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Canadian Med Center

Introduction to Sleep Apnea

Thursday 29 February 2024
Sleep Apnea
8 minute(s) read

Table of Contents

I. What is Sleep Apnea?

II. Obstructive Sleep Apnea

III. Central Sleep Apnea

IV. Complex Sleep Apnea

V. Conclusion

Sleep apnea is a serious condition that can have life-threatening consequences. Surprisingly, it affects millions of Americans, making it more prevalent than you might realize. [1]

In this article, we'll dive into the definition of sleep apnea and explore its types, causes, risks, and symptoms.

What is Sleep Apnea?

Sleep apnea occurs when breathing stops and starts repeatedly during sleep. These pauses in breathing (called apneic events) last 10 seconds or longer and can occur more than 30 times an hour. [2] Based on the number of apneic events you experience, your sleep apnea will be classified as mild, moderate, or severe: [1]

  • Mild: Five to fourteen apneic events per hour. You may feel drowsy during low-attention activities like TV watching or reading.
  • Moderate: Fifteen to twenty-nine apneic events per hour. You may nod off during more engaging activities such as meetings or conversations.
  • Severe: Thirty or more apneic events per hour. You may fall asleep during high-attention activities like eating, talking, or driving. [2]

During an apneic event, air can't flow into or out of your airways despite your body's breathing attempts. This leads to lower oxygen and higher carbon dioxide levels in your blood, signaling your brain to open airways to resume breathing. You'll often make a loud snoring or choking sound as your airway reopens. Then, the cycle starts over. [1]

While these frequent arousals are necessary for breathing to restart, they prevent deep sleep and can cause:

There are three types of sleep apnea: obstructive, central, and complex. [1] We'll discuss each of these in more detail in this article. Diagnosing your type is key to proper treatment and gaining back healthy sleep.

Obstructive Sleep Apnea

man snoring and woman covering her ears with a pillow

Obstructive sleep apnea (OSA) is a common sleep-related breathing disorder that affects a staggering number of adults worldwide. In fact, it is estimated that around one billion adults worldwide suffer from OSA, although the actual figure may be even higher due to the large number of undiagnosed cases. [3]

If left untreated, OSA can have serious health consequences. This is why it is crucial to be aware of the signs of OSA and seek medical attention when necessary.


During the day, the muscles surrounding our throat open the airway for easy breathing. At night, these muscles naturally relax, which can narrow or even close off the airway, which reduces space for airflow. [3]

For many individuals, this narrowing does not cause issues. However, breathing against a closed or narrowed airway can cause airflow limitations for those at risk for OSA. This can cause abnormal blood levels of oxygen and carbon dioxide, disrupting sleep. [3]

Risk Factors

Various risk factors can increase someone’s risk for OSA:

  • The risk tends to increase with age, peaking between 60 to 70 years old before stabilizing
  • Males are at a higher risk compared to females
  • A high BMI
  • A tongue that’s larger at the base
  • Large tonsils
  • A small lower jaw
  • A lower jaw that is positioned further back
  • Neck circumference over 17 inches
  • Excess fat around the throat
  • A family history of OSA [3]


While some individuals with OSA may not exhibit noticeable symptoms, others may experience nighttime and daytime symptoms. [3]

Nighttime symptoms may include:

  • Loud snoring
  • Tossing and turning
  • Sudden awakenings to urinate
  • Breathing through the mouth [3]

Daytime symptoms may include:

  • Morning headaches
  • Dry throat
  • Daytime sleepiness
  • Reduced mental clarity
  • Waking up unrefreshed after a full night’s sleep [3]

Central Sleep Apnea

Central sleep apnea (CSA) occurs when the brain fails to signal properly to breathing muscles. This results in pauses or decreases in breathing during sleep.

Unlike obstructive sleep apnea (OSA), where breathing is blocked, in central sleep apnea, the airway remains open, but breathing stops or slows due to a lack of effort from breathing muscles. CSA affects 0.9% of people over 40 years old in the U.S. [4]


Central sleep apnea (CSA) can stem from various underlying causes. Understanding the different types of CSA is crucial in identifying the root cause and implementing appropriate treatment strategies.

