A Meaning of Adaptive Servo-Ventilation

[dsm]

Ever since DME Guy started the thread on the new Resmed CS 2 machine, the term Adaptive Servo Ventilation has been used to describe an emerging cpap therapy.

SWS & I looked at a block diagram of the internals of the new CS2 & were trying to work out what this machine did & how. It has two impellers to blow air. At first we thought the two worked independently, we even wondered if one blew air & the other sucked air . In time we both agreed that is not how it worked.

So having had time to contemplate what this new approach is trying to achieve, I believe I can describe how it works in layman's terms & hopefully in an easy to understand fashion. The really interesting aspect of this therapy approach is the discussion we can have on if it is the future of cpap therapy.

1stly I will highlight what I believe are the major advances in commercial *cpap machine* therapy - this is not a history of Sleep Disordered Breathing (SDB), just of cpap machines. If anyone wants a crash course in respiratory physiology, try this link ...

http://www.4um.com/tutorial/icm/ventilat.htm

1) Early 1980s, Dr Colin Sullivan (from Sydney Australia & while researching in Toronto Canada), describes how a positive airway pressure applied via the nose/mouth, greatly reduces the effects of apnea in sleep disordered breathing (SDB) by splinting the airway open during inspiration. Colin experiments with vaccume cleaners & washing machine motors & pool pump motors combined with hand moulded face masks stuck on with rubber glue.

2) early 1980s - Sullivan cpap machine is born. Colin works with ResCare to develop the 1st commercial machine called the APD2. ResCare later become ResMed. In 1985, Respironics introduce their commercial cpap called the Sleep Easy. Several other companies start to market similar machines for the hospital & home market.

3) early-mid 1990s - A big leap forward occurs when Respironics produce the 1st Bilevel (called the 'Bipap'), Bilevels operate at 2 pressures 1 for inhale & a lower one for exhale. Other companies create their own versions.

4) mid-late 1990s - Another big leap forward occurs when Sullivan with Resmed introduce the Sullivan Autoset-T which pioneers AUTO titration. Other companies produce their own versions

3) mid 2000s - Resmed starts producing cpaps for special SDB such as Cheynes-Stokes breathing. Respironics also produces specialist machines. Also at this time Respironics introduce an AUTO Bipap which combines the benefits of Bilevel and AUTO titration.

4) 2006 Resmed announce the ASV CS2 machine which introduces a general cpap product that uses 'Adaptive Servo-Ventilation'.

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The use of the word servo may be ascribed to mean that an object can be controlled remotely to behave a particular way and the process of this remote control requires feedback from the object being controlled.

In remote control models, a 'servo' is a small device with a motor and gears that receives an input signal that tells it to rotate an arm one way or another and the amount of movement is also controlled.

So put simply there is a servo (in our case the machine) and a controller (in our case the person's breathing). For this use, the controller is aided by computer software in the machine that interprets the information from the controller.

So the person's breathing is monitored and sensed and the signals picked up back at the machine are then used to control the dual-impeller blower in the machine. The design is to maintain the user's breathing pattern (# of breaths/min and volume of airflow) to within 90% of the previous 10 minutes of monitoring. By making it 90%, it allows for the person to slowly adjust the intensity of their breathing naturally, as they drift off into the various stages of sleep. Thus if a sudden irregular breathing pattern occurs the machine takes over and acts as a ventilator and tries to maintain the prior breathing pattern.

This machine also concurrently *can* monitor for Apneas as well as Hypopneas, and follow the traditional reactions to those just like a good AUTO does today.

Dual impeller blower ...
This dual impeller is unique in that it is a single motor with a low inertia (lightweight) hi-torque (hi performance) brushless 'rotor' and has a small fan impeller at each end of this rotor shaft. This allows for a very low-noise well balanced fan motor that eliminates the big problem plaguing cpaps that use changing motor speeds to change the air flow. Most modern machines now use changing motor speeds to change airflow output 'on-the-fly'. The downside has been the motor whine/hum. When the hum stays constant a user and their partner can usually get used to it, when the hum varies up and down many people can't get used to it. The new Resmed dual impeller blower is one way to eliminate the noise.

So repeating, the use of the word servo-ventilation seems to describe the link between a users breathing and the machine acting as a servo. The servo *is* the machine, the controller is the person's breathing, the person feeds info to the machine which can adjust & that may alter the direction of the person's breathing. I think this can be called a 'controlled loop feed-back system'.

