CPAP stands for continuous positive airway pressure, and it’s a breathing machine used primarily to treat obstructive sleep apnea. The device delivers a steady stream of pressurized air through a mask while you sleep, keeping your airway open so you don’t stop breathing throughout the night. It’s the most widely recommended treatment for sleep apnea and has been in use for decades.
How CPAP Works
During sleep apnea, the soft tissue at the back of your throat relaxes and collapses inward, partially or fully blocking your airway. This causes you to stop breathing repeatedly, sometimes dozens of times per hour, which drops your blood oxygen levels and fragments your sleep.
A CPAP machine solves this by acting as a pneumatic splint. It pushes a constant flow of air through a hose and mask into your airway, creating just enough pressure to hold the tissue open. Think of it like inflating a balloon: the air pressure inside keeps the walls from caving in. Most machines deliver pressure in a range of 4 to 20 centimeters of water pressure (cm H2O), with the average setting for sleep apnea landing around 9 cm H2O. Your specific pressure is determined during a sleep study or through an auto-adjusting machine that finds the right level on its own.
Who Needs CPAP
Sleep apnea severity is measured by how many times per hour your breathing stops or becomes dangerously shallow, a number called the apnea-hypopnea index (AHI). An AHI of 5 to 14 is mild, 15 to 30 is moderate, and above 30 is severe. The American Academy of Sleep Medicine recommends CPAP as the preferred treatment for moderate to severe sleep apnea and considers it an option for mild cases as well.
Beyond reducing breathing interruptions, CPAP is specifically indicated for improving daytime sleepiness, improving quality of life, and helping lower blood pressure in people who have both sleep apnea and hypertension. In clinical settings, CPAP has been shown to bring the AHI down dramatically. One study of patients with moderate to severe sleep apnea (average AHI of 56) found that proper CPAP use reduced the index to about 4, essentially bringing breathing events down to a near-normal level.
Cardiovascular and Health Benefits
Untreated sleep apnea places serious strain on your heart and blood vessels. It has been linked to a 140% increased risk of heart failure, a 60% increased risk of stroke, and a 30% increased risk of coronary heart disease. CPAP can partially reverse that damage, though the benefit depends on your risk profile.
Research presented through the European Society of Cardiology found that in patients with high-risk obstructive sleep apnea, CPAP lowered the risk of heart attack, stroke, and cardiovascular death by about 17%. Among high-risk patients who did not feel excessively sleepy during the day, the reduction was even larger, around 24%. The cardiovascular benefits appear most clearly in people who have underlying heart risk factors or hypertension alongside their sleep apnea.
What the Equipment Looks Like
A CPAP setup has a few basic parts: the machine itself (roughly the size of a lunchbox), a flexible air hose, and a mask. Inside the machine, a small motor draws in room air, pressurizes it, and sends it through the tubing. Most machines also include a built-in humidifier that warms and moistens the air before it reaches you, which helps prevent dryness in your nose and throat. Air filters inside the machine trap dust and pet dander.
The mask is the part most people have to experiment with. There are three main styles:
- Nasal pillows sit just at the entrance of your nostrils. They’re the smallest and lightest option, good for people who feel claustrophobic.
- Nasal masks cover your entire nose but not your mouth. These are the most common choice.
- Full-face masks cover both your nose and mouth. They’re necessary if you breathe through your mouth at night.
Each mask has a frame, a cushion that seals against your skin, and headgear straps to hold it in place. Getting the right fit matters more than most people expect, because a poorly fitting mask causes air leaks, skin irritation, and discomfort that makes you less likely to use the machine.
CPAP vs. BiPAP vs. APAP
CPAP delivers one fixed pressure all night long, both when you inhale and when you exhale. Some people find it uncomfortable to breathe out against that constant pressure, which is where the alternatives come in.
BiPAP (bilevel positive airway pressure) uses two different pressure settings: a higher one when you inhale and a lower one when you exhale. This can feel more natural and is sometimes prescribed for people who need very high pressures or who have other breathing conditions alongside sleep apnea.
APAP (automatic positive airway pressure) continuously adjusts the pressure throughout the night based on what your airway needs at any given moment. If you roll onto your back and your airway narrows, the pressure increases. If you’re sleeping in a position where your airway stays open easily, the pressure drops. APAP is increasingly popular because it adapts to changing conditions rather than blasting one steady pressure all night.
Common Side Effects
CPAP is safe, but the adjustment period can be frustrating. The most common complaints are dry mouth, dry nasal passages, and skin irritation where the mask sits. Using the built-in humidifier and making sure your mask fits properly addresses most of these. If the mask leaves red marks, rashes, or pressure sores on your nose or cheeks, you likely need a different size or style.
Aerophagia, or swallowing air, is another frequent issue. The pressurized air can end up in your stomach instead of your lungs, causing bloating, gas, and belching. This tends to happen when the pressure is set too high or when air leaks from the mask cause you to swallow reflexively. Switching to an APAP machine, which uses only as much pressure as needed, can help. Chin straps can also reduce air swallowing by keeping your mouth closed.
Sticking With It
The biggest challenge with CPAP isn’t the technology. It’s using it consistently. Adherence is typically defined as wearing the mask at least four hours per night on at least 70% of nights. By that standard, studies report adherence rates between 30% and 60%, though some populations do better. One large study found that about 68% of patients were adherent at six months, dropping to roughly 59% at one year.
The people who stick with CPAP tend to notice the benefits quickly: less daytime sleepiness, fewer morning headaches, better concentration, and partners who no longer complain about snoring. If you’re struggling with comfort, small changes often make a significant difference. Trying a different mask style, adjusting your humidifier settings, or switching from a fixed-pressure CPAP to an auto-adjusting machine can turn a miserable experience into a manageable one.