Sleep Apnea-Hypopnea Syndrome: Difference between revisions
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This behavior of UA to collapse is countered by the phasic contraction of airway dilator muscles, which precedes the diaphragmatic contraction by a few milliseconds <ref name="18">Strohl KP, Hensley MJ, Hallett M, Saunders NA, Ingram RH. Activation of upper airway muscles before onset of inspiration in normal humans. J Appl Physiol 1980;49(4):638-642.</ref>. The only structures able to help maintain a certain caliber of the pharyngeal lumen are the UA muscles, especially the genioglossus muscle, resulting in a delicate balance between the compressive forces and the pharynx dilators <ref name="18" />. In the presence of OSAHS, the compressive forces on the pharynx exceed those that tend to dilate the UA, although the tonic activity of the muscles of the UA at rest is exaggerated in comparison with healthy subjects, both during awakening and sleep. This is generally interpreted as a neuromuscular compensation, but the actual compensation is obviously insufficient to counter the obstructive force <ref name="19">Mezzanotte WS, Tangel DJ, White DP. Waking genioglossal electromyogram in sleep apnea patients versus normal controls (a neuromuscular compensatory mechanism). J Clin Invest 1992;89(5):1571-1579.</ref>. The transpharyngeal pressure at which the UA are closed is called critical closing pressure (Pcrit). Pcrit is negative in normal subjects, that is less than the atmospheric pressure, but becomes less negative in non-apneic snorers and positive in apneic subjects. | This behavior of UA to collapse is countered by the phasic contraction of airway dilator muscles, which precedes the diaphragmatic contraction by a few milliseconds <ref name="18">Strohl KP, Hensley MJ, Hallett M, Saunders NA, Ingram RH. Activation of upper airway muscles before onset of inspiration in normal humans. J Appl Physiol 1980;49(4):638-642.</ref>. The only structures able to help maintain a certain caliber of the pharyngeal lumen are the UA muscles, especially the genioglossus muscle, resulting in a delicate balance between the compressive forces and the pharynx dilators <ref name="18" />. In the presence of OSAHS, the compressive forces on the pharynx exceed those that tend to dilate the UA, although the tonic activity of the muscles of the UA at rest is exaggerated in comparison with healthy subjects, both during awakening and sleep. This is generally interpreted as a neuromuscular compensation, but the actual compensation is obviously insufficient to counter the obstructive force <ref name="19">Mezzanotte WS, Tangel DJ, White DP. Waking genioglossal electromyogram in sleep apnea patients versus normal controls (a neuromuscular compensatory mechanism). J Clin Invest 1992;89(5):1571-1579.</ref>. The transpharyngeal pressure at which the UA are closed is called critical closing pressure (Pcrit). Pcrit is negative in normal subjects, that is less than the atmospheric pressure, but becomes less negative in non-apneic snorers and positive in apneic subjects. | ||
These obstructive forces can be of different sources. First, it might be related to anatomical features, such as enlarged tonsils, retrognathia and nasal obstruction <ref name="20">Aihara K et al. Analysis of anatomical and functionnal determinants of obstructive sleep apnea. Sleep Breath 2012;16(2):473-481.</ref>. Obesity is also an extremely important anatomical factor, possibly by increasing the mass of adipose tissue around the pharynx <ref name="3" />. Second, there is a significant decrease of muscle control during REM sleep by loss of metabolic control, exacerbated by alcohol or hypnotics, causing a decrease in tonic and phasic activity of skeletal muscle associated with sleep, particularly affecting the muscles of the UA, with preservation of diaphragmatic activity <ref name="21">Phillipson EA. Control of breathing during sleep. Am Rev Respir Dis 1978;118(5):909-939.</ref>. Then, weakness of the respiratory muscles may also contribute to compressive forces in the case of muscular hypotonia or secondary to adverse mechanical conditions, as in the case of chronic obstructive pulmonary disease <ref name="22">Howard RS, Wiles CM, Hirsch NP, Spencer GT. Respiratory involvement in primary muscle disorders: assessment and management. Q J Med 1993;86(3):175-189.</ref>. In addition, metabolic and mechanical stimuli will influence the activity of pharyngeal dilator muscles. More specifically, the mechanical stimuli consist of reflex activation of stabilizing muscles to UA negative pressure. This reflex activation decreases during sleep. Finally, these factors will also be amplified by the sleeping position of the subject, specifically the supine position | These obstructive forces can be of different sources. First, it might be related to anatomical features, such as enlarged tonsils, retrognathia and nasal obstruction <ref name="20">Aihara K et al. Analysis of anatomical and functionnal determinants of obstructive sleep apnea. Sleep Breath 2012;16(2):473-481.</ref>. Obesity is also an extremely important anatomical factor, possibly by increasing the mass of adipose tissue around the pharynx <ref name="3" />. Second, there is a significant decrease of muscle control during REM sleep by loss of metabolic control, exacerbated by alcohol or hypnotics, causing a decrease in tonic and phasic activity of skeletal muscle associated with sleep, particularly affecting the muscles of the UA, with preservation of diaphragmatic activity <ref name="21">Phillipson EA. Control of breathing during sleep. Am Rev Respir Dis 1978;118(5):909-939.</ref>. Then, weakness of the respiratory muscles may also contribute to compressive forces in the case of muscular hypotonia or secondary to adverse mechanical conditions, as in the case of chronic obstructive pulmonary disease <ref name="22">Howard RS, Wiles CM, Hirsch NP, Spencer GT. Respiratory involvement in primary muscle disorders: assessment and management. Q J Med 1993;86(3):175-189.</ref>. In addition, metabolic and mechanical stimuli will influence the activity of pharyngeal dilator muscles. More specifically, the mechanical stimuli consist of reflex activation of stabilizing muscles to UA negative pressure. This reflex activation decreases during sleep. Finally, these factors will also be amplified by the sleeping position of the subject, specifically the supine position that may contribute to push the tongue against the posterior pharyngeal wall <ref name="3" />. | ||
