ASV: HOW DOES IT WORK?

[dsm]

Are all these from Resmed also ASVs?

36004 S9 VPAP S
36006 S9 VPAP Auto
36008 S9 VPAP ST
26119 VPAP S
26101 VPAP Auto 25
26110 VPAP ST
24116 VPAP III ST-A USA
24117 VPAP III ST-A Canada and Latin America

Those are all Bilevels

Vpap s is a spontaneous only bilevel (meaning it has no timed feature such as being able to swich epap-ipap-epap at a min or fixed rate)
Vpap s/t is spont & timed
Vpap Auto uses OSA algorithm in combo with bilevel pressures
Vpap III are the oldest in the list, the others without S9 are 2nd oldest & the S9 all the newest.
The Vpap III ST-A models are fitted with alarms & mainly used in clinics/hospitals

DSM

[borgready]

To the users of ASV:

When your using the machine and you get that increased push of air, doesn't that wake you up? Since a lot of problems with not breathing usually occur in the REM stage of sleep, doesn't that mess up your ability to get REM (dreaming) sleep? So if you REM sleep is disrupted then don't you feel tired all the time.

[dsm]

To the users of ASV:

When your using the machine and you get that increased push of air, doesn't that wake you up? Since a lot of problems with not breathing usually occur in the REM stage of sleep, doesn't that mess up your ability to get REM (dreaming) sleep? So if you REM sleep is disrupted then don't you feel tired all the time.

borgready

If you had have asked me that question before I got an ASV I personally would have been hard to convince that up to 10 CMs increase in up to 3 breaths, would not wake a sleeper up often.

Then having got my original Bipap AutoSV, had some of soundest deepest dreamiest sleeps for a long time. So much so I named my ASV 'Dream Machine'.

What *does* wake me up when it happens, is mask leaks & squeaks - horrible experience & it is a process that starts with a few then in a couple of weeks becomes almost nightly & messes up sleep. I keep having to replace the seals on my quattro at least every 6 months. Those mask leaks are a spoiler with ASV. Also use an anti-leak strap.

DSM

[avi123]

Question:

During central apneas and hypopneas, when there is no respiration drive by muscles, how could an ASV machine with plain face mask, push air into the lungs by raising the pressure ?

Anesthesiologists, during invasive ventilation, are using intubation tubes b/c of the higher pressure for lungs inflation.

OK, during intubation, gas* is given to patients for muscle relaxation. But still, the pressure there is above 30 cm H2O.

But how the ASV machine forces air into the lungs during central apneas?


*-Sedation and Paralysis

Most intubated patients receive intravenous sedation through a continuous infusion or scheduled dosing to help with anxiety or psychological stress. Sedation also helps the patient tolerate the constant irritation of the endotracheal tube in their mouth, pharynx and trachea. Without some form of sedation and analgesia, it is common for patients to "fight" the ventilator. This fighting increases work of breathing and may cause further lung injury. Daily interruption of sedation is commonly helpful to the patient for reorientation and appropriate weaning. These interruptions are frequently described as "sedation vacations" and have been shown to reduce the time patients stay on mechanical ventilation.[11]

It is not uncommon for patients on a mechanical ventilator to be given a muscle relaxant or paralytic to aid in ventilation. These "neuromuscular blockades" prevent skeletal muscle from contracting and thereby stop all patient movement including respiratory efforts. These types of pharmaceutical agents must always be given in conjunction with sedation as the effects of the paralytics is not only uncomfortable but would cause significant psychological stress and anxiety.

[avi123]

DSM,


In your above presentation in which you relied on this source, you have not shown the top of the back side of the page:





Notice there the following statements:


To ensure ventilatory support is synchronized to the
patient’s breathing effort, AutoSet CS2 relies on the first
two factors. When a central apnea/hypopnea occurs,
support initially continues to reflect the patient’s recent
breathing pattern. However, as the apnea/hypopnea
persists, the device increasingly uses the backup
respiratory rate.

And from the back side of the pg:

Support when it is needed:

When a central hypopnea/apnea occurs and ventilation
suddenly drops below the target:
• pressure support rapidly increases, over a few
breaths, to keep ventilation at the target
• the default maximum pressure support value of
10 cm H2O should fully ventilate a centrally apneic
patient with an open airway and normal lungs.


The question in my above post also relates the these statement.