  • Central sleep apnea with Cheyne-Stokes breathing: This is the most common form of CSA and is often found in people with heart conditions. Breathing is distinct and includes a pattern of small and large breaths followed by long pauses.
  • Central sleep apnea due to a medical disorder without Cheyne-Stokes breathing: While relatively rare, this type of CSA is typically caused by damage to the brain stem resulting from injury or disease. Unlike the previous type, individuals with this variant do not exhibit the distinctive Cheyne-Stokes breathing pattern.
  • Central sleep apnea due to medication or substance: Certain medications, such as opioids or methadone, can interfere with the brain's ability to initiate and regulate breathing effectively.
  • Central sleep apnea due to high altitude: Ascending to altitudes exceeding 8,000 feet can trigger this form of CSA in otherwise healthy individuals. The lower oxygen concentration prompts the body to compensate by increasing the depth and frequency of breaths. However, this can lead to disruptions in breathing during sleep by causing periodic pauses.
  • Treatment-emergent central sleep apnea: Five to fifteen percent of people being treated for obstructive sleep apnea with positive airway pressure devices can develop treatment-emergent central sleep apnea. This often goes away on its own as the body adjusts. [4]

Risk Factors

Some individuals face a higher risk of CSA than others. Understanding these risk factors is an important first step to getting the treatment you need.

  • CSA becomes more likely after age 65, as conditions like heart failure, stroke, and other cardiovascular issues become more prevalent.
  • Men have a higher risk than women. Researchers believe this is related to testosterone's effects on carbon dioxide levels in the blood during sleep.
  • Medical conditions such as heart failure, stroke, kidney failure, atrial fibrillation, excessive growth hormones, spinal cord injuries, and certain metabolic disorders.
  • Medications such as opioids, benzodiazepines, antidepressants, anticonvulsants, antiplatelet medications, and some muscle relaxants. [4]


If you often find yourself feeling excessively sleepy during the day or struggling with poor sleep at night, it's crucial to understand that these symptoms could be related to disrupted nighttime breathing. Many individuals with CSA are unaware that these issues are connected, but it's important to reach out to your doctor if you experience any of the following symptoms.

  • Daytime sleepiness. You may nod off easily during boring tasks or have trouble staying alert.
  • Frequent waking at night. CSA can disrupt your sleep, causing multiple awakenings during the night. This leaves you feeling unrested in the morning.
  • Abnormal breathing patterns at night. Your partner may notice times when your breathing is irregular, with short cycles of rapid breaths and pauses. [4]

Complex Sleep Apnea

A CPAP machine

Complex sleep apnea occurs in some people who have underlying obstructive sleep apnea (OSA) and start treatment with a continuous positive airway pressure (CPAP) machine or a bilevel positive airway pressure (BiPAP) machine. These machines deliver air pressure through a mask you wear while sleeping. The increased pressure helps keep your airway open to breathe freely while sleeping. [5]

For a few people, the air pressure from these machines can change the nature of their sleep apnea. Instead of just obstructive sleep apnea events where your breathing is blocked, you may experience central sleep apnea events where your brain temporarily stops telling your muscles to breathe. [5]


Around 20% of patients with OSA start experiencing complex sleep apnea during CPAP titration or in the early stages of treatment. The good news is that in most cases, only 2% of patients on long-term CPAP therapy continue to have symptoms. [5]

There are a few reasons why PAP therapy for OSA can trigger or uncover complex sleep apnea:

  • Some people have a highly sensitive breathing response during sleep, known as high loop gain. This means their breathing overreacts to small changes, and the use of PAP can cause their breathing pattern to alternate between rapid, deep breathing and pauses in breathing.
  • PAP therapy can increase ventilation and eliminate too much carbon dioxide from the body. The drop in carbon dioxide levels can then inhibit the brain's drive to breathe, leading to central sleep apnea. 
  • Mask air leaks from the CPAP mask during pressure titration can also lower carbon dioxide levels and trigger central apneic events. [5]

Risk Factors

While complex sleep apnea is not very common, researchers have identified key risk factors that make someone more likely to develop it.

  • Men have a higher risk than women
  • Older adults
  • Sleeping on your back
  • Opiates
  • Heart disease
  • Severe obstructive sleep apnea
  • High altitude
  • Treatment with CPAP or BiPAP on a high setting [5]


Complex sleep apnea can have several symptoms affecting your quality of life.

  • Daytime drowsiness
  • Poor sleep
  • Waking up frequently during the night
  • Headaches in the morning
  • Chest pain or discomfort
  • Difficulty concentrating
  • Mood changes [5]

It's important to note that some individuals with complex sleep apnea may not display any symptoms. In these cases, doctors typically recommend a repeat sleep study two to three months after the initial diagnosis to determine if the condition has resolved. [5]


Sleep apnea is a complex sleep disorder that requires proper care and management. By recognizing the different types—obstructive, central, and complex—we can better understand the various causes, symptoms, and risks tied to each one. 

For more information on sleep apnea, visit our dedicated sleep apnea blog.

The content in this article is intended for informational purposes only. This website does not provide medical advice. In all circumstances, you should always seek the advice of your physician and/or other qualified health professionals(s) for drug, medical condition, or treatment advice. The content provided on this website is not a substitute for professional medical advice, diagnosis or treatment.