What is the Difference Between CPAP, BiPAP, and Oxygen Therapy?

What is the Difference Between CPAP, BiPAP, and Oxygen Therapy?

Around 70 million people in the United States suffer from some form of sleep disorder such as narcolepsy, insomnia, or obstructive sleep apnea (OSA). These conditions can appear anytime during our lives and they have a significant impact on our general health and well-being.


Unfortunately, there are many obstacles that prevent people from receiving the treatment they need for sleep disorders. Chief among them is the fact that many people don’t even realize they have a problem in the first place. Symptoms such as daytime sleepiness, restlessness, or difficulty concentrating are often shrugged off as an inevitable part of life.


Another obstacle preventing sleep disorder patients from getting the help they need is confusion about their disease and the treatment options that are available to them. People hear terms like CPAP, BiPAP, EPAP, or APAP, but they never actually receive a simple explanation of what these terms mean and how they relate to each other.


In this post, we’re going to clarify any confusion about these terms as well as how they pertain to other types of respiratory therapy like supplemental oxygen. Remember to check in with your doctor if you have any questions or if you are thinking of making any changes to your treatment plan.


What is Obstructive Sleep Apnea (OSA)?

There are several types of sleep apnea, but one of the most common is obstructive sleep apnea. OSA occurs when the muscles in your throat relax intermittently at night causing you to stop breathing and lose sleep. It’s estimated that about 22 million Americans have some form of sleep apnea. 


obstructive sleep apnea


Obstructive sleep apnea is notoriously difficult to self-diagnose because the patient will likely have no recollection of what caused them to lose sleep or wake up frequently at night. In fact, many undiagnosed OSA patients believe that they get great sleep each night. This is why it’s important to speak with your doctor about having a sleep study done so that a medical specialist can examine your sleep patterns and determine if OSA is present.


A sleep study (polysomnography) is a non-invasive exam where you will stay in a sleep center overnight. During this study, electrodes will be placed on your head that measure brain activity, you will have a pulse oximeter attached to your finger which measures blood oxygen levels, and a belt will be wrapped around your chest to monitor breathing.  




This is one of the most effective ways for a health professional to diagnose OSA because it will show them exactly what’s going on in your body during sleep. For example, if your breathing is interrupted, your blood oxygen levels will likely drop and you’ll wake up. Occasional sleep interruptions are normal, but if it’s happening frequently throughout the night there is a more serious underlying issue at play. According to worldsleepday.org, patients with severe sleep apnea may wake up more than 30 timers each hour.   


Why is it Important to Treat Sleep Disorders?

For many people, the term “sleep disorder” doesn’t bring about a huge amount of urgency. You may be thinking that a sleep disorder can be cured with an extra cup of coffee in the morning or an energy drink for lunch, but the issues extend far beyond a little extra drowsiness in your day-to-day life.


Tired man


Not only can a sleeping disorder sap your energy, but it’s a risk factor for many different life-threatening illnesses as well. According to the Mayo Clinic, complications of obstructive sleep apnea (OSA) include high blood pressure, heart problems, metabolic syndrome, and liver problems.   


Furthermore, a medical report published in the Journal of Clinical Sleep Medicine states that sleep apnea increases the risk of heart failure by 140 percent and the risk of stroke by 60 percent. What’s more, it states that obesity is by far the most significant risk factor with about 60 to 90 percent of sleep apnea patients being obese. Other risk factors include cigarette smoking, alcohol consumption, and diabetes mellitus.


Man smoking


Knowing this information, it’s not hard to see how sleep disorders are a much more serious condition than most people realize. While it may only manifest itself with minor symptoms in your daily life, its impact on your long-term health is far worse. It can also contribute to other unhealthy lifestyle choices such as a poor diet or exercise routine, so it’s important to seek out appropriate treatment options.


What is Continuous Positive Airway Pressure (CPAP)? 

Continuous positive airway pressure is a therapy that is used to treat obstructive sleep apnea. It’s considered the first non-invasive treatment because, prior to the 1980s, the only effective treatment for OSA was tracheostomy, a surgical procedure that involves making an incision into the trachea in order to bypass an obstructed airway.


CPAP machine


The first CPAP machine was invented by Dr. Colin Sullivan in 1981. It works by administering a gentle stream of pressurized air through oxygen tubing that’s connected to the patient’s nose. At night, the patient can breathe freely while the pressurized air prevents the throat from closing up during sleep. Although modern CPAP machines use the same principles as the one created in 1981, they are much quieter and more comfortable, allowing the patient to get a better night’s sleep.  


One important thing to note is that CPAP is not the same thing as oxygen therapy. While CPAP does blow air into the nose, it uses ambient air including oxygen, nitrogen, and all the other gases that we normally breathe rather than medical grade oxygen. The sole purpose of CPAP therapy is to keep the airways open while you sleep. 


