Disordered breathing during sleep is a hallmark of obstructive sleep apnea syndrome. Breathing abnormalities include apnea (cessation of air flow) and hypopnea (decreased air flow). In addition, in contrast to adults, some children exhibit a variation of obstructive sleep apnea termed obstructive hypoventilation (OH). Children with obstructive hypoventilation demonstrate periods of hypercarbia that occur in the absence of discrete respiratory events that fulfill criteria for apnea or hypopnea.
Physiologic recording methods can differentiate the types of apnea. During obstructive apnea, an individual makes respiratory efforts, but no airflow occurs because of upper airway obstruction. Central apnea is an interruption in both airflow and breathing effort. Mixed apneas have both central and obstructive components to them. A typical mixed event begins with a central apnea, which is followed immediately by one or more obstructed breaths.
Hypopneas are episodes of shallow breathing during which airflow is decreased by at least 50%. They are usually accompanied by some degree of oxygen desaturation, which can be minor and transient. Like apnea, hypopnea is subdivided as being obstructive, central, or mixed. Obstructive hypopneas are episodes of partial upper airway obstruction. Respiratory efforts occur, but airflow is reduced. In central hypopnea, breathing effort and airflow are both decreased. Mixed hypopneas have both central and obstructive components.
In adults, episodes of disordered breathing must last 10 seconds or more before being considered an apnea or hypopnea. Normal resting respiratory rates in children are faster than those in adults. The child has a smaller functional residual capacity and a more compliant chest wall. As a result, children undergo oxygen desaturation more rapidly than adults whenever airflow is interrupted. A definition of apnea or hypopnea requiring that an event last 10 seconds or more before it is considered significant is somewhat arbitrary and does not take into account the physiologic differences between adults and children. Consequently, pediatric sleep centers use different duration criteria for labeling events such as apnea or hypopnea. In children, if obstruction occurs with 2 or more consecutive breaths, the event can be called an apnea or hypopnea, even if it lasts less than 10 seconds.
Individuals with obstructive sleep apnea syndrome have pathologic degrees of obstructive apnea, obstructive hypopnea, or both. Severity is quantified using a polysomnographic-derived index known as the apnea hypopnea index (AHI). The AHI is the total number of apneas and hypopneas that occur divided by the total duration of sleep in hours. An AHI of less than or equal to 1 is considered to be normal by pediatric standards. An AHI of 1-5 is very mildly increased, 5-10 is mildly increased, 10-20 is moderately increased, and greater than 20 is severely abnormal.
OH in children is a sleep-related breathing disorder that is considered a variation of obstructive sleep apnea. Children with OH may have a normal ranged AHI, but they have episodic periods of hypercarbia, as identified based on end-tidal (ET) CO2 monitors. Peak ET CO2 measurements of greater than 53 mm Hg are considered abnormal. The percentage of sleep time spent with ET CO2 measurements greater than 50 mm Hg should not be more than 9%.
Most physicians who treat children with sleep apnea generally recommend specific interventions when the AHI is greater than 5 or respiratory events are associated with oxygen desaturations of less than 85%. When the AHI falls between 1 and 5, other clinical factors must be taken into account to determine whether to pursue adenotonsillectomy or other therapy.
Obstructive apnea and hypopnea are related to upper airway obstruction. Upper airway obstruction may occur at one or more levels, including nasopharynx (area from the nose to the hard palate), mouth, velopharynx (space behind the palate), retroglossal region (area behind the tongue), hypopharynx (region between the tongue base and larynx), and larynx.
The upper airway is a pliant tube whose sidewalls consist of muscle and other soft tissues. During wakefulness, neural input to a number of small muscle groups in the pharynx maintains muscle tone and airway patency. With sleep, an increased resistance to airflow normally accompanies muscular relaxation of these muscle groups. Although most people compensate for these changes, individuals with certain anatomic problems have repeated episodes of partial or complete upper airway obstruction when they sleep.
Childhood differs from adult obstructive sleep apnea. Adults with sleep apnea frequently present with hypersomnia, whereas children often demonstrate short attention spans, emotional lability, and behavior problems. Among adults, obesity is a major risk factor for obstructive sleep apnea. Fatty infiltration of the pharyngeal soft tissues narrows the caliber of the upper airway and contributes to airway resistance. Although obesity plays a role in some cases of childhood sleep apnea, the airway obstruction is usually related to tonsillar hypertrophy, adenoid hypertrophy, or craniofacial abnormalities. Children with some types of neuromuscular disease (eg, Duchenne muscular dystrophy, spinal muscular atrophy, cerebral palsy) may also have a higher risk of developing sleep apnea.
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