What causes sleep apnea?
Central night apnea
The central form of nocturnal apnea is characterized by the absence of respiratory movements and air flow through the nasopharynx. This group includes diseases in which nocturnal apnea is the result of a violation of the central mechanisms of the regulation of breathing: ischemic, inflammatory, alcoholic, atrophic, medicamentous brain lesions, organic lesions of the brainstem and posterior cranial fossa; brain damage in Alzheimer's disease; poststansephalic parkinsonism. The same group includes a rare syndrome of primary alveolar hypoventilation ("Undine's Curse Syndrome") due to the primary insufficiency of the respiratory center. Central nocturnal sleep apnea is usually seen in children who are cyanotic with birth in the absence of cardiac or pulmonary pathology. In children with this disease, the function of the central chemoreceptors is reduced, and in the medulla oblongata and in the region of the respiratory center the number of nerve fibers is reduced. The syndrome of central sleep apnea is about 10% of all cases of apnea.
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Obstructive nocturnal apnea
In obstructive nocturnal apnea, the airflow periodically stops completely, while the respiratory excursions of the anterior abdominal wall and thorax are preserved.
The main causes of obstructive sleep apnea are as follows:
- violation of patency of the upper respiratory tract due to collapse of the pharyngeal wall due to a decrease in the tone of the pharyngeal muscles - dilators of the pharynx, abductors of the tongue, pharynx. As a rule, this is observed in persons with initially narrowed oropharynx. Obstruction occurs at the level of the root of the tongue, since in this part of the pharynx, its lumen is supported not by bony and cartilaginous formations, but only by the optimal tone of the pharyngeal dilator muscles, mainly the chin-lingual muscle, which prevents the tongue from sinking to the posterior wall of the pharynx. During sleep, there comes a decrease in the tone of the muscles of the tongue and the oropharynx, which causes obstruction of the airways.
It is assumed that there is a defect in controlling the tone of the pharyngeal muscles by specialized structures of the brainstem.
There is also the assumption that a decrease in the tone of the pharynx muscles during sleep causes the development of obstructive sleep apnea only if there is a narrowing of the lumen of the upper respiratory tract (the causes of narrowing are indicated below). This view is based on the fact that a decrease in the tone of the pharynx muscles is observed during sleep in completely healthy persons (ie under physiological conditions), and obstructive nocturnal sleep apnea nevertheless occurs if there is narrowing of the lumen of the airways;
- developmental anomalies (micrognathia - small size of the lower jaw, retrognathia, macroglossia, wrong position of the hyoid bone, etc.), leading to a decrease in the diameter of the airways;
- proliferation of pharyngeal lymphoid tissue (adenoids, tonsillar hypertrophy, lymphoproliferative diseases);
- tumors and cysts in the pharynx;
- edematous inflammatory changes in the soft tissues of the neck; pronounced hyperplasia of the submucosal layer of the upper respiratory tract.
Important predisposing factors for the development of obstructive sleep apnea are obesity, chronic obstructive pulmonary disease, kyphoscoliosis, acromegaly (with it there is macroglossia), tranquilizers, alcohol abuse, age over 50 years, weighed weights.
Mixed sleep apnea
The syndrome of mixed sleep apnea develops when the causes of both groups are combined. For the most part, the central mechanisms of regulation are violated in all types of sleep apnea.
The pathogenesis of nocturnal sleep apnea
The pathogenesis of the main disorders that occur during nocturnal sleep apnea is primarily in hypoxemia and sleep fragmentation.
The episode of apnea lasting more than 10 seconds causes the development of hypoxemia. With more prolonged apnea, hypoxemia is much more pronounced, and also hypercapnia develops. After reaching a certain threshold level of hypoxemia and hypercapnia, there is a transition from deep sleep to a more superficial stage, at which the tone of the muscles of the pharynx and mouth rises, and the patency of the pharynx is restored, which is accompanied by strong snoring. Ventilation of the lungs and gas exchange are normalized, again the deep sleep phase begins until the next episode of apnea and obstruction develops. According to AM Wein et al. (1998), the average duration of apnea periods is 40 s, but can reach even 200 s, periods of apnea can occur so often that in severe cases occupy 60% of the total time of night sleep. Thus, nighttime apnea, which often occurs and lasts for a long time, disturbs sleep, reduces the duration of the surface and deep phases. This has a huge pathophysiological significance. During the REM-phase (the rapid eye movement phase), processing and assimilation of information obtained during the waking period occurs, and during the deep sleep, the processes of energy recovery in the brain occur. Violation of the duration of the phases of sleep leads to a decrease in memory, intelligence. Frequent episodes of apnea lead to hypoxemia, which is accompanied by spasm in the system of small blood vessels, increased pressure in the pulmonary artery, leads to the formation of the pulmonary heart, arterial hypertension in a large circle, contributes to the development of cardiac arrhythmias, sudden death.
With the syndrome of sleep apnea, the functional state of the endocrine system undergoes great changes. A decrease in the secretion of somatotropin (Grunstein et al., 1989) has been established, which contributes to an increase in the body weight of patients due to a decrease in the lipolytic effect of growth hormone. Along with this, there is an increase in the night secretion of catecholamines (Tashiro et al., 1989), atriopeptide. Ehlenz et al. (1991) found an increase in endothelin production - a potent vasoconstrictor factor in patients with sleep apnea syndrome. These changes contribute to the development of hypertension.
In patients with sleep apnea syndrome, testosterone secretion is significantly reduced, which causes the development of sexual weakness in men.