How a CPAP machine actually works: pressurized air, not oxygen

Part of the series: The Complete CPAP Guide

The most common misconception in sleep therapy, corrected: a CPAP is an air splint for your airway, and the physics is almost embarrassingly simple.

Start with the misconception, because it changes purchases: a CPAP machine does not deliver oxygen. It takes ordinary room air — the same 21% oxygen you're breathing now — filters it, and delivers it at gentle pressure. That pressure is the entire therapy: in obstructive sleep apnea the airway's soft tissue collapses during sleep, and continuous positive airway pressure holds it open mechanically, the way air pressure keeps a bounce house standing. It's a splint made of air.

The machinery is correspondingly simple: a small, precisely governed blower, a filter, usually a heated humidifier chamber, and a pressure sensor closing the loop. Pressures are measured in centimeters of water (cmH2O) — most prescriptions land somewhere between 4 and 20 — and the engineering achievement in a modern machine isn't force, it's finesse: holding pressure steady against your breathing, quietly enough (mid-20s dBA for current bedside units) that the mask seal is louder than the motor.

This is also why CPAP and oxygen therapy are different aisles entirely. An oxygen concentrator changes what you breathe; a CPAP changes whether your airway stays open to breathe it. They treat different problems — hypoxemia versus obstruction — and some people with both conditions use both at once, under a prescriber's direction. If you arrived here shopping for oxygen, our oxygen concentrator guide covers that side of the house.

Everything else in the sleep catalog is a variation on this theme: auto-titrating machines vary the pressure intelligently, bi-level machines use two pressures, travel machines shrink the blower. But the core mechanism — filtered room air, held at prescribed pressure, splinting an airway that would otherwise close — is the whole trick. Understanding that makes every spec sheet in the category suddenly legible.

This article is general health information, not medical advice, and doesn’t replace evaluation by your own physician. Talk to a doctor about anything specific to your own diagnosis or treatment.

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How a CPAP machine actually works: pressurized air, not oxygen

Part of the series: The Complete CPAP Guide

The most common misconception in sleep therapy, corrected: a CPAP is an air splint for your airway, and the physics is almost embarrassingly simple.

This article is general health information, not medical advice, and doesn’t replace evaluation by your own physician. Talk to a doctor about anything specific to your own diagnosis or treatment.