RE: Auto-Adjusting Positive Airway Pressure [copied from old forum]
APAP Bench Test: Vendors Respond
Sleep Review: In a couple of brief paragraphs, please generally summarize the approach used in your auto-adjust CPAP machine's algorithm to detect sleep-disordered breathing events?
Fisher & Paykel:
The Fisher & Paykel Healthcare SleepStyle 200 Auto Series device uses a flow-based auto-adjusting algorithm, designed to detect and respond to flow limitation, hypopnea, and apnea.
The research clearly shows that flow limitation is a strong precursor to upper airway collapse. Therefore, detection and elimination of flow limitation prevent more severe indices of sleep-disordered breathing (SDB) from occurring, such as apnea or hypopnea. Complex statistical analysis of each breath allows us to accurately detect flow-limited breathing.
An additional algorithm called SensAwake has also been incorporated into this device to enhance comfort during wakefulness. Patients are often intolerant of the pressure while they are awake, and it is during this time that comfort is critical for long-term use. SensAwake is a sophisticated pressure relief technology that detects the transition from sleep to awake and promptly reduces the pressure in order to aid the transition back to sleep. SensAwake, combined with Ambient Tracking Plus humidification technology, works to enhance the comfort and performance of the auto-adjusting algorithm for improved therapy acceptance and clinical outcomes.
The DeVilbiss IntelliPAP AutoAdjust is a flow-based autotitrator that senses and categorizes events as either responding and nonresponding events (ie, potential central events). The AutoAdjust will increase pressure to detected responding events and will maintain pressure to nonresponding events, because a pressure response may complicate the event. Once breathing stabilizes, the AutoAdjust will reduce the pressure gradually to avoid arousals.
The responding events are snoring, obstructive apneas, and hypopneas. The algorithm analyzes flow patterns the same way a sleep technician would visually identify respiratory events during a sleep study. Snoring is defined as an interruption of the flow signal on inspiratory waveform. Obstructive apneas are defined by a major decrease in the amplitude of the total respiratory waveform, and hypopneas are defined by a partial reduction of the respiratory waveform. A unique feature of the DeVilbiss AutoAdjust algorithm is the ability to change the sensitivity of the algorithm by changing definitions of respiratory events, almost creating a customized algorithm.
The treatment pressure required by a patient may vary through the night-and from night to night-due to changes in sleep state, body position, and airway resistance. Pressure needs for maintaining an open upper airway in a sleep apnea patient can also be influenced by long-term variance due to weight gain or loss and use of alcohol or pharmaceuticals.
ResMed's AutoSet algorithm monitors the patient on a breath-by-breath basis to maintain upper airway patency for any given breath. The AutoSet algorithm adjusts treatment pressure as a function of three parameters: inspiratory flow limitation, snore, and apnea. By analyzing inspiratory flow limitation in minute detail during each respiratory cycle, the AutoSet algorithm is able to detect and distinguish obstructive hypopnea from central hypopnea: the AutoSet algorithm is able to detect and treat obstructive hypopnea (with flow limitation) and detect and record central hypopnea (without flow limitation) events. These three lines of defense allow the AutoSet algorithm to treat the patient effectively, as the patient needs it, throughout the night.
The main goal of the REMstar Auto algorithm is to normalize sleep by delivering the lowest CPAP pressure. What makes the REMstar Auto algorithm unique is its sophisticated three-layered algorithm. Unlike other auto-titrating devices in the market, the REMstar Auto can manage a respiratory event in the early stages rather than waiting for it to occur.
The primary function of the algorithm is to conduct a proactive analysis of the patient's upper airway and its potential to collapse. It makes subtle, programmed CPAP pressure adjustments in response to detected changes in flow.
The second layer consists of programmed responses to apneas, hypopneas, flow limitations, and vibratory snores.
In the third layer, the algorithm operates in a variety of exception conditions. For example, the algorithm ceases to increase pressure for patients who may experience sleep-disordered breathing events that are not responsive to pressure increases (such as central apneas). The algorithm decreases CPAP pressure when the patient is experiencing a large mask leak. The result is clinically proven, effective therapy at minimal CPAP pressure.