How could this ASV by using the backup respiratory rate (i.e. additional respiratory cycles) at a pressure of 10 cm to ventilate a centrally apneic patient with an open airway and normal lungs.

Don't central apneas and hypopneas mean the lack of respiration drive? So no matter how many cycles and the level of the pressure the ASV would assume, it will not effect the present central apnea and hypopnea lack of ventilation. But it might effect the target of total of the Tidal Volumes and discourage emergence of new centrals.

[dsm]

avi

]The question in my above post also relates the these statement.
How could this ASV by using the backup respiratory rate at a pressure of 10 cm ventilate a centrally apneic patient with an open airway and normal lungs.
Don't central apneas and hypopneas mean the lack of respiration drive?

I had seen the back page re the 10 CMs. Best way to understand if added 10CMs of pressure can 'encourage' you to breathe is try it. I have

DSM

PS your post had "How could this ASV by using the backup respiratory rate at a pressure of 10 cm ventilate a centrally apneic patient with an open airway and normal lungs." but that is not what the document says. It in part mentions increasing pressure by 10CMS over your eep (epap). It says this with "the default maximum pressure support value of 10 CM H20 should fully ventilate a centrally apneic patient with an open airway and normal lungs" (which you also quoted).

[avi123]

RE EDIT:

DSM,

Can you suggest (explain?) how an ASV machine could ventilate a person during real central apneas and hypopneas, at any pressure, if the muscles responsible for ventilation are not participating, and even if the airway is open ?

And since the ASV (or any ventilator) can't do that (push air into the alveolai without the cooperation of the breathing muscles), unless the person is sedated and unconscious, why Resmed has published the following statement:


Support when it is needed:

When a central hypopnea/apnea occurs and ventilation
suddenly drops below the target:
• pressure support rapidly increases, over a few
breaths, to keep ventilation at the target
• the default maximum pressure support value of
10 cm H2O should fully ventilate a centrally apneic
patient with an open airway and normal lungs.



DSM, it's OK if you skip answering

[dsm]

DSM,

It seems to me that you're dancing around the bush:

Can you suggest (explain?) how an ASV machine could ventilate a person with real central apneas and hypopneas, at any pressure, if the muscles responsible for ventilation are not participating and the airway is open ? By looking at my own and other posters' Flow traces of ResScans, there are hours when the many central apneas add up to 50% of sleep time. How would the ASV deal with it? You would not make the patient wake up to breathe after each central apnea, would you?

I don't think I am dancing around any bush as much as spending a lot of time trying to figure out the meaning of your questions. You do seem to, at times, misinterpret things such as in this case the statements made by a manufacturer - see an example from your prior post (highlighted in red) - I have been trying to 2nd guess such misunderstandings

Have you tried holding your breath against a burst of pressure varying from around 10-15 to 20-25 CMs ? - let me know if you succeed without a *lot* of resistance - such a test should help you understand your own question.

I doubt I can explain to you how your ASV may or may not inflate you. I know that mine works ok with me.

Read this manufacturers statement again "the default maximum pressure support value of 10 CM H20 should fully ventilate a centrally apneic patient with an open airway and normal lungs".

I agree that if you are dead or if you deliberately hold your breath against an ASV machine. It won't succeed, you will. But by comparison, a true volume ventilator can make you breathe (or appear to) dead or alive (but if dead, to no avail ). Those machines can go way over 60+ CMs of pressure (but best done with a tracheotomy). They blow you up with the required safe volume at a steadily applied increasing pressure. ASVs are not intended to quite do that. They just seek to 'encourage' a person to breathe while the airway is already held open (inflated) at epap (eep) pressure. The added pressure support (up to 10 CMs in 3 breaths) works very effectively at this for most people. Your respiratory muscles don't try to resist inflation, they aren't rigid (unless rigor mortis has set in ).

DSM

[JohnBFisher]

avi123, though the ASV machine does encourage breathing, the more important intent is to actually cause some respiration to occur. While it is not as much as a ventilator, nor could it replace a ventilator, by causing upto 90% of the ventilation to occur, enough CO2 is expelled to break the cycle of central sleep apnea.

See the following quote from an early (2001) article describing ASV therapy:

If the subject suddenly ceases all central respiratory effort, machine support (i.e., pressure swing amplitude) will increase from the minimum of 4 cm H2O up to whatever is required to maintain ventilation at 90% of the long-term average (up to a maximum of 10 cm H2O, reached in approximately 12 s).