Man sleeping with CPAP machine


While CPAP machines deliver constant pressure, this pressure can be changed when you aren’t using the device. All CPAP devices use the measurement centimeters of water (cmH20) which is the same unit that lung pressure is measured in. Most patients require between 6 and 14 cmH20 and the average setting is 10 cmH20, however, the setting you use will depend entirely on your condition and the setting that your doctor prescribes. It’s also important to note that every CPAP machine has different capabilities, so you’ll want to make sure it meets your needs before purchasing it.


What is Bilevel Positive Airway Pressure (BiPAP)?

Although CPAP is still the most widely used PAP therapy device to this day, one of the major complaints about it is that it’s difficult to exhale against the air put out by the device. This typically isn’t a problem for someone with healthy lungs, but if you suffer from a low FEV1/FVC ratio, this could be a different story. In simple terms, FEV1/FVC ratio measures your lungs’ ability to exhale effectively. Low FEV1/FVC is often a sign of obstructive lung diseases like chronic bronchitis or emphysema.

BiPAP machine

BiPAP or Bilevel positive airways pressure is an alternative to CPAP which has two different pressure settings: one for inhalation (inspiratory positive airways pressure) and one for exhalation (expiratory positive airway pressure). The BiPAP machine will automatically detect whether you’re inhaling or exhaling and administer the pressure accordingly. Typically, a higher pressure will be applied when you’re inhaling.


CPAP With C-Flex versus BiPAP

Many people get confused when they hear about C-Flex which is a special feature that comes with some newer CPAP machines. This setting will help decrease the expiratory pressure by up to 3 cmH20. So, in other words, it’s more of a comfort feature that doesn’t completely eliminate the expiratory pressure. On some devices, this feature is called “expiratory pressure relief” or “EPR” for short.


What is Automatic Positive Airway Pressure (APAP)?

APAP is the third and final category of positive airway pressure device. Unlike CPAP and BiPAP, APAP machines automatically adjust airway pressure depending on what is needed at any given time. For example, if the APAP machine detects that your airways have closed, it will increase the pressure to open them up. Similarly, it can detect other episodes like hypopnea (slow and shallow breathing), flow limitation (when an increase in esophageal pressure is not accompanied by a flow increase), or snoring which can also disrupt sleep.


Stages of sleep


One of the obvious benefits of APAP is that it’s significantly more adaptable than CPAP or BiPAP. It contains a lot more technology and as a result, it’s often better for treating complex sleep apnea conditions. One complex form of apnea, REM-related obstructive sleep apnea occurs specifically during the rapid eye movement (REM) phase of sleep. 


Another type of apnea that can be remedied with APAP is positional apnea. This is when your apneic episodes can be attributed to one or more specific sleeping positions. If you tend to move around a lot at night, the APAP machine will recognize this and adjust accordingly.


What is Supplemental Oxygen Therapy?

While supplemental oxygen therapy is often confused with CPAP, BiPAP, and APAP, it is an entirely different therapy that is used to treat respiratory conditions rather than sleep disorders. Oxygen therapy is the administration of medical grade (high purity) oxygen via a nasal cannula. Oxygen therapy ensures the lungs are fully saturated so that a patient can maintain oxygen levels in their blood.

Oxygen tank

Most commonly, oxygen therapy is used to treat chronic obstructive pulmonary disease (COPD). This is an umbrella term used to describe two different chronic diseases: emphysema and chronic bronchitis. Emphysema is characterized by swollen and damaged alveoli. These are the small air sacs in the lungs that are responsible for the transfer of oxygen and carbon dioxide to and from the blood. Chronic bronchitis is characterized by inflamed and swollen bronchial tubes, the small airways in the lungs.  


COPD is one of the most common progressive lung diseases in the world, affecting an estimated 328 million people. Although it’s primarily caused by cigarette smoking, some people contract COPD due to a rare condition called alpha-1 antitrypsin deficiency. COPD is characterized by a chronic cough, chest pain, increased phlegm and sputum production, and exercise intolerance.


Symptoms of COPD


Depending on the severity of COPD that a patient has, they will need different flow rates of oxygen. Supplemental oxygen is measured in either liters per minute (LPM) or milliliters per minute (ml/min) depending on the oxygen device that is being used.


What Kind of Oxygen Devices Are There?

There are several different types of oxygen device: oxygen tanks, liquid oxygen tanks, stationary oxygen concentrators, and portable oxygen concentrators. Oxygen tanks are the oldest type of oxygen therapy and they work by storing oxygen at high pressures inside of an aluminum tank. Liquid oxygen tanks are similar to regular oxygen tanks but they’re stored in liquid form meaning they need to be kept at very low temperatures.

