CPAP 101

Different Types of Sleep Apnea Machines: CPAP, BiPAP, and APAP

If you’re new to the idea of having sleep apnea and treating it with some form of continuous positive airway pressure (CPAP), you may be confused by seeing different terminology for apnea treatment therapies on websites like this one. CPAP, BiPAP, and APAP, for example—what do all of these acronyms mean?

All three are forms of airway pressure therapy for obstructive sleep apnea (OSA). All three describe machines that, in conjunction with a CPAP mask and tubing, provide a gentle flow of pressurized, filtered air to keep your airway splinted open. All three use this air to keep obstructions from blocking your ability to breathe when you’re asleep.

However, the acronyms themselves stand for variations in how the air pressure is used to help keep your airway open and to assist sleep breathing.

The acronyms for the different types of sleep apnea machines, and what they stand for:

CPAP: Continuous Positive Airway Pressure. With CPAP, an air pressure level is prescribed by your physician, and this pressure maintains itself constantly, without variation, throughout the duration of your sleep.

You breathe in with the assistance of this pressure setting, and you exhale against this same pressure setting (if your mouth and nose are both covered by your mask, that is). CPAP remains the gold standard for treating OSA and is the most popular choice of apnea therapy machine.

BiPAP: Bi-level Positive Airway Pressure. As the name implies, a BiPAP machine offers two levels of airway pressure, so you can have two different settings. For example, your inspiratory setting, or the pressure level at which you inhale (called IPAP) can be set at a higher pressure than the pressure at which you exhale, a.k.a. your expiratory pressure setting (EPAP).

We’ll discuss why you might want BiPAP, or why your doctor may suggest it, below.

APAP: Automatic Airway Pressure. An APAP is automated to work within a pre-set pressure range. Your physician programs the machine for a high and a low pressure and the machine fluctuates between these throughout your sleep as needed. Read on for more details on why the APAP therapy option may be the right one for certain users.

CPAP: Why Choose Continuous Positive Airway Pressure Therapy?

If you have apnea, why choose a CPAP machine? If you snore or have the indications for obstructive sleep apnea or upper airway resistance syndrome, CPAP therapy may be a reasonable choice for you.

CPAP therapy can treat obstructive sleep apnea by keeping the airway open. If you have apnea, you likely have excess throat tissue that loses tone and relaxes during sleep, falling backward and blocking your ability to breathe. These moments when you gasp yourself awake to get a breath are called Apneas. Using a CPAP keeps your airway open throughout the night, preventing these Apnea events.

CPAP can also treat Upper Airway Resistance Syndrome (UARS). UARS is a precursor to obstructive sleep apnea. Instead of experiencing a full blockage, you have a reduction in your air intake because your airway is crowded due to a buildup of loose tissue. (Similar to the way arteries get clogged due to a buildup of plaques.)

You may not gasp yourself awake due to a total loss of oxygen, but you will experience labored breathing; your lungs need to work harder to suck in air as you sleep. And although you are breathing and taking in some oxygen, it may not be enough; sometimes your brain will wake you up anyway, so you can breathe more freely. Without treatment (CPAP or otherwise), UARS will usually progress into full-blown OSA.

If you’re an otherwise healthy individual with no history of lung or respiratory disease, and if your obstructive sleep apnea is moderate, CPAP is likely to be your first step when treating apnea. Most apnea patients who are prescribed an airway pressure therapy start here.

If you’re unable to tolerate CPAP for some reason, for example, due to difficulty exhaling against the continuous air pressure, your doctor may then look at alternatives: either BiPAP or APAP. For more on the basics of CPAP therapy, click here.

BiPAP: Why Is Bi-level Pressure Helpful?

First, it’s important to note that “BiPAP” is a trademarked brand name for a Philips Respironics product; however, it’s become popular and many physicians and suppliers use the term as a generic. You may also see BPAP. Both acronyms are different terms for the same therapy: bilevel positive airway pressure therapy.

Why would someone with apnea require two airway pressure settings instead of one?

A lower expiratory setting is helpful if you have difficulty exhaling against the pressure setting you use to inhale. An example of when this might happen is if you have severe apnea and your inspiratory setting needs to be high in order to keep your airway open. If you wear a full face mask that goes over the mouth and nose, exhaling against such a high setting may be difficult.

Over time, not being able to exhale carbon dioxide can be as dangerous for your health as not being able to inhale enough oxygen. The CO2 can build up in your system, throwing off your blood gas levels and leading to severe health problems like organ damage. In the shorter term, having trouble exhaling may disturb your sleep and wake you up.

Other reasons a doctor may prescribe a BiPAP rather than CPAP include if you have breathing issues that may affect your ability to exhale against a higher air pressure. These include conditions like:

  • Central Sleep Apnea
  • COPD
  • Overlap Syndrome
  • Obesity Hypoventilation
  • Health condition with an obstructive or restrictive component that affects your breathing during sleep

For more on BiPAP machine therapy and how it works, click here.

APAP: Advantages to Automated Pressure

Why might someone prefer to use, or need, an APAP, or apnea machine that offers automated pressure? An APAP machine (sometimes referred to as an “automatic” or “autoset” machine) uses computer algorithms to determine what air pressure you require at any given moment, depending on variables such as your body position or how your breathing changes during various sleep stages.

If you have sleep breathing patterns that vary over the course of the night, this type of therapy may be more comfortable for you.

While most people with Obstructive Sleep Apnea do fine with a CPAP, others may get better results with an APAP because the APAP may feel more like natural breathing. For example, you may prefer APAP if:

Your apnea events increase during REM sleep and decrease during other sleep stages. Some people need a higher air pressure during REM sleep only. If that high pressure remains high during other sleep stages when they don’t really need it, they may wake up due to discomfort. The APAP, with its automation, can adjust pressures accordingly.

You toss and turn during sleep. If you spend part of the night on your back and part on your side, your snoring and apnea events may change depending on position. You may need a higher inspiratory pressure when you’re on your back, due to gravity pulling the loose tissue downward toward the back of your throat.

When you’re on your side, your apnea events may decrease. The APAP can adjust the air pressure depending on your sleep position, so you don’t need to use the higher pressure at all times.

APAP is also a good choice for people who want to get started with therapy right away, without the delay of a titration study to determine the ideal single air pressure for their needs. Some users appreciate using an APAP or AutoSet machine because of its flexibility; whereas a CPAP cannot function like an APAP, an APAP machine can be set to perform like a CPAP, using a single continuous air pressure setting.


What’s the difference between a CPAP, BiPAP (BPAP) or APAP? All three help to open your airway and enable breathing. All three offer positive airway pressure to help reduce apnea events when you sleep. While CPAP is the standard therapy for most people with apnea, BiPAP and APAP may offer greater comfort if you have variable breathing patterns or respiratory conditions that make exhaling against a higher pressure uncomfortable.


  1. Cheryl Watkins Reply

    I just received the Phillips Dream Station and used it for the first time last night and it was great. I have been using a CPAP for over 20 years and they have really gotten better, and the price here was great too. It does surprise me that the mask here in proportion to the machines are so high? Had originally purchased this for my step-father, who broke his and I had let him use mine because I still had a older one set for me. I think that I will let him use mine until next year when he is eligible for a new one and then purchase him one of these as well.

Write A Comment