The source article for that quote is:

http://ajrccm.atsjournals.org/cgi/reprint/164/4/614

Please remember, as I have described it, the ASV therapy attempts to break the repetitive undershoot/overshoot cycle that lurks behind various forms of Central Sleep Apnea. That is, for some reason we fail to expel enough CO2. It builds up in our blood. This is the undershoot side of the cycle. Eventually, our bodies kick in and the respiration resumes. But not at a normal rate or flow. Instead we tend to hyperventilate. This is the overshoot side of the cycle. We tend to blow off too much CO2. This of course, sets us up for the repeat of the undershoot side of the cycle. By blowing off too much CO2, we depress the respiratory drive. Breathing ceases and the cycle starts all over again.

By causing SOME respiration to occur ("90% of the long-term average"), the ASV therapy breaks the cycle.

And trust me, it DOES work. I have an AHI of 0 to 1 most mornings when I check. That compares to a huge value without it.

Does it eliminate central sleep apnea? Nope. It just helps break the repetitive cycle.

Is an ASV therapy device a ventilator? Nope. It just helps maintain breathing for ONE of those cycles. There is no way it would suffice for long term ventilation support. But it does not have to do so. It just has to be adaptive enough to help sustain breathing during one central apnea. That helps expel the CO2 and break the undershoot/overshoot cycle.

I hope that helps explain how ASV therapy works.

[dsm]

avi
Just to hone in on this aspect of your questions "And since the ASV (or any ventilator) can't do that (push air into the alveolai without the cooperation of the breathing muscles), unless the person is sedated and unconscious, why Resmed has published the following statement:"

I believe a ventilator machine can inflate the lungs and can feed air to the alveoli. I also believe that a person with normal lungs and an open airway can have fresh air passed into the alveoli by an ASV machine.

The respiratory muscles don't try to explicitly resist external inflation but yes they can and may not want to cooperate but that is entirely different to 'resisting' the effort. Your contention seems to be that respiratory muscles must resist inflation unless being signaled to activate. Can you explain where you got that notion as that is the heart of your question.

DSM

PS consider that yes the airway will provide some resistance to an ASV but it isn't total resistance. Both a ventilator and an ASV will see 'some' resistance to the effort of inflation. A ventilator ignores the resistance. As the manufacturer stated, if the lungs are normal & the airway is open then the ASV should fully ventilate the patient.

[avi123]

avi
Just to hone in on this aspect of your questions "And since the ASV (or any ventilator) can't do that (push air into the alveolai without the cooperation of the breathing muscles), unless the person is sedated and unconscious, why Resmed has published the following statement:"

I believe a ventilator machine can inflate the lungs and can feed air to the alveoli. I also believe that a person with normal lungs and an open airway can have fresh air passed into the alveoli by an ASV machine.

The respiratory muscles don't try to explicitly resist external inflation but yes they can and may not want to cooperate but that is entirely different to 'resisting' the effort. Your contention seems to be that respiratory muscles must resist inflation unless being signaled to activate. Can you explain where you got that notion as that is the heart of your question.
DSM

PS consider that yes the airway will provide some resistance to an ASV but it isn't total resistance. Both a ventilator and an ASV will see 'some' resistance to the effort of inflation. A ventilator ignores the resistance. As the manufacturer stated, if the lungs are normal & the airway is open then the ASV should fully ventilate the patient.

Can you explain where you got that notion as that is the heart of your question.


Reply:

From the Textbook of Medical Physiology, Pulmonary Ventilation, Mechanic of Respiratinn.

But not as you stated above: "consider that yes the airway will provide some resistance to an ASV but it isn't total resistance".

just that you need the cooperation of the ventilatory muscles to breathe. Otherwise, you need to be sedated and use those ventilators from the ICU. OR, use a resuscitator (Attainable Delivery Pressure > 80cm H2O), instead of the ASV .


Check these:


Muscles of Respiration

http://oac.med.jhmi.edu/res_phys/Encycl ... fResp.HTML

and, The "work" of breathing:

http://www.medicalgeek.com/pathophysiol ... -help.html


DSM:

I agree with your previous statement that you, the patient, better obey the ASV machine and synchronize with it , and trust it. Only then you could benefit.
This also jibes with John Fisher "break the sequence" rule.

