What is sleep apnoea?

Medical report

A.1. DESCRIPTION OF OBSTRUCTIVE SLEEP APNOEA

A.1.1 Obstructive sleep apnoea (OSA) is the most serious form of the medical conditions which are bracketed together under the heading ‘ sleep disordered breathing ‘ (SDB).  The commonest form of SDB is snoring.  This occurs in 40% of adult males.

A.1.2. Snoring results from the breathing passageway at the back of the tongue becoming too narrow.  This part of the upper airway is referred to as the pharynx.  The narrowing can occur for a variety of reasons.  Enlarged tonsils can protrude into the pharynx, as can the tongue if it is enlarged, or pushed back by a receding chin. If the soft palate is floppy and has a large uvula hanging down from it this will also effectively narrow this breathing passage.

A.1.3. However, the commonest cause is weight gain. With increasing weight the girth of the neck increases from deposition of fatty tissue. In men, a collar size of 17 inches or greater is commonly seen in loud snorers and individuals with sleep apnoea.

A.1.4 As the pharynx narrows it causes the airflow through it to become turbulent.  This turbulence causes vibration in the soft tissues and the noise we recognise as snoring. Snoring is disruptive for the bed partner, but quite commonly, the snorer is unaffected.

A.1.5 During sleep, the muscles which normally hold the pharynx open relax.  If the snorer drinks alcohol or takes night sedation before going to bed, these muscles relax more.  This is why snoring is always much worse after alcohol.  When the individual enters the really deep phases of sleep (this is the type of sleep which is essential if sleep is to be refreshing) the muscles are maximally relaxed.  If the pharynx becomes really narrowed the individual has to work hard to drag air in through this small passageway.  The additional effort required to breathe, may well be sufficient to disrupt the normal sleep architecture with the result that sleep is no longer refreshing. Consequently, the individual wakes up still feeling tired.  This is known as Upper Airways Resistance Syndrome (UARS).

A.1.6. If the pharynx actually closes off when the muscles relax during deep sleep the airway is effectively blocked.  This results in an apnoea (from the Greek meaning “without breath”. See glossary of terms for formal definition).  We all do this occasionally, but in someone with OSA can happen hundreds of times per night.  In this situation, because the individual is unable to get air into their lungs, the oxygen level in the bloodstream starts to fall.  Fortunately, the brain is constantly monitoring our physiology, even when we are asleep.  As a result, when the oxygen levels start to fall, the brain causes the individual to be woken from the deep, restorative sleep, bringing them to a lighter level of sleep.  At this point the muscles in the pharynx start to work again and pull the breathing passages open.  The individual make a loud snorting gasping sound, and takes several deep breaths. Because there is now air getting to the lungs the oxygen levels rise. However, within seconds the cycle is repeating. Thus, the individual does not stay in the deep, restorative sleep, and as a result of this deficit, will feel un-refreshed by sleep, and will tend to catnap during the day.

A.1.7. When the individual is provoked to move to a lighter level of sleep this is referred to as an arousal. Other physiological changes occur at this time. The pulse rate rises, hormones are released that cause blood vessels to constrict and this results in raised blood pressure. It also means that the heart is pumping against more resistance, so has to work harder, just at the time when the oxygen supply in the bloodstream is reduced. Untreated OSA has been linked to development of high blood pressure, strokes, heart problems, diabetes, mood changes and male impotence. On occasions the individual will awaken rather than just move to a lighter level of sleep. The response to this is often to get up and pass urine on the assumption that this is why they have woken up. OSA sufferers often wrongly attribute frequent awakening to a need to pass urine frequently. Another symptom commonly experienced is heartburn. Because, during an apnoea, very negative pressures are generated in the chest as the body tries to suck air in, sometimes acid will be sucked up from the stomach.

A.1.8. It was estimated in 1991 that in the UK 4% of adult men and 2% of adult women suffer from OSA1. However, with the increasing obesity of the population the prevalence has increased and in a recent American review was reported as 11.4% in men and 4.7% in women2. There is considerable research from America3-5, Canada6;7, Australasia8;9, Scandinavia10 and Europe11;12 demonstrating that individuals with untreated OSA have a significantly increased risk of falling asleep whilst driving.
Additional research has shown that professional lorry drivers are a group in whom OSA is more prevalent than the general population3;13. It is postulated that this is because of the age profile of professional drivers, and their propensity to gain weight because of their sedentary occupation. A recent review of sleep apnoea in commercial drivers has been published in America highlighting the problems in this group14. UK research, for which the author was the medical adviser, has shown that the prevalence in this professional group is of the order of 19% (personal communication, Melanie Marshall, study being presented in PhD thesis for Cranfield University).

