What Is CPAP Therapy

CPAP (continuous positive airway pressure) therapy is a medical treatment for obstructive sleep apnea that uses a bedside machine to pump pressurized air through a hose and mask into the upper airway, preventing its collapse during sleep. The device maintains a single set air pressure throughout the breathing cycle, acting as a pneumatic splint for the pharyngeal tissues. It is the first-line treatment for moderate to severe obstructive sleep apnea and is available only by prescription following a formal sleep study.

Obstructive sleep apnea produces repeated episodes of airway obstruction during sleep, each one triggering a cascade of oxygen desaturation, arousal from deeper sleep stages, and sympathetic nervous system activation. Over months and years, this nightly pattern contributes to systemic inflammation, endothelial dysfunction, insulin resistance, and sustained elevation of cortisol and catecholamines. The downstream consequences span multiple organ systems: accelerated atherosclerosis, increased incidence of atrial fibrillation, impaired glucose regulation, and hippocampal volume loss that correlates with memory decline.

From a longevity perspective, untreated sleep apnea compresses healthspan by degrading the restorative functions that depend on uninterrupted sleep architecture. Deep slow-wave sleep, during which growth hormone is pulsed and the glymphatic system clears metabolic waste from the brain, is fragmented by apnea-related arousals. REM sleep, essential for emotional processing and synaptic consolidation, is similarly disrupted. CPAP therapy restores normal breathing patterns, allowing the body to cycle through sleep stages without interruption and reducing the cumulative physiological burden that apnea imposes night after night.

The CPAP machine contains a motor that draws ambient air through a filter, compresses it to a clinician-prescribed pressure (measured in centimeters of water, typically between 4 and 20 cm H₂O), and delivers it through a heated or unheated hose to a fitted mask. The pressurized air enters the nasal passages (or mouth and nose, depending on mask type) and creates a column of air pressure in the pharynx. This positive pressure exceeds the collapsing force of the surrounding soft tissues, the tongue base, and the soft palate, holding the airway open mechanically.

When the airway remains patent, oxygen saturation stays stable throughout the night instead of cycling between normal levels and desaturations that can dip below 70 percent in severe cases. The elimination of apnea events removes the trigger for cortical micro-arousals, the brief awakenings that the brain initiates to restore breathing. Without these arousals, sleep progresses through its normal architecture: light N1 and N2 stages, deep N3 slow-wave sleep, and REM sleep, each occurring in roughly 90-minute cycles.

The downstream physiological effects of restored breathing during sleep are extensive. Sympathetic nervous system activity during sleep normalizes, reducing nocturnal blood pressure surges and lowering resting heart rate. Inflammatory markers such as C-reactive protein and interleukin-6 tend to decrease with consistent use. Insulin sensitivity improves as the stress hormone cascade calms. In the brain, improved oxygenation and restored glymphatic clearance during deep sleep reduce the accumulation of amyloid-beta and tau proteins associated with neurodegeneration. Modern auto-titrating CPAP (APAP) machines can adjust pressure breath by breath in response to detected flow limitation, reducing the average pressure delivered and improving comfort without sacrificing efficacy.

The evidence base for CPAP therapy in obstructive sleep apnea spans several decades of clinical research. Multiple randomized controlled trials have demonstrated that CPAP reduces daytime sleepiness, improves quality of life, and lowers blood pressure in patients with moderate to severe apnea. Observational cohort studies with follow-up periods exceeding ten years have found associations between consistent CPAP use and reduced rates of fatal and nonfatal cardiovascular events, including myocardial infarction and stroke. The relationship is dose-dependent: greater nightly hours of use correlate with larger reductions in cardiovascular risk.

However, the evidence is not uniformly straightforward. A large multicenter randomized trial (the SAVE trial) in patients with moderate to severe apnea and established cardiovascular disease found no significant reduction in the primary composite cardiovascular endpoint with CPAP compared to usual care, though compliance in the treatment arm averaged only 3.3 hours per night, well below the threshold many consider clinically meaningful. This trial highlighted the persistent challenge of adherence: real-world compliance rates vary widely, and the benefits of CPAP appear strongly dependent on consistent, adequate nightly use. Evidence for cognitive protection is supported by smaller trials and neuroimaging studies showing improvements in white matter integrity and hippocampal volume with treatment, but large-scale, long-duration randomized data are limited. The weight of evidence supports CPAP as a reliable treatment for the symptoms and many of the physiological consequences of sleep apnea, while acknowledging that the magnitude of long-term benefit depends heavily on how consistently the therapy is used.

Common side effects include nasal dryness, congestion, skin irritation from mask contact, and aerophagia (air swallowing that causes abdominal bloating or gas). Claustrophobia or general mask discomfort leads a significant minority of users to abandon therapy. Poorly fitting masks can cause air leaks that reduce efficacy and disturb sleep. In rare cases, CPAP use has been associated with complex sleep apnea, a condition where central apnea events emerge after obstructive events are treated. Machines require regular cleaning to prevent bacterial or mold growth in the humidifier chamber, tubing, and mask. A healthcare provider experienced in sleep medicine should oversee device setup, pressure titration, and ongoing management.