The reason why men are more affected than women is not yet fully understood, but it has been suggested that there is a higher pharyngeal resistance in men with a deficient activity of pharyngeal dilator muscles. There also appears to have a protective effect of female sex hormones, resulting in a lower AHI when postmenopausal women are treated with hormone therapy, and also a lower AHI during the luteal phase compared with the follicular phase of the menstrual cycle <ref name="23">Popovic RM, White DP. Upper airway muscle activity in normal woman: influence of hormonal status. J Appl Physiol 1998;84:1055-1062.</ref>. | The reason why men are more affected than women is not yet fully understood, but it has been suggested that there is a higher pharyngeal resistance in men with a deficient activity of pharyngeal dilator muscles. There also appears to have a protective effect of female sex hormones, resulting in a lower AHI when postmenopausal women are treated with hormone therapy, and also a lower AHI during the luteal phase compared with the follicular phase of the menstrual cycle <ref name="23">Popovic RM, White DP. Upper airway muscle activity in normal woman: influence of hormonal status. J Appl Physiol 1998;84:1055-1062.</ref>. | ||
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Introduction[edit | edit source]
The sleep apnea-hypopnea syndrome (SAHS) is divided into two categories. First, it can be linked with a complete or partial obstruction of the upper airway (UA) during sleep. This is known as obstructive sleep apnea-hypopnea syndrome (OSAHS). Then, it may also be consistent with central neurological respiratory abnormalities, causing the central sleep apnea syndrome (CSAS). Although some knowledge of sleep-disordered breathing goes as far back as ancient times, it was Charles Dickens in 1836, which drew up the first clinical presentation of OSAHS, without knowing it, by the detailed description of a character Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. The first physicians to recognize the syndrome in 1956 suggested Pickwick syndrome as nomenclature Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title, in honor to the novella containing the character described by Dickens, Posthumous Papers of Pickwick Club.
Definition and prevalence[edit | edit source]
An apnea is defined as an interruption of airflow for a period of at least 10 seconds Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Hypopnea for its part is less well defined but can be considered an incomplete but significant decrease in flow associated with desaturation Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title, arousal Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title, or both Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. The severity of SAHS is established according to the total amount of apneas and hypopneas per hour during sleep. In fact, there are several indexes but the apnea-hypopnea index (AHI), in which apneas and hypopneas are grouped, is most often used as both event types seem to have the same consequences Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Mild SAHS ranges from 5 to 15 events per hour of sleep, moderate OSAHS falls in the range of 15–30 events per hour of sleep, and severe SAHS would be a patient having over 30 events per hour of sleep Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. When strictly an AHI greater than 5 is considered, the prevalence of OSAHS can then reach 24% for men and 9% for women Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. However, when we take into account the presence of sleepiness, we then obtain a prevalence of 4% for men and 2% for women Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. CSAS for their part are much less frequent than OSAHS Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Signs and symptoms[edit | edit source]
Loss of ventilation during sleep will usually result in excessive daytime sleepiness, which can cause drowsiness and accidents, such as when sleep occurs while driving. In addition, sleep apnea subjects are regularly habitual snorers. But snoring is far from being specific to OSAHS since about 60% of adult men are habitual snorers Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Snoring and apnea events during the night might be witnessed by others and affects not only the apneic subject, but also the entourage. Other symptoms may include headaches, irritability, night sweats, attention deficit, memory loss, decreased libido, and depression Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In addition, by reducing the partial pressure of oxygen in the blood and causing oxygen desaturation, the resulting hypoxemia may be responsible for arterial hypertension Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title and the emergence of other chronic cardiovascular disorders Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title, mediated by the sympathetic nervous system through increased adrenergic tone in the daytime Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Diagnosis[edit | edit source]
The diagnosis is based on polysomnographic study (PSG), which includes electroencephalogram, electrocardiogram, oximetry, and recordings of the respiratory rate, respiratory sounds, thoracoabdominal movements and movements of the subject Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Thus, the PSG readings will ensure the quantification of the number of events per hour and the associated desaturation Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. At the same time, sleep stages and micro-awakenings will be also described and measurement of respiratory efforts will qualify obstructive or central apnea, according to the absence or presence of these efforts, since the latter is a reflection of obstruction Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. It is important to note that the central or obstructive nature of the episodes of apnea and hypopnea can also be mixed.
