how to interpret Flow Limitation graphs

[avi123]

Back to the scheduled program . . .

. . .There are no good explanations what FL really means. . .

I agree there are many ideas about what meaning should be attached to many things that are less than desaturating apneas, for the average person. However, still, the bottom line for me is what is expressed in the book Nonivasive Mechanical Ventilation: Theory, Equipment, and Clinical Applications, by Antonio Matías Esquinas (Nov 4, 2010), p. 101:

In patients with OSA, progressively higher CPAP levels applied during sleep turn obstructive apneas into hypopneas, hypopneas into continuous inspiratory flow limitation, with or without snoring, and flow limitation into unobstructed breathing. When breathing becomes unobstructed, "respiratory arousals" (i.e., arousals that may follow increased inspiratory efforts associated with obstructed breathing) are eliminated, while sleep becomes more stable and sleep cycles more regular, contributing to improvements in subjective sleep quality, daytime sleepiness, and quality of life usually observed after just a few nights of CPAP application. Also, relief of upper airway obstruction is associated with resolution of intermittent hypoxemia and hemodynamic swings that accompany obstructive events, with a consequent reduction in long-term cardiovascular morbidity and mortality.

The objective of CPAP treatment are elimination of symptoms and of cardiovascular and, possibly, metabolic risk related to OSA. Today, the best way to accomplish these aims is usually considered to fully eliminate all degrees of upper airway obstruction during sleep. The lowest CPAP that eliminates upper airway obstruction in all sleep stages and body postures in a patient is indicated as "optimal" CPAP.

Therefore, the question for an average OSA patient, in my opinion, is generally a matter of "more pressure or less?" rather than a question of "do those squigglies mean I have IFLs or not?" If you feel better with a higher pressure than what gets rid of apneas and hypopneas, then by all means, raise your pressure, if your doc doesn't mind, no matter what it is you are eliminating.

Question:

Why don't you quote from this book by Robert L. Chatburn:

http://www.amazon.com/Robert-L.-Chatbur ... dp_epwbk_0

[SleepingUgly]

I read this as him saying eliminating flow limitations, the lowest level of the interferences with breathing, equals having unobstructed breathing. The progression that results from increasing CPAP pressure is: convert OAs into HAs, then convert those HAs into FLs, and then convert those FLs into unobstructed breathing. When you achieve unobstructed breathing you will have no arousals.

Well, that is true that if you eliminate all respiratory events entirely, you will have no respiratory induced arousals. However, that doesn't mean that if you still have some FLs, you necessarily will always have arousals associated with them.

This gets back to a debate that I wasn't around for. Someone who was around for the debate, does Dr. Barry Krawkow like to titrate people until their FLs are eliminated even if the FLs are not associated with arousals? If so, why?

Oh, it's desirable to eliminate arousals alright.

But at what cost in terms of the complexity of the required therapy?

I don't know what you mean by "complexity of the required therapy", but if you mean what if eliminating arousals causes other problems, such as aerophagia, etc., then it's an individual decision. I think everyone agrees that oxygen saturations are to be eliminated. After that, it's a cost-benefit analysis. That's my uninformed opinion.

How good a handle can we get on the extent to which therapy resources need to be expended?

What?

To my way of thinking all this balances out only if the CPAP level that eliminates upper airway obstruction is also less than the highest CPAP level that will not induce CAs or OAs.

Right.

Is this in fact the case with all patients?

You want absolutes? Then, no.

I'm going to bow out here. Considering I know less than nothing and my carpal tunnel is acting up, I think my typing skills should be reserved for topics I know something about, like...um, uh... Well, something else.

[jnk]

. . . That's a new book, isn't it? . . .

Yep. Relatively speaking.

. . . So this author is saying the goal is no upper airway restrictions or disturbances at all. In other words the air passage should be clear and clean and slick as can be so air moves in and out with absolute freedom of movement, i.e., no OAs, no FLs, and a flow graph with uniform amplitude. I wonder, in light of the complexity of the human body and how it interacts with the environment it's in every day and night, how realistically needful or desirable this is. . . .

