Resmed vs. Respironics - Help

I have not had a chance in quite some time to look through Resmed's patent descriptions. However, I do have a few random thoughts to kick around about Resmed's repeatedly renewed FOT patents.

First, I would like to point to Resmed's S8 Autoset marketing literature on their own web site: http://www.resmed.com/en-us/dealers/med ... clinicians
Reading that description I still get the impression that the latest S8 AutoSet model employs A10---an algorithm that responds to snores and flow limitations above and below 10cm, but does not respond to apneas occurring above 10cm.

So what's going on with Resmed's FOT in the A10 algorithm (if anything) and why is it not given top billing in the marketing literature? Or perhaps more importantly, why does Resmed's own patented and long-standing implementation of FOT receive absolutely no flattering marketing play (assuming FOT is and was resident in A10)?

One possibility is that FOT plays a minor role in the algorithm, yet is not the mainstay of A10's pressure-based treatment strategy. Rather, the classic A10 pressure strategy is probably still the mainstay of the current S8 AutoSet's treatment. Quite possibly the current S8 AutoSet still cautiously refrains from responding to apneas at pressures above 10 cm.

However, some small yet significant rate of central induction (slight and transitional homeostatic maladaptation) still occurs across the patient population at pressures less than 10cm. While FOT may not be the mainstay of A10 treatment, it can still provide at least some added margin of efficacy improvement for apnea differentiation below 10cm. I suspect this basic FOT technique may have lower sensitivity and/or specificity compared to cardiac-oscillation-based differentiation of central apneas. Regardless, when employed at pressures below 10cm A10 may yield apnea response similar to this speculative statement:

Perhaps: 1) A10 cautiously refrains from responding to all apneas occurring at or above 10cm, and 2) A10 responds to all apneas below 10cm, except those apneas that FOT can definitively identified as central (thus only some added margin of efficacy via this highly basic FOT differentiation.

Here FOT plays a minor role toward only a slight margin of increased efficacy. Here a highly basic FOT implementation presumably does not enjoy high sensitivity and/or specificity. So what incentive, then, would there be to place this very basic, very minor contributor in the marketing literature if this scenario were real? None that I could think of.

A closer examination of this highly basic FOT technique (but with older sensor technology in mind):

patent 6,138,675 wrote:As further shown in Figure 14, the air flow induced by the pressure modulation is separated from air flow induced by other factors (such as heartbeat), by demodulating the measured air flow signal, fn, by a demodulator.

This is not to say the the sensor and algorithmic technique can accurately detect cardiac oscillations (heartbeat) for purposes of differentiation. This statement simply speaks of the need to filter out various sources of signal noise, such as heartbeat. To say that heartbeat signal noise cannot be accurately processed does not say that the noise source itself does not need to be filtered out as noise.

patent 6,138,675 wrote:Approximately 5 seconds into the apnea a 2 Hz, 1 cm H2O pressure oscillation is induced (applied) for 6 seconds (i.e., between t=14 s to t=20.5 s). It can be seen that this pressure modulation induces a corresponding 2 Hz modulation in the respiratory air flow signal.

The older hall-effect flow sensor should have been able to employ this highly basic technique. And the algorithm would have had incentive to clean up cardiac oscillation and other flow-signal noise sources. Yet the algorithm would have understandably not relied on cardiac flow pulsations, as if they somehow comprised reliable signal information (with respect to Resmed's older hall-effect flow-based transducer).

I'm currently thinking this highly basic forced oscillation technique may have been employed by Resmed throughout the years, toward but a slight margin of increased efficacy for apneas occurring below 10cm. If so, then Resmed may have perceived no great incentive to place such a basic technique in their marketing literature---a technique that conceivably yields but marginal and circumstantial support to the A10 algorithm. Regardless, I suspect this very basic forced oscillation technique must be useful to Resmed. Otherwise they would not have continually renewed the corresponding patents throughout the years.