Sleep Review: How does your product respond once a sleep-disordered breathing event is detected?
Fisher & Paykel:
Once a sleep-disordered breathing event is detected, the pressure increase will vary according to the severity of the event and the current pressure. For example, the device will respond more aggressively to an apnea than to a hypopnea or flow-limitation event.
An important factor that will impact the response of the auto algorithm is the apnea-cap setting. The apnea cap is designed to prevent unnecessary pressure increases due to central events. The apnea cap is a changeable parameter that by default is set to 10 cm H2O . Below the apnea-cap pressure, the device will respond to all forms of sleep-disordered breathing. At or above this pressure, the device will only respond to SDB events that are clearly obstructive in nature, ie, events associated with flow limitation.
As the cycle of sleep apnea begins, a precursor to obstructive apneas and hypopneas is snoring. The DeVilbiss AutoAdjust algorithm senses snoring and begins to increase the pressure prior to obstructive apneas and hypopneas in an attempt to prevent these events from occurring. The patient may still have apneas and hypopneas, especially during REM or while in a supine position during the night. There is a need to respond to apneas and hypopneas as they occur during a patient's sleep cycle to keep the airway patent. Dynamic changes in pressure are able to keep the airway open as the patient needs change.
The AutoSet algorithm is truly a predictive approach allowing proactive treatment of sleep apnea rather than simply reacting with a pressure change after an event has occurred; this is achieved by detailed analysis of the inspiratory flow versus time curve. Flow limitation analysis in the AutoSet algorithm is a complex blend of clinical sleep science and engineering; it provides very small adjustments in pressure, sometimes as little as 0.2 cm H2O at a time to ensure that the patient is not aroused from sleep (as measured by EEG) with such pressure changes. This approach allows AutoSet to preemptively treat many obstructive sleep apnea events before they even occur. When an event does occur that is not possible to prevent by the flow limitation approach, AutoSet will respond reactively as well. ResMed's AutoSet algorithm assesses the severity of the event using a blend of the inputs such as duration of the event severity and frequency of the event over time. The AutoSet algorithm then determines the optimal pressure change solution to treat the event and prevent future events and applies it comfortably with minimal disturbance to the patient's sleep.
AutoSet responds to events based on a five-breath moving average of the inspiratory flow-time curve in order to prevent the device from responding to sporadic breathing events, such as sighs or coughs. Inspiratory flow limitation, or partial airway closure, usually precedes snoring and obstructive hypopnea and apnea events; it is also most often associated with obstructive hypopneas as they occur. AutoSet adjusts in increments as small as 0.2 cm H2O to ensure that pressure increases only as much as is necessary.
For flow limitation, AutoSet calculates the shape of the inspiratory flow-time curve and the value for every breath (using a metric known as the flattening index); however, it responds based on the average value of the most recent five breaths, as described above. Detection of flow limitation enables the device to increase the pressure before obstruction occurs, making treatment preemptive, and thus reducing the number of respiratory events and arousals. The apnea response is determined by the severity of the event and current therapy pressure. Apnea pressure changes are delivered after the event such that the pressure change will not arouse the patient. Snore response is measured using the severity of the vibrations of the snore. A more severe snore will give a larger pressure response, but this proportional response is delivered over the next series of breaths such that the pressure change does not disturb the sleeping patient.
If no further flow limitation, snore, or apneas are detected, therapy is reduced over time toward the minimum pressure prescribed by the physician with a 20-minute time constant. This approach allows the pressure from ResMed's AutoSet algorithm to return to lower pressures for increased patient comfort in the absence of any respiratory events.
With its proactive and continuous analysis throughout the therapy session, the REMstar Auto algorithm has the unique ability to deliver just enough CPAP pressure necessary to ward off a potential event. Since the pressure delivered at any given time is slightly higher than the pressure level necessary to open the airway, if an event does occur, the device does not need to rapidly respond by increasing pressure quickly. When the REMstar Auto detects a clustering of events, it determines the patient's airway to be unstable and slowly increases pressure to achieve a higher level of CPAP for a new 5-minute period.
