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Sleep apnea

Sleep apnea (alternatively sleep apnoea) is a common sleep disorder characterised by brief interruptions of breathing during sleep. These episodes, called apneas, last 10 seconds or more and occur repeatedly throughout the night. People with sleep apnea partially awaken as they struggle to breathe, but in the morning they may not be aware of the disturbances in their sleep.

The most common type of sleep apnea is obstructive sleep apnea (OSA), caused by relaxation of soft tissue in the back of the throat that blocks the passage of air.
Central sleep apnea (CSA) is caused by irregularities in the brain’s normal signals to breathe.

Some people with sleep apnea have a combination of both types.

Symptoms

The hallmark symptom of the disorder is excessive daytime sleepiness. Additional symptoms of sleep apnea include restless sleep, loud snoring (with periods of silence followed by gasps), falling asleep during the day, morning headaches, trouble concentrating, irritability, forgetfulness, mood or behavior changes, anxiety, and depression. Sleep apnea is more likely to occur in men than in women, and in people who are overweight or obese.

History

Considering how common a condition it is, it is remarkable that the first reports of what is now called obstructive sleep apnea date only from 1965 when it was independently described by French and German investigators. The term “Pickwickian syndrome”, inspired by Charles Dickens’ account in The Pickwick Papers of Joe, the fat boy, has been used in medicine to describe various conditions associated with obesity, excessive appetite and sleepiness and it was once presumed to be due to an endocrine problem. “Pickwickian syndrome” soon became the descriptor for the newly identified disorder but as more cases were recognised it became clear that neither obesity nor somnolence were necessarily present. “Pickwickian” was later reserved for “the obesity-hypoventilation syndrome” and today the term is best avoided because of its ill-defined meaning.

The early reports of sleep apnea 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 in these very obese and short-necked individuals.

The management of obstructive sleep apnea was revolutionized with the introduction of continuous positive airway pressure (CPAP), first described in 1981 by Colin Sullivan and associates in Sydney, Australia. The first models were bulky and noisy but the design was rapidly improved and by the late 1980s CPAP was widely adopted. The availability of an effective treatment stimulated an aggressive search for affected individuals and led to the establishment of hundreds of specialized clinics dedicated to the diagnosis and treatment of sleep disorders. Though many types of sleep problems are recognized, the vast majority of patients attending these centers have sleep disordered breathing.

Obstructive sleep apnea (OSA)

Most people with sleep apnea have obstructive apnea, in which the person stops breathing during sleep due to airway blockage. Sufferers usually resume breathing within a few seconds, but periods of as long as sixty seconds are not uncommon in serious cases. It is more common amongst people who snore, who are obese, who consume alcohol, or who have anatomical abnormalities of the jaw or soft palate. However, atypical cases do occur, and the condition should not be ruled out unilaterally merely because the patient does not fit the profile.

“OSA” is caused by the relaxation of the muscles in the airway during sleep. Whilst the vast majority of people successfully maintain a patent (open) upper airway and breathe normally during sleep, a significant number of individuals are prone to severe narrowing or occlusion of the pharynx, such that breathing is impeded or even completely obstructed (Mortimore & Douglas, 1997). As the brain senses a build-up of carbon dioxide, airway muscles are activated which open the airway, allowing breathing to resume but interrupting deep sleep.

Recurrent airway obstruction gives rise to the obstructive sleep apnoea (OSA) syndrome, the most common category of sleep-disordered breathing, with 2% of female and 4% of male subjects meeting the minimal diagnostic criteria for OSA of at least 10 apneic events per hour. An “event” can be either an apnea, characterised by complete cessation of airflow for at least 10 seconds, or a hypopnea in which airflow decreases by 50 percent for 10 seconds or decreases by 30 percent if there is an associated decrease in the oxygen saturation or an arousal from sleep (American Academy of Sleep Medicine Task Force, 1999). To grade the severity of sleep apnea the number of events per hour is reported as the apnea-hypopnea index (AHI). An AHI of less than 5 is considered normal. An AHI of 5-15 is mild; 15-30 is moderate and more than 30 events per hour characterizes severe sleep apnea.

These recurrent episodes of airway obstruction are associated with asphyxia, hypertension, depression, and daytime fatigue, since a transient interruption of the sleep cycle accompanies the restoration of airway patency. Most sufferers are not aware of these events, and are informed of the symptoms by their sleep partner. The apneic episodes are thought to account for the clinical sequelæ (symptoms that arise from a particular condition), which include increased incidence of chronic hypertension, a 700% rise in road traffic accidents, excessive daytime somnolence (similar, but unrelated to narcolepsy), social and family disruption, and cardiac arrhythmias and morbidity (Strollo, Jr. & Rogers, 1996). Obstruction of the upper airway may also be a cause of or may contribute to sudden infant death syndrome (SIDS) (Mathur & Douglas, 1994).

