Sleep apnea is a common disorder in which an individual periodically stops breathing during sleep. These temporary interruptions can last ten seconds or longer and may occur hundreds of times during a night. The disorder is broadly classified into two types, obstructive and central.

Obstructive sleep apnea (OSA) is the most common type of apnea. In OSA, an individuals airway becomes temporarily blocked preventing normal gas exchange from occurring.

Oxygen in the blood eventually falls to critical levels, increasing the individuals efforts to breathe and resaturate the blood. This can result in a gasping or sometimes choking response as the person struggles to start breathing again. Luckily, reduced oxygen wakes the sleeper just enough to start breathing again but unfortunately not enough to remember the event. The obstruction may be localized to one or two areas, or may encompass the entire upper airway passages to include the nasal cavity (nose), oropharynx (palate, tonsils, tonsillar pillars) and hypopharynx (tongue base).^[2]

Central sleep apnea (CSA) is the far less common type of apnea. In CSA, the message that is normally sent from the brain to the intercontinental muscles and diaphragm to initiate breathing does not occur. As a result, patients with CSA show no signs of attempting to breathe despite having an open airway. Therefore unlike OSA, there is no audible gasping or choking making it harder to diagnose without extensive testing at a sleep center.^[2] A sleep partner may become aware of CSA if the the chest gradually starts moving regularly again after frequently coming to a stop.

The signs and symptoms of OSA and CSA overlap, making the type of apnea difficult to determine. The most common signs and symptoms include:

1. Excessive daytime sleepiness (hypersomnia)
2. Loud snoring, which is usually more prominent in obstructive sleep apnea
3. Episodes of breathing cessation during sleep witnessed by another person
4. Abrupt awakenings accompanied by shortness of breath, which more likely indicates central sleep apnea
5. Awakening with a dry mouth or sore throat
6. Morning headache
7. Difficulty staying asleep (insomnia)
8. Attention problems

Sleep apnea can affect anyone. But certain factors put you at increased risk:

• Excess weight: Fat deposits around your upper airway may obstruct your breathing. However, not everyone who has sleep apnea is overweight. Thin people develop this disorder, too.
• Neck circumference: People with a thicker neck may have a narrower airway.
• A narrowed airway: You may have inherited a naturally narrow throat. Or, your tonsils or adenoids may become enlarged, which can block your airway.
• Being male: Men are twice as likely to have sleep apnea. However, women increase their risk if they're overweight, and their risk also appears to rise after menopause.

• Being older: Sleep apnea occurs significantly more often in adults older than 60.
• Family history: If you have family members with sleep apnea, you may be at increased risk.
• Race: In people under 35 years old, blacks are more likely to have obstructive sleep apnea.
• Use of alcohol, sedatives or tranquilizers: These substances relax the muscles in your throat.
• Smoking: Smokers are three times more likely to have obstructive sleep apnea than are people who've never smoked. Smoking may increase the amount of inflammation and fluid retention in the upper airway. This risk likely drops after you quit smoking.
• Nasal congestion: If you have difficulty breathing through your nose — whether it's from an anatomical problem or allergies — you're more likely to develop obstructive sleep apnea.

• Head trauma: Damage to the respiratory centers in the brain.
• Heart disorders: People with atrial fibrillation or congestive heart failure are more at risk of central sleep apnea.
• Stroke or brain tumor: These conditions can impair the brain's ability to regulate breathing.

The most notable study investigating the prevalence of sleep apnea is the Wisconsin Sleep Cohort Study. It is an ongoing 26-year longitudinal study on sleep disorders, particularly sleep apnea. In the most recent report, researchers stated that the prevalence of sleep apnea (defined as more than five apneas or hypopneas per hour of sleep plus excessive daytime sleepiness) was 4% in middle-aged men and 2% in middle-aged women. They also noted that after menopause the prevalence between the two sexes becomes more or less on par at 4%. Although they did not give a reason for the increase, they hypothesized it was because of the changes in body fat composition after menopause. ^[10] Some newer subsequent studies conflict with the findings from the Wisconsin Sleep Cohort Study. Peppard et al., suggest that the prevalence in high-income countries may be higher than previously reported at 10% in women and 20% in men. They cite obesity as the main contributing factor in the western world. ^[6] However, both studies agree that that the problem is widespread while being vastly undiagnosed within the population.