A.1.9. OSA develops gradually over a period of time.  Typically, men aged between 40 and 60 will put on weight, and at the same time their muscles become lax.  Consequently they start to snore, and gradually this progresses through UARS to OSA.  Initially they are able to maintain wakefulness during their working shift, whilst they are involved in activities requiring concentration and attention.  However, as the condition progresses, they are likely to find it more difficult to stay awake even when they are occupied by activities which require their attention.  Because OSA develops slowly they often attribute this excessive daytime sleepiness to the ageing process.  Indeed, when a significant number of their colleagues are suffering the same problem it is easy to understand why this may be regarded as normal.

A.1.10. Not all drivers with OSA will have accidents. Whilst all OSA sufferers have a degree of impairment, studies to date have not managed to identify which OSA sufferers are most at risk of having an accident15. Because OSA sufferers feel tired all the time they may not get the same warning symptoms that other people experience.  Most drivers will have felt tired at some time whilst they are driving. If they start to feel that they may actually fall asleep, the responsible driver will pull over as soon as it is safe to do so.  The OSA sufferer, however, feels tired all the time and may simply fall asleep.

A.1.11. Diagnosis of OSA usually depends on a combination of history and investigation. In some severe cases the history alone is sufficient to warrant a trial of therapy. The provision of sleep services in the NHS is sporadic across the UK. Some areas are well provided for, some are not. All sleep clinics are cash limited and some will have lengthy waiting lists. Sleep medicine has not been taught in the medical school curriculum so many doctors have limited knowledge of OSA.

A.1.12. The level of investigation also varies between clinics. Some will diagnose on the basis of measuring the blood oxygen level and pulse rate alone (oximetry). Others will use devices that monitor airflow, respiratory effort, sleeping position, movement and snoring levels (multichannel recorders). These allow a more detailed analysis of the breathing problems. A small number of units have access to full overnight polysomnography. This gives all the information of a multichannel recorder with the addition of monitoring of the brainwaves (electro-encephalogram or EEG) and eye movements. This allows identification of the level of sleep that the individual is in at any point during the night. Some units will also use infra-red video to record movements as well.

A.1.12 Assessment of daytime sleepiness is much more difficult. Questionnaires designed to evaluate this are subjective16-18. As long as they are answered honestly they do provide a reasonable assessment of an individuals ability to manage daily activities without falling asleep. There are objective assessments that involve the subject having to remain vigilant for a prolonged period, using driving simulators, or resisting falling asleep when allowed to rest in a quiet darkened room. These tests are not routinely used as they are labour intensive.

A.1.13. The criteria for a diagnosis of OSA have been summarised by the Scottish Intercollegiate Guidelines Network (SIGN)19. The Apnoea Hypopnoea Index (AHI) allows the terms mild, moderate or severe to be used to classify the severity. Independently of this there should be an assessment of daytime sleepiness. It is the combination of OSA and excessive daytime sleepiness that is required for a diagnosis of obstructive sleep apnoea/hypopnoea syndrome.

A.1.14. Treatment of moderate to severe OSA is usually with Continuous Positive Airways Pressure (CPAP). This is now something of a misnomer as many of the therapeutic devices deliver variable pressures according to the needs of the patient. This involves wearing a mask that fits over the nose alone, or the nose and mouth. This mask is connected via a flexible hose to a machine that adds pressure to the air that the wearer is breathing. This positive pressure in the airways prevents them from collapsing even during deep sleep. As a result the sleep is undisturbed. Individuals who are unable to tolerate the CPAP mask or those who have mild OSA can try a mandibular advancement splint (MAS). This is an orthodontic appliance that fits over top and lower teeth and pushes the lower jaw forward. This in turn pulls the tongue out of the pharynx and increases the diameter of the airway thus helping to prevent obstruction. The wearer does need to have at least 8 good teeth in upper and lower jaws. A number of surgical interventions have been attempted but unless there is a very specific anatomical problem to be corrected there is no specific surgical treatment. The only other surgical option is gastric surgery to promote weight loss.

A.1.15 Symptoms can improve rapidly once CPAP is started. If the subject finds it easy to tolerate the mask there can be a dramatic improvement after only one night. Most will see gradual improvement within the first week20.

