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Pathology and causes of Sleep apnea

Sleep apnea occurs when breathing frequency drops substantially or there are episodes of suspended breathing during sleep, causing a lack of oxygen. If a patient stops breathing or their breathing frequency drops more than 25% during sleep for 10 seconds or more, causing a drop of blood oxygen for more than 4%, it may be regarded as sleep apnea. Breathing less frequently or suspended breathing may cause patients to wake up or move out of deep sleep and into light sleep. In mild cases, suffocation may take place several times an hour or even a few dozen times in severe cases. This affects the sleep quality of patients.

Sleep apnea is affecting more and more people in Hong Kong; about 4% of male and 2% of female. This disease prevents patients from having a deep sleep, adversely affecting their quality of sleep. Fatigue may lead to accidents to the patients if they need to drive or operate machinery; this may also harm those around them or even lead to fatalities. The lack of oxygen may cause damage to major organs, increase the risk of cardiovascular disease, and may lead to sudden death during sleep.

There are three types of sleep apnea:

  1. Central sleep apnea
    The brain cannot relay messages as normal and cannot control breathing, causing suffocation in patients. This type of sleep apnea usually affects young children or adults who have heart disease, brain disease or damage, or hereditary diseases, or those who have previously suffered a stroke. Medications and high altitude may trigger the disease.
  2. Obstructive sleep apnea
    This is the most common type of sleep apnea, which may be caused by many factors: a deviated septum, enlarged turbinates or tonsils, severe nasal allergies, or airways blocked by the uvula or tongue, etc. In this case, airways may collapse or become obstructed, hindering or even stopping breathing, resulting in a drop in the blood oxygen level. When blood oxygen drops to a certain level, the brain will signal breathing again.
  3. Mixed sleep apnea
    It is a combination of central sleep apnea and obstructive sleep apnea.

High risk group

  • Aged; males under 50 have a higher propensity for developing sleep apnea than females under the same age range. Once over 50, the difference between the two genders becomes smaller. 
  • About 70% of obese individuals have sleep apnea; the severity of symptoms is proportional to the level of obesity. 
  • Those with a small lower jaw or a short neck.
  • Those with heart disease or those who had a stroke before.
  • Premature babies have a higher risk of developing sleep apnea.


Sleep apnea affects the sleeping pattern of patients, preventing them from getting enough rest on a long-term basis. This results in a low blood oxygen level during sleep. Patients may develop these symptoms:

  • Difficult to concentrate
  • Forgetfulness
  • Delayed reaction
  • Loud snoring; very loud and abrupt after a pause
  • Sleepiness
  • Feeling tired after waking up
  • Fatigue during the daytime; falling asleep
  • Headache
  • Depression or anxiety
  • Sexual dysfunction


If neglected, sleep apnea may be the indirect cause of other diseases like hypertension, heart failure, irregular heart-beat, ischemic stroke, or even sudden death.


Use the Epworth Sleepiness Scale to measure and assess sleepiness in specific circumstances.

0 = would never doze
1 = slight chance of dozing
2 = moderate chance of dozing
3 = high chance of dozing

  Situation Chance of Dozing
1 Sitting and reading  
2 Watching TV  
3 Sitting inactive in a public place  
4 Being a passenger in a motor vehicle for an hour or more  
5 Lying down in the afternoon  
6 Sitting and talking to someone  
7 Sitting quietly after lunch (no alcohol)  
8 Stopped for a few minutes in traffic while driving  

Total score(add the scores up) is your Epworthm score, it indicate the severness of your daytime sleepiness:
Score of 0 - 7             : within the normal range
Score of 8 - 11           : subject to MILD day time sleepiness
Score of 12 - 15         : subject to MODERATE day time sleepiness
Score of 16 - 24         : subject to SEVERE day time sleepines

Patients with obstructive sleep apnea usually score higher than 16, combining with a complete medical history is needed for evaluation.

Patients may also take polysomnography, in which sensors are connected to certain parts of the body which monitor the sleeping patterns of patients, and collect physical and physiological data for analysis and diagnosis.

Polysomnography includes:

  • monitoring brain wave
  • monitoring eye movement
  • monitoring muscle movement
  • monitoring blood oxygen level
  • measuring airflow in the oral and nasal cavities
  • measuring chest and abdomen movement
  • measuring the loudness of snoring
  • video-recording the sleeping patterns of patients