No one breathes perfectly. The goal is to find the lowest pressure at which one feels one's best, as I understand it.

Also, relief of upper airway obstruction is associated with resolution of intermittent hypoxemia and hemodynamic swings that accompany obstructive events, with a consequent reduction in long-term cardiovascular morbidity and mortality.

What the heck do those terms mean?

Steady O2 leads to improved blood chemistry and better heart health.

. . . But, as has been said many times on this forum, too high a pressure can prompt centrals. . . .

An overhyped fear in the context of simple OSA, in my opinion. When you are home-titrating for better numbers, the centrals show up as apneas and are thus accounted for and factored into your pressure choice.

. . . My sleep doc's assistant said too high a pressure can also cause OAs. How does the author address the conflicting results that may result from the pressure that eliminates "all degrees of upper airway obstruction?" but prompts CAs and possibly OAs?

The words I quoted were an overview of the state of mainstream OSA treatment, as I read them.

The important thing to remember is that the significance of any given "degree of upper airway obstruction" differs from patient to patient. That is why titration is about the effect the breathing seems to have on the sleep of that particular patient, not just how the patient breathes in general in comparison to other patients or some theoretical ideal, from what I've read as a patient.

I guess too high of a pressure during a titration might sometimes cause a central that then allows the airway to close, I don't know, I ain't no tech--but the temporary nature of the unstable breathing that can cause those kinds of centrals in a plain-vanilla OSA patient would mean that those temporary centrals likely would not matter in the long run, once they go away. That's why, in my opinion, home-machine data over time allows for the sweet-spot to be hit: the lowest pressure with the least number of significant events.

But I'm still learning this stuff.

Slowly.

And I have a long way to go.

[jnk]

. . . this book by Robert L. Chatburn . . .

Not sure which book you meant, since that link takes me to several. But whichever one you meant, feel free to send me a copy.

[idamtnboy]

This discussion has given me increased interest in setting my machine into auto mode and investigating pressure changes. My sleep doc's assistant said "go for it," the other day when I was there. I've been on steady 9 cm pressure since mid-August, no EPR, have leak rate down to zero almost every night, and have an AHI less than 1 with an erratic frequency of OAs and CAs. I have a lot of FL spikes every night generally ranging from about 0.05 to .35 and lasting only a few seconds. It'll be interesting to see what happens in APAP mode. I'll run that for a few weeks and then probably go back to CPAP mode, and then probably adjust CPAP pressure in small increments for a few weeks.

So, in two or three months I should be back here with some data, objective and subjective, to let you all know what effect pressure changes have on FL numbers. I have no compelling need to make changes as I feel good, but maybe could feel a bit better. My doc's assistant said there is value in the advice that if everything is going good, "leave well enough alone," but neither did she discourage doing some experimenting.

[jnk]

If I had a propensity for centrals, I would hesitate to run in auto mode. I would likely run a constant pressure, but just try a half-cm more pressure for a week and see how my numbers did and how I felt. If my numbers got worse or I felt worse, I would put my pressure back down. But if my numbers got better and I felt better, I might try another half cm for a week and see how I felt and how my numbers were then. And personally, I would want my doc on board with my doing that.

But that's just what I'd do. And mental stability isn't always my strongest suit.

[rested gal]

. . . But, as has been said many times on this forum, too high a pressure can prompt centrals. . . .

An overhyped fear in the context of simple OSA, in my opinion.

I agree with Jeff (jnk) that concerns about high CPAP pressures bringing on central apneas is not going to happen for most people with Obstructive Sleep Apnea and really shouldn't worry people as much as it does. Not that I think you're "worrying" about it, idamtnboy.

