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CPAP vs. BiPAP: Defining the Differences

Jun 2, 2018 1:53:07 AM / by Cory Luckner

When diagnosed with obstructive sleep apnea (OSA), central sleep apnea (CSA) or complex sleep apnea, you may be confused on the differences and benefits of a CPAP, BiPAP, Auto-CPAP, VPAP, and ASV device. Depending on your diagnosis different machines will be more beneficial than another. After this you will be equipped with the knowledge to make the most informed purchasing decision according to your prescription so you can enjoy the highest level of sleep apnea treatment quality. Remember to always follow your prescription, as a CPAP prescription won’t work for a BiPAP prescription and vice versa.

Defining a CPAP, BiPAP, Auto-CPAP, ASV, and VPAP

  • CPAP: Stands for Continuous Positive Airway Pressure (Fixed Pressure Setting)
  • BiPAP (BPAP): Refers to Bilevel or Two Level Positive Airway Pressure; Used if CPAP is Ineffective
  • ASV: Adaptive Servo Ventilation
  • Auto-CPAP: Auto Adjusting Positive Airway Pressure. Which Automatically Adjusts Your Therapy Pressure While Sleeping
  • VPAP: Variable Positive Airway Pressure (Similar to BiPAP)

What is Obstructive Sleep Apnea?

Obstructive Sleep Apnea (OSA) is a very serious sleep based disorder that causes one or more pauses in breathing or shallow breaths while sleeping. This is also the most common type of sleep apnea. Typically the pause in breathing will last for a few seconds, occurring 30 times or more per hour. Regular breathing will resume after that is commonly followed by a loud snort or chocking sound.

Sleep apnea is a chronic condition that disrupts your sleeping pattern. In the event that your breathing is shallow or paused, you will go from a deep sleep into a light sleep. Your reduced quality of sleep will result in tiredness and reduced energy levels the next day.

What is Central Sleep Apnea?

Central sleep apnea is less common than OSA, however they can occur together (complex sleep apnea). This type of sleep apnea is diagnosed when the area of your brain that controls breathing doesnt send the proper signals to your breathing muscles.

What is Complex (Mixed) Sleep Apnea?

Complex sleep apnea may develop in patients with OSA that are using a CPAP for their sleep therapy treatment. This condition is referred to as complex sleep apnea because its a combination of obstructive sleep and central sleep apneas.

CPAP Machines

CPAP is used to treat both obstructed and central sleep apnea patients. If you are diagnosed with either one, the most common option to begin your sleep therapy treatment is with a CPAP machine. Due to their incredible reliability of treating sleep apnea.

CPAP machines can only be set to a single pressure that remains throughout the entire night. For some with a higher prescribed pressure setting, the constant singular pressure makes it difficult to exhale against. Although, many CPAP machines offer a ramp feature that starts off with a reduced pressure setting and gradually builds to your prescribed pressure.

After using a CPAP machine for a couple of weeks, like many patients treatment may be uncomfortable and bothersome.  Before giving up on CPAP treatment in all, try adjusting the fitting of your mask or try different types of masks (nasal, full face, under nose). While also talking to your doctor about adjusting the machines settings to make your CPAP treatment more comfortable.

Before you decide that you cannot handle the constant airways pressure, certain machines such as those from Respironics offer c-flex comfort technology. Which acts like a BiPAP machine by offering pressure relief, but only up to 3 cm. Compared to a BiPAP that begins relief at 4 cm and above.

If you have a high pressure setting and continue to find that the constant airway pressure makes it difficult to exhale against or your oxygen levels remain low, then the use of a BiPAP or Auto-CPAP may be recommended by your doctor.

Popular CPAP Options:

BiPAP Machines

Unlike CPAP machines that deliver a constant airway pressure for the duration of treatments, BiPAP or BPAP machines deliver two prescribed pressure settings. You may enter them Inspiratory Positive Airway Pressure (IPAPA), which is the prescribed pressure setting during inhalation. While the Expiratory Positive Airway Pressure (EPAP) is the pressure setting during exhalation. The dual flow settings allow for more air to enter and leave your lungs.

Another difference between CPAP and BiPAP machines is the ability to set a breath timing feature. A BiPAP machines breathe timing feature measures the number of breaths per minute you should be taking. In the event that the time between breaths exceeds your set limit, the device will force you to breath by temporarily increasing the delivered airway pressure.

 A BiPAP Machine will Benefit You If:

  • You Have a High Pressure Setting
  • Low Oxygen Levels
  • CPAP has Failed to Provide Adequate Treatment
  • You are Diagnosed with a Lung Disorder such as COPD, or Certain Neuromuscular Disorders
  • You have a Cardiopulmonary Disorder such as Congestive Heart Failure

The results obtained from your CPAP titration sleep study will provide enough insight for your doctor or sleep technician to see whether a BiPAP is the way to go or not.