Some questions in my mind: Does A10's FOT deserve mid- or low-level billing merely as "supporting actor", applied toward all apneas under 10cm? Might FOT simply enjoy a rare cameo appearance, perhaps much more rarely employed under certain infrequent scenarios based on analysis of temporal variables? Or is FOT completely absent from the A10 algorithm? When I do get a chance to look through the Resmed patents, I'll be looking with an eye toward just how that highly basic FOT may factor in Resmed's A10 algorithm (unless Bill has already spotted the answer for us!).

-SWS wrote:First, I would like to point to Resmed's S8 Autoset marketing literature on their own web site: http://www.resmed.com/en-us/dealers/med ... clinicians
Reading that description I still get the impression that the latest S8 AutoSet model employs A10---an algorithm that responds to snores and flow limitations above and below 10cm, but does not respond to apneas occurring above 10cm.

Color me confused now. When I went to the ResMed site you referenced, -SWS, I expected to see some reference to the machine's ability to detect central apneas (in some form), but not a word about that capability is there.

Here's what they say:

ResMed S8 Autoset website wrote:Autoset® Technology
Automatically adjusts pressure on a breath-by-breath basis to suit patient needs as they vary throughout the night.

As a result, the patient receives the minimum pressure required for effective therapy - improving comfort, reducing pressure-related side effects, and improving compliance.

Our AutoSet devices also maintain pressure by compensating for mask leak.

Preemptive Response
Increases pressure in response to inspiratory flow limitation, which typically precedes snore and obstruction. This early intervention prevents snoring and obstructive apneas, thereby reducing respiratory arousals.

Sudden Apnea Response
Increases pressure relative to the severity of the event. If no further events occur, AutoSet devices reduce the pressure back to a minimum level.

Apneas may occur suddenly, without being preceded by flow limitation or snore. These sudden apneas are generally associated with sleep onset, change in body position, or rapid eye movement (REM) onset.

AutoSet Algorithm
Increases pressure in response to the severity of the three parameters (inspiratory flow limitation, snore, and apnea):
* The greater the flow limitation, the more pressure delivered
* The louder the snoring, the more pressure delivered
* The longer the apnea, the greater the increase in pressure
Normalizes sleep while delivering a mean pressure typically 37% lower than fixed pressure therapy.

OK. For me the picture seems a lot clearer now. I looked in the clinicians sections of the ResMed website, too, and not a word about either FOT or CA detection. (The patient manual for the S8 Autoset was absolutely worthless, by the way - a total waste of internet resources to spend the bandwidth downloading it.) The characteristics above are certainly in agreement with the patent descriptions. The machine attempts to pre-emptively prevent apnea events, but failing that it will raise pressure almost immediately as described in the patents.

It looks like those central apnea detection features are
1) reserved for another machine, or
2) didn't bear out in clinical trials, or
3) associated sensor technology is currently too costly to implement.

Just my speculation, of course, but how many possibilities can there be anyway.

I feel like I'm getting a pretty good idea of how the ResMed S8 Autoset machine compares with both the Respironics and PB APAP's. My preconceived notion of it being inferior looks to be borne out by the evidence. That doesn't mean it won't work well for most folks. That doesn't even mean that it wouldn't be the best APAP for some folks. It just means that the other machines appear to offer real advantages over the ResMed S8 Autoset. Am I being too judgemental? Perhaps. My opinion can be easily changed. It wasn't very many hours ago that I entertained thoughts about trying out an S8 Autoset to see if it might work better for me. I'm finding it kinda hard to even begin to justify the cost of doing that now though, just based on what's been discussed in this thread about the Respironics and PB machines.

Regards,
Bill

Bill, the summary of my own ruminations with respect to FOT is that a couple possibilities are likely (with FOT playing either no role or a very minor role in AutoSet). Those two FOT scenarios in my own mind entail: 1) CA detection via FOT is just not occurring in A10 (most likely scenario IMO), or 2) if CA detection via FOT occurs in A10, then it yields such low utility (presumably via low CA sensitivity/specificity) that perhaps it's not even worth mentioning to the general public (the less likely of those two scenarios IMO).

