Definition: Defining the Meaning of Sleep Apnea
Sleep apnea (sleep apnoea in British English) is a sleep disorder characterized by pauses in breathing or instances of shallow or infrequent breathing during sleep. Each pause in breathing, called an apnea, can last for several seconds to several minutes, and may occur 5 to 30 times or more in an hour. Each abnormally shallow breathing event is called a hypopnea. Sleep apnea is classified as a dyssomnia, meaning abnormal behavior or psychological events occur during sleep. When breathing is paused, carbon dioxide builds up in the bloodstream. Chemo-receptors in the blood stream note the high carbon dioxide levels. The brain is signaled to wake the person sleeping and breathe in air. Breathing normally will restore oxygen levels and the person will fall asleep again. Sleep apnea is often diagnosed with an overnight sleep test called a polysomnogram, or sleep study.
Sleep apnea is a sleep disorder characterized by pauses in breathing during sleep. Each episode, called an apnea lasts long enough so that one or more breaths are missed, and such episodes occur repeatedly throughout sleep.
Sleep apnea symptoms may be present for years (or even decades) without identification, during which time the sufferer may become conditioned to the daytime sleepiness and fatigue associated with significant levels of sleep disturbance.
Sleep apnea is diagnosed with an overnight sleep test called a polysomnogram, or a "Sleep Study".
Clinically significant levels of sleep apnea are defined as five or more episodes per hour of any type of apnea (from the polysomnogram).
There are three distinct forms of sleep apnea: central, obstructive, and complex.
Central Sleep Apnea
In central sleep apnea, the basic neurological controls for breathing rate malfunctions and fails to give the signal to inhale, causing the individual to miss one or more cycles of breathing. If the pause in breathing is long enough, the percentage of oxygen in the circulation will drop to a lower than normal level (hypoxia) 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.
Obstructive Sleep Apnea
Common symptoms include loud snoring, restless sleep, and sleepiness during the daytime. Diagnostic tests include home oximetry or polysomnography in a sleep clinic.
The early reports of obstructive sleep apnea in the medical literature described individuals who were very severely affected, often presenting with severe hypoxemia, hypercapnia and congestive heart failure. Tracheostomy was the recommended treatment and, though it could be life-saving, post-operative complications in the stoma were frequent.
Some treatments involve lifestyle changes, such as avoiding alcohol or muscle relaxants, losing weight, and quitting smoking.
Complex Sleep Apnea
Complex sleep apnea has recently been described by researchers as a novel presentation of sleep apnea.
Patients with complex sleep apnea exhibit OSA, but upon application of positive airway pressure, the patient exhibits persistent central sleep apnea. This central apnea is most commonly noted while on CPAP therapy, after the obstructive component has been eliminated. This has long been seen in sleep laboratories, and has historically been managed either by CPAP or Bi-Level therapy.
Adaptive servo-ventilation modes of therapy have been introduced to attempt to manage this complex sleep apnea. Studies have demonstrated marginally superior performance of the adaptive servo ventilators in treating Cheyne-Stokes breathing, however, no longitudinal studies have yet been published, nor have any results been generated which suggest any differential outcomes versus standard CPAP therapy.
The diagnosis of sleep apnea is based on the conjoint evaluation of clinical symptoms (e.g. excessive daytime sleepiness and fatigue) and of the results of a formal sleep study (polysomnography, or reduced channels home based test).
The latter aims at establishing an "objective" diagnosis indicator linked to the quantity of apneic events per hour of sleep (Apnea Hypopnea Index(AHI), or Respiratory Disturbance Index (RDI)), associated to a formal threshold, above which a patient is considered as suffering from sleep apnea, and the severity of their sleep apnea can then be quantified.
- Mild OSA (Obstructive Sleep Apneas) ranges from 5 to 14.9 events per hour of sleep,
- Moderate OSA falls in the range of 15-29.9 events per hour of sleep,
- Severe OSA would be a patient having over 30 events per hour of sleep.
Treatment of Sleep Apnea
The most common treatment and arguably the most consistently effective treatment for sleep apnea is the use of a continuous positive airway pressure (CPAP) device , which splints the patient's airway open during sleep by means of a flow of pressurized air into the throat. However the CPAP machine only assists inhaling whereas a BiPAP machine assists with both inhaling and exhaling, and is used in more severe cases.
Facts: Sleep Apnea
Severity of sleep apnea depends on how often the breathing is interrupted:
- Normal - less than five interruptions an hour
- Mild sleep apnea - between 5 and 15 interruptions an hour
- Moderate sleep apnea - between 15 and 30 interruptions an hour
- Severe sleep apnea - over 30 interruptions an hour.
Causes of sleep apnea:
- Nasal congestion and obstruction.
- Large tonsils, especially in children.
- Medications, such as sleeping tablets and sedatives.
- Facial bone shape and the size of muscles, such as an undershot jaw.
- Certain illnesses, like reduced thyroid production or the presence of a very large goitre (swelling of the neck or larynx)
- Alcohol, especially in the evening, this relaxes the throat muscles and hampers the brain's reaction to sleep disordered breathing.
- Obesity is one of the most common causes of sleep apnea. A loss of around 5kg to 10kg may be enough to dramatically reduce the severity of the disorder.
Statistics: Sleep Apnea
- The Wisconsin Sleep Cohort Study estimated in 1993 that roughly one in every 15 Americans was affected by at least moderate sleep apnea. It also estimated that in middle-age as many as nine percent of women and 24 percent of men were affected, undiagnosed and untreated.
- The costs of untreated sleep apnea reach further than just health issues. It is estimated that in the U.S. the average untreated sleep apnea patient's annual health care costs $1,336 more than an individual without sleep apnea. This may cause $3.4 billion/year in additional medical costs. Whether medical cost savings occur with treatment of sleep apnea remains to be determined.