Diagnosis

The typical patient with sleep apnea is an overweight middle-aged male with a neck size of more than 17 inches. However, the condition is also common in women and not all sufferers are overweight. Almost everybody who has sleep apnea is a snorer, often a very heavy snorer. Pauses in breathing during sleep are commonly noticed by a bed partner but this history is often lacking and up to five “events” per hour are considered normal. One of the more consistent symptoms is “nonrestorative sleep” meaning that the patient wakes in the morning feeling unrefreshed no matter how much he slept during the night. Excessive daytime sleepiness is common in sleep apnea of any severity but some patients complain of fatigue rather than sleepiness. However, many patients with severe sleep apnea have no complaint of sleepiness or fatigue.

The most accurate diagnostic tool, polysomnography, can confirm the diagnosis and assist the doctor in identifying the type of sleep apnea present. In the past, this test was only done in hospitals and in specialized sleep laboratories. There are now portable sleep recording systems that can perform unattended polysomnography in the patient’s home but in-laboratory testing with a technician present remains the number 1 standard and it is required by many insurers, (eg. Medicare of the United States) before they will pay for treatment of the condition.

With advances in portable electronics, patients can now use a small device called a pulse oximeter, which is attached to a fingertip to measure the oxygen saturation of the blood (percent of the total hemoglobin that is combined with oxygen). This non-intrusive monitor measures the difference in the color of the oxygenated and of the deoxygenated hemoglobins. Recordings of blood oxygen saturation during sleep may give an estimate of the severity of the problem. However, oximetry is not a reliable screening tool. See: http://www.mayoclinicproceedings.com/inside.asp?AID=871&UID=

Treatment

There are a variety of treatments for sleep apnea, depending on an individual’s medical history and the severity of the disorder. Most treatment regimens begin with lifestyle changes, such as avoiding alcohol and medications that relax the central nervous system (for example, sedatives and muscle relaxants), losing weight, and quitting smoking. Some people are helped by special pillows or devices that keep them from sleeping on their backs, or oral appliances to keep the airway open during sleep. If these conservative methods are inadequate, doctors often recommend continuous positive airway pressure (CPAP), in which a face mask is attached to a tube and a machine that blows pressurized air into the mask and through the airway to keep it open. There are also surgical procedures that can be used to remove tissue and widen the airway. Some individuals may need a combination of therapies to successfully treat their sleep apnea.

Physical intervention

The most widely used current therapeutic intervention is positive airway pressure whereby a breathing machine pumps a controlled stream of air through a mask worn over the nose, mouth, or both. The additional pressure splints or holds open the relaxed muscles, just as air in a balloon inflates it. There are several variants:

  • (CPAP), or Continuous Positive Airway Pressure, in which a controlled air compressor generates an airstream at a constant pressure. This pressure is prescribed by the patient’s physician, based on an overnight test or titration.
  • (VPAP), or Variable Positive Airway Pressure, also known as bilevel or BiPAP, uses an electronic circuit to monitor the patient’s breathing, and provides two different pressures, a higher one during inhalation and a lower pressure during exhalation. This system is more expensive, and is sometimes used with patients who have other coexisting respiratory problems and/or who find breathing out against an increased pressure to be uncomfortable or disruptive to their sleep.
  • (APAP), or Automatic Positive Airway Pressure, is the most advanced form of such treatment. An APAP machine incorporates pressure sensors and a computer which continuously monitors the patient’s breathing performance. It adjusts pressure continuously, increasing it when the user is attempting to breathe but cannot, and decreasing it when the pressure is higher than necessary.

While the face mask makes some sufferers hesitant to try treatment, many patients find that the initial difficulty of adapting to the machine is quickly surpassed by improved, deeper sleep. In addition, the introduction of masks that resemble an oversized oxygen cannula have been better tolerated by some users. The vast majority of patients are surprised to find that they tolerate the mask fairly easily and sleep well while wearing it. Despite their nature as “air compressors”, modern CPAP machines are extremely quiet.

These treatments are often used with accompanying humidification, as some users experience a drying effect of the airway and mucous membranes. In the United States, these machines require a prescription. A sleep study is first done to determine what kind of treatment is needed, and to determine the proper settings for the nPAP device.

A second type of physical intervention, a Mandibular advancement splint (MAS), is sometimes prescribed for mild or moderate sleep apnea sufferers. The device is a mouthguard similar to those used in sports to protect the teeth. For apnea patients, it is designed to hold the lower jaw slightly down and forward relative to the natural, relaxed position. This position holds the tongue further away from the back of the airway, and may be enough to relieve apnea or improve breathing for some patients.

Medical (pharmaceutical) treatment

Few drug-based treatments of obstructive sleep apnea are known despite over two decades of research and tests.

Oral administration of the methylxanthine theophylline (chemically similar to caffeine) can reduce the number of episodes of apnea, but can also produce side effects such as palpitations and insomnia. Theophylline is generally ineffective in adults with OSA, but is sometimes used to treat Central Sleep Apnea (see below), and infants and children with apnea.

In 2003 and 2004, some neuroactive drugs, particularly a couple of the modern-generation antidepressants including mirtazapine, have been reported to reduce incidences of obstructive sleep apnea. As of 2004, these are not yet frequently prescribed for OSA sufferers.