One hypothetical Resmed design philosophy supporting that second scenario might go something like this: "Any reasonably-achieved efficacy gain is worth supporting---even if only a marginal gain and even if reserved for limited apnea response below 10cm." Manufacturers acknowledge a statistical likelihood of central induction at 8cm and an even greater statistical margin of likelihood occurring at 10cm across the patient population. Resmed conceivably may employ that highly basic and less sensitive FOT to better cope with central induction probabilities between 8cm and 10cm. Again, marginal gains being better than no gains whatsoever (yet perhaps not worth mentioning or "spinning" to the general public).

Interestingly, I don't see any other Resmed models having been better candidates to employ this highly basic FOT over all those years than AutoSet itself. And, of course, FOT patent 6,138,675 is listed as one of the patents employed by the current S8 AutoSet.

So a compelling question is: if Resmed does not employ this highly basic FOT (which even older hall-effect flow sensors are capable of) , then why keep renewing this FOT-based patent again and again? What a compelling little Resmed patent mystery. But to simply observe that FOT is not mentioned to the public is not sufficient evidence to completely dismiss the possibility from the algorithm IMHO.

As to which APAP machine is superior? Almost everybody seems better at determining that without supporting epidemiology than I am. I suppose that's my own data-oriented hesitancy at play. I personally suspect a variety of social factors may have skewed very many of the APAP-efficacy anecdotes on the apnea message boards (peer-based dynamics, typical socioeconomic and even sociopolitical interplay, etc). And deductive/syllogistic type reasoning alone very often seems to fall short regarding analysis of high-order complexity (even in this case of endeavoring to project a complex two-way response of proprietary biomed systems---against a more complex and diversely disordered human physiology).

-SWS, I'll respond to your comment about AutoSet, FOT and patent 6,138,675 first.

-SWS wrote:Interestingly, I don't see any other Resmed models having been better candidates to employ this highly basic FOT over all those years than AutoSet itself. And, of course, FOT patent 6,138,675 is listed as one of the patents employed by the current S8 AutoSet.

Patent 6,138,675 includes twenty-one claims, of which eleven are independent. ResMed might have used any combination of those independent claims in the AutoSet. Only one of the independent claims relates to FOT, although there is also one associated dependent claim relating to FOT. Of the eleven independent claims, two are independent apparatus claims for BiPAP, while two are independent apparatus claims for CPAP.

Now, the FOT claim makes no mention of applicability to either CPAP or BiPAP, so presumably the original intention was to keep options open and allow use with either CPAP or BiPAP. Or neither, for that matter. FOT falls under an independent (i.e., stand-alone) claim. When ResMed states that patent 6,138,675 is used in AutoSet, that could mean that only one independent claim from the patent actually is being used in that particular machine, however unlikely that might actually be.

So, with that as background ...

-SWS wrote:Bill, the summary of my own ruminations with respect to FOT is that a couple possibilities are likely (with FOT playing either no role or a very minor role in AutoSet). Those two FOT scenarios in my own mind entail: 1) CA detection via FOT is just not occurring in A10 (most likely scenario IMO), or 2) if CA detection via FOT occurs in A10, then it yields such low utility (presumably via low CA sensitivity/specificity) that perhaps it's not even worth mentioning to the general public (the less likely of those two scenarios IMO).

Continuing that thought ... It strikes me that if FOT had lived up to initial expectations then ResMed would be employing it in all of their high-end products. ResMed is, after all, competing in a competitive marketplace where performance differentiators matter, at least for similarly priced products. The fact that there is no mention of FOT in their marketing literature suggests that it is not being used at all, likely because of the problems ResMed states are associated with its use (as I detailed earlier today).

Patent 6,988,498 wrote:This 'forced oscillation method' requires the ability to modulate the mask pressure at 4 Hz, which increases the cost of the device. Furthermore, the method does not work in the presence of high leak, and can falsely report that the airway is closed if the subject has a high nasal or intrapulmonary resistance.

