What is a CPAP Machine? (Difference Between CPAP, APAP, BiPAP and ASV)

It’s important to know the basic about the different types of PAP (positive airway pressure) devices that are used to treat sleep apnea. Whether you’re newly diagnosed with sleep apnea or a more seasoned user or healthcare provider, this post outlines the basics of each of the devices.

Our goal is to help you understand the differences in the devices or better understand the device you’re currently using. Ultimately, we want to help those who suffer from sleep apnea be successful with PAP therapy. Read on!

What is a CPAP machine?

Formal definition: CPAP, or Continuous Positive Airway Pressure, delivers pressurized ambient air (regular room air) through a delivery system (tubing and mask), thus eliminating apnea events during sleep. CPAP is the most effective treatment for sleep apnea and can potentially improve the patient’s sleep overnight; dramatically improving the quality of life for individuals afflicted with obstructive sleep apnea (learn about sleep apnea here).

What you need to know: CPAP is the most common PAP device. If you had a sleep study and a titration in a sleep center, this probably the type of PAP machine you will be recommended. Many sleep specialists agree that the fixed pressure is best for treating obstructive sleep apnea (we’ll talk about variable pressures later) and it’s the most affordable device.

What is an APAP or autoset PAP machine?

Formal definition: Auto titrating continuous positive airway pressure (autoPAP or APAP) machines are devices that are set at a variable pressure and adjust the pressure based on the patient’s needs using an internal algorithm. The pressure is monitored and adjusted breath to breath to treat the obstruction.

What you need to know: Since 2007, this device is become very popular after Medicare approved home sleep apnea testing (learn about that here). Some insurance companies are even denying requests for in-lab titrations in favor of APAPs (they want to save $$, learn about insurance coverage for sleep studies here). Here are the benefits and drawbacks of APAP:


(1) Having a device that can adjust its own pressure means that many patients can skip the sleep center altogether. These patients can use a home sleep apnea test and then an APAP. Easy peasy. No overnight at the sleep lab.

(2) APAP can be used immediately following a home sleep test for four to 6 weeks with a wide pressure range. Your healthcare provider can then assess the usage data to determine an optimal fixed pressure setting on a CPAP device.

(3) You can have a couple of beers, knowing it will make your sleep apnea worse that night, but rely on your APAP to adjust to your pressure needs (want to know if it’s OK to have a drink before your sleep study? Read this.) 


(1) Not every patient can skip the sleep center or use an APAP. Patients with CHF (congestive heart failure), COPD (chronic obstructive pulmonary disorder), CO2 retention, daytime hypoxemia or obesity hypoventilation syndrome, should use a fixed pressure CPAP and have a titration in a sleep center (learn about different types of sleep studies here).

(2) The device works by sensing resistance in the upper airway and then delivering more or less pressure; however, it feels the airflow at the mask, not where the obstruction is actually happen in the airway, which increases the peak airway pressure that can increase risk of pulmonary complications (it’s a small chance, but important to consider). Additionally, there’s always a bigger chance of airleak. Mask fitting is extremely important with APAP.

(3) APAP may be more expensive than CPAP. Insurance companies don’t recognize a difference between CPAPs and APAPs as far as coverage is concerned. The CPT code is the same, E0601 and reimbursement varies by insurance company. Cash rates may vary greatly between the two devices as the APAP is a more advanced device and more expensive for your provider to purchase from the manufacturer (learn more about what PAP costs and what insurance will cover here).

Which is better: CPAP or APAP?

Formal answer: It depends. As discussed above, it’s only an option if you don’t have any of contraindications listed above.

But really, which is better? It really depends. Our chief medical officer, Said Mostafavi, MD has this to say: 

Available data does not show any difference in efficacy between CPAP and APAP. There are several benefits of having a titration in a sleep center- like better mask fitting and patient education- but for many patients, especially those whose sleep apnea is diagnosed with HST, APAP could be considered. APAP could also be used during an in-center titration as well as being dispensed for a period of up to six weeks in order to determine fixed pressure and then be switched to CPAP.

