What is sleep apnoea?
Apnoea is a Greek word meaning ‘without breath’. There are three types of apnoea that occur during sleep: central, obstructive, and a third type of mixed apnoea which is a combination of the two.
Central Sleep Apnoea
Central sleep apnoea affects 5% of sufferers and results from the brain failing to send the signal to breathe. The person stops breathing during sleep and no effort is made by the breathing muscles to resume breathing. Eventually, the brain sends the right signals and breathing resumes.
Obstructive Sleep Apnoea (OSA)
During your school days, you may remember reading about Joe the “fat boy” from the Pickwick Papers written by Charles Dickens in 1837. Joe ate food in great quantities and was liable to fall asleep during any situation. His breathing was heavy, he snored, and he was continuously sleepy.
“Sleep!” said the old gentleman, “He’s always asleep. Goes on errands fast asleep, and snores as he waits at table.” 1
Originally described as Pickwickian syndrome, this type of breathing was later categorised as obstructive sleep apnoea syndrome by Dr Christian Guilleminault. In the early 1970s, while working at the Stanford University Sleep Disorders Clinic, Dr Guilleminault teamed up with cardiologists to monitor the blood pressure of sleeping patients. The team discovered that when patients stopped breathing during sleep, their blood pressure dramatically increased. When this continued over time, the increase to blood pressure became permanent, occurring both day and night.
Obstructive sleep apnoea is the most common type of sleep apnoea in humans, and involves a repetitive pausing of the breath during sleep caused by the collapse of the upper airways and throat. Breathing may stop for as long as one minute or more, even as the brain continues to send signals to the breathing muscles to breathe.
Upon resumption of breathing, the individual takes a number of large gasps of air into their lungs, snores for a period of time, and then stops breathing again. This cycle of snoring, apnoea, gasping, and snoring continues all night long. Needless to say, obstructive sleep apnoea exerts considerable stress on the body, resulting in poor quality sleep. Sleep apnoea has also been implicated in increasing the chances of developing a number of conditions, including heart disease 2 and cancer. 3
(A list of the symptoms resulting from sleep apnoea can be found below.)
During an episode of apnoea, the sleeper may not even be conscious of holding their breath, or the racket created as they resume breathing. It is usually their sleeping partner who lies awake, listening and worrying, sometimes too fearful to go to sleep. Often, snorers are urged by their partner to visit their family doctor to get the condition checked out. The doctor, in turn, will usually refer the snorer to a sleep clinic, where they may participate in a study on how they breathe during sleep. This study is called a polysomnogram and can be conducted overnight at the sleep clinic or at home. During the study, brain activity, eye movement, heart rate, blood pressure, breathing and blood oxygen saturation are recorded. The most important data during the sleep study is known as the apnoea hypopnoea index (AHI).
The apnoea hypopnoea index was developed by Dr Guilleminault and is still used today to characterise the presence and severity of sleep apnoea. The AHI is generally expressed as the number of apnoeas and hypopnoeas per hour:
- An apnoea describes a complete stopping of the breath during sleep for ten seconds or longer
- A hypopnoea describes a reduction to breathing flow of greater than 30% during sleep, lasting for 10 seconds or more, which causes a decrease to blood oxygen saturation of at least 4%
An AHI of 5 to 15 is classified as mild obstructive sleep apnoea; 15 to 30 is moderate OSA; 30 or more is severe OSA.
To understand how the breath stops during sleep, imagine a collapsible paper straw. If you were to place one end of the straw in your mouth and inhale air forcefully through it, the pressure would cause the inner walls of the straw to collapse in on themselves. If you continued to draw air in through the straw, the collapse would become more severe. In engineering terms this is called the Bernoulli Principle: as fluid (or in this case, air) flows, negative pressure develops at the periphery of the flow. As the flow velocity increases, so too does the negative pressure. 4
In essence, this is what happens during obstructive sleep apnoea. The individual breathes out, and just as they are about to breathe in, the negative pressure created by trying to take air into the lungs causes the walls of the upper airways to collapse. As the breath hold continues, the breathing centre in the brain sends messages to the diaphragm to resume breathing. As the diaphragm contracts to draw air into the lungs, increased negative pressure enforces the breath hold.
During the pause in breathing, oxygen is continually extracted by the cells to power the functions of the body but is not replenished by breathing. After a time, the oxygen de-saturation of the blood decreases enough to partially wake the brain and resume breathing. The sleeper finally takes in a
breath with a loud gasp, followed by a series of heavy and intense breaths.
When the breath is stopped during sleep for a period of time, it is normal for the individual to resume breathing with a series of gasps as they suck much-needed air into their lungs. However, during this catch-up period of breathing, too much carbon dioxide is lost from the lungs and blood. To restore carbon dioxide levels to normal, breathing reduces, which may be responsible for initiating the next instance of apnoea. This in turn causes another collapse of the airways and the cycle repeats throughout the night.
Just like snoring, there are two main factors we need to consider: the first is the width of the upper airways and the second is breathing volume.
People with narrow upper airways – such as adults who persistently breathed through their mouth during childhood – are more prone to obstructive sleep apnoea. To ensure normal development of the upper airways, it is vital that children are encouraged to breathe through the nose.
Most procedures for improving obstructive sleep apnoea involve attempting to open the airways – either by bringing the lower jaw forward with surgery or using a continuous positive airway pressure (CPAP) machine to splint open the airway at night. The CPAP machine, which is considered the gold standard for treatment of sleep apnoea, was invented by Australian doctor Colin Sullivan. The CPAP machine is a small unit comprising a hose attached to a mask. The sleeper wears the mask at night, and the machine blows air through the hose and into the mask at a pressure sufficiently powerful to splint open the upper airways during sleep.
While the CPAP machine and the use of dental appliances to advance the lower jaw are relatively successful in their own right, they only target one half of the problem. To reduce and resolve sleep apnoea on a more permanent basis, it is also necessary to correct breathing volume. Any engineer considering the diameter of a tube (or in this case, airway) will also need to take into account the flow (breathing rate and volume) – after all, one is entirely dependent on the other.
IMPLICATIONS OF OBSTRUCTIVE SLEEP APNOEA (ADULTS)
- Excessive daytime sleepiness (falling asleep while eating, talking or driving)
- Waking up tired
- Causing sleeping partner to worry (while the sufferer may be unaware of sleep disturbance)
- Loud snoring
- Problems with memory and concentration
- Morning or night headaches (affecting approximately 50% of patients)
- Heartburn or reflux
- Needing to visit the bathroom during the night
- Elevated blood pressure during the day, increasing the risk of hypertension and heart disease
- Blood oxygen desaturation
IMPLICATIONS OF OBSTRUCTIVE SLEEP APNOEA (CHILDREN)
Children younger than five years of age may exhibit the following symptoms:
- Frequent waking
- Mouth breathing
- Failure to thrive
Children over five years of age may exhibit the following symptoms:
- Short attention span
- Poor academic performance
- Behavioural problems
- Bed wetting
- Not growing as quickly as they should for their age
4. Snoring and Obstructive Sleep Apnea. David N.F. Fairbanks and Samuel A. Mickelson.