In addition to PSG, the diagnosis is also based on a careful history. One must be aware of the risk factors that have been well recognized: male, older age, being overweight, alcohol consumption, and certain anatomical factors inducing an anatomically smaller pharynx Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In addition, there are also a few other risk factors whose effect is controversial like smoking, nasal obstruction, ethnicity, genetic component, endocrine diseases, and the action of some drugs Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. There are also some questionnaires such as the Epworth scale that are regularly used, aimed to objectively quantify daytime sleepiness Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Finally, the body mass index is also regularly used to quantify obesity but most of the time the neck circumference will be favored Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Mechanisms[edit | edit source]
Let's start by saying that the pharynx, in opposition to the larynx and trachea, is not a rigid tube, so as to allow some non-respiratory functions such as swallowing and vocalization. In fact, to model the mechanical behavior of the pharynx, it is common to assimilate it with a physical model of collapsible tube, known as the Starling resistor Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. When there is an inspiratory drive originating from the upper respiratory control centers, a nervous impulse volley is traveling down in the phrenic nerves, resulting in a contraction of the diaphragm. This contraction, which induces a negative endopharyngeal pressure, added to the weight of the tissues surrounding the pharynx, tends to induce the closure of UA, especially at the oropharyngeal and velopharyngeal levels Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
This behavior of UA to collapse is countered by the phasic contraction of airway dilator muscles, which precedes the diaphragmatic contraction by a few milliseconds Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. The only structures able to help maintain a certain caliber of the pharyngeal lumen are the UA muscles, especially the genioglossus muscle, resulting in a delicate balance between the compressive forces and the pharynx dilators Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In the presence of OSAHS, the compressive forces on the pharynx exceed those that tend to dilate the UA, although the tonic activity of the muscles of the UA at rest is exaggerated in comparison with healthy subjects, both during awakening and sleep. This is generally interpreted as a neuromuscular compensation, but the actual compensation is obviously insufficient to counter the obstructive force Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. The transpharyngeal pressure at which the UA are closed is called critical closing pressure (Pcrit). Pcrit is negative in normal subjects, that is less than the atmospheric pressure, but becomes less negative in non-apneic snorers and positive in apneic subjects.
These obstructive forces can be of different sources. First, it might be related to anatomical features, such as enlarged tonsils, retrognathia and nasal obstruction Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Obesity is also an extremely important anatomical factor, possibly by increasing the mass of adipose tissue around the pharynx Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Second, there is a significant decrease of muscle control during REM sleep by loss of metabolic control, exacerbated by alcohol or hypnotics, causing a decrease in tonic and phasic activity of skeletal muscle associated with sleep, particularly affecting the muscles of the UA, with preservation of diaphragmatic activity Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Then, weakness of the respiratory muscles may also contribute to compressive forces in the case of muscular hypotonia or secondary to adverse mechanical conditions, as in the case of chronic obstructive pulmonary disease Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In addition, metabolic and mechanical stimuli will influence the activity of pharyngeal dilator muscles. More specifically, the mechanical stimuli consist of reflex activation of stabilizing muscles to UA negative pressure. This reflex activation decreases during sleep. Finally, these factors will also be amplified by the sleeping position of the subject, specifically the supine position that may contribute to push the tongue against the posterior pharyngeal wall Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
The reason why men are more affected than women is not yet fully understood, but it has been suggested that there is a higher pharyngeal resistance in men with a deficient activity of pharyngeal dilator muscles. There also appears to have a protective effect of female sex hormones, resulting in a lower AHI when postmenopausal women are treated with hormone therapy, and also a lower AHI during the luteal phase compared with the follicular phase of the menstrual cycle Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
During the episodes of obstructive apnea during sleep, increased inspiratory efforts, not oxygen desaturation, will cause micro-awakenings, allowing respiratory control centers to send a drive command to the UA muscles. This will result in a rapid increase of the pharyngeal diameter, causing the sudden and characteristic entry of air which is frequently reported by input environment. This same cycle is repeated again and again during sleep. Micro-awakenings will also fragment sleep and be involved in the reported daytime sleepiness Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In addition, as previously mentioned, by reducing the partial pressure of oxygen in blood and causing oxygen desaturation, the resulting hypoxemia can cause high blood pressure Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title and the appearance of other chronic cardiovascular disorders Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. The sympathetic nervous system is largely responsible for this through increased adrenergic tone in the daytime Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