Because of the adaptive nature of this servo ventilation system. The machine can be programmed with a range of algorithm's suited to a variety of preferred therapies. Cheyne's Stokes breathing, mixed centrals/apneas, centrals etc:

Hope this helps explain where we are heading with cpap therapy.

Adaptive servo-ventilation seems to be the next big leap forward and it seems it is able to adapt to all the major types of ventilation required by users.

DSM

[-SWS]

A link to the other current adaptive servo thread as well:
viewtopic.php?t=11458&start=0

[GoofyUT]

Fascinating stuff. And the way that any of this is different than the current auto-titration paradigm (regardless of algorithm) is..........????

It sounds like it combines the para-invasiveness of an S/T with an auto-titrating CPAP machine.

Chuck

[dsm]

Chuck,

What it does that no other standard xpap does, is to switch between acting as a ventilator and acting as an xpap.

A ventilator is different in that it drives the person's breathing. S/T machines are classified as ventilators because of the BPM setting. The T part is usually set as BPM (Breaths per minute), is used to determine if the person is not meeting the min breaths-per-minute & the machine will flip from epap to ipap.

So the VPAP Adapt goes further. It actually will 'pump air' in in a controlled fashion (adapted to the prior 10 mins breathing pattern).

BiLevels merely flip between epap & ipap & deliver according to the static settings set up for ipap & epap. Bilevels with timed control are marginally better & generally used for mix apnea & people with centrals.

AUTOs *don't attempt to treat centrals - the VPAP Adapt (when in the correct mode) specifically treats centrals including Cheynes/Stokes breathing.

AUTOs (depending on brand & design) aren't really able to clear a quick apnea, it appears the VPAP Adapt may be fast enough to do so. (this area is still an interesting seperate topic of discussion).


DSM

[GoofyUT]

It still sounds to me that it will non-invasively ventilate depending on what it senses are degradations from the pattern it "saw" for the preceding 10 minutes. In this regard, it sounds no different than an APAP except that it will non-invasively ventilate rather than simply titrate presssure. So again, it sounds like an S/T married to an APAP with degradations rather than time being the critical factor that dteermines the degree of ventilation.

I am VERY interested in hearing Steve's thoughts regarding the impact of this on hypo/hypercapnic triggers and trigger irritability as may be seen in CSDB.

Chuck

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CPAPopedia Keywords Contained In This Post (Click For Definition): APAP

[dsm]

http://72.14.235.104/search?q=cache:Zl8 ... =clnk&cd=1

The above link is the detail for this ...


Traditional 510(k) Premarket
Notification
510(k) Summary - AutoSet CS2
[As required by §807.92 (c)]


Submitter Name: ResMed Corp.
Submitter Address: 14040 Danielson Street,Poway CA 92064-6857,USA
Contact Person: David D'Cruz, VP Regulatory & Clinical Affairs US
Phone Number: (858) 746 2238
Fax Number: (858) 746 2915
Date Prepared: May 19, 2005
Device Trade Name VPAP ADAPT
Device Common Name/Bi level Positive Pressure Ventilator/ Continuous
Classification Reference Ventilator,Passive Exhalation Port, Non-Critical Care

[dsm]

[quote="GoofyUT"]It still sounds to me that it will invasively ventilate depending on what it senses are degradations from the pattern it "saw" for the preceding 10 minutes. In this regard, it sounds no different than an APAP except that it will invasively ventilate rather than simply titrate presssure. So again, it sounds like an S/T married to an APAP with degradations rather than time being the critical factor that dteermines the degree of ventilation.

I am VERY interested in hearing Steve's thoughts regarding the impact of this on hypo/hypercapnic triggers and trigger irritability as may be seen in CSDB.

Chuck

[GoofyUT]

Got it!

Interestingly, the pre-release studies report that the ADAPT is MORE effective than their VPAP III S/T (P<.001).

[-SWS]

Great explanation, DSM. Just a note that "adaptive servo" technology precedes the world of respiratory ventilation. And that "adaptive servo" as a general engineering concept refers to a servo mechanism that specifically maintains "tuned inertia" toward a very precise rotational control with minimal energy loss. Thus "adaptive servo" applied to ventilation aims to accomplish a difficult-to-achieve highly precise impeller rotational control, which in turn, achieves ventilatory support that is perfectly synchronized with respiration---given an algorithm that is up to the challenge.

