What Is an ASV Machine?

Joseph Krainin, M.D.

Adaptive Servo-Ventilation (ASV): Indications, Requirements, and Risks

asv machine

Sleep apnea, whether obstructive, central, or complex, is a common sleeping disorder affecting millions of men and women worldwide. It can impair quality of life as well as increase the risk for a number of dangerous medical consequences. People suffering from sleep apnea have problems breathing while sleeping but the root cause of the breathing problem varies depending on the type of sleep apnea.

Sleep Apnea Overview and Types

Obstructive sleep apnea (OSA) results when the throat muscles collapse and block the upper airway while sleeping. Central sleep apnea (CSA) is neurologically-mediated; it is essentially a problem where the brain does not tell the lungs to breathe enough. 

Complex sleep apnea is defined in various ways. One definition is that the diagnostic sleep study shows a combination of obstructive and central sleep apnea. Another scenario that is commonly referred to as complex sleep apnea is when the patient starts out with obstructive sleep apnea but, on initiation of CPAP, central sleep apnea emerges. Sometimes this is felt to be because the CPAP pressure is too high but in other cases even low CPAP pressures are associated with "treatment-emergent" CSA. There is controversy about whether the CPAP causes CSA or merely treats the OSA and reveals an underlying component of CSA that was initially not apparent on the diagnostic sleep study

How Sleep Apnea is Treated

The best way to treat moderate or severe obstructive sleep apnea is by using positive airway pressure (PAP). PAP machines treat OSA by delivering constant air pressure to keep patients' airways open as they sleep.

Patients can breathe better during sleep, reducing daytime sleepiness and cognitive impairment, improving their quality of life, and protecting their health. A mask is put under or around a patient's nose (and sometimes mouth) to deliver air pressure with a hose connecting it to the PAP machine.

PAP can be provided as:

  • Continuous positive airway pressure (CPAP)
  • Auto-titrating positive airway pressure (APAP)
  • Bi-level positive airway pressure (BPAP or BiPAP)
  • Auto-titrating bilevel positive airway pressure (Auto-BPAP or Auto-BiPAP)
  • Bilevel positive airway pressure with a backup rate (BPAP S/T or BiPAP S/T)
  • Adaptive servo-ventilation (ASV).

CPAP machines are basic machines that deliver continuous air pressure, while BiPAP has two different settings for inhalation and exhalation.

While CPAP and BiPAP work well in the case of obstructive sleep apnea, people suffering from central and complex sleep apnea usually get the most benefit from using an ASV machine.  

What is Adaptive Servo-Ventilation (ASV)?

ASV is a non-invasive PAP machine that monitors a person's breathing throughout the night. Unlike the simpler machine versions, ASV can customize the delivery of air pressure in response to the specific breathing rhythm of the sleep apnea patient. 

ASV uses innovative technology to increase air pressure when breathing is off due to sleep apnea events and reduces the air pressure when breathing stabilizes (see cartoon below). ASV machines use complex algorithms to regulate and personalize the amount of air pressure released in the airways of a person suffering from sleep apnea.

Such customization of an individual's breathing pattern provides added comfort and effectiveness to the person suffering from central sleep apnea while regulating their breathing pattern.

how ASV works

What Are the Differences between CPAP and ASV?

Both CPAP and ASV are PAP machines designed to relieve breathing problems in sleep apnea patients. They differ in the degree of flexibility while delivering air pressure.

While CPAP machines deliver a consistent stream of air pressure to remove any blockage in obstructive sleep apnea patients' airways, ASV machines provide a customized stream of air pressure.

The adaptive servo-ventilation technology that powers ASV machines helps synchronize air pressure release with a person's breathing. It automatically increases air pressure when the person's breathing becomes shallow, while reducing the air pressure when the breathing stabilizes.

The Benefits of Using ASV in Central Sleep Apnea Conditions 

    cheyne stokes respiration

    Indications for Adaptive Servo-Ventilation

    Sleep doctors often recommend starting treatment for all types of sleep apnea with a simple machine like a CPAP. This recommendation is often driven by insurance companies who will not pay for a more advanced machine without trying and proving that a less expensive PAP machine failed to sufficiently treat the patient's sleep-disordered breathing. ASV is often used if the patient has a component of central sleep apnea and fails a reasonable trial of CPAP and/or BiPAP. However, having central sleep apnea or complex sleep apnea on the initial diagnostic sleep study where > 50% of the apneas are central/mixed in nature can an indication to use ASV as an initial treatment. Due to the high cost of ASV machines, insurance policies often dictate which patients are a candidate for them and what criteria need to be met before an ASV machine will be dispensed to a patient.   

    Who Benefits from ASV Machines?

    Although CPAP is effective when dealing with obstructive sleep apnea, doctors recommend using ASV machines in the following situations:

    • For people who suffer from central sleep apnea and who have failed to get adequate relief from CPAP and/or BiPAP.
    • For patients who have developed complex sleep apnea defined as CPAP-induced central sleep apnea.
    • For patients who demonstrate at least 50% of central apnea events on the diagnostic night of an in-lab sleep study.
    • For patients with opiod-related central sleep apnea. Notably, ASV therapy has been shown to provide better outcomes than other treatment modalities for this diagnosis.

    What are the Requirements to Qualify for ASV?

    Doctors ordinarily treat obstructive sleep apnea using CPAP and BiPAP machines. However, when patients exhibit central respiratory events as >50% of their total abnormal breathing events or have evidence of ongoing complex sleep apnea despite consistent CPAP or BiPAP use, doctors may recommend ASV machines.

    For insurance coverage purposes, the primary requirement to qualify for ASV is documenting that CPAP/BiPAP failed to treat the central component of sleep apnea. This may require an in-lab CPAP/BiPAP titration or documentation from CPAP/BiPAP machine downloads in conjunction with an attestation from a sleep physician. In some cases, a full-night ASV titration is then performed.

    What are the Adaptive Servo-Ventilation (ASV) Risks? 

    While ASV therapy is effective in moderate to severe cases of central and complex sleep apnea, there are risks to using adaptive servo-ventilation for people with certain underlying chronic heart problems. In such cases, the use of ASV can has actually been associated with increased mortality.

    In 2015, ResMed, a global manufacturer of CPAP and ASV devices, issued a field safety notice based on the results of new research, stating that patients with chronic heart failure with reduced left ventricular ejection fraction (LVEF less than or equal to 45%) and, having central sleep apnea symptoms, have a 33.5% higher risk of cardiovascular death when treated with ASV therapy, compared to those not on it.

    The American Academy of Sleep Medicines advises assessing sleep apnea patients for heart failure symptoms before treating them with ASV, and communicating the risks of ASV to patients before starting the therapy.

    Are There Alternatives to ASV?

    For patients with residual problematic central sleep apnea despite the use of CPAP or BiPAP or for those who do not qualify for ASV, the following alternatives to ASV are available: 

    • Adding supplemental oxygen therapy to CPAP or BiPAP. Typically an oxygen concentrator is used and the oxygen is directly connected to the patient's PAP machine through a designated oxygen port. Supplemental oxygen can be an effective therapy for the central component of the patient's sleep apnea. 
    • BiPAP S/T: this is a form of BiPAP with a backup respiratory rate. In the event that the patient has a central apnea, i.e. completely forgets to breathe, the BiPAP S/T will provide breaths for the patient. In this author's experience, BiPAP S/T tends to not be as effective or well-tolerated as ASV.  Another downside to BiPAP S/T is that there are currently no available auto-titrating models of it so a full-night, in-lab BiPAP S/T titration sleep study is necessary to properly setup the machine for the patient. 

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