SNORING AND SLEEP APNEA

Why do some people snore?

Snoring is the sound made when the upper airway partially obstructs. The lower part of the airway, that is, the larynx, trachea, and bronchi are stented open by rings of stiff cartilage in much the same manner as a vacuum cleaner hose's wire reinforcement keeps it from collapsing when the vacuum is turned on. The upper airway, which includes everything from the nose and mouth down to the level of the larynx, does not possess the same intrinsic reinforcement. The upper airway is kept open by the actions of the muscles of the mouth and throat and normally remains patent or open throughout the breathing cycle. Since the same level of resistance to obstruction or collapse is not present in this portion of the airway, in the face of negative pressure (inhalation) there is a tendency for the airway to collapse or obstruct when drawing in a breath. A good analogy is to imagine trying to suck water through a hose. If the hose is reinforced (as the rings of cartilage do for the lower airway) the hose will not collapse. However, if the hose is not reinforced, when enough pressure is applied it will eventually collapse on itself, eventually occluding. This is similar to the mechanics of snoring and sleep apnea. When trying to breath through a partially occluded airway, pressure, especially negative pressure, will cause the partially blocked off airway to vibrate, producing a noise. This is the classic sound of nocturnal snoring, namely the vibration made as air is drawn through a partially closed off upper airway. So, in short, snoring results from breathing through an airway that has collapsed somewhat. This is illustrated below.

Is snoring bad for you or dangerous?

The honest answer to that question is that no one is completely sure. When snoring reaches a certain level of severity the body is no longer getting enough oxygen at night. This condition is called obstructive sleep apnea and will be discussed in some detail later. There are specific diagnostic criteria to distinguish sleep apnea from "regular" snoring and it is well known that once snoring becomes serious enough, there are definite deleterious and serious effects on general health. Since this observation, some investigators have attempted to determine if simple or non-apneic snoring is itself dangerous. The initial studies compared large populations of snores with non-snorers to determine whether snoring was itself an independent risk factor for cardiac or other systemic diseases and these studies did, apparently show that snoring was an independent risk factor for hypertension (high blood pressure) and other cardiac disease, akin to smoking or male sex or high dietary fat intake. Later studies, however, have failed to duplicate these results which cast some significant doubts on the validity of the initial reports. So the current answer remains that no one is really sure. One thing is certain, however, when snoring becomes severe enough that obstruction occurs, there are profound and quite serious effects on general health.

 

What is sleep apnea?

Apnea refers to the cessation of respiration or breathing due to any cause with sleep apnea referring in particular to such lapses in breathing occurring during sleep. Breathing can cease due to two major causes: central and obstructive. In the case of central apnea, breathing ceases because there is no respiratory effort. In other words, the brain never tells the chest and diaphragm to draw a breath. This is the type of apnea (central) that is observed with drug overdoses or brain injuries and is extremely rare as a sole cause of sleep apnea. Much more common is obstructive apnea as a cause of sleep apnea. Obstructive apneas occur when there is a physical obstruction or blockage that prevents breathing. In obstructive sleep apnea, by far the most common type, the brain sends the message to the body to breathe and, in fact, the body responds by activating the diaphragm and other muscles of respiration but the obstruction in the upper airway prevents respiration from occurring. In other words the patient is trying to breathe but fails because the airway is blocked. If you recall the above discussion of snoring, noise occurs because the upper airway becomes partially occluded and vibrates as air is drawn through this diminished space. When the occlusion becomes worse, the airway eventually becomes blocked, preventing the passage of any air at all. At this point the muscles of respiration are activating and trying to draw in a breath but the occlusion in the airway prevents it. As respiration ceases the level of oxygen in the blood begins to drop, often to alarmingly low levels. Eventually the low levels of oxygen and frustrated attempts to breathe arouse the "sleeper" and upon partially awakening he is finally able to take a breathe. The apneic time (or time without breathing) may be as long as one or two minutes and it is this time of apnea and hypoxia (low oxygen levels) that produces the physical pathology of the disease, discussed below.

 

Why is sleep apnea bad for you?

The effects of sleep apnea can be generally categorized into two main issues, those due to the poor sleep quality that results from the disease and those due to the chronic poor ventilation and oxygenation that occur nightly during sleep. In the first case, the need to partially awaken every several minutes in order to arouse and draw an unobstructed breath, prevents the sleeper from obtaining quality sleep. In normal sleep architecture, the sleeper progresses in an organized fashion into progressively deeper stages of sleep eventually reaching REM (rapid eye movement) or dream sleep. This typically occurs in roughly 90 minute cycles. As one might deduce, the need to constantly partially awaken to breathe at night alters this sleep architecture and prevents the sleeper from obtaining restful sleep. The consequence is that sleep apneics are constantly tired, suffering from what has become the hallmark of the disease...."excessive daytime sleepiness". Additional complaints may be morning headache, sore or dry throat, memory loss, confusion, loss of concentrating ability and other complaints related to the poor sleep quality obtained. The second category of consequences of the disease relate to the chronic, unrelentingly poor oxygenation that occurs nightly. These issues are more significant and may, in fact, threaten the life of the patient. The obstructive phenomena produce regular, recurring drops in the sleeper's oxygenation causing hypoxia, as mentioned. This ongoing hypoxia, in turn, causes the blood pressure to rise, especially in the circuit that supplies the lungs (pulmonary hypertension). Additionally the hypoxia produces an elaboration of stress hormones that puts additional strain on the heart. Cardiac rhythm disturbances are common as the blood oxygen level drops further. To try to put the level of crisis in ventilation that some patients experience into perspective, note the following observation. A normal SaO2 or arterial blood oxygen saturation is 99 - 100%. It would be difficult and somewhat remarkable if one could drop that number to even 95% by breath-holding to the voluntary limit. A level of below 90% is worrisome and levels in the 80 - 85% are dangerous. It is not at all uncommon for sleep apneics to display levels in the 30 - 70% range where they are literally life threatening. The consequence of this phenomenon is the vastly accelerated rates of vascular disease in apneics. In a given year a sleep apneic is roughly five times more likely to suffer a stroke or myocardial infarction (heart attack) than a non-apneic and has roughly nine times the overall mortality rate.