What is a BiPAP or bi-level PAP machine?

Formal definition: BiPAP, or Bi-Level Positive Airway Pressure, is another form of sleep therapy, which delivers alternating levels of a higher inspiratory pressure (IPAP) to keep the airway open as a patient breathes in, and a lower expiratory pressure (EPAP) allowing the patient to exhale easily. Thus, a BiPAP is much easier for users with neuromuscular disease to adapt to. The dual settings allow patients to get more air in and out of the lungs without the natural muscular effort needed to do so.

Who can benefit from bi-level PAP?

(1) This device is usually recommended when the recommended CPAP pressure is really high and can be uncomfortable. Most insurance plans will cover it once the patient has tried CPAP in the lab and “failed” or did not tolerate CPAP. Because this machine is much more expensive than CPAP, insurance wants proof that it’s needed. 

(2) Patients with neuromuscular disease who have difficulty breathing.

(3) Patients who have hypoxemia or retain CO2 at night.

(4) Patients who have aerophagia (excessive swallowing of air causing abdominal discomfort). 

What is an ASV machine?

Formal definitionASV is a BiPAP or bi-level PAP with a back-up rate. It is used primarily to treat central sleep apnea (CSA). ASV provides positive expiratory airway pressure (EPAP) and inspiratory pressure support (IPAP), which is servocontrolled based on the detection of CSA. The device provides a fixed EPAP determined to eliminate obstructive sleep apnea. The ASV device changes the inspiratory pressure above the expiratory pressure as required to normalize patients’ ventilation.  With normal breathing, the device acts like fixed CPAP by providing minimal pressure support. When the device detects CSA, the device increases the pressure support above the expiratory pressure up to a maximum pressure.

Recent studies show that ASV isn’t for everyoneASV therapy is contraindicated in patients with chronic, symptomatic heart failure (NYHA 2-4) with reduced left ventricular ejection fraction (LVEF ≤ 40%) and moderate to severe predominant central sleep apnea. These patients may benefit from BiPAP or bi-level PAP and low flow oxygen. For more information, see the study links at the end of this post.

What are the complications of PAP therapy?

Regardless of the device type you use, there are things to keep in mind:

(1) Irritation on the bridge of the nose caused by the mask and headgear (learn more about different types of masks here).

(2) Irritation of the eyes (dryness or even conjunctivitis) from mask leak. Proper mask fitting is very important.

(3) Irritation of the airways. Especially in dry climates, for older patients or patients taking medications that dry the sinuses. Heated humidification will alleviate this.

(4) Aerophagia (excessive swallowing of air causing abdominal discomfort).

How can I order a new machine?

First, you’ll need a sleep study (learn more about that process here). If you’ve already been diagnosed with sleep apnea, you will need to find a provider, usually a DME (durable medical equipment) provider or HME (home medical equipment) provider. We are contracted with all major PPOs and many medical groups in California. To see if we are contracted with your insurance, see our list here

Request CPAP appt.


Other posts you may find interesting:



    Hi,Madam, My name is Fazal Subhan from karachi pakistan, I am sleep apnea patient and doctor advised me to take cpap macine for breathing at night sleep. unfortunately I can not afford this expensive machine, so please if you have some special relief for needy people than help me. I am very thankful to you. God bless you. thank you very much

  2. john Watkins Reply

    Hi my name is John Watkins my bipap machine went out i can not afford the dedutable my instance wants me to pay for new machine…I’ve recently has an amputation and my wife had cancer..we are behind due to in the only provider. Is there someplace in Iowa that helps people in need…i live by des Moines…

  3. Betty Clements Reply

    Does Medicare A and B pay for a clean air machine to clean cpap machine I have to try to disinfect my cpap as best I can .