[dsm]

avi
Just to hone in on this aspect of your questions "And since the ASV (or any ventilator) can't do that (push air into the alveolai without the cooperation of the breathing muscles), unless the person is sedated and unconscious, why Resmed has published the following statement:"

I believe a ventilator machine can inflate the lungs and can feed air to the alveoli. I also believe that a person with normal lungs and an open airway can have fresh air passed into the alveoli by an ASV machine.

The respiratory muscles don't try to explicitly resist external inflation but yes they can and may not want to cooperate but that is entirely different to 'resisting' the effort. Your contention seems to be that respiratory muscles must resist inflation unless being signaled to activate. Can you explain where you got that notion as that is the heart of your question.
DSM

PS consider that yes the airway will provide some resistance to an ASV but it isn't total resistance. Both a ventilator and an ASV will see 'some' resistance to the effort of inflation. A ventilator ignores the resistance. As the manufacturer stated, if the lungs are normal & the airway is open then the ASV should fully ventilate the patient.

Can you explain where you got that notion as that is the heart of your question.


Reply:

From textbooks on physiology of ventilation in human.

But not as you stated above: "consider that yes the airway will provide some resistance to an ASV but it isn't total resistance".

just that you need the cooperation of the ventilatory muscles to breathe. Otherwise, you need to be sedated and use those ventilators from the ICU.


DSM:

I agree with your previous statement that you, the patient, better obey the ASV machine and synchronize with it (i.e. and trust it). Only then you could benefit.
This also jibes with John Fisher "break the sequence" rule.

avi

Lets look at both issues

1) QUOTE: avi = "just that you need the cooperation of the ventilatory muscles to breathe. Otherwise, you need to be sedated and use those ventilators from the ICU".

&
2) Breaking the CO2 undershoot overshoot cycle

For 1) to consciously breathe, yes you do need the cooperation of the respiratory muscles. That is self evident. But to argue that you can't breathe without the cooperation of the respiratory muscles seems to me to be misunderstanding the point - to say that someone must be sedated / unconscious for a ventilator to work also misses the point. The sedation is to assist with breathing in an ICU - patients in ICU on a volume ventilator are normally being ventilated through a tube in the neck !. That is to allow their lungs or other parts to heal and to handle the large pressures those machines can apply. They are also usually at max oxygen (99% to 100% SpO2).

2) For John's point about breaking the overshoot undershoot cycle, you can't do that unless the ASV has moved increased airflow into the lungs. The muscles don't put up a fight against inflation from the ASV (Remember the manufacturers statement - lungs are normal & the airway is open).


DSM

PS are you going to try the experiment ? - try breathing in or out (to keep airway open) suddenly & very very slowly & see what your ASV does & the extent that you can resist it. Remembering that if your resistance is conscious & tightly exercised, yes you will win. Also remember that it is how your body really works that overrides how you may think it works from reading a book.

[LittleRedTruck]

Guys, Ive followed this thread. I can add I feel the best Ive felt in ten years after going on the Resmed S9 adapt SV about 3 weeks ago. Ive included a graph that shows a tendency to flat line on the flow trace, then a bump in pressure to about 24. You can see a recovery in flow, then another pressure shot ! This transpires all nite long but its all transparent to me. Im sleeping soundly about 8 hours and seldom a bathroom visit. I seldom know the machine is helping me. You can disassemble the applied technology, If you wish. Meanwhile Ill happily dream about you as I peacefully sleep. Dan

[dsm]

Dan

Thanks for that chart - it is helpful because it shows the new S9 ASV.
I can see 3 pressure rises in the pressure hump just to the right of the middle where it appears to really be pushing pressure up to the max. Certainly doesn't trigger an arousal which is one of the good features of these machines allowing how high & quickly pressure can go.

DSM

[avi123]

Dan

Thanks for that chart - it is helpful because it shows the new S9 ASV.
I can see 3 pressure rises in the pressure hump just to the right of the middle where it appears to really be pushing pressure up to the max. Certainly doesn't trigger an arousal which is one of the good features of these machines allowing how high & quickly pressure can go.

DSM

DSM,

The "Pressure hump" that you mention is correlated with an hypopnea (shown by the Flow in the lower panel) and I wonder why the pressure was boosted?
Overall, it would be nice to also show the Events, Snore, and Leak traces next to the present traces.