CPAP Machine Explained

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What is a CPAP Machine?

You have been diagnosed with obstructive sleep apnea (OSA) which means you stop breathing during your sleep. What happens in OSA is that the airway becomes blocked which limits or prevents the air coming in from the nose to the lungs. The airway can become blocked in more than one place along the airway, not everyone is the same.  Sometimes the blockage occurs because of excess fatty tissue or enlarged tonsils and adenoids.  Sometimes the structure of the jaw contributes to the blockage.  The blockage causes your oxygen levels to drop and increases your work of breathing.  At the end of each blockage event, you have a mini awakening, you may or may not remember this.  This is why people with OSA are very sleepy during the day.  When the airway in your upper respiratory tract is blocked ( it does not matter where the blockage is), Continuous positive airway pressure (CPAP) can work to keep the airway open.  CPAP is the considered the first line treatment for adults with OSA.

The purpose of a CPAP machine is to make sure you keep breathing while you sleep.

Try this experiment…

Find a piece of typical printing paper, roll it into a tube. Create a seal with your mouth around the tube. Now, put your hand on the other end and breath in and out.  You will see the middle of the “tube” collapse.  That is what happens to your airway when you have a blockage.  Imagine now, that you blow air into the tube with enough force to push the hand out of the way, which is how a CPAP Machine works, except it splints or pushes the blocked airway open and holds it open as long as the CPAP is used.

In order for CPAP to work, some form of a facial mask is required.  Masks come in all different shapes and sizes.  Search here to see the different ones –  Some people use a mask that covers both the nose and the mouth, some people use what are called “pillows” which fit into the front part of the nose.  There are masks that have gel cushions and some have silicone which help to form the seal. Finding the mask that works the best for you is important.

Sometimes people go to the sleep laboratory for a “titration” study. This study finds the best pressure to keep your airway open.  Some people have an autotitration machine (see below) which automatically adjusts the pressure based on changes it detects in the airway.  After a period of time, the doctor will look to see what the best pressure is that provides the best therapy. Sometimes people just use the autotitrating machines all of the time and sometimes they go on CPAP.

The titrated pressure is the pressure of air at which most (if not all)  apnea events have been prevented.  The pressure is measured in centimeters of water pressure (cmH2O).  Most machines can provide pressures from 4-20 cmH2O.  The majority of people need a pressure between 6 and 14 cmH2O.

According to the National Sleep Foundation, many people report immediate symptom relief from CPAP therapy. Patients also report increased energy, feeling less sleepy and have better mental alertness during the day. Not everyone responds the same, but over time, the benefits are many.  In addition to just feeling better, the use of CPAP has been shown to improve insulin resistance, blood pressure, brain function and a whole lot more! .  Wow, all that and very few side effects!

Not everyone takes to CPAP right away, but persistence pays off!  Figure out a plan that works for you to adjust to using CPAP.  For example, some people wear the mask while awake to get used to having it on with or without the CPAP machine on.

FUN FACT: Did you know CPAP machines have been around since 1981!  The first machines were almost as big as window air conditioning unit!  But the clinicians who worked with sleep apnea patients were excited because before CPAP, there were few options to be treated. A whole new era began.

Now, the new machines very small and much quieter.  If your CPAP machine seems outdated, contact your healthcare provider or your insurance company. Typically, the devices are covered by insurance and may be replaced every 5 years or so.

Now that you know how CPAP works, what kind of CPAP machines are there?

Fixed-pressure CPAP

Most patients are prescribed what is called “fixed CPAP”. A fixed pressure CPAP machine delivers a constant flow or pressure of air into your airway .  It is important to understand, however, that it is the air pressure, and not the movement of the air, that prevents the airway from collapsing. When the machine is turned on, but prior to the mask being placed on your face, a flow of air comes through the mask. After the mask is placed on your face, it creates a seal. It is the combination of the seal and the flow of air that creates the pressure.

Automatic positive airway pressure  

An automatic positive airway pressure device (APAP, AutoPAP, AutoCPAP) automatically finds the right pressure and fine tunes the amount of pressure delivered to the patient. The pressure may have many changes through out the night.  Why does it do this? During certain positions or changes in sleep, the pressure may need to go up or down, however, the goal is to have the  minimum amount of pressure required to keep the airway open.

Most machines do this on a breath-by-breath basis.  Each manufacturer has a special way measure and provide pressure.

Other Settings and things

There are also some other settings to help make things more custom to your needs.  These include a setting to help for breathing out, sometimes called expiratory pressure relief or C-Flex.  There is also a ramp feature.  The ramp feature lets you set the pressure lower when you go to bed.  As you fall asleep, the pressure gradually and gently ramps up over a set amount of time.


Almost all the machines can be used with a humidifier, usually heated and moist airCPAP machines with a humidifier are especially good for those who get runny noses, dry noses or dry mouths. A good CPAP machine that includes a humidifier can help you avoid these problems.  Depending on the climate where you live, a humidifier may be something you will want to investigate.

Bi-level pressure devices

Bi-level pressure devices “VPAP” or “BPAP” (variable/bi-level positive airway pressure) provide two levels of pressure: inspiratory (breathing in) positive airway pressure (IPAP) and a lower expiratory (breathing out) positive airway pressure (EPAP) for easier exhalation.  Sometimes these machines are used to help with other respiratory needs as well, not just OSA.

There are different ways these types of machines can be set up. Should you need one of these types of CPAP machines, your physician will write a prescription that specifically meets your needs.  But, as an overview, here are some of the settings you might need to know.

S (Spontaneous) – In spontaneous mode the device triggers IPAP when flow sensors detect your spontaneous inspiratory effort and then cycles back to EPAP.

T (Timed) – In timed mode the IPAP/EPAP cycling is purely machine-triggered, at a set rate, typically expressed in breaths per minute (BPM).

S/T (Spontaneous/Timed) – Like spontaneous mode, the device triggers to IPAP on patient inspiratory effort. But in spontaneous/timed mode a “backup” rate is also set to make sure you still receive a minimum number of breaths per minute should you have problems.

This is but a quick overview of OSA and CPAP Machines.  We hope this has been helpful for you, but should you have additional questions or concerns, please contact your personal representative.

Read more about mask problems at this post – Sleep Apnea Mask Problems and Solutions

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