These problems do not appear to be either insignificant or restricted to a small percentage of the patient population. My guess would be that while FOT might work just fine for some, it was a disaster in a clinical trial, and that the simpler approach of just raising pressure worked better than FOT in clinical trials. That would certainly explain why ResMed pursued the four "identically" worded patents which included 6,988,498. If FOT had worked, it would have been a clearly superior capability, at least compared with the simple pressure increase responses which have the drawback of actually making therapy worse for those minority of patients who are susceptible to pressure-induced CA. All just my best guess, of course. FOT sure looks like a dead-end though. The patents which describe FOT in detail were renewed, IMHO, because of their other independent claims having nothing to do with FOT. (Again, just my guess.)

Let me know if you think my logic is faulty here, -SWS. (Did I mention I'm no expert on the subject matter?) My conclusions are drawn strictly from the info we've been discussing here. That info is beginning to look rather compelling, but perhaps that's just an illusion.

Patent 6,988,498 wrote:One hypothetical Resmed design philosophy supporting that second scenario might go something like this: "Any reasonably-achieved efficacy gain is worth supporting---even if only a marginal gain and even if reserved for limited apnea response below 10cm." Manufacturers acknowledge a statistical likelihood of central induction at 8cm and an even greater statistical margin of likelihood occurring at 10cm across the patient population. Resmed conceivably may employ that highly basic and less sensitive FOT to better cope with central induction probabilities between 8cm and 10cm. Again, marginal gains being better than no gains whatsoever (yet perhaps not worth mentioning or "spinning" to the general public).

That would certainly be a rosy scenario, -SWS, but we already have evidence suggesting otherwise (I think). The most utility for FOT, as I understand things, would be at pressures above 10 cm. It is at those higher pressures that differentiation between central and obstructive apnea becomes most important.

ResMed acknowledged the failure mode for FOT is that it often indicates obstructive apnea when central apnea is actually present. This would be a disastrous failure mode. This failure mode would result in increased apnea for some significant percentage of the patient population as the machine kept raising pressure in the presence of centrally-based events. Even if the failure mode had been reversed, so that some folks who had only obstructive apnea were labeled with central apnea, that would have also led to a large percentage of the patient population being under-treated; again an increase in residual apnea events compared with the simple algorithm which simply quits raising pressure at 10 cm upon apnea detection.

-SWS wrote:So a compelling question is: if Resmed does not employ this highly basic FOT (which even older hall-effect flow sensors are capable of) , then why keep renewing this FOT-based patent again and again? What a compelling little Resmed patent mystery. But to simply observe that FOT is not mentioned to the public is not sufficient evidence to completely dismiss the possibility from the algorithm IMHO.

Granted, I didn't make a compelling case in my earlier post, -SWS. Perhaps I have done better in this post. The FOT portion of the patent simply got a free ride. ResMed had no need for FOT, per se, but did need the other independent claims within the patents.

-SWS wrote:As to which APAP machine is superior? Almost everybody seems better at determining that without supporting epidemiology than I am. I suppose that's my own data-oriented hesitancy at play. I personally suspect a variety of social factors may have skewed very many of the APAP-efficacy anecdotes on the apnea message boards (peer-based dynamics, typical socioeconomic and even sociopolitical interplay, etc). And deductive/syllogistic type reasoning alone very often seems to fall short regarding analysis of high-order complexity (even in this case of endeavoring to project a complex two-way response of proprietary biomed systems---against a more complex and diversely disordered human physiology).

Now, that's a mouthful, -SWS. .

I'm in general agreement with ya though. Only thing is, I think that by determining the operational and performance differences between machines (at least to the best of our judgement) and explicitly outlining what those differences are all of us here benefit from having the ability to make better informed decisions about which machine might benefit our own unique circumstances. (Not that I'm on a crusade or anything ... ). Besides that, I'm actually having fun going through this stuff.