Sleep apnea can have a significant impact on personal health, particularly on the cardiovascular system. During episodes of apnea, blood oxygen levels are reduced as the individual cannot breathe effectively. The heart tries to cope with the loss of oxygen by increasing its workload. A harder working heart becomes more prone to disease. As a result, those with sleep apnea typically have higher rates of blood pressure, heart failure, and stroke.^[10] The identification of the mechanisms underlying the disease processes have been of major importance and, despite significant effort being made, the process remains incompletely understood. Nonetheless, inflammation, oxidative stress and endothelial dysfunction have been identified as possible mechanisms.^[2] In addition, with each episode of apnea, sleep is disturbed as the sleeper must wake briefly to resume breathing. If this happens repeatedly during the night, it may interfere with the normal sleep that an individual needs to feel rested. As a result, the individual may become prone to certain injuries such as those sustained in motor vehicles.^[10]

A mandibular advancement device is a mouth device that attaches to the dental arches to stop snoring. It moves the upper teeth in the distal direction and lowers the teeth in the anterior direction. By snapping over the upper and lower dental arches, it makes it possible for the lower jaw to be moved forward, helping to keep the airway opened. ^[5] It is easy to use, non-invasive, removable, and only needs to be worn during sleep. The possible short-term side effects of the MADs include excessive salivation, tooth pain, mouth dryness, headaches, increase in degree of mouth opening, and overjet reduction (distance between maxillary anterior teeth and mandibular anterior teeth). ^[1]

Continuous positive airway pressure is another possible treatment for sleep apnea, involving a machine that blows air through the upper air passages via a mask on the throat or nose to help keep the throat open. ^[4] The machine is attached to a generator which is set to a certain pressure that provides a force to help keep the airway open. ^[4] This treatment improves daytime sleepiness, lowers an individual’s blood pressure, and help treats coronary artery disease. ^[4] The side effects, however, of CPAP include pressure on the face, mask leak, dry upper airways, stuffy nose, skin irritation, and nightmares. ^[4]

In order to see which treatment is beneficial in the short-term and long-term, a study was conducted by Smith, D and Stradling, J.^[8] Their study involved recruiting fifty participants with obstructive sleep apnea, who have also used CPAP as a treatment option, in order to determine if MADs can be used as a short-term substitute for this disease. Each participant was provided with a MAD, and then sleep studies were conducted using this device.^[8] It was concluded that most patients found MAD useful for a weekend. These devices were less successful at controlling both sleep fragmentation (measured by transient blood pressure) and inspiratory effect (measured by respiratory blood pressure). This data suggests that MADs are only partially helping to keep the lungs open. Thus, CPAP is thought to be more effective at keeping the airway open during the night, specifically in the long-term. The MADs can definitely help to treat mild sleep apnea in the short-term.^[8]

Obstructive sleep apnea can often be treated by directly treating or removing the responsible obstruction through surgery. The most common type of obstruction is elongation of the uvula and thus accordingly the most common procedure is uvulopalatopharyngoplasty, which is removal of the uvula, tonsils, and part of the soft palate^[7]. The surgery is largely affordable, safe and effective; however, it does cause scarring and long term side effects such as taste alteration, voice changes and pharyngeal dryness^[7]. Due to these, there has been an increase in alternative surgeries such as Radiofrequency Tissue Volume Reduction (RFTVR) of the soft palate, laser assisted uvuloplasty (LAUP) and cautery assisted palatal stiffening operation (CAPSO)^[7]. Although newer and thus with less evidence of effectiveness, CAPSO in particular shows great promise^[7]. Other popular surgeries include maxillomandibular advancement, which acts as a permanent MAD by moving the jaw forward with the help of screws and plates affixed to the lower jaw^[6].

Apneas are often a result of arterial carbon dioxide falling below the apnea threshold, the level required required to stimulate respiration. Administering carbon dioxide externally can thus stabilize respiration during sleep by minimizing hypocapnia (reduced carbon dioxide in the blood). One method that has been shown by multiple studies to have positive effects, both combined with PAP and on its own, is enhanced expiratory rebreathing space (EERS)^[9]. This is the addition of a closed volume to exhalation which increases rebreathing of exhaled air, thereby increasing the amount of CO₂ breathed in - similar to breathing into a paper bag when dealing with hyperventilation. in this treatment, a nonvented (NV) mask with 50-150 mL of added “dead space”, depending on the patient's personal ETCO₂ is worn while sleeping^[9]. The key challenge has been delivering doses of CO₂ that are adequate and precise, as amounts greater than 300 mL cause discomfort from the increased CO₂ retention and volume effects^[9].

Nasal administration of oxygen has shown to have some positive effects in treating sleep apnea, especially when combined with CPAP^[9]. The downsides are that effectiveness is partial, and it is prohibitively expensive in the long term. However, it can still be a useful part of a multimodal treatment approach, particularly for central sleep apnea^[9].