When other treatments do not completely treat the OSA, drugs are sometimes prescribed to treat a patient’s daytime sleepiness or somnolence. These range from stimulants such as amphetamines to modern anti-narcoleptic medicines. The anti-narcoleptic modafinil is seeing increased use in this role as of 2004.

In some cases, weight loss will reduce the number and severity of apnea episodes, but for most patients overweight is an aggravating factor rather than the cause of OSA. In the morbidly obese a major loss of weight, such as occurs after bariatric surgery, can sometimes cure the condition.

Neurostimulation

Many researchers believe that OSA is at root a neurological condition, in which nerves that control the tongue and soft palate fail to sufficiently stimulate those muscles, leading to over-relaxation and airway blockage. A few experiments and trial studies have explored the use of pacemakers and similar devices, programmed to detect breathing effort and deliver gentle electrical stimulation to the muscles of the tongue.

This is not a common mode of treatment for OSA patients as of 2004, but it is an active field of research.

Surgical intervention

A number of different surgeries are often tried to improve the size or tone of the patient’s airway. For decades, tracheostomy was the only effective treatment for sleep apnea. It is used today only in very rare, intractable cases that have withstood other attempts at treatment. Modern treatments try one or more of several options, tailored to the patient’s needs. Often the long term success rate is low, prompting many doctors to favour CPAP as the gold standard.

  • Nasal surgery, including turbinectomy (removal or reduction of a nasal turbinate), or straightening of the nasal septum, in patients with nasal obstruction or congestion which reduces airway pressure and complicates OSA.
  • Tonsilectomy and/or adenoidectomy in an attempt to increase the size of the airway.
  • Removal or reduction of parts of the soft palate and some or all of the uvula, such as uvulopalatopharyngoplasty (UPPP) or laser-assisted uvulopalatoplasty (LAUP). Modern variants of this procedure sometimes use radiofrequency waves to heat and remove tissue.
  • Reduction of the tongue base, either with laser excision or radiofrequency ablation.
  • Genioglossus Advancement, in which a small portion of the lower jaw which attaches to the tongue is moved forward, to pull the tongue away from the back of the airway.
  • Hyoid Suspension, in which the hyoid bone in the neck, another attachment point for tongue muscles, is pulled forward in front of the larynx.
  • Maxillomandibular advancement (MMA). A more invasive surgery usually only tried in difficult cases where other surgeries have not relieved the patient’s OSA, or where an abnormal facial structure is suspected as a root cause. In MMA, the patient’s upper and lower jaw are detached from the skull, moved forward, and reattached with pins and/or plates.
  • Pillar procedure, three small inserts are injected into the soft palate to offer support, reducing snoring and sleep apnea.

Central apnea

In central sleep apnea, a problem in the central nervous system (particularly the areas of the brainstem responsible for respiratory drive) interrupts breathing.

See prevalence of different apneas in: http://ajrccm.atsjournals.org/cgi/content-nw/full/157/1/144/T1

For men aged 65 to 100 the prevalence is very common, nearly the same as for obstructive apnea.

Overdoses of opiates, such as heroin and morphine, kill by inducing a severe central apnea; these drugs are thus called “respiratory depressants”. Central sleep apnea is more common at high elevations.

A combination of Obstructive and Central Apnea is called Mixed Apnea.

References

  • Sullivan, C.E., Issa, F.G., Berthon-Jones, M. & Eves, L. (1981). Reversal of obstructive sleep apnoea by continuous positive airway pressure applied through the nares. Lancet. 1,862-865.
  • Mortimore, I. L. & Douglas, N. J. (1997). Palatal muscle EMG response to negative pressure in awake sleep apneic and control subjects. Am.J.Resp.Crit.Care Med. 156, 867-893.
  • American Academy of Sleep Medicine Task Force (1999). Sleep-related breathing disorders in adults: recommendations for syndrome definition and measurement techniques in clinical research. The Report of an American Academy of Sleep Medicine Task Force. Sleep 22, 667-689.
  • Strollo, P. J., Jr. & Rogers, R. M. (1996). Obstructive sleep apnea. N.Engl.J.Med. 334, 99-104.
  • Caples, S.M., Gami, A.S. & Somers, V,K. (2005) Obstructive sleep apnea. Ann.Intern.Med. 142, 187-197.
  • Mathur, R. & Douglas, N. J. (1994). Relation between sudden infant death syndrome and adult sleep apnoea/hypopnoea syndrome. Lancet 344, 819-820.
  • Slovis, B. & Brigham, K. (2001). Disordered Breathing. In Cecil Essentials of Medicine, ed. Andreoli, T. E., pp. 210-211. W.B. Saunders, Philadelphia.
  • Bass GA. (2003). Respiratory Phase Sensitivity of the Upper Airway Negative Pressure Reflex and Superior Laryngeal Nerve Laterality in the Mediation of Upper Airway Motor Activity. Thesis Dissertation, National University of Ireland, Dublin.

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