[Pathophysiology of sleep-disordered breathing].

Sleep is a phase during which the respiratory system undergoes major changes. These changes lead to greater vulnerability and a greater risk of abnormalities, even in normal individuals. In the transition from wakefulness to sleep, there is commonly an increase in upper airway resistance and impairment of various protective responses and reflexes, which are efficient in promoting and maintaining upper airway patency during wakefulness. In individuals who present risk factors, such as anatomical abnormalities in the upper airway, these sleep-related changes cannot be efficaciously compensated, which increases the chances that sleep-disordered breathing will occur. Sleep-disordered breathing is characterized by a reduction in the size of upper airways, although the degree of the reduction varies. This reduction has multifactorial causes, which include anatomical abnormalities in the upper airway, alterations in the neuromuscular response and impairment of receptors in the upper airway. Upper airway functional and anatomical changes are likely to have genetic components, and, therefore, individuals exposed to certain environmental factors, such as allergies, have a greater chance of developing sleep-disordered breathing.