Obstructive sleep apnea

Clinic

• OSA is the most common sleep-related breathing disorder and is characterized by recurrent episodes of complete or partial obstruction of the upper airway leading to reduced or absent breathing during sleep.
• These episodes are termed "apneas" with complete or near-complete cessation of breathing, or "hypopneas" when the reduction in breathing is partial. In either case, a fall in blood oxygen saturation, a disruption in sleep, or both may result.
• A high frequency of apneas or hypopneas during sleep may interfere with restorative sleep, which – in combination with disturbances in blood oxygenation – is thought to contribute to negative consequences to health and quality of life. The terms obstructive sleep apnea syndrome (OSAS) or obstructive sleep apnea–hypopnea syndrome (OSAHS) may be used to refer to OSA when it is associated with symptoms during the daytime (e.g. excessive daytime sleepiness, decreased cognitive function).
• Most individuals with OSA are unaware of disturbances in breathing while sleeping, even after awakening
• Obstructive sleep apnea has been associated with neurocognitive morbidity, as well as a link between snoring and neurocognitive disorders.

Classification

• OSA is classified amongst the sleep-related breathing disorders and is divided in two categories, namely adult OSA and pediatric OSA.

• OSA is differentiated from central sleep apnea (CSA), which is characterized by episodes of reduction or cessation in breathing attributable to decreased effort, rather than upper airway obstruction.
• The respiratory effort must then be assessed in order to correctly classify the apnea as obstructive given the specificity of the diaphragmatic activity in this condition: the inspiratory effort is continued or increased through the entire episode of absent airflow.
• When hypopneas are present alongside apneas, the term obstructive sleep apnea-hypopnea is used and when it is associated with daytime sleepiness and other daytime symptoms, it is called obstructive sleep apnea-hypopnea syndrome.
• To be categorized as obstructive, the hypopnea must meet one or more of the following symptoms: (1) snoring during the event, (2) increased oronasal flow flattening, or (3) thoraco-abdominal paradoxical respiration during the event. If none of them are present during the event, then it is categorized as central hypopnea.

Signs / Symptoms

• Common symptoms of OSA syndrome include unexplained daytime sleepiness, restless sleep, and loud snoring
• Less common symptoms are morning headaches; insomnia; trouble concentrating; mood changes such as irritability, anxiety, and depression; forgetfulness; increased heart rate or blood pressure; decreased sex drive; unexplained weight gain; increased urinary frequency or nocturia; frequent heartburn or gastroesophageal reflux; and heavy night sweats.
• Many people experience episodes of OSA for only a short period. This can be the result of an upper respiratory infection that causes nasal congestion, along with swelling of the throat, or tonsillitis that temporarily produces very enlarged tonsils.

Adults

• The hallmark symptom of OSA syndrome in adults is excessive daytime sleepiness. Typically, an adult or adolescent with severe long-standing OSA will fall asleep for very brief periods in the course of usual daytime activities if given an opportunity to sit or rest. This behavior may be quite dramatic, sometimes occurring during conversations with others at social gatherings.
• The hypoxia related to OSA may cause changes in the neurons of the hippocampus and the right frontal cortex. Research using neuro-imaging revealed evidence of hippocampal atrophy in people with OSA. They found that OSA can cause problems in mentally manipulating non-verbal information, in executive functions and working memory. This repeated brain hypoxia is also considered to be a cause of Alzheimer's disease.

Children

Although this so-called "hypersomnolence" (excessive sleepiness) may also occur in children, it is not at all typical of young children with sleep apnea. Toddlers and young children with severe OSA instead ordinarily behave as if "over-tired" or "hyperactive"; and usually appear to have behavioral problems like irritability, and a deficit in attention.

Pathophysiology

• The transition from wakefulness to sleep (either REM sleep or NREM sleep) is associated with a reduction in upper-airway muscle tone. This allows the tongue and soft palate/oropharynx to relax, reducing airway patency and potentially impeding or completely obstructing the flow of air into the lungs during inspiration, resulting in reduced respiratory ventilation.
• If reductions in ventilation are associated with sufficiently low blood-oxygen levels or with sufficiently high breathing efforts against an obstructed airway, neurological mechanisms may trigger a sudden interruption of sleep, called a neurological arousal. This arousal can cause an individual to gasp for air and awaken. These arousals (In Stage 3 and REM sleep) rarely result in complete awakening but can have a significant negative effect on the restorative quality of sleep.
• Individuals with decreased muscle tone and structural features that give rise to a narrowed airway are at high risk for OSA.