Sleep apnea
Apnea = Airflow absent for at least 10 seconds.
OSAS = More than 5 apneas in an hour
4% of men and 2% of women in the United States have OSAS
The sleep apnea, is present when the airflow at the nose or the mouth is absent for at least 10 seconds
Sleep apnea can be classified as obstructive, central, or mixed, depending on the presence or absence of respiratory muscle effort. With each type of apnea, airflow at the nose or the mouth is absent for at least 10 seconds.
- In obstructive apnea, ribcage and abdominal movements are still present; in central apnea, both types of movement are absent.
- In mixed apneas, both central and obstructive patterns occur during the same apneic event. The magnitude of any associated decrease in oxygen saturation depends on the degree and duration of apnea
Sleep-disordered breathing events that do not cause total cessation of airflow -- hypopneas -- may occur in conjunction with apneas. A hypopnea is defined as a 50% reduction in airflow, accompanied by significant oxygen desaturation (typically, 4%). The Apnea plus Hypopnea Index (AHI), sometimes called the Respiratory Disturbance Index, represents the degree of sleep-disordered breathing. It is calculated by adding the number of apneic and hypopneic episodes and dividing the total by the duration of sleep (in hours).
Persons who have symptoms compatible with sleep apnea and an AHI greater than 5 meet the minimum criteria for OSA syndrome (OSAS). The morbidity associated with any given AHI value varies, depending on the duration of apnea, the degree of associated arterial oxygen desaturation, and the extent of sleep disturbance.
Pathophysiology
The anatomic features and physiologic changes associated with upper airway collapse in patients who have OSA are similar to, but more pronounced than, those seen in healthy nonapneic subjects. Patients with OSA commonly have pharyngeal narrowing related to obesity, edema, or large tonsils . Pharyngeal collapsibility may be aggravated by retrognathia, increased upstream resistance (nasal obstruction), or increased inspiratory negative intrathoracic pressure related to obesity. About half of the patients with OSA obstruct at the level of the palate and half obstruct at the level of the hypopharynx.