It was also noted that the apneic subjects demonstrate signs of inflammation in the mucosa and submucosa, in addition to interstitial and inter-fascicular fibrosis, and a greater proportion of type II muscle fibers than type I. However, since these changes are visible in both the apneic and the simpler snorer, they are seen as a consequence of repeated trauma secondary to airway tissue vibrations during sleep, especially because of snoring, rather than a cause. However, these effects may in turn be a contributing factor to sleep apnea by changing the tissue characteristics of the UA. For example, stiffness of the uvula was observed in vivo in patients with sleep apnea. It might therefore represent a vicious circle Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
It looks like inflammation is present locally in the mucosa of OSAHS patients, but also systemically. More specifically, cytokines and C-reactive protein are elevated in OSAHS patients and those molecules have been found to be linked to sleepiness, fatigue and the development of cardiovascular and metabolic disorders Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Concerning the central events, they are caused by a decrease or instability of the central ventilatory drive. Any disease affecting the central nervous system in the area related to the control of breathing may cause CSAS. Central apnea may be isolated or in connection with Cheyne-Stokes, with periods of hyper or hypoventilation. Unlike obstructive apnea, it occurs mostly in the non-REM sleep stage Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Clinical Aspects[edit | edit source]
Subjects will usually consult due to excessive daytime sleepiness, excessive snoring, or as episodes of apnea have been reported by the entourage. Excessive sleepiness and snoring are not specific to OSAHS, hence the need to establish the diagnosis with the PSG. Moreover, the reverse is also true, that is to say, a subject may have an AHI indicative of the presence of OSAHS, but without any symptoms Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. In these circumstances, treatment can still be considered as a preventive measure according to the severity of the disease since the significant cardiovascular adverse side effects attributed to OSAHS. Although it does not seem unanimous, it has been reported that mortality increases significantly when the AHI is greater than 20 Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Treatments[edit | edit source]
Since 1981, the recommended treatment for OSAHS is continuous positive airway pressure ventilation (CPAP), which keeps the airway open by pushing air into the respiratory system Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Although very effective, it is unfortunately not always well tolerated. After 5 years of usage, only 50% will still be using it. Note that for CSAS, the bilevel positive airway pressure ventilation (BPAP) is sometimes used Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. As an alternative to CPAP, there is mandibular advancement devices (MAD), which tries to push the mandible forward in order to increase the caliber of the UA. However, even among the patients who tolerate well the device, MAD systems provide benefits in approximately only 50% of patients and is usually more effective with mild to moderate severity sleep apnea Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. There is also an approach using hypoglossal nerve neurostimulation, but it is still under study, requires an invasive surgery, and is very expensive for the moment Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Finally, when craniofacial anatomical features are obviously causative in the pathophysilogy of a specific subject, then a surgery executed by an otorhinolaryngology might be indicated Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
In parallel to those treatment procedures, as obesity is a known risk factor to OSAHS, it is often proposed to lose weight. As needed, the input of a dietetician might be of interest. Aerobic activities are often recommended as a safe way to lose weight. It also have been suggested that physical activity could improve the inflammatory profile in patients with OSAHS Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
An other approach gaining interest is using exercises to treat the OSAHS. Didgeridoo playing already have been shown to improve significantly the AHI Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title and an other study revealed that playing a double reed musical wind instrument is associated with a lower risk of OSAHS Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. Oropharyngeal exercises Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title and speech therapy Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title also demonstrated beneficial effects of rehabilitation. More studies are necessary to determine to best exercises paradigms but it seems like a very promising avenue. There is discussions on the plausibility of upper airway remodeling as an outcome of orofacial exercise Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title and the increase of UA muscles endurance which were shown to be more prone to fatigue Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title.
Conclusion[edit | edit source]
OSAHS is a therapeutic challenge. There are many treatment options but some patients can not tolerate these actual therapeutic approaches or do not have the desired results. Thereby, more studies are necessary but current evidences brings physical therapy and exercises in the front row in the treatment arsenal for sleep apnea.
Recent Related Research (from Pubmed)[edit | edit source]
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References[edit | edit source]