In summary, sleep apnea causes poor ventilation and oxygenation during sleep. This effects the quality of sleep, resulting in excessive sleepiness and memory/concentration problems. Furthermore, the poor oxygenation causes or accelerates a number of potentially quite serious general health problems such as hypertension and cerebral and coronary vascular disease. The former impacts one's quality of life while the latter impacts general health.

How do I know if I have sleep apnea?

When patients have a history of complaints similar to those discussed above, they will likely be referred for a monitored sleep study, performed in a sleep lab. The patient will have a number of monitors placed to measure things like the depth and quality of sleep and breathing, as well as keeping track of the cardiac events and blood oxygenation. They are then allowed to sleep in a room somewhat like a hotel room where they can be observed by the technician monitoring the study. During the course of the study if it becomes evident that the patient is having significant apneic episodes they may be awakened at the halfway point of the study and have a treatment device placed (CPAP) to determine how best to treat their apneic episodes. Once the data from the study are interpreted, the doctor who ordered the study will discuss the results with the patient and explore the treatment options available. After discussing these options the patient and doctor will together choose a therapy which will be both effective and tolerable to the patient. The most common choice, and probably the best initial choice is CPAP or continuous positive airway pressure, discussed below.

What is CPAP (continuous positive airway pressure) and what are my options for treating my sleep apnea?

CPAP, as the name implies, is a device which applies a constant but low positive air pressure to the upper airway in an attempt to keep it patent or open. Recall, if you will, the above example of sucking water through a collapsible hose, used to illustrate the process of airway obstruction. Remember that collapse and obstruction occur because negative pressure is being applied to a collapsible, non-reinforced tube. Imagine now applying a pump to the end of that tube and at the same time that the negative pressure is being applied on one end, a positive pressure is being applied at the other.

The result is that collapse and obstruction is much less likely to occur and is, in fact, entirely preventable as long as an appropriate balance can be maintained between the positive and negative forces. This is exactly how CPAP machines work. A small mask is worn over the nose and a gentle but constant pressure is applied from the pump device attached to the mask via a hose. This gentle pressure stents or pushes the airway open allowing normal inhalation and exhalation to occur. The device is quite effective with "cure" rates in the 85 - 95% range.

In spite of the success of this CPAP machine and its unquestionable safety and benefit, some cannot tolerate the device and as a consequence simply cannot wear it. For these patients, CPAP failures, a variety of surgical procedures have been developed to treat sleep apnea. Additionally, some selected patients may be candidates for a dental repositioning device which may open the airway as well. The dental devices all work by temporarily (during sleep) positioning the lower jaw forward and thereby pulling the muscles of the tongue base and throat forward to some degree as well. This tends to stent the airway open reducing the tendency for obstruction. The devices may work well for some patients and are certainly appropriate for snoring although their success in treating apnea is only now being well investigated.

 

What surgeries are available to treat sleep apnea and how well do they work?

There are a variety of different surgeries available to treat sleep apnea, most of which address particular areas or sites of obstruction. Recall that the upper airway, the collapsible portion of the airway, includes everything from the nose and mouth down to the larynx. Obstruction may occur at any point along this path although there are some typical areas of note. The nose itself is rarely an exclusive cause of apnea. Nasal obstruction may encourage mouth breathing which will worsen apnea. This occurs because as the mouth opens to facilitate mouth breathing, the lower jaw, by necessity, rotates down and back allowing the tongue base to collapse and further decreasing the airway space. For this reason, functional nasal surgery may sometimes be recommended to improve the airway patency.

There are several surgical procedures which have been developed to reshape the back of the soft palate in an effort to treat obstruction in that area with varying levels of success. In terms of evaluating the success of the various surgeries for apnea it is important to realize that partial treatment is really of very minimal worth to the patient. Because the consequences of the disease, namely accelerated cardiac disease and greatly increased risks of stroke and heart attack, are so significant, making a patient "better" but not cured with an operation still obligates that patient to use CPAP if they are to enjoy "normal" risks for these events. This, of course, is the same situation that would exist without the "non-curative" surgery. Therefore the goal of all surgical procedures for apnea should justifiably be to cure the patient to the extent that they are no longer CPAP dependent.