The Causes of Sleep Apnea - Understanding Why We Can't Breathe

The cause of sleep apnea can stated simplisticly as the closing of the upper airway due to the relaxation of the muscles during sleep that usually help keep the airway open during wakefulness. The end result being the sleeper not having the ability to breathe and their blood oxygen level lowering until their body forces them awake to take a quick breath. However, there are a lot of different factors that contribute to that simplified explanation, and the exact causes of sleep apnea vary from person to person.

So to understand the causes of sleep apnea at a more in depth level and why so many people cannot breathe properly during sleep, it is essential that we first understand a bit about how we breathe when we are awake.

The human breathing apparatus essentially breaks down to three components: the chest (or thorax), the upper airway, and the brain's control system.

The first component, the chest, contains the lungs, the diaphragm, the rib cage, and the surrounding muscles that are crucial for inspiration, receiving inspired air, and dispersing oxygen through the use of hemoglobin.

The second component, the upper airway, includes the nose and mouth, nostrils, palate, pharynx, larynx, and most importantly when it comes to the causes of sleep apnea, the muscles of the tongue and throat.

But before we get to that, we can briefly mention that the third component of our breathing system is the control system in the brain that regulates breathing and makes sure that the amount of air going into and out of the lungs corresponds with the body's need to get oxygen and get rid of carbon dioxide. It can be expected that this mechanism takes over and wakes up a sleeping victim when an apnea episode lasts too long and the body is in desperate need of oxygen.

While awake and breathing easily, when the volume of the chest begins to expand the air pressure inside the lungs becomes negative with respect to the outside atmosphere as air floods in through the upper airway. If you try to inhale while holding your mouth and nose closed you can feel that negative pressure skyrocket, and essentially this is what happens during an obstructive sleep apnea episode, the only difference (besides being asleep) being that the upper airway gets closed from the inside instead of from you plugging your own nose. But how does it get closed?

There are several reasons why the airway can get closed, but a key thing to understand for all of them is the design of the upper airway itself, which is made up of a flexible mixture of bone, muscle, and cartilage.

For whatever reason, as humans we have been endowed with somewhat of a parsimonious design for our airways--we use the same tube to speak, eat/drink, and to breathe. And while our soft, flexibe upper airway is great for speaking and eating, it is horribly flawed for breathing during sleep because it can get sucked close and prevent us from breathing. It is this soft, pliable design that is really the root cause of sleep apnea, for if we had a more rigid tube specifically for breathing, sleep apnea likely wouldn't be a problem.

When we breathe in while we are awake, our tongue muscles contract to pull the tongue in a bit. In addition, inhaling also causes muscles on the sides of our throats to contract. These throat muscles hold the upper airway open, kind of like tent poles holding up a tent, so that we can breathe. But during sleep the vigor of the throat contracting muscles is reduced, more so in some than in others. When it is reduced enough in individuals with small airways, a strong inspiratory effort can bypass the muscles' weakened support and suck the flexible airway closed, causing an apnea episode.

The reduction of contraction in the tongue during sleep can also cause the tongue to flop back enough to block the airway, which can also be the cause of an apnea, and it is for this reason that sleeping on one's back, also known as supine position (where gravity leads the tongue straight back into the throat), is often the worst spot to sleep for sufferers of sleep apnea.

Sometimes the collapsing throat and tongue muscles don't completely block off the entire airway, and breathing continues with a significantly decreased amount of air. This situation is called a hypopnea (see right). However, these hypopneas can still lead to large drop offs of blood oxygen, great increases of inspiratory effort, and often can only be terminated by an arousal, just like an apnea episode.

This last sentence points to the link between sleep apnea and obesity. Somewhere around half of the victims of sleep apnea are overweight, and it makes sense that if one has more fatty tissue around the neck that ones airway stands a greater risk of becoming too narrow to breathe. So excess fat is yet another one of the contributing causes of sleep apnea. Visit this article to learn more about the link between sleep apnea and obesity.

In the same light, any other sort of physical feature that can reduce the size of the airway can contribute to the cause of sleep apnea. For example (and this is somewhat of a repeat of above), people with large tongues, large tonsils, small jaws, or large paletes can be predisposed to having sleep apnea.

Although sleep apnea can occur at all ages, sparing neither infants or the elderly, more than half of all patients are 35 years or older when they are diagnosed. However, abnormal breathing during sleep usually precedes extreme daytime sleepiness and diagnosis by at least a few years, so sleep apnea does typically show a worsening progression with time. Dr. Dement comments on this progression when it comes to predicting sleep apnea cases a bit below:

The above words contribute to the point that no snoring is normal. Breathing during sleep should not be labored, although it is frequently the case that it is. If snoring is ever accompanied by persistent fatigue throughout the day when it seems like you should have obtained enough rest, it is absolutely crucial for your health that you see a sleep specialists and let him or her know your situation. And sooner, rather than later.