The REMstar Auto detects and responds to apneas, hypopneas, flow limitations, and vibratory snores. To detect an apnea or hypopnea, the algorithm calculates a baseline patient flow based on a moving average of patient flow. The baseline flow and any changes in flow are based on the algorithm's analysis of four parameters of the flow signal: flatness, roundness, peak, and shape. This precise recognition of unique patient flow patterns is the reason why the REMstar Auto reacts better than other devices.
Sleep Review: Finally, what was the basis or reference for incorporating the above-described approach to detecting and responding to sleep-disordered breathing events?
Fisher & Paykel:
Flow-based algorithms have become industry standard due to the evidence supporting flow limitation as the most effective means to predict upper airway collapse (Ayappa, 1998). By using this well-established detection method in combination with SensAwake technology, the Fisher & Paykel SleepStyle 200 Auto is able to offer an effective treatment solution that addresses pressure intolerance that can adversely affect compliance.
The creation of the DeVilbiss IntelliPAP AutoAdjust algorithm was initiated in the early 1990s. The algorithm was first born based on several clinical resources and references, then grew through the utilization of a computer-assisted diagnostic algorithm to accurately define respiratory events. Finally, the AutoAdjust and its algorithm furthered evolved as a result of fine-tuning based on extensive real-world clinical testing.
ResMed's AutoSet algorithm was the first published auto-titration positive airway pressure algorithm in the peer-reviewed literature. The AutoSet was first developed in the early 1990s by researchers in Sydney, Australia, and Essen, Germany. Michael Berthon-Jones, MD, PhD, and Professor Helmut Teschler, MD, PhD, published a seminal article in the peer-reviewed literature (Thorax, 1998) comparing AutoSet versus continuous positive airway pressure. This study showed clinical equivalence of outcomes from AutoSet and CPAP in terms of respiratory disturbance index (RDI) and other important SDB parameters. Another important early analysis in the peer-reviewed press from the mid 1990s was published in the blue journal by Lloberes et al (Am J Respir Crit Care Med, 1996) showing equivalence of sleep architecture in terms of sleep efficiency, stage 1-2 sleep, slow-wave sleep, and REM sleep between AutoSet and CPAP using gold-standard PSG analyses.
Just a few of the many dozen other articles published on AutoSet in the last 15 years are summarized below:
Improvement in compliance as well as quality-of-life parameters such as SF-36 Vitality Scores and mental health metrics for patients on AutoSet versus CPAP, when CPAP pressures are equal to or greater than 10 cm H2O (Massie et al. Am J Respir Crit Care Med, 2003)
Superiority of AutoSet versus competitive APAP algorithms in studies completed by independent, non-industry-sponsored analyses (Farre et al. Am J Respir Crit Care Med, 2002)
Equivalent clinical outcomes (AHI, oxygen saturation) as well as equivalent or superior quality-of-life (SF-36, FOSQ, EuroQOL) when AutoSet was compared to gold-standard CPAP (Am J Respir Crit Care Med, 2004)
Economic and cost-effective use of AutoSet in the home setting for treating obstructive sleep apnea (Bachour et al. Sleep Medicine, 2007)
Literally millions of patients have been prescribed the AutoSet algorithm by physicians globally during the last decade, on products across product platforms from ResMed since the mid 1990s, including the AutoSet Clinical, the AutoSet Portable, the AutoSet P2+, the AutoSet T, and the S8 AutoSet. Today, patients can receive therapy from the latest AutoSet algorithm in the S8 AutoSet II device. The S8 AutoSet II device combines not only the advances of the world-pioneering auto-adjusting algorithm described in this article, but also one of the smallest, quietest, and most reliable sleep apnea devices in the world.
Philips Respironics: The theory of the algorithm was developed based on clinical understanding and practices used in titrating CPAP pressures during a PSG titration process. Additionally, there has been extensive clinical and bench test validation of the algorithm's effectiveness. These studies have been conducted by Philips Respironics and independent medical professionals. Several studies have been published in medical and other trade journals.