Regards,
Bill ( ... whose true motivation is for purely selfish reasons regarding his own therapy ... )

Bill SWS,

Good stuff, keep it coming

DSM

NightHawkeye wrote:Patent 6,138,675 includes twenty-one claims

Bill, that's a very good point. Any one of those claims showing up in the S8 AutoSet warrants a citing of that patent number.

NightHawkeye wrote:Now, the FOT claim makes no mention of applicability to either CPAP or BiPAP, so presumably the original intention was to keep options open and allow use with either CPAP or BiPAP.

Bill, I can't think of what straight-pressure CPAP or fixed BiLevel would have been doing with FOT detection from 1998 until very recently. Back when Resmed's FOT patent first started, neither CPAP nor BiLevel detected events, let alone responded to them. Fixed-pressure CPAP delivered straight pressure while BiLevel delivered two fixed settings. In recent years only some Resmed CPAP and BiLevel machines started recording AHI---with none of them reporting central apneas.

IMO Resmed AutoSet was the only likely candidate for FOT throughout the years: AutoSet event-detects and then either responds to those detected events or selectively refrains. FOT would conceivably serve that purpose about selectively refraining.

Aside from that 10cm statistical margin, there is also a lesser 8cm margin acknowledged by the industry. That 8cm statistical margin is precisely where Respironics starts imposing their three-pressure-increment limit. IMO it's not inconceivable that Resmed might employ FOT-based caution toward observing this less significant 8cm barrier---then completely refrain to all apnea-response beyond the more burdensome 10cm statistical margin.

If Resmed is or was using this highly basic FOT, then it truly must have been marginally useful at best IMO. This FOT implementation is so basic that even a hall-effect flow sensor could measure those highly basic returns. Bottom line is that I still suspect FOT is not in A10, and yet I can't completely rule it out in my own mind either.

Would love to hear SAG's FOT ruminations also. I know he has fiddled with this mystery fraught with FOT on more than one occasion...

...or so I thought.

-SWS wrote:Bill, I can't think of what straight-pressure CPAP or fixed BiLevel would have been doing with FOT detection from 1998 until very recently. Back when Resmed's FOT patent first started, neither CPAP nor BiLevel detected events, let alone responded to them. Fixed-pressure CPAP delivered straight pressure while BiLevel delivered two fixed settings. In recent years only some Resmed CPAP and BiLevel machines record AHI---with none of them reporting central apneas.

Very interesting point, -SWS. I have been assuming applicability was to APAP. Hence our discussion centering on the Autoset. However, if a machine could differentiate between obstructive and central events that would be a useful piece of information for fine-tuning therapy, even with fixed pressure CPAP, or BiPAP. (Although it would only matter to a handful of physicians, I suspect that handful of guys are the target audience for the high-end machines.) Then, there's the matter of BiPAP ... (I wondered if you'd correct me on that -SWS. ), specifically auto-BiPAP. (Oops, wrong company again ... )

Regards,
Bill

NightHawkeye wrote:

Snoredog wrote:Only problem is back in 2000 when the patent was granted, they didn't have a machine with a sensor installed that could detect cardiac oscillations.

This particular patent was filed in 1997, but is a continuation of a 1994 application. Seems like a long time ago.

Not that that matters too much now. I took a peek at ResMed patent 7,320,320, dated January 22, 2008. Brand spanking fresh new patent, except that it's got the same stuff as the 2000 patent, including the exact same 20 pages of charts and flow graphs. Guess if you've seen one, you've seen 'em all. I'm sure they musta changed something. It describes sonic bursting as well as the cardiac sensing. Sure seems about the same as what I read last night.

Now I see what changed ... they gave the the sonic burst technique a name. They now call it Forced Oscillation Technique (just like ya said, -SWS). Funny, they didn't call it FOT earlier. But, hey, the name's almost novel enough to warrant a patent all by itself.

-SWS wrote:That patented technique seems basic compared to some forced oscillation techniques employed in respiratory medicine. Regardless I would have expected Resmed to capitalize with a flattering spin in their marketing literature.