Popular BiPAP Options:

Auto-CPAP (APAP) Machines

APAP or an auto-CPAP machine offers a non-invasive sleep therapy treatment. They work by delivering a pressurized level of air through a mask, to keep your airways open and free of obstructions while sleeping.

APAP machines often delivers the highest level of comfort, its also like having to two breathing machines in one device. An APAP machine can be used in CPAP mode, which will deliver continuous positive airway pressure. Secondly it can be used in Auto-CPAP mode, which is when you set a minimum and maximum pressure that the machine automatically fluctuates between. Delivering the optimal level of pressure for each individual breath.

Popular APAP Options:

ASV Machines

If CPAP or BiPAP is not effective at treating your central or complex sleep apnea, then your doctor will recommend an adaptive servo-ventilation device (ASV). ASV devices deliver a fixed level of pressurized air during exhale (EPAP) just like a CPAP. But unlike a CPAP an ASV machine will adjust the amount of pressure during the inspiration cycle on a breath-by-breath analysis. Which results in a smoother breathing pattern. ASV is often the last option in treating central sleep apnea.

The major difference in ASV sleep therapy is that it offers support to regular breathing. This is achieved using an algorithm that detects significant pauses or reductions in breathing. When this occurs the device steps in with the right amount of support to maintain your breathing at 90% of the normal rate prior to decreased breathing. The algorithm goes off of a set rate of breaths per minute that you should regularly be taking. If your breathing rate drops below these rates, the ASV device will deliver to right amount of air pressure to keep your breathing properly.

An ASV Machine will Benefit You If:

  • You Have Central Sleep Apnea and a BiPAP Machine has Been Unable to Reduce the Occurrence of Apnea/Hypopnea Events
  • You Begin to Develop Mixed Sleep Apnea after using CPAP, BiPAP, or APAP
  • You Have Both Obstructed Sleep Apnea and Central Sleep Apnea (Mixed Sleep Apnea) with 50% of the Sleep Therapy Study Showing Central Apnea Events

Popular ASV Options:

VPAP Machines

A variable positive airway pressure or VPAP machine is a specialized form of positive airway pressure (PAP) that was developed to specifically treat central sleep apnea. VPAP’s provide two levels of continuous pressure, which is why a VPAP is also called a Bi-Level Device.

The reason it is called a “Variable” PAP is because it fluctuates between two levels of pressure (IPAP & EPAP) that can be adjusted manually or automatically (VPAP Auto) depending on the specific machine.

If you have a machine with automatic pressure adjustment, based off of a breath by breath analysis the machine will adjust the inhale and exhale pressure accordingly so that it is always providing the ideal pressure for you. Which makes breathing feel more natural and enables the device to more effectively meet your sleep therapy needs.

When using a non-auto adjusting VPAP, you simply enter your prescribed pressure settings during inhalation (IPAP) and exhalation (EPAP). The machine will then fluctuate between those two settings during treatment.

A VPAP is similar to an APAP, in the essence that it is prescribed if you are unable to effectively use or handle CPAP for your sleep therapy treatment.

A VPAP Machine will Benefit You If:

  • You are Prescribed Higher Pressure Settings
  • You have Central Sleep Apnea in Combination with COPD, Neuromuscular Conditions, or Chest Wall Deformity
  • Unable to Tolerate CPAP for Obstructed Sleep Apnea Treatment

Popular VPAP Machines:

  • S9 VPAP S
  • S9 VPAP Auto


Another important aspect to consider while weighing the different options for your sleep apnea treatment is whether or not you want to add humidity to your treatment. There are numerous benefits to using a humidifier in congruence with your PAP machine.

The increased airflow delivered with PAP therapy is greater than what your body is used to, which can lead to dryness of the nose and throat as well as nasal congestion. Research has also shown that nasal congestion can encourage mouth breathing, leading to further dryness. Experiencing these symptoms frequently can lead to you avoiding treatment in all, which can be resolved with the use of a heated humidifier.

If you also suffer from certain allergies or have a difficult time adapting to climate change, the use of a humidifier will greatly benefit you.

A major reason why humidifiers are so popular amongst patients is their incredible ability to greatly reduce rainout. Since the humidifier adds heat and moisture to the delivered airflow, the excess build up of moisture (rainout) can be effectively removed with a quick adjustment to the humidifiers heating settings. Using a heated tube such as those from Respironics will further reduce rainout.

The majority of CPAP, BiPAP, VPAP, and APAP devices will either come with a humidifier, or will offer an optional humidifier attachment.


We hope that this article was able to clarify the exact use of the varying PAP devices. The most important thing is to abide by your sleep therapy prescription, if you are prescribed a CPAP you will be allowed to and should only purchase a CPAP device. The same goes with other PAP treatment devices. If throughout your treatment you feel as if your current prescribed option is no longer effective, then talk to your doctor about getting tested for other treatment options.

What questions do you have about PAP treatment options? Leave a comment below and we would be more than happy to answer them for you!


Cory Luckner

Written by Cory Luckner

[Blog 2nd part here]