I particularly like this information from "StillAnotherGuest" on the page of links to Central Apnea discussions:

viewtopic.php?t=14225
Page 2

The phenomena of pressure-induced central apneas is tossed around far too freely. The vast majority of people do not get centrals because of ultra-therapeutic CPAP levels. BiLevel, Pressure Support (PSV) and Proportional Assist (PAV) Ventilation are another matter. You need some mechanism to drive the pCO2 below the sleeping apneic threshold, and plain old CPAP rarely is able to do that. OK, if you wanna argue that CPAP increases base lung volume (Functional Residual Capacity)(FRC), and since that increases gas exchange, some people can generate centrals that way, fine. But it's not as many as you might think.
SAG

SAG ("StillAnotherGuest") is also "deltadave", "Muffy" and "NotMuffy" on cpaptalk... and was "sleepydave" on another board long ago and far away.

[NotMuffy]

I don't celebrate Lent...

Actually, one does not really "celebrate" Lent, one "observes" (as in "complies with" vs "watches from the sideline") Lent.

[NotMuffy]

...so fork it over.

Of course!

Peace Be With You.

[NotMuffy]

To NotMuffy:
After some PMs with another forum member, and going back and rereading your November posts about flow limitations, I have a sufficient understanding of who, or what, you are to not be concerned about your credibility.

Wow, that's great! Thank you so !*#%ing much! I really can't tell you much I !*#%ing appreciate that!

(I said I observe Lent, not that I don't have plenty of faults.)

OK, off to Confession. Coming, SU?

[NotMuffy]

The vast majority of people do not get centrals because of ultra-therapeutic CPAP levels.

This incidence would be the number of patients with CompSAS tendency, which, although is generally considered to be 15%, I believe that's a very aggressive number. They threw tons of people in there with low CAIs, current definition of CompSAS being CAI > 5. But when they show examples of CompSAS, they show these huge runs of chain centrals of like 50 in a row.

The argument:

Yes!

No!

...if you wanna argue that CPAP increases base lung volume (Functional Residual Capacity)(FRC), and since that increases gas exchange, some people can generate centrals that way, fine. But it's not as many as you might think...

Especially when one considers that (1) there is a relationship between low FRC and the incidence of SBD; and (2) increasing FRC will undoubtedly improve obstructive SDB (see all of split_city's work).

We need an FRC-CPAP (PEEP) cartoon:

[SleepingUgly]

Wow, that's great! Thank you so !*#%ing much! I really can't tell you much I !*#%ing appreciate that!

(I said I observe Lent, not that I don't have plenty of faults.)

There's a glimpse of the Muffy we know! I was starting to worry that you had a terminal illness or something!

OK, off to Confession. Coming, SU?

All I have to do is go in that little room and say what I did wrong and I'm absolved, right?? My 7-year-old didn't even get off that easy this week when he had to do reparation for something he'd done wrong! What a deal! I'm there!

I really should give up sugar for Lent. Now that would be a true sacrifice. Just the thought makes my blood sugar dip dangerously low. Pass the jellybeans before I faint.

[NotMuffy]

All I have to do is go in that little room and say what I did wrong and I'm absolved, right??

Not exactly. You gotta do some stuff before, and some stuff after.

[avi123]

All I have to do is go in that little room and say what I did wrong and I'm absolved, right??

Not exactly. You gotta do some stuff before, and some stuff after.

We need to understand that those scholars who fill out thousands of pages in medical magazines get advancements and paid more by the noise that they are making with their publications. They also spread their hypotheses willy neely in the hope of fetching a Nobel award in the far future.

But how can we comply with our dumb CPAPs machines with any of those theories or should we let the Baby in the Avatars mature first? By that time the Task Force of the American Academy of Sleep Apnea might decide that some the verbiage is actually accurate.

[SleepingUgly]

All I have to do is go in that little room and say what I did wrong and I'm absolved, right??

Not exactly. You gotta do some stuff before, and some stuff after.

I hope it doesn't involve getting down on my knees, for whatever reason.