Assuming that they're even using FOT. They might not be. They don't have to use it. Maybe they don't. I also ran across a hose-cleaning patent of ResMed's which includes a patient warning mechanism to make sure the patient isn't hooked up to the machine when the cleaning technique fires up. Great stuff! I can hardly wait to spend my money on one of those.

Regards,
Bill

Definition of CIP - Continuation-In-Part: According to Patent Prospector (http://www.patenthawk.com)

"A continuation-in-part is an application filed during the lifetime of an earlier nonprovisional application, repeating some substantial portion or all of the earlier nonprovisional application and adding matter not disclosed in the said earlier nonprovisional application."

Definition of Divisional Application: According to Patent Prospector

a divisional application is defined as "[a] later application for an independent or distinct invention, carved out of a pending application and disclosing and claiming only subject matter disclosed in the earlier or parent application . . . ." MPEP § 201.06. A divisional application "is often filed as a result of a restriction requirement made by the examiner.

I've been assuming that FOT (which senses whether the airway is "open" or "closed") and the cardiac sensing capabilities resulted from the patent examiner rejecting those portions of the original application, however, when I went back and looked at the claims in patent 5,704,345 this morning, I found that they were, in fact, already included in the original claims. Hence, CIP.

Thank you for the correction, Snoredog, along with the elaboration on Continuation-In-Part.

Regards,
Bill

Snoredog wrote:I'm sure FOT is included in models like the Adapt SV and ST

I'm not so sure I agree with that statement, Snoredog.

So far I don't see how FOT could have been utilized by any past or present ST treatment algorithm. The ST machines (to date) deliver but two fixed pressures, with absolutely no event handling. And the ST doesn't bother to factor in obstructive-versus-central differentiation to either trigger or provide a timed backup rate. The ST doesn't even report central apneas. In my view there's no central-versus-obstructive differentiation going on in the ST model. FOT does not seem likely in the ST platform for that reason IMHO.

I have yet to spot any central-versus-obstructive differentiation going on in the Adapt SV algorithm either (FOT based or otherwise). EEP is set up in the Adapt SV model to manually address obstructive components (with absolutely no automated obstructive event handling occurring in that machine). Then the remaining PS and F parameters in the Adapt SV are used exclusively to centrally ventilate a patient (with no obstructive differentiation occurring). And even in the enhanced model there is no reporting of central apneas.

I'm still of the opinion that AutoSet was the only good candidate for FOT throughout the years (short of machines reserved for clinical or research use). But the new VPAP Malibu and VPAP Auto are two recent candidates for FOT IMO. Both of those BiLevel machines are targeted for the OSA crowd. Both models event-handle. And both models would have incentive to selectively refrain from increasing their static pressure component (after detection of either induced or incidental central apneas).

-SWS wrote:

snoredog wrote:I'm sure FOT is included in models like the Adapt SV and ST

I'm not so sure I agree with that statement, snoredog.

Curious, though, how you suspect FOT might be utilized by any ST treatment algorithm. The ST machines deliver but two fixed pressures (with absolutely no event handling). And the ST doesn't bother to factor in obstructive-versus-central differentiation to either trigger or provide a timed backup rate. The ST doesn't even report central apneas. In my view there's no central-versus-obstructive differentiation going on in the ST model. FOT does not seem likely in the ST case IMHO.

I have yet to spot any central-versus-obstructive differentiation going on in the Adapt SV algorithm either (FOT based or otherwise). EEP is set up in the Adapt SV model to manually address obstructive components (with absolutely no obstructive event handling occuring in that machine). Then the remaining PS parameters in the Adapt SV are used exclusively to centrally ventilate a patient (with no obstructive differentiation occurring). And even in the enhanced model there is no reporting of central apneas.

I'm still of the opinion that AutoSet was the only good candidate for FOT throughout the years. But the new VPAP Malibu and VPAP Auto are two recent candidates for FOT IMO. Both of those BiLevel machines are targeted for the OSA crowd. Both models event-handle. And both models would have incentive to selectively refrain from increasing their static pressure component (after detection of either induced or incidental central apneas).

