CPAP Therapy

APAP (Automatic Positive Airway Pressure): A Historical Perspective

Obstructive Sleep Apnea (OSA) is commonly treated with positive airway pressure therapy (PAP). Traditionally, optimal treatment pressure for sleep-disordered breathing was determined through manual titration of the machine by a sleep professional during a polysomnography (sleep study). Now, the emergence of alternative methods for determining optimal PAP, like auto-titrating PAP (APAP) is seeing immense growth.

Unattended auto-titrating positive airway pressure titration seems to be a cost-effective and simple method of OSA treatment.

What is Automatic Positive Airway Pressure?

If you’ve received a sleep apnea diagnosis, automatic positive airway pressure (APAP) probably sounds familiar to you since your doctor may have even prescribed this treatment to you. APAP is one of three primary types of PAP therapy.

The three primary types of PAP therapy are:

  1. Continuous positive airway pressure (CPAP)
  2. Bilevel, or variable positive airway pressure (BPAP or VPAP)
  3. Automatic positive airway pressure (APAP)

All of these forms of PAP therapy typically involve the use of a machine with a connected tube and mask you wear while sleeping as it delivers air generated by the machine. PAP therapy is the delivery of pressurized air to your airway (nose, mouth or nose and mouth) to help you breathe.

While CPAP therapy provides you with one continuous pressure air level, APAP will automatically adjust the air level pressure needed to meet your specific breathing needs. These needs can often change during the night as you move in and out of the various sleep stages.

The APAP device constantly measures the resistance that’s present in your breathing and knows when it should decrease pressure as your upper airway becomes stable and increase the pressure when an airway event is sensed such as:

  • An apnea
  • Flow limitation
  • A hypopnea
  • Snoring

Unlike CPAP devices, APAP devices, with Philips Respironics as one of the main manufacturers of these machines, only deliver the exact pressure amount necessary at any giving time. Doctors sometimes find patients with more complicated sleep apnea disorders (like positional apnea or REM-related apnea) or those who simply can’t tolerate standard CPAP therapy might experience better results with APAP therapy.

How APAP Has Evolved

APAP and the various other names it was called like demand positive airway pressure (DPAP) has evolved through the years. While CPAP has already been established as a highly effective OSA treatment, poor adherence had limited its effectiveness. CPAP users often experience these problems:

  • Congestion
  • Nasal discomfort
  • Claustrophobia
  • Mask leaks

These lead to fluctuating levels of long-term compliance that ranges from 46 to 85 percent, based on how compliance is described.

There is a fairly sequential dose-response relationship, such as the greater the use of CPAP, the greater the improvement of quality-of-life, sleepiness or blood pressure outcomes. Because of this, there’s been much research on different ways to optimize CPAP compliance, and one of those strategies involved the evolution of APAP.

Advances to Improve Compliance

Machine manufacturers, like Respironics, have developed innovations and advances in PAP technology to help improve acceptance and compliance. Auto-titrating PAP is just one of these advanced PAP features.

One objective of PAP interventions has been lowering the delivered pressure to the airway because of the concern that a higher pressure leads to decreased patient adherence.

Auto Pressure Settings

APAP doesn’t operate at one set pressure, but rather monitors your respiratory activity so it can provide you with the lowest PAP level necessary for eliminating respiratory disturbances. Manufacturers have designed algorithms to automatically increase pressure when episodes are sensed and slowly decrease pressure if there haven’t been any episodes for a period of time.

Since the minimum PAP level needed for eliminating airway obstruction can vary over the night by sleep stage, sleep position, and other factors, APAP has the ability to provide you with the lowest pressure needed at each time, thereby lowering the overall mean pressure throughout the entire night. APAP, when compared with CPAP, demonstrates a small but significant adherence superiority statistically (+11 minutes) as well as in sleepiness reduction.

For instance, the popular DreamStation Auto CPAP Machine, Philips Respironics manufacturers, is an auto-adjusting machine that adjusts pressure during the night automatically on a breath-by-breath basis to deliver the optimal pressure required.

Physiological Variables

A wide variety of APAP devices are available today, varying in the physiological variables they monitor like:

  • Apnea
  • Snoring
  • Airflow limitation
  • Hypopnea
  • Impedance
  • A combination of variables

They also vary in their algorithms for responding to these factors.

Addressing Mouth/Mask Leaks

The issues of how to handle central apnea and mouth/mask leaks have been challenging for APAP designers. But, technologists performing CPAP titration are quite familiar with these two challenges.

To handle the leak issue, many APAP devices have algorithms that limit increases of pressure when a leak goes over certain values or when blower speed increases no longer lead to mask pressure increases. Other devices have “leak alarms” prompting patients or staff to re-adjust the mask.

Addressing Expiratory Pressure Relief (EPR)

Another strategy for improving compliance is through the use of EPR. Similar to bilevel positive airway pressure (BPAP), devices programmed for performing pressure relief deliver less airway pressure when you exhale compared to a standard PAP with the same set pressure.

With APAP, each manufacturer will vary in their EPR algorithm and several provide advances that go beyond pressure relief in expiration by itself, including adding inspiratory pressure relief in late inspiration for individuals on BPAP. A study that compared APAP by itself, APAP with EPR and APAP with EPR and inspiratory found the highest adherence level was among individuals randomized to APAP with EPR.

The older generation of APAP machines included simplistic sensors that measured only the pressure inflections or vibrations of a specific amplitude and frequency snoring caused.

The next generation of APAP machines became more innovative and sophisticated having the ability to sense flow-based changes like:

  • Hypopnea
  • Apnea
  • Inspiratory flow limitation

More recently, machines use:

  • Rapid injection of air or forced oscillation technique to differentiate central from obstructive apneas
  • Breath-by-breath peak flow changes to identify Cheyne-Stokes respiration
  • Measurements of minute ventilation or tidal volume using calibrated flow sensors to identify hypoventilation
  • Forced oscillation techniques to measure both lower and upper airway resistance
  • Sophisticated flow-based algorithms to compensate for air leaks

These signals are instantaneously computed and analyzed by a built-in microprocessor with preset algorithms that will determine the magnitude and rate of pressure response.

Today’s APAP Machines

The scientific evidence surrounding auto-titration and other alternative techniques for titrating PAP devices is continuing to evolve. APAP therapy use in individuals who haven’t undergone a conventional polysomnography (PSG) sleep study for diagnosing OSA has also seen immense growth.

Long-term APAP adherence appears to be good. A study showed 75 percent of individuals stayed compliant with their APAP therapy over five years.

Like CPAP machines, APAP machines are undergoing continuous change and evolution. Both the clinical evidence supportive of APAP and other methods and technology has seen rapid developments. The innovative APAP machines today are a result of many incremental changes throughout the years since the start of the “auto” concept.

Here at, we currently have more than 30 APAP machines, with a variety of features including for travel, with built-in humidifier, designed for women, and more.

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