Although not a front-line treatment option, certain drugs have been shown to have beneficial effects on central sleep apnea symptoms in various ways. Acetazolamide is a carbonic anhydrase inhibitor which has been successfully used to treat central apneas by diminishing the ventilatory response of chemoreceptors to hypoxia and lowering the CO₂ apnea threshold^[9]. Acetazolamide can be used on its own or in combination with EERS or CPAP; it can also be substituted by zonisamide and topiramate, carbonic anhydrase inhibitors with similar effects^[9]. Certain sedatives such as benzodiazepines induce stable non-REM sleep can be used for treating NREM-dominant apnea, in which frequent arousals worsen the symptoms by destabilizing sleep^[9]. Finally, clonidine has recently been studied as an additional treatment, specifically for hypocapnic apnea symptoms. A report showed that patients given clonidine experienced decreased hypocapnic apneic threshold relative to placebo, increased CO2 reserve, and decreased hypocapnic ventilatory responses^[9]. This indicates a promising future for clonidine in apnea treatment.

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Other than the treatment options mentioned above, a significant difference in symptoms can be achieved simply by making lifestyle changes. A certain subset of central and complex sleep apnea, for example, can be helped greatly by changing sleeping position. Doctors strongly discourage sleeping in a supine position, while recommending sleeping on the side^[9]. The reasons for this positional dependency include fluid redistribution from the caudal to the cranial parts of the body, as well as upper airway and lung volume effects ^[9]. Opioid consumption, especially before sleep, is strongly linked to sleep apnea; the presence of a large number of opiate receptors allows opiates to modulate ventilatory response and induce ataxic breathing^[9]. Reducing opioid consumption can therefore have a significant positive effect on central sleep apnea. Major weight reduction can also help with obstructive apnea^[9].

1. Chan, A., Lee, R., & Cistulli, P. (2007, August). Dental Appliance Treatment for Obstructive Sleep Apnea. Chest Journal. Retrieved September 28, 2014, from http://journal.publications.chestnet.org/article.aspx?articleid=1085270#t3

2. Clinical Guideline for the Evaluation, Management and Long-term Care of Obstructive Sleep Apnea in Adults. (2009). Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine, 5(3), 263–276.

3. Foster GD, Borradaile KE, Sanders MH, et al. (2009). A randomized study on the effect of weight loss on obstructive sleep apnea among obese patients with type 2 diabetes: the Sleep AHEAD study. Arch Intern Med; 169: 1619–26.

4. Giles, T., Lasserson, T., Smith, B., White, J., Wright, J., & Cates, C. (2006, July 19). Continuous positive airways pressure for obstructive sleep apnoea in adults. Wiley Online Library. Retrieved September 28, 2014, from http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD001106.pub3/pdf/standard

5. Marklund, M., Franklin, K., & Persson, M. (2001, April 23). Orthodontic side-effects of mandibular advancement devices during treatment of snoring and sleep apnoea. European Journal of Orthodontics. Retrieved September 28, 2014, from http://ejo.oxfordjournals.org/content/23/2/135.full.pdf

6 Peppard PE, Young T, Barnet JH, Palta M, Hagen EW, Hla KM (2013). Increased prevalence of sleep-disordered breathing in adults. Am J Epidemiol; 177: 1006–14.

7. Sforza E, Chouchou F, Collet P, Pichot V, Barthelemy JC, Roche (2011) F. Sex diff erences in obstructive sleep apnoea in an elderly French population. Eur Respir J; 37: 1137–43.

8. Smith, D., & Stradling J. (2001, July 16). Can mandibular advancement devices be a satisfactory substitute for short term use in patients on nasal continuous positive airway pressure? Thorax. Retrieved September 28, 2014, from http://thorax.bmj.com/content/57/4/305.full

9. Thomas, R. J. (2013). Alternative Approaches to Treatment of Central Sleep Apnea. Sleep Medicine Clinics, 9, 87-104. 10.. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S (1993).The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med 32: 1230–35.

10. Young T, Palta M, Dempsey J, Skatrud J, Weber S, Badr S (1993).The occurrence of sleep-disordered breathing among middle-aged adults. N Engl J Med 32: 1230–35

11. Aneeza, W., Marina, M., Razif, M., Azimatun, N., Asma, A., & Sani, A. (2011). Effects of uvulopalatopharyngoplasty: a seven year review. Medical Journal of Malaysia , 66(2), 129-32.

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