A CPAP machine delivers a steady stream of pressurized air through a mask while you sleep, keeping your airway open so you can breathe without interruption. It’s the most common treatment for obstructive sleep apnea, a condition where the soft tissues in your throat relax and collapse during sleep, blocking airflow dozens or even hundreds of times per night.
How It Keeps Your Airway Open
When you fall asleep, the muscles in your throat naturally relax. For people with sleep apnea, that relaxation lets the tongue, uvula, and soft palate shift far enough backward to partially or fully block the airway. Each blockage triggers a brief awakening (often so short you don’t remember it) as your brain jolts you back to a breathing state. This cycle can repeat 30 or more times per hour in severe cases.
A CPAP machine solves this by acting like a pneumatic splint. The continuous flow of pressurized air pushes against those soft tissues, holding them in place so they can’t collapse into the airway. Your breathing stabilizes, the repeated awakenings stop, and your body can cycle through normal sleep stages uninterrupted.
What It Feels Like to Use One
A CPAP setup has three main parts: a small bedside unit that pressurizes room air, a hose, and a mask. You put the mask on before sleep, turn the machine on, and breathe normally. The air pressure is typically set somewhere between 4 and 20 centimeters of water pressure, depending on how severe your apnea is.
Most people notice two things immediately: the sensation of air flowing into their nose or mouth, and the sound of the machine (modern units are quiet, roughly comparable to a white noise machine). Exhaling against the incoming air can feel unnatural at first, which is why most machines include comfort features to ease the transition.
A “ramp” setting gradually increases pressure over the first 30 to 45 minutes, letting you fall asleep at a lower, more comfortable pressure before the machine reaches its full therapeutic level. Many machines also offer expiratory pressure relief, which briefly drops the air pressure each time you breathe out. This makes exhaling feel more natural without reducing the pressure needed to keep your airway open when you inhale. For people who need high pressure settings, expiratory pressure relief can make the difference between tolerating the machine and abandoning it.
Types of Positive Airway Pressure Machines
The standard CPAP delivers one fixed pressure all night long. It’s effective, but it treats every breath the same whether your airway is fully obstructed or wide open. Two variations address this limitation:
- APAP (auto-adjusting): Monitors your airflow in real time and raises or lowers pressure as needed. Your doctor prescribes a range (often 4 to 20 cmH2O), and the machine finds the right pressure moment to moment. This means you get lower pressure when you’re sleeping on your side with a clear airway and higher pressure when you roll onto your back and your airway narrows.
- BiPAP (bilevel): Delivers two separate pressures, one for inhaling and a lower one for exhaling. This is particularly useful for people who need very high pressure or who have other breathing conditions alongside sleep apnea. BiPAP machines can reach peak pressures of 25 cmH2O, higher than standard CPAP.
Your doctor determines which type you need based on your sleep study results and how your body responds to treatment.
Choosing the Right Mask
The mask is the part that makes or breaks the experience for most people. There are three main styles, each suited to different situations.
Nasal pillow masks are the smallest option. Two small cushions sit just inside or at the opening of your nostrils. They leave your field of vision completely open, work well with glasses, and are a good fit if larger masks make you feel claustrophobic or if you have facial hair that prevents a good seal with other styles.
Nasal masks cover the entire nose but not the mouth. They distribute pressure over a wider area, which makes them more comfortable at higher pressure settings. They also tend to stay in place better if you move around a lot during sleep.
Full-face masks cover both the nose and mouth. These are the go-to option if you breathe through your mouth at night or have chronic nasal congestion that makes nose-only breathing unreliable. They’re bulkier, but for mouth breathers, the other styles simply won’t deliver air effectively.
How Quickly You’ll Notice a Difference
Some improvements happen fast. Even one night of CPAP use can lead to noticeably better attention and alertness the next day. Many people describe their first morning after using CPAP as the best they’ve felt in years, though this varies. Reduced daytime sleepiness and sharper thinking are among the earliest benefits.
Other changes build gradually over weeks or months. The goal of treatment is to bring your apnea-hypopnea index (the number of breathing interruptions per hour) below five, down from what it was during your sleep study. For someone with severe apnea registering 40 or 50 events per hour, that’s a dramatic reduction that plays out across many systems in the body over time.
Effects on Blood Pressure and Heart Health
Every time your airway collapses during sleep, your blood oxygen drops and your body releases stress hormones. Repeated hundreds of times nightly, this puts significant strain on the cardiovascular system. Untreated sleep apnea is strongly linked to high blood pressure, heart disease, and stroke.
CPAP therapy produces a modest but real reduction in blood pressure, averaging about 3 mmHg based on pooled research. That number sounds small, but at a population level, even a 2 to 3 mmHg reduction in blood pressure translates to meaningful decreases in heart attack and stroke risk. The effect tends to be slightly larger in people with more severe apnea.
The long-term picture is more striking. A large systematic review published in The Lancet Respiratory Medicine found that people using positive airway pressure therapy had a 37% lower risk of dying from any cause and a 55% lower risk of dying from cardiovascular disease compared to those who didn’t use it. The benefit increased with more consistent use.
Effects on Blood Sugar and Metabolism
Sleep apnea and type 2 diabetes frequently overlap, and there’s been hope that treating apnea would improve blood sugar control. The evidence is mixed. CPAP therapy does appear to improve insulin sensitivity, meaning your body becomes better at using the insulin it produces. However, this doesn’t consistently translate into lower blood sugar readings or better long-term glucose markers. A meta-analysis in BMJ Open Respiratory Research concluded that CPAP is unlikely to produce clinically meaningful improvements in blood sugar control for people with both sleep apnea and type 2 diabetes, though the insulin sensitivity benefit may still matter for metabolic health more broadly.
What Compliance Looks Like
CPAP only works when you use it, and insurance companies track usage to verify compliance. The standard set by Medicare (and followed by most insurers) requires a minimum of 4 hours per night on at least 70% of nights within a consecutive 30-day period. In practical terms, that means wearing your CPAP for at least 4 hours on 21 out of 30 nights. You have 90 days from the time you receive the equipment to meet this threshold.
Modern CPAP machines track your usage automatically and transmit the data wirelessly. If you fall short of the compliance window, your insurance may stop covering the equipment. But the compliance standard is really a floor, not a goal. Four hours covers only part of your sleep. The cardiovascular and cognitive benefits scale with usage, so wearing it all night, every night, delivers the most benefit.