval we use in sleep studies), oxygen could start at 94%, drop to 91 in 10 seconds, go back up to 93$ in another 5 seconds, and then drop again to 89% in another 15 seconds.  In more severe cases, these fluctuations deteriorate into what are known as desaturations, where the oxygen level drops frequently below 90% for 10, 20, 30 seconds or longer, before returning to the normal level above 90%.  Sometimes oxygen drops even lower, particularly in REM sleep or when you sleep on your back.

These two components--sleep fragmentation and oxygen fluctuations/desaturations are the key to understanding the nature of SDB.  Most importantly, it will help you understand why the term "obstuctive sleep Apnea" (OSA) is a misleading term.  Sleep apnea literally refers to the process in which you stop breathing for anywhere from 10 seconds or longer, amazingly up to 60 seconds in unusually severe cases.  As you would expect, sleep disruption and oxygen desaturations are quite severe following an apnea. 

However, SDB comprises more than just a series of sleep apnea events.  Indeed, you can suffer from extremely severe SDB without ever once stopping breathing.  How could this be so?  The answer is quite simple if you think about this analogy:  a sleep apnea event is similar to a choking episode in which you stop breathing, say from inhaling a piece of food into your windpipe.  This obstruction will surely produce intense fear if not outright panic in most people, bringing them to absolute alertness to solve the problem and solve it fast.

SDB can produce a response this severe when the airway closes down and all breathing stops, but to continue the analogy, how do you think you would react when you "choke a little?"  I'm sure you guessed that it would still be very uncomfortable, and that's why SDB is often misunderstood and why the term sleep apnea is misleading.  As you will learn, SDB can include a whole range of sleep breathing events in which you don't stop breathing, but your effort to bring in a full breath is compromised.  Two events described below are usually more common than apneas in most patients with SDB: 

• Hypopneas:  In this event instead of a complete cessation of breathing, you lose about 50% of your normal breath, which unsurprisingly is more than sufficient to trigger sleep fragmentation and to cause your oxygen to fluctuate or desaturate.
• Flow Limitation:  In this event, the airway experiences resistance, which is diffiucult to quantity, but it might be reasonable to consider these events as a 10% reduction.  Yet even this small reduction of breathing (a wee bit of choking) can still cause sleep fragmentation and oxygen fluctuations.

So, to reiterate, you will understand this condition much better and make better decisions about your healtcare choices by recognizing that when you suffer from SDB, it might be only apneas, only hypopneas or only flow limitations or as in most cases, some combination of all three event types.  But even if you only suffer flow limitation events, they can cause severe sleep fragmentation and constant oxygen fluctuations that damage your sleep along with your mental and physical health.