How Does a CPAP Machine Work to Treat Sleep Apnea?

These machines provide a constant flow of pressurized air

If you have been told that you need to use a continuous positive airway pressure (CPAP) machine to treat your sleep apnea, you may wonder how a CPAP machine works. CPAP machines relieve snoring and sleep apnea with pressurized air and what special considerations may be necessary if you have central sleep apnea.

This article discusses sleep apnea machines, including the history of CPAP, how CPAP works, and side effects of CPAP treatment for sleep apnea.

Man with sleep apnea and CPAP in bed
nicolesy / E+ / Getty Images

The History of CPAP Machines

CPAP machines have been used for the treatment of sleep apnea since 1981. Dr. Colin Sullivan first recognized the potential benefit of a constant, pressurized airflow created with the motor of his mother’s vacuum cleaner. Sleep apnea had previously required a tracheostomy to resolve, bypassing the collapse of the throat.

Now, with a fitted mask, tubing, and a machine that could generate air pressure, he found, the disorder resolved. It was a remarkable discovery—and one met with initial skepticism. It would take five years before the devices became more widely available commercially.


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This video has been medically reviewed by Sanja Jelic, MD.

How Does A CPAP Work?

Modern CPAP machines work based on the same principles as the initial devices developed by Dr. Sullivan. The pressures are now generated with smaller, quieter motors. Nevertheless, room air (not oxygen) is taken in through a filter and pressurized according to settings prescribed by your sleep specialist.

Sleep apnea machines are set to deliver pressure from 4 centimeters of water pressure (CWP) up to a maximum of 25 CWP. This air is often passed through a heated humidifier and delivered via tubing to the mask interface.

The constant flow of pressurized air creates a cushion along the upper airway. Some have described it as a pneumatic (air) splint that keeps the throat from collapsing. This prevents the soft palate, uvula, and tongue from shifting into the airway. It reduces the vibration that creates the sound of snoring.

It may also relieve swelling within the nose and clear out mucus from along the airway. By supporting the airway, breathing normalizes and sleep quality improves as fragmented sleep resolves. Oxygen levels can be maintained. The serious consequences of sleep apnea can be averted.

Automatic CPAP machines vary slightly in that they can detect a collapse of the airway by measuring resistance and react by increasing the pressure as needed during the night to further resolve the sleep apnea. These devices will also test lower pressures and adjust downward if possible.

Side Effects and Risks

Some inevitably worry about the consequences of seemingly artificial or “unnatural” CPAP therapy. Fortunately, there are surprisingly few side effects.

Still, in order to avoid side effects and ensure successful use, it is important that you have support when you first begin using a CPAP machine. Early communication with your healthcare team so they can help you troubleshoot problems is essential.

Two of the most common problems associated with CPAP use are an ill-fitting mask and dry mouth. These can be alleviated with mask shape adjustments and humidification. Similarly, air leaks, challenges for bed partners, and air swallowing (aerophagia) are all commonplace and can be addressed to avoid discontinuation.

CPAP therapy does not worsen asthma or chronic obstructive pulmonary disease (COPD). Rather than causing a stroke, therapy actually reduces the risk of having one.

The nasal sinuses and inner ears are not typically impacted by the treatment, though case reports suggest it is possible for small amounts of pressure to be transduced across the tissues of the face.

There is some evidence that an overly tight or restrictive mask could affect the growth of the mid-face in children, but treatment can be monitored and adjusted to avoid this.

Treatment of Central Sleep Apnea

It is important to review the special case of a related condition. Central sleep apnea is defined by pauses in breathing that are characterized by a lack of effort to breathe, rather than a collapse of the airway. It most often occurs secondary to stroke, congestive heart failure, or narcotic or opioid medication use.

It can also occur in response to CPAP therapy itself, in a condition called complex sleep apnea. In central sleep apnea, it is sometimes necessary to consider other therapy modalities.

In particular, bilevel therapy is sometimes necessary. Bilevel therapy delivers two pressures, one to breathe in and a lower pressure to breathe out, and can adjust the pressure on the fly to compensate for breathing pauses. This timed mode inflates the lungs to ensure a minimum number of breaths occur.

In addition, a more sophisticated level of treatment called adaptive (or auto) servo-ventilation can be used. This allows control of breath rate, volume, the timing of the delivered airflow, and other variables in those who have more significantly compromised breathing.

A Word From Verywell

Using a CPAP machine can take some time to get used to and optimize. Overall, you're likely to find that, given the benefits of CPAP therapy, its side effects are minimal and easily overcome.​ Fortunately, you don’t need to know a lot about how your machine works.

Be sure to check in with your healthcare provider if you're uncomfortable in any way: a well-qualified, board-certified sleep specialist will be able to assess your health, review your sleep study, and select the optimal treatment methods to improve your condition.

Frequently Asked Questions

  • How many hours should you use a CPAP overnight?

    Ideally, you should use a CPAP machine for sleep apnea for the entire duration of your sleep. However, many people have difficulty using it all night. Research suggests the sleep apnea machine should be used for at least six hours a night to reap the benefits.

  • Does using CPAP weaken the lungs?

    No, CPAP machines do not weaken the lungs. If you experience a burning sensation in your lungs after using a sleep apnea machine, it is likely because the air is too dry. Talk to your healthcare provider about using a heated humidifier with your CPAP.

  • Which is better BiPAP or CPAP?

    It depends on the person. CPAP machines deliver pressurized air continuously, while BiPAP machines have two levels of pressure, on for inhaling and the other for exhaling. People who need higher air pressure to relieve their apnea may benefit from BiPAP instead of CPAP.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Dinh-thi-dieu H, Vo-thi-kim A, Tran-van H, Duong-quy S. Efficacy and adherence of auto-CPAP therapy in patients with obstructive sleep apnea: a prospective study. Multidiscip Respir Med. 2020;15(1):468. doi:10.4081/mrm.2020.468

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  4. NIH National Heart, Lung, and Blood Institute. CPAP: also known as continuous positive airway pressure.

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  6. Roberts SD, Kapadia H, Greenlee G, Chen ML. Midfacial and dental changes associated with nasal positive airway pressure in children with obstructive sleep apnea and craniofacial conditionsJ Clin Sleep Med. 2016;12(4):469–475. doi:10.5664/jcsm.5668

  7. Sands SA, Owens RL. Congestive heart failure and central sleep apneaCrit Care Clin. 2015;31(3):473‐495. doi:10.1016/j.ccc.2015.03.005

  8. Akamine RT, Grossklauss LF, Moreira GA, et al. Treatment of sleep central apnea with non-invasive mechanical ventilation with 2 levels of positive pressure (bilevel) in a patient with myotonic dystrophy type 1Sleep Sci. 2014;7(2):117–121. doi:10.1016/j.slsci.2014.09.002

  9. Masa JF, Corral-Peñafiel J. Should use of 4 hours continuous positive airway pressure per night be considered acceptable compliance? Eur Respir J. 2014;44(5):1119–20. doi:10.1183/09031936.00121514

  10. Cleveland Clinic. CPAP machine.

  11. American Association of Sleep Technologists. BiPAP™ (Bilevel positive airway pressure) or CPAP Therapy?

Additional Reading

By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.