Respironics SimplyGo

Oxygen concentrators are electronic oxygen therapy devices that take in ambient air and remove unnecessary gases like nitrogen and argon, then it puts out medical grade oxygen through a nasal cannula. Stationary oxygen concentrators need to be plugged into a wall outlet at all times but portable oxygen concentrators run off lightweight batteries that can be taken anywhere.


Pulse Dose versus Continuous Flow

There are two different delivery methods for oxygen: continuous flow and pulse flow. The best way to think of these is like the difference between a drinking fountain and a water bottle. Drinking fountains are like continuous flow oxygen concentrators because they put out a constant stream of water irrespective of how much you drink. On the other hand, pulse flow concentrators are like water bottles because you’re drinking all of the water that comes out of the bottle.


Pulse dose and continuous flow oxygen concentrators.

Pulse dose oxygen concentrators are more advanced than their continuous flow counterparts because they are able to detect your breathing rate and deliver oxygen at the right moment similar to how an APAP machine changes the pressure in your airways based on your breathing and sleep patterns. However, in certain situations, your doctor may advise you to only use continuous flow oxygen machines. One of the best pulse flow portable oxygen concentrators currently available is the Caire FreeStyle Comfort and one of the best continuous flow portable oxygen concentrators is the Respironics SimplyGo.


How are PAP Therapy and Supplemental Oxygen Therapy Related?

Although PAP therapy and oxygen therapy are used to treat entirely different diseases, that doesn’t mean that they aren’t related. Both therapies are used to improve breathing and to promote lung health as well as general well-being. And in certain situations, you may need to use both CPAP and oxygen therapy at the same time.


What is COPD-OSA Overlap Syndrome?

Just like the name suggests, COPD-OSA overlap syndrome is when symptoms of both COPD and OSA are present. In other words, a patient can have both damaged lungs and airways that collapse during sleep. As you can imagine, this is a pretty bad combination and it can lead to a lot of complications when it comes to getting a good night’s sleep.


Man with his hands on his face.


There is no evidence to suggest that OSA causes COPD or vice versa, but a COPD patient who is obese or smokes will be at a higher risk of also contracting OSA. It’s important to remember that COPD is an “obstructive” lung disease, not a “restrictive” lung disease. What this means is that it affects the lung’s ability to expel air rather than inspire air. This is why COPD patients with OSA will likely be prescribed an APAP machine rather than a CPAP machine because it doesn’t add any unnecessary strain on their lungs when they expel air.


They Both Require a Prescription

Another similarity between oxygen therapy and PAP therapy is that they both require a prescription. Under the U.S. Food and Drug Administration, CPAP, BiPAP, and APAP machines are considered “Class II Medical Devices.” This means that these devices have potential risks and you’ll need a prescription to purchase one.



Similarly, oxygen is considered a controlled substance by the FDA, and as such, any device that puts out high purity or medical grade oxygen is regulated. If you decide to purchase an oxygen tank, liquid oxygen tank, stationary or portable oxygen concentrator, you will need to provide a prescription from your doctor. 


How to Connect an Oxygen Machine to CPAP

If you have COPD-OSA overlap syndrome, you may need to use both oxygen therapy and PAP therapy at the same time. If this is the case, you’ll need to make sure that your PAP device and oxygen device are compatible. Most CPAP machines are compatible with oxygen machines, but you’ll need to make sure you have a continuous flow oxygen concentrator. Pulse dose concentrators like the Inogen One G5 rely on your breathing to deliver oxygen correctly and CPAP will mess with this.


CPAP tubing


Your oxygen tubing will connect to the CPAP between the mask and the input valve, but if there is no place to connect them, then you will need to purchase an oxygen bleed adapter. Once the devices are connected you should make sure both devices are on before you go to sleep at night. If your nasal passages get dry while using both the CPAP machine and oxygen machine, you can typically purchase a humidifier for either unit that will allow you to sleep more comfortably.




Although CPAP therapy and oxygen therapy are commonly confused, they are not the same thing. CPAP, BiPAP, and APAP are used to treat obstructive sleep apnea, one of the leading sleep disorders in the country. Oxygen therapy, on the other hand, is used to treat COPD and other chronic respiratory diseases.


However, under certain conditions such as COPD-OSA overlap syndrome, your doctor may advise you to use both of these therapies. It can be confusing trying to pick out the right CPAP machine or oxygen concentrator, especially if you want to ensure that they’re compatible with each other. To make this process as easy as possible, reach out to our respiratory specialists here at LPT Medical and we’ll walk you through it and get you the exact device you’re looking for.

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