  4. Betty Clements Reply

    I’m referring to the so clean machine please let me know, I do get all my.cpap supplies as needed on a schedule, I’m 70 yrs.old and I have severe obstructive sleep apnea I have to use my machine all night every night.I.need a.so clean machine to be sure my machine is cleaned properly.

  5. Christa Taylor Reply

    Hello, I was recently diagnose with complex sleep apnea. I do have Medicade in my state of Colorado. I received my bipap machine and was told that in order to keep the machine I have to meet an 80% usage rate. However when I did my initial study they used a nose pillow mask and I did just wonderful with it, even noticing a difference in how I felt the very next day. When I was given my machine I was also given a full face mask which I have not done well with at all. I have now given up on the full face mask. It slips around on my face due to me being a very active person when I sleep or it makes me wake up tearing the mask off of my face with the feeling like I’m being smothered. I was told when I received my equipment that I couldn’t under no circumstances receive another mask until my 2 months were up and I met the 80% usage. I really need this machine but I dont know what to do because now Medicade wont help me and I looked up these above websites and couldn’t find the applications online. I’m scared because my condition is very severe already causing me to have heart failure. Please any info will be most helpful. Thank you

  6. Jim Lankford Reply

    I have been diagnosed with sleep apnea. For a number of reasons I think have central apnea. Question, do you think a spine or cervical injury could cause central sleep apnea? I haven’t spoken to my doctor about this yet. Thanks.

  7. David Gulick Reply

    Complex and severe tyes apnea hallucinogenic dr standard dreams and other dreams where I talk clear ball a fist and directly hit and COPD my lit

    just don’t understand that they are great but they’re more pulmonary doctors with a side label of sleep not not dual education courses but I love my town I really need help David Gulick 772-486-6168 I’m a very interesting case and it might be worth the trip out to

    California because I’ve got about four different ranges for example my doctor did not even know anything about the ResMed ASV never even seen it heard of it we only have one supplier in town and they are so busy just trying to service people for all types of medical equipment recently has very mad at him but you know you have to take him to all the account so thank you very much I hope you can call me I’ll be much briefer on phone thank you

  8. DaWayne Janzen Reply

    Hi Julia, thank you for the information on this site. I am in 3rd stage heart failure with reduced left ventricular ejection fraction (LVEF ≤ 15%). 2 years ago I was misdiagnosed with obstructive sleep apnea and now on bipap. Its not helping me and now the doctor said that maybe the ASV would work, possibly having a 4th sleep study for it. I read a study that said with my condition, the ASV could shorten my life with heart situation. You heard of anything one way or the other? Close to having heart transplant if I drop below 15%. Thank you

  9. Aditya Pallati Reply

    Hi, Madam. I am 30yrs old. One year back I experienced mental traumatic situation (extreme fear and guilt) in my office. This resulted in broken sleep cycle right after the traumatic situation. 6 hour continuous sleep which I used to get automatically was split(3 hrs of sleep at night then automatically I wake up in the middle of night and not get sleep untill 8am in the morning and then I could sleep for 3 hours more) I also experienced extreme depression for 2 days. Thankfully I recovered from depression but my sleep cycle has not recovered. It has been 1 year since I am suffering from this kind of sleep. Its not that I am not feeling sleepy its that the time at which I feel sleepy has changed and the continuous 6 hr sleep has split into two parts 3 hrs each. How can I get back my 6 hour continuous deep sleep. Doctor gave me “Etizola Plus 5mg” which seems not perfectly working. Does the organ which sits on kidneys regulate sleep?

  10. Aharon Glucksman Reply

    had a test years ago and was prescribed a machine. had again a test a year ago and was told no need for one. but the bottom line is I don’t sleep well and walk like zombi during the day. any advice?

