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Central sleep apnea (CSA) or central sleep apnea syndrome (CSAS) is a sleep-related disorder in which the effort to breathe is diminished or absent, typically for 10 to 30 seconds, either intermittently or in cycles and is usually associated with a reduction in blood oxygen saturation. It is a collective term referring to two breathing disorders: Cheyne-Stokes respiration and periodic breathing. CSA is usually due to an instability in the body's feedback mechanisms that control respiration.
In pure central sleep apnea, the brain's respiratory control centers are imbalanced during sleep. Blood levels of carbon dioxide, and the neurological feedback mechanism that monitors them, do not react quickly enough to maintain an even respiratory rate, with the entire system cycling between apnea and hyperpnea, even during wakefulness. The sleeper stops breathing for up to two minutes and then starts again. There is no effort made to breathe during the pause in breathing: there are no chest movements and no struggling. After the episode of apnea, breathing may be faster (hyperpnea) for a period of time, a compensatory mechanism to blow off retained waste gases and absorb more oxygen. There are symptoms that one can find for the two different types of sleep apnea (central versus obstructive) as follows.
Symptoms of central sleep apnea
Symptoms of obstructive sleep apnea
While sleeping, a normal individual is "at rest" as far as cardiovascular workload is concerned. Breathing is regular in a healthy person during sleep, and oxygen levels and carbon dioxide levels in the bloodstream stay fairly constant. The respiratory drive is so strong that even conscious efforts to hold one's breath do not overcome it. Any sudden drop in oxygen or excess of carbon dioxide, even if tiny, strongly stimulates the brain's respiratory centers to breathe.
In central sleep apnea, the basic neurological controls for breathing rate malfunction and fail to give the signal to inhale, causing the individual to miss one or more cycles of breathing. A part of the human brain known as the preBotzinger complex, regulates ones breathing habits. If the pause in breathing is long enough, the percentage of oxygen in the circulation will drop to a lower than normal level (hypoxaemia) and the concentration of carbon dioxide will build to a higher than normal level (hypercapnia). In turn, these conditions of hypoxia and hypercapnia will trigger additional effects on the body. Brain cells need constant oxygen to live, and if the level of blood oxygen goes low enough for long enough, the consequences of brain damage and even death will occur. Fortunately, central sleep apnea is more often a chronic condition that causes much milder effects than sudden death. The exact effects of the condition will depend on how severe the apnea is and on the individual characteristics of the person having the apnea. Several examples are discussed below, and more about the nature of the condition is presented in the section on Clinical Details.
In any person, hypoxia and hypercapnia have certain common effects on the body. The heart rate will increase, unless there are such severe co-existing problems with the heart muscle itself or the autonomic nervous system that makes this compensatory increase impossible. The more translucent areas of the body will show a bluish or dusky cast from cyanosis, which is the change in hue that occurs owing to lack of oxygen in the blood ("turning blue"). Overdoses of drugs that are respiratory depressants (such as heroin, and other opiates) kill by damping the activity of the brain's respiratory control centers. In central sleep apnea, the effects of sleep alone can remove the brain's mandate for the body to breathe. Even in severe cases of central sleep apnea, the effects almost always result in pauses that make breathing irregular, rather than cause the total cessation of breathing.
|5 to <15 apneas or hypopneas per hour of sleep||Mild sleep apnea/hypopnea|
|15 to <30 apneas or hypopneas per hour of sleep||Moderate sleep apnea/hypopnea|
If the majority of the events are central apneas or hypopneas it is classified as central sleep apnea/hypopnea.
If the majority of the events are obstructive apneas or hypopneas it is classified as obstructive sleep apnea/hypopnea.
Polysomnography of sleep apnea shows interruption in breathing, that are followed by drops/reduction in blood oxygen and hike/increase in blood carbon dioxide level. In adults, a pause must last 10 seconds to be scored as an apnea. However in young children, who normally breathe at a much faster rate than adults, the pause may be shorter and still be considered apnea. The cessation of airflow in central sleep apnea has an association with no physical attempts to breathe. On polysomnograms, there is an absence of rib cage and abdominal movements while airflow ceases at the nose and lips. Obstructive sleep apnea shows pauses in breathing for at least 10 seconds causing a decrease in blood oxygen and associates with physical attempts to breathe.
Hypopneas in adults are defined as a 30% reduction in air flow for more than ten seconds, followed by either an oxygen desaturation of a 3% drop or more and/or EEG arousal. The Apnea-Hypopnea Index (AHI) is expressed as the number of apneas or hypopneas per hour of sleep.
