Sleep Lab
//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.