  11. Healthy Nutrition Reply

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  16. Emmanuel Heaven Reply

    Apparently I’m supposed to be on a Cpap machine. But when I was a kid I tried a cpap machine and the pressure was set to high for me. It was set at a pressure for severe sleep apnea which my father had. I used his for a couple of nights and it hurt my stomach and my chest so the sleep doctor set it lower. I was 7 year’s old at the time and vowed to never go on the Cpap machine again. They were going to put me on a Bipap machine set on mild sleep apnea but I didn’t want to cause I was afraid it would happen again. Well, I very recently went on the Apap machine cause it self adjusts as you sleep. Well, the apap did the exact same thing and now not only has it hurt my stomach and lungs again, but it’s made it so I have trouble breathing even on the lowest setting that they can do that would help me. The worst part is my oxygen level drops to 72 or even lower in less then an hour, and causes my heart to race because of it. I want them to stick me on the ASV machine but they refuse cause Medicare won’t cover it unless it’s life threatening. Well, I consider a racing heart, oxygen that drops in less than an hour, and breathing so shallow that I either stop breathing or don’t take in enough oxygen life threatening. Especially when now it hurts to even breathe at all. Now it hurts my chest just to walk especially up hill. How can I convince the sleep doctor and Medicare that I need the ASV machine? I now live in Washington state, but when I was a kid I lived in Batavia NewYork. Please help?

  17. gmail Reply

    I’m meant to be on a Cpap machine, according to my doctor. However, when I was younger, I tried a cpap machine and found that the pressure was too much for me. It was set at a pressure that was appropriate for my father’s severe sleep apnea. After a couple of nights of using his, it hurt my stomach and chest, so the sleep doctor adjusted it lower. At the time, I was 7 years old and pledged never to use a Cpap machine again. They wanted to put me on a Bipap machine with a mild sleep apnea setting, but I refused because I was frightened it might happen again. So, I recently started using an Apap machine, which self-adjusts as you sleep. The apap, on the other hand, did the exact same thing, and now not only has it injured my stomach and lungs again, but it’s also made it such that I’m having difficulties breathing even on the lowest level that will help me.

  18. jakson lee Reply

    thanks for sharing your article, BiPAP, or Bi-Level Positive Airway Pressure, is another form of sleep therapy, which delivers alternating levels of a higher inspiratory pressure (IPAP) to keep the airway open as a patient breathes in, and a lower expiratory pressure (EPAP) allowing the patient to exhale easily. Thus, a BiPAP is much easier for users with neuromuscular disease to adapt to. The dual settings allow patients to get more air in and out of the lungs without the natural muscular effort needed to do so.

  19. Ralph Larry Rentz Reply

    A very informative article, thank you .
    I underwent an overnight “Sleep Study” 25 years ago and was definitely diagnosed with Sleep Apnea . The Physician prescribed a CPAP. Upon trying to use the CPAP , I was unable to fall asleep due to the fixed air lowest level of 12 being too high for me personally . So, for more than 25 years I have NOT used any sleep device .
    However , at the age of 75 on 8-1-2022 ,
    the need for a Sleep Device becomes more obvious each morning waking up feeling out of breath, high anxiety and exhausted .
    I am ACTIVELY seeking help ASAP and will schedule a Sleep Apnea Machine Consultation with a Sleep Specialist MD within days .
    Which type of sleepapnea machine would hou generally recommend ;
    CPAP, BiPAP, APAP, ASV or another ,if any.

  20. redactle Reply

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  21. jakson lee Reply

    this is probably the type of PAP machine you will be recommended.

  22. Autocad Reply

    I have sleep apnea and I was looking for relief. This blog will help me alot in understanding the cppap machine.

  23. Rediffmail pro Reply

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  24. ovo game Reply

    The most popular positive airway pressure device for sleep apnea is the CPAP machine, although other options include APAP, BiPAP, and ASV depending on the patient’s demands and condition.

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  26. Andrew Reply

    If you had a sleep study and a titration in a sleep center, this probably the type of PAP machine you will be recommended.

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