An ASV (adaptive servo-ventilation) machine is a type of breathing device used during sleep that automatically adjusts air pressure breath by breath to match your breathing pattern. Unlike standard sleep apnea machines that deliver a fixed or preset level of air pressure, an ASV machine uses a built-in algorithm to monitor your breathing in real time and respond to changes as they happen. It’s primarily prescribed for central sleep apnea, a condition where the brain intermittently fails to signal the muscles to breathe, rather than the more common obstructive type where the airway physically collapses.
How an ASV Machine Works
Every ASV machine continuously tracks two things while you sleep: your breathing rate and the volume of air you move with each breath (called minute ventilation). Using these measurements, the device builds a profile of your normal breathing and sets a target ventilation level. When your breathing weakens or pauses, the machine increases pressure support to keep air flowing. When your breathing normalizes, it backs off. This all happens automatically, breath by breath, throughout the night.
The machine delivers two layers of pressure. A baseline pressure keeps your upper airway open, similar to what a standard CPAP does. On top of that, it adds variable support during each inhale, adjusting the boost depending on how much help your lungs need at that moment. Some newer models, like the ResMed AirCurve 11 ASV, also auto-adjust that baseline pressure so both layers adapt independently to your needs.
How ASV Differs From CPAP and BiPAP
All three devices push pressurized air through a mask to help you breathe during sleep, but they differ in how smart that pressure delivery is.
- CPAP delivers one continuous, fixed pressure all night. It’s the first-line treatment for obstructive sleep apnea and works well when the problem is a collapsing airway.
- BiPAP uses two preset pressure levels, one for inhaling and a lower one for exhaling. This can feel more comfortable for people who struggle with CPAP, and it helps those who need higher pressures.
- ASV goes further by constantly recalculating and adjusting pressure support based on your real-time breathing. Nothing is truly “preset” in the same way.
The core distinction is that CPAP and BiPAP are reactive in a limited sense. They deliver what they’re programmed to deliver. ASV is genuinely adaptive, learning your breathing rhythm and intervening only when your effort drops below what it should be. This makes it far more effective for central apneas, where the issue isn’t a blocked airway but an absent breathing signal.
Who Needs an ASV Machine
ASV was originally developed for people with Cheyne-Stokes breathing, a pattern of gradually deepening and then shallowing breaths followed by complete pauses. This pattern is common in people with heart failure. Since then, its use has expanded to several related conditions:
- Central sleep apnea caused by stroke, kidney failure, neurological conditions, or opioid use
- Complex sleep apnea (also called treatment-emergent central sleep apnea), where central apneas appear or worsen after someone starts CPAP therapy for obstructive sleep apnea
- Mixed sleep apnea, which involves both obstructive and central events during the same night
ASV is typically suggested only after CPAP or BiPAP has been tried and either failed to control the apneas or proved difficult to tolerate. Standard CPAP is largely ineffective at correcting central sleep apnea and is often poorly tolerated in these patients, which is a major reason ASV exists.
How Effective ASV Is
For the right patients, ASV significantly outperforms CPAP. In a controlled trial of people with complex sleep apnea, ASV reduced the apnea-hypopnea index (a measure of how many breathing disruptions occur per hour) from roughly 37 events per hour down to about 4.7 after a single titration night. CPAP, by comparison, only brought that number down to 14.1. After 90 days, the gap held: ASV patients averaged 4.4 events per hour versus 9.9 for CPAP users. Central apneas specifically dropped to near zero on ASV (0.7 per hour) while remaining significantly higher on CPAP (4.8 per hour).
These numbers matter in practical terms. Fewer breathing disruptions mean fewer awakenings, more time in deep sleep, and less strain on the heart and cardiovascular system overnight.
The Heart Failure Warning
There is one critical safety concern with ASV. A large trial called SERVE-HF, involving 1,325 patients, found that ASV actually increased the risk of death in people who had heart failure with reduced pumping ability (specifically, a weakened left ventricle). Patients in the ASV group experienced 28% higher all-cause mortality and 34% higher cardiovascular mortality compared to the control group, with no improvement in quality of life.
Researchers speculate this may happen because central sleep apnea in heart failure patients could actually be a protective adaptation, and suppressing it with ASV might do more harm than good. The positive pressure from the device may also reduce the amount of blood the heart can pump by limiting blood flow back to the heart. As a result, ASV is now contraindicated for people with heart failure and reduced ejection fraction. If you have heart failure, your sleep specialist will evaluate your heart function before considering ASV.
What Getting Started Looks Like
Before you use an ASV machine at home, you’ll typically undergo a titration study in a sleep lab. During this overnight session, a technician monitors your sleep while adjusting the machine’s settings to find the pressure ranges that best control your apneas. The device has several configurable parameters: the baseline expiratory pressure, the minimum and maximum amount of extra support during inhalation, and the backup breathing rate the machine uses if you stop breathing entirely.
Once your settings are dialed in, you take the machine home and use it nightly, just like a CPAP. Modern ASV machines connect to cloud-based platforms that let your provider monitor your data remotely, review reports on how many events you’re having, and even troubleshoot issues without requiring an office visit. Patient-facing apps also give you feedback on your own therapy, which can help with building the habit.
Adherence and Side Effects
Sticking with ASV therapy is a real challenge for many people. In one study of veterans prescribed ASV, only 55% met minimum adherence criteria. Interestingly, patients whose apnea was predominantly obstructive (rather than central) tended to have worse adherence, possibly because the variable pressure delivery feels less intuitive when the underlying problem is airway collapse rather than absent breathing signals.
The side effects are similar to other positive airway pressure devices: nasal dryness, mask discomfort, skin irritation from the mask, and occasionally a sensation of difficulty exhaling against the pressure. Most ASV machines include heated humidifiers and pressure relief features to address these issues. Finding the right mask fit is often the single biggest factor in whether someone sticks with therapy long term.
ASV machines are more expensive than CPAP or BiPAP devices, and insurance coverage can vary. Because ASV is considered a specialized therapy, most insurers require documentation that simpler treatments were tried first and that central or complex apnea has been confirmed through a sleep study.