Any individual, no matter how healthy, who is given enough of a central respiratory depressant drug will develop apnea on a central basis. Generally, drugs that are central respiratory depressants also have sedative effects, and so the individual taking a toxic dose of such a drug is likely to be asleep, or at least in an altered state of consciousness, when breathing becomes irregular. Alcohol is such a central respiratory depressant in large doses; so are opiates, barbiturates, benzodiazepines, and many other tranquilizers. Some individuals have abnormalities that predispose them to central sleep apnea. The treatment for the condition depends on its specific cause.
Similarly, in any person who has some form of sleep apnea (including obstructive sleep apnea), breathing irregularities during sleep can be dangerously aggravated by taking one of these drugs. Quantities that are normally considered safe may cause the person with chronic sleep apnea to stop breathing altogether. Should these individuals have general anesthesia, for example, they require prolonged monitoring after initial recovery, as compared to a person with no history of sleep apnea, because apnea is likely to occur with even low levels of the drugs in their system.
Premature infants with immature brains and reflex systems are at high risk for central sleep apnea syndrome, even if these babies are otherwise healthy. Fortunately, those premature babies who have the syndrome will generally outgrow it as they mature, providing they receive careful enough monitoring and supportive care during infancy to survive. Because of the propensity toward apnea, medications that can cause respiratory drive depression are either not given to premature infants, or given under careful monitoring, with equipment for resuscitation immediately available. Such precautions are routinely taken for premature infants after general anesthesia. Caffeine has been found to help reduce apnea in preterm infants and to aid in care after general anesthesia.
Sudden infant death syndrome is sometimes theorized to be attributable to sleep apnea.
Congenital Central Hypoventilation Syndrome (CCHS): This very severe condition of abnormally low breathing during sleep is rare and is an inborn condition that involves a specific gene, PHOX2B. This homeobox gene guides maturation of the autonomic nervous system, and loss-of-function mutations lead to the failure of the brain to effectively control breathing during sleep in patients with the syndrome. There may be a recognizable pattern of facial features among individuals affected with this syndrome.
Once almost uniformly fatal, CCHS is now treatable. The children who have it must have tracheotomies and access to mechanical ventilation on respirators while sleeping, but most do not need to use a respirator while awake. The use of a diaphragmatic pacemaker may offer an alternative for some patients. When pacemakers have enabled some children to sleep without the use of a mechanical respirator, reported cases still required the tracheotomy to remain in place because the vocal cords did not move apart with inhalation. This form of central sleep apnea has been called Ondine's curse. People with the syndrome who survive to adulthood need to avoid certain risk factors, such as alcohol use, which can easily prove lethal.
Adults suffering from congestive heart failure are at risk for a form of central sleep apnea called Cheyne-Stokes respiration. This is periodic breathing with recurrent episodes of apnea alternating with episodes of rapid breathing. In those who have it, Cheyne-Stokes respirations occur while both awake and asleep. There is good evidence that replacement of the failed heart (heart transplant) cures central apnea in these patients. The use of some medications that are respiratory stimulants decrease the severity of apnea in some patients.
There is an association between atrial fibrillation (AF) and central sleep apnea. A study found that the prevalence of atrial fibrillation among patients with idiopathic central sleep apnea was significantly higher than the prevalence among patients with obstructive sleep apnea or no sleep apnea (27%, 1.7%, and 3.3%, respectively). The study was based on 180 subjects with 60 people in each of the 3 groups. Possible explanations for the association between CSA and AF are a causal relationship between the two conditions, or an abnormality of central cardiorespiratory regulation.
A diagnosis of sleep apnea requires examination by a physician. The examination will require a study of an individual in a sleep lab. There, the patient will be monitored at rest to measure the periods when breathing ceases. After a patient receives a diagnosis, the physician can provide different options of treatment. One of the more common treatments is CPAP (continuous positive airway pressure). During CPAP a mask that fits over the nose, or nose and mouth, is used and is connected to a device that compresses normal room air, and blows it into the airway at a constant pressure. This pressure must be optimal to prevent the airway from collapsing in patients suffering from Obstructive Sleep Apnea. Treatment for central sleep apnea differs slightly in that the device is not set at one optimal constant pressure as with CPAP, but at two different settings for inhalation (IPAP) and for exhalation (EPAP), therefore aiding respiration. Other specifications, for instance the breathing rate and the duration of a single breath, can also be programmed. This device is called BiPAP (bi-level positive airway pressure, meaning it is set at two different pressures). Both CPAP and BiPAP devices can be connected to a humidifier to humidify and heat the inhaled air, thus reducing unpleasant symptoms such as a sore throat or blocked nose that can result from inhaling cold, dry air.