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Sleep apnea consists of repeated episodes of breathing pauses (apneas) during sleep as a result of anatomical or functional upper airway alternations affecting the permeability and impacting negatively their tendency to collapse hampering the normal functioning of the respiratory cycle. Apnea is defined as a temporary cessation of breathing for more than ten seconds.
Subjects with SAHS suffer continuous episodes of cessation of airflow in which they stop breathing, what dues to hypoventilation, oxygen desaturation and respiratory effort in response to hypoxia and hypercapnia. These episodes of asphyxia may have a variable duration of a few seconds, reaching in some cases a level up to a minute long and recurrently occur hundreds of times overnight.
The interruption of airflow is due to an obstruction of the upper airway. The occlusion occurs preferentially at the throat, which is the only region of the respiratory tract without rigid frame. This anatomical composition of soft tissue converts it into an area predestinated for potential collapse. During sleep (mainly in REM sleep), the muscle tone of the pharyngeal muscles decreases (hypotonia) and the equilibrium is lost, which normally coordinates the respiratory muscles, the diaphragm and the throat.