You'll note that in the patent descriptions even CPAP is referred to as providing ventilatory support. Adaptive servo ventilation, as you said, differs from PAP in the precise synchronization of wave shape regarding slope, phase, period, and peak characteristics. Traditional PAP does not come close to achieving that.

Because PAP does not come close to achieving precise ventilatory synchronization, CSDB patients find PAP's ventilatory "overshoot" to inherently dysregulate their central respiratory drives. Chuck, you'll note that the adaptive servo technique, in and of itself, is not largely based on CO2 kinetic mediation as additional dead space is. Rather, that avoidance of a CSDB dysregulated respiratory drive is implicitly attributed by Resmed's literature to the ventilatory synchronization itself. And that will get me right back to my speculative thoughts that CSDB is a two-stage disorder of central dysregulation, driven initially by neural plasticity's maladaptive prioritization or misinterpretation of chemoreceptor signals.

The neural correlates of voluntary breathing show brain stem neural activity as being very busy, facilitating relinquishment, yet very presumably with a survival-driven high degree of supervisory control over the primary motor cortex. Very specifically I suspect autonomic breathing's adaptive plasticity neurally exercises it's own local and maladaptive neural adjustment to the very CO2-based inspiratory target itself. If autonomic breathing can override it's own closed neural respiratory loop to the relinquishment to voluntary breathing, then so can it likely override that same loop for survival-based responses to afferent signals.

I suspect that adaptive servo's ventilatory slope, phase, and period match likely avoids a maladaptive mis-prioritization/misinterpretation of the stretch receptors, that typically occurs in CSDB patients with traditional PAP ventilatory "overshoot". The highly unnatural pressure discrepency itself of discoordinate PAP seems to be at play in the case of CSDB: as soon as PAP is applied the central events appear or significantly increase. The vocal-chord-based defensive airway closures seem to imply an initial afferent response and subsequent misinterpretation as well.

The caveat with adaptive servo is whether it can maintain that highly precise synchronization, breath after breath, throughout an entire night of respiratory variability. One adaptive servo caveat that has already been correctly identified is the fact that it is highly leak intolerant. Given even slight leaks, adaptive servo can be very prone to desyncronization. The other obvious caveat is the algorithm's ability to run an entire night's gauntlet of pattern-matching challenges regarding perfect respiratory synchronization. That last one is a very tall design challenge given real time constraints. However, pattern-rich CHF/CSR breathing patterns were selected as adaptive servo's first application because it was a comparatively easy pattern-challenge. At least that is my take.

[dsm]

SWS,

To sum that up - what Resmed really need to come up with is either or both a new nasal mask that seals better than today's standard models, a new full face mask that does the same.

In the case of people with centrals, The effort from the machine is to ventilate their lungs. I am not sure what cms that might require, perhaps not as much as is needed to splint the airway of an apnea sufferer.

The issue with mas leaks is that the usual culprit is breathing out against the cpap machine pumping air in,

i.e. For a cpap - I am breathing out at say 15+ (allowing for overcoming the input cms) against the machine that is pumping air in at 15- (allowing for co2 vent leak). The combination is going to be either the addition of the two pressures for machines that don't sense & adjust their output pressure, or just above 15 cms allowing for machines that do adjust to their sensed output pressure.

Same applies to BiLevels.

The VPAP Adapt appears to be able to not put any back pressure on the user as they exhale ?. This alone is new, if true. So mask leaks may be greatly diminished.

Point I am making here is that most mask leaks initiate when there is a conflict of pressure between the user and the machines (which in most cases, is going to be potentially every breath). This conflict starts at the point the user begins to exhale. Foe Bilevels the conflict is reduced to the EPAP cms pressure & resumes as soon as the machine flips to IPAP.

I am thinking the VPAP Adapt may greatly reduce this pressure conflict.

DSM

[Guest]

It sure sounds like the ultimate device, but I am anxiously awaiting more clinical research data and unbiased medical studies to support Resmed's claims re the effective treatment of CSDB. It is disappointing the reported results thus far have not been more positive.

[Guest]

Sorry-- I meant to put the previous post in the main thread. I didn't realize another one had been started on the same topic. My bad! I don't suppose there's any way the two can be combined?

At any rate, for those interested who might have missed it, here again is a link to the main thread: Resmed VPAP Adapt SV - for Central Sleep Apnea