What is Obstructive Sleep Apnea?
Obstructive Sleep Apnea (OSA) is a breathing disorder that occurs during sleep. It occurs when the throat muscles and the tongue relax during sleep and partly or completely block the airway. The dynamic intermittent obstruction to breathing can sometimes be seen at the entrance to the voice box in contrast to the relatively fixed blockage seen within the nose. The nocturnal obstruction to breathing can be complete or partial. A total blockage to breathing with no air movement for ten or more seconds is called an apnea. OSA patients may have apneic events that last 45 seconds or even longer and happen multiple times during the night.
When breathing ceases for long periods of time, oxygen levels in the blood will drop. The lowest oxygen saturation (LSAT) recorded during sleep is one feature used as an indicator of disease severity. Partial blockages to breathing that reduce airflow below normal by more than one half for more than ten seconds are called hypopneas. The average number of apneas and hypopneas per hour is called the respiratory disturbance index (RDI). The repetitive night-time blockage to breathing interferes with the normal physiology of sleep. Normal sleep architecture is seen as characteristic electroencephalogram (EEG) waveforms and durations at the different levels of sleep. With OSA the normal EEG architecture is altered such that the deepest and most restful levels of sleep are minimized or abolished.
Signs and Symptoms
Some of the most common signs and symptoms of OSA include:
- Loud snoring
- Excessive daytime sleepiness
- Observed episodes of breathing cessation during sleep
- Abrupt awakenings with shortness of breath
- Awakening with dry mouth or sore throat
- Morning headache
How does this happen?
While in the depth of sleep, airway obstruction occurs due to poor muscular tone. In response to an obstructive event, the brain partly awakens which is called an arousal. During an arousal, muscular tone is increased and the obstruction to breathing is relieved. Multiple arousals from deep sleep occur all night long in response to the repetitive apneic and hypopneic events. Perhaps this is a natural defense mechanism which prevents suffocation, but at the expense of high quality sleep. Repetitive nocturnal obstruction to breathing results in poor quality sleep with visible symptoms of sleep deprivation.
Who is at risk for OSA?
Many factors may lead to OSA. The characteristics of the skeletal and soft tissues supporting the throat are important. Some include:
- A small lower jaw
- Large tongue
- Intrusive tonsils
- Enlarged adenoids
- A long, floppy soft palate
- Male gender, excess weight or obesity, and aging are also typical risk factors for OSA.
- Additionally, the use of alcohol, sedatives, tranquilizers or antihistamines around bedtime can lead to snoring and OSA.
Diagnosis of OSA
The diagnosis of OSA is made by a test commonly called a sleep study or polysomnogram. This is performed in a facility accredited by the American Sleep Disorders Association (www.sleepassociation.org) and requires an overnight stay. The study measures multiple body functions, including efforts at breathing, oxygen levels, heart rhythms and EEG while you sleep.
The repetitive night-time blockage to breathing interferes with the normal physiology of sleep. Normal sleep architecture is seen as characteristic electroencephalogram (EEG) waveforms and durations at the different levels of sleep. With OSA the normal EEG architecture is altered such that the deepest and most restful levels of sleep are minimized or abolished.