Snoredog wrote:I think Bill is a bit confused with the 420e's cardiac oscillations vs FOT. I see FOT more like sonar,

LOL. Yeah, I get confused a lot. Not on that one though, at least I don't think I am.

The ResMed patents describe two distinctly different algorithms relating to central apnea. One is the FOT ("sonar"), while the other measures cardiac rhythm. Both of these algorithms are used to determine independently whether a central apnea has occurred. According to the patents, it appears that each algorithm is capable of independently determining central events without help from the other algorithm.

I spoke of them together only because they were described as providing very similar capability. -SWS and I went back and forth a lot on FOT, but didn't get into much detail on cardiac sensing, even though that is a prominent feature in the ResMed patents. Sorry about that ... Neither capability appears to be supported in the Autoset.

Regards,
Bill

Snoredog wrote:

Abstract

The forced oscillation technique (FOT) is a noninvasive method with which to measure respiratory mechanics. FOT employs small-amplitude pressure oscillations superimposed on the normal breathing and therefore has the advantage over conventional lung function techniques that it does not require the performance of respiratory manoeuvres.

The present European Respiratory Society Task Force Report describes the basic principle of the technique and gives guidelines for the application and interpretation of FOT as a routine lung function test in the clinical setting, for both adult and paediatric populations.

FOT data, especially those measured at the lower frequencies, are sensitive to airway obstruction, but do not discriminate between obstructive and restrictive lung disorders. There is no consensus regarding the sensitivity of FOT for bronchodilation testing in adults. Values of respiratory resistance have proved sensitive to bronchodilation in children, although the reported cutoff levels remain to be confirmed in future studies.

Forced oscillation technique is a reliable method in the assessment of bronchial hyperresponsiveness in adults and children. Moreover, in contrast with spirometry where a deep inspiration is needed, forced oscillation technique does not modify the airway smooth muscle tone. Forced oscillation technique has been shown to be as sensitive as spirometry in detecting impairments of lung function due to smoking or exposure to occupational hazards. Together with the minimal requirement for the subject's cooperation, this makes forced oscillation technique an ideal lung function test for epidemiological and field studies. Novel applications of forced oscillation technique in the clinical setting include the monitoring of respiratory mechanics during mechanical ventilation and sleep.

http://erj.ersjournals.com/cgi/content/ ... /22/6/1026

O.K. The above FOT method is a much more refined technique than Resmed's method and it is used toward a broader objective as well. It is employed as a recommendation by one or more third parties (not Resmed) as a : "method with which to measure respiratory mechanics.".

By contrast Resmed uses a highly basic FOT technique to differentiate central apneas from obstructive apneas. What you just cited: 1) isn't Resmed, 2) isn't the same FOT method employed by any of Resmed's xPAP machines, and 3) doesn't even serve the same objective Resmed states in their patent.

Let's acknowledge that there are different FOT methods employed for a narrow albeit interrelated variety of reasons in respiratory medicine. Resmed's methods and reasons do not fit the third-party statements above IMO.

Snoredog wrote:FOT is really not needed when you use the A10 as you are not going to respond to either obstructive or central once that kicks in.

And this is my good bud who so freely claims that everyone else is high on the BS meter. Wasn't it my insightful friend, Snoredog, who has repeatedly claimed throughout many posts that central induction can occur below 10cm. Say, maybe around 8cm in significant numbers warranting design observances by manufacturers. There's a viable incentive to deploy FOT-based central differentiation below 10cm, Snoredog.

Broad objective statements aside, I have yet to see any specific reason or method warranting that Resmed's ST or Adapt SV algorithms have come even close to utilizing FOT. However, as a broad design objective I agree that we can certainly dream up algorithmic uses for FOT in machines that are targeted for central patients. However, those FOT techniques would need to be more sophisticated than the patented FOT currently up for discussion IMO. .

-SWS, in the heat of debate you made a comment which piqued my interest a little ...

-SWS wrote: ... central induction can occur below 10cm. