Sleep apnea
Sleep apnea (alternatively sleep apnoea) is a sleep disorder in which breathing is interrupted during sleep. It is a kind of dyssomnia.
Obstructive sleep apnea
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.
"O.S.E." is caused by the relaxation of the muscles in the airway during sleep. Whilst the vast majority of people successfully maintain a patent 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" is characterised by complete closure of the upper airway for at least 10 seconds, wherein airflow is prevented despite continued respiratory efforts (American Academy of Sleep Medicine Task Force, 1999).
Patent airway vs. occluded airway (Bass, 2003)
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
In the past, the only way to diagnose the condition was in hospital, using a camera and other equipment to monitor sleep. With advances in portable electronics, patients may now use a small device that is strapped to a fingertip to measure the oxygen content of the blood, a procedure called pulse oximetry. This is non-intrusive procedure because only the color of the finger need to be monitored. Recordings of blood oxygen saturation during sleep indicate the severity of the problem.
Treatment
The most widely used current therapeutic intervention is continuous positive airway pressure (CPAP), whereby a breathing machine pumps a controlled stream of air through a face mask, forcing open the relaxed muscles. Other variations, such as bi-PAP, can deliver varied levels of pressure by monitoring breathing patterns. 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.
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.
Surgical therapy involving the removal of the tonsils, adenoids, portions of the soft palate, and/or the back of the tongue, such as uvulopalatopharyngoplasty (UPPP), has also been used for patients with apnea of a predominantly obstructive nature (Slovis & Brigham, 2001). A newer treatment uses a probe passed via the nasal cavity to irradiate the soft tissues with radio waves. After the initial swelling subsides, the airway opens up. This procedure is too new to have revealed any long term side effects, though it is believed that the radio waves are harmless.
Some call Sleep Apnea the invisible monster, as it works against sufferers while they are powerless to fight it. Ongoing research is aimed at providing a better understanding of the pathophysiology of OSA, and at uncovering novel alternative therapies for patients who poorly tolerate currently available interventions.
Central apnea
Another, rather rare form is central sleep apnea, where a problem in the central nervous system (particularly the areas of the brainstem responsible for respiratory drive) interrupts breathing. Overdoses of opiates, such as heroin and morphine, kill by inducing a severe central apnea; these drugs are thus called "respiratory depressants".
Training apnea
(Training Apnea; informal suggestion for identification)
Noted amongst a minority of active freedivers, this is the case of subjects performing apnea while sleeping, generally coincident with a related dream. Some cases have been determined to last until the point at which diaphramatic contractions occur, and are estimated to be greater than one minute in length.
References
- 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.
- 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.