Reference List

(1) Stradling JR, Crosby JH. Predictors and prevalence of obstructive sleep apnoea and snoring in 1001 middle aged men. Thorax 1991; 46(2):85-90.
(2) Chung SA, Yuan H, Chung F. A systemic review of obstructive sleep apnea and its implications for anesthesiologists. Anesth Analg 2008; 107(5):1543-1563.
(3) Stoohs RA, Bingham LA, Itoi A, Guilleminault C, Dement WC. Sleep and sleep-disordered breathing in commercial long-haul truck drivers. Chest %1995 May ;107 (5):1275 -82(5:1275-82).
(4) Aldrich MS. Automobile accidents in patients with sleep disorders. Sleep %1989 Dec ;12 (6 ):487 -94(6:487-94).
(5) Stoohs RA, Guilleminault C, Itoi A, Dement WC. Traffic accidents in commercial long-haul truck drivers: the influence of sleep-disordered breathing and obesity. Sleep %1994 Oct ;17(7 ):619 -23(7:619-23).
(6) George CF, Smiley A. Sleep apnea & automobile crashes. Sleep %1999 Sep 15 ;22 (6 ):790 -5(6:790-5).
(7) George CF, Nickerson PW, Hanly PJ, Millar TW, Kryger MH. Sleep apnoea patients have more automobile accidents. Lancet %1987 Aug 22 ;2(8556 ):447(8556:447).
(8) Connor J, Whitlock G, Norton R, Jackson R. The role of driver sleepiness in car crashes: a systematic review of epidemiological studies. Accid Anal Prev 2001 Jan;33(1):31-41 2001; 33(1):31-41.
(9) Desai AV, Ellis E, Wheatley JR, Grunstein RR. Fatal distraction: a case series of fatal fall-asleep road accidents and their medicolegal outcomes. Med J Aust %2003 Apr 21;178 (8 ):396 -9(8:396-9).
(10) Haraldsson PO, Carenfelt C, Diderichsen F, Nygren A, Tingvall C. Clinical symptoms of sleep apnea syndrome and automobile accidents. ORL J Otorhinolaryngol Relat Spec %1990 ;52 (1):57 -62(1:57-62).
(11) Cassel W, Ploch T, Becker C, Dugnus D, Peter JH, von WP. Risk of traffic accidents in patients with sleep-disordered breathing: reduction with nasal CPAP. Eur Respir J %1996 Dec ;9 (12 ):2606 -11(12:2606-11).
(12) Teran-Santos J, Jimenez-Gomez A, Cordero-Guevara J. The association between sleep apnea and the risk of traffic accidents. Cooperative Group Burgos-Santander. N Engl J Med %1999 Mar 18 ;340 (11):847 -51(11:847-51).
(13) Moreno CR, Carvalho FA, Lorenzi C, Matuzaki LS, Prezotti S, Bighetti P et al. High risk for obstructive sleep apnea in truck drivers estimated by the Berlin questionnaire: prevalence and associated factors. Chronobiol Int 2004; 21(6):871-879.
(14) Hartenbaum N, Collop N, Rosen IM, Phillips B, George CF, Rowley JA et al. Sleep apnea and commercial motor vehicle operators: statement from the joint Task Force of the American College of Chest Physicians, American College of Occupational and Environmental Medicine, and the National Sleep Foundation. J Occup Environ Med 2006; 48(9 Suppl):S4-37.
(15) George CF. Reduction in motor vehicle collisions following treatment of sleep apnoea with nasal CPAP. Thorax %2001 Jul ;56 (7 ):508 -12(7:508-12).
(16) Netzer NC, Stoohs RA, Netzer CM, Clark K, Strohl KP. Using the Berlin Questionnaire to identify patients at risk for the sleep apnea syndrome. Ann Intern Med 1999; 131(7):485-491.
(17) Johns MW. A new method for measuring daytime sleepiness: the Epworth sleepiness scale. Sleep 1991; 14(6):540-545.
(18) Weaver TE, Laizner AM, Evans LK, Maislin G, Chugh DK, Lyon K et al. An instrument to measure functional status outcomes for disorders of excessive sleepiness. Sleep 1997; 20(10):835-843.
(19) Scottish Intercollegiate Guidelines Network. Management of obstructive sleep apnoea/hypopnoea syndrome in adults.  Guideline 73. 2003.
Ref Type: Report
(20) Turkington PM, Sircar M, Saralaya D, Elliott MW. Time course of changes in driving simulator performance with and without treatment in patients with sleep apnoea hypopnoea syndrome. Thorax %2004 Jan ;59 (1):56 -9(1:56-9).

back to top