Considered a sleep disorder, apnea literally means "without breath." In sleep apnea, the patient involuntarily stops breathing over and over during the night. Sleep apnea as a disorder can include episodes of a similar condition called hypopnea or "slow breathing." Hypopnea means the patient takes very shallow breaths or breathes at an abnormally slow rate.
According to the National Heart, Lung and Blood Institute, pauses between breaths last a few seconds to minutes, and can occur between five and 30 times each hour, sometimes more often. A pause in breathing followed by a loud snort or snore, or a sound described as "gasping" or "choking," can signal an apneic episode.
The National Sleep Foundation puts the number of American adults afflicted with sleep apnea at more than 18 million.
Symptoms of Sleep Apnea
Apneic episodes cause a patient's blood oxygen to drop as the carbon dioxide found in the blood rises. The heart rate increases, and the stops and starts in breathing disrupt sleep. Deep sleep is interrupted and light sleep ensues, or the patient wakes up in order to breathe and then must begin the sleep process again.
Upon awaking for the day, the apneic patient can have a headache (possibly due to the changes in blood levels), or a dry mouth and throat. During the day, the patient feels extreme sleepiness, exhibits slow reaction time, and can have problems with vision.
The periods of low blood oxygen can damage the brain, and if that happens it leads to cognitive deficits. Frequently the brain-damaged patient lacks planning skills and cannot concentrate or pay attention consistently, function efficiently, or learn very well. In general, the damage results in poor assimilation and use of information.
The loss of sleep, plus brain damage, can disturb a patient's mood, producing irritability or even belligerence. People who have sleep apnea often don't realize it, and people who observe them sleeping are the ones who first notice the difficulty they experience in trying to breathe.
The patient's cognitive and mood problems are very often thought to stem from other causes, and since the patient doesn't realize he can't breathe well at night, it's easy to overlook sleep apnea in a diagnosis.
The amount of sleep interruption sleep apnea produces can be very severe indeed. As an example, one published somnographic recording of an apneic patient logged 411 episodes of apnea and hypopnea, plus 481 respiratory arousals (meaning partial or complete awakening).
Three Types of Sleep Apnea
Obstructive Sleep Apnea
Obstructive sleep apnea (OSA) is the first type. This condition requires that during breathing, the patient's airflow is partially or completely blocked. The airway collapses to some extent, which has these results: hypopnea (less breathing), apnea (no breathing), and/or respiratory effort-related arousal.
In respiratory effort-related arousal, the patient tries to breathe despite the obstruction, and wakens. When air passes through the narrowed airway, the movement causes loud snoring. There are numerous factors that can cause such obstructions, and while some are obvious, others can't be detected without medical assistance.
Overgrowth in or near the airway can cause OSA. Examples of overgrowth include enlarged tonsils or adenoids, or a large neck or tongue. The extra flesh produced by obesity can narrow the airway enough to cause OSA, and excess weight does produce many cases of OSA.
Congenital narrowing or malformation of the airway, in which the patient is born with an abnormal configuration, creates a predisposition to OSA. A lower jaw that is short in comparison to the upper (micrognathia) can have the same effect. Lower muscle tone (even the relaxation caused by alcohol or some medications) can also induce partial airway collapse.
Risk factors for OSA include obesity, age, and smoking. Sleeping on your back can also lead to OSA.
Central Sleep Apnea
Central sleep apnea (CSA) occurs when that part of the brain that should signal the muscles to breathe fails to do so. Unlike OSA, in which the body tries to breathe but cannot breathe normally, CSA means the body makes no effort to breathe, or tries less often than usual.
CSA and OSA are quite different, and often occur separately. For example, the somnographic recording mentioned above includes only OSA episodes and no CSA events at all.
In normal breathing, a rise in blood carbon dioxide triggers a breath. Specifically, the respiratory control center of the brain receives the information about the blood level and tells the respiratory muscles to inhale. But in CSA, that feedback loop operates only intermittently.
Very often, CSA is a side effect of some other medical problem. A deformed or diseased cervical spine (the vertebrae in the neck), bulbar poliomyelitis, illnesses that cause the nerves to degenerate, diseases of the brainstem, primary hypoventilation syndrome (causing respiratory arrest in sleep), and use of opiates can all result in CSA.
In fact, chronic opiate use, which depresses the action of the brain's respiratory control center, usually does result in CSA, and sometimes death.
Mixed Sleep Apnea
The medical community has known about the existence of this condition for many years. In mixed sleep apnea, a patient who has had severe OSA for a long time develops CSA as well, and experiences episodes of both during the night. Sometimes the CSA is thought to be a concomitant of heart disease (for example, congestive heart failure or atrial fibrillation).
Complex Sleep Apnea
This is a recently identified disorder, and did not become apparent until doctors began to prescribe continuous positive airway pressure (CPAP) machines as a means of treating OSA. In complex sleep apnea, when positive airway pressure is applied, the patient's OSA resolves and CSA then appears.
Effects of Sleep Apnea
The immediate effects of sleep apnea are the disruption of sleep and the low levels of oxygen and high levels of carbon dioxide in the blood. Those primary changes in normal physical processes lead to a host of other medical problems. Some conditions, like obesity, are both risk factors for sleep apnea and potential results of sleep apnea.
Effects Caused By Loss of Sleep
The lack of sleep alone causes deterioration in the patient's quality of life, producing irritability, troublesome sleepiness during the day, or even falling asleep while trying to work or drive. Thus, the patient runs a much greater risk of an accident in the workplace or a car crash.
Any professional responsible for driving a vehicle like a truck, train, or bus, or for operating heavy equipment, can present a real danger to the public in the event of untreated sleep apnea.
Effects Caused By Changes In Blood Levels
The low blood oxygen level is called hypoxemia, and the high blood carbon dioxide level is known as hypercapnia. Hypoxemia can cause the skin of a sleeping apnea patient to acquire a bluish tint (a condition called cyanosis).
Brain cells require a constant supply of oxygen in order to stay alive, and they may die during the hypoxemia experienced in sleep apnea. Prolonged hypoxemia causes death. Brain damage leads to noticeable disturbance of mood, including depression, and impairment of memory.
Hypoxemia can also cause seizures even in non-epileptic patients, or in epileptics who are on medication that previously succeeded in preventing their seizures. A disorder called metabolic acidosis (meaning the presence of excess acid in the body's fluids) has been detected in patients who have suffered from sleep apnea for many years, and is thought to be a direct result of the frequent hypercapnia they undergo during sleep.
Sleep apnea increases not only the heart rate (to compensate for hypoxemia) but also the risk of high blood pressure (hypertension), cardiac arrhythmia or arrest, congestive heart failure, and stroke. That risk of cardiovascular problems is especially high for patients who have coronary artery disease.
The type of hypertension caused by OSA differs from ordinary high blood pressure because the level of pressure fails to drop while the patient is sleeping. That continual elevation of blood pressure explains why stroke is associated with OSA.
Patients suffering from sleep apnea are also at risk for heartburn, gastrointestinal reflux, diabetes, obesity, and erectile dysfunction.
See our sleep apnea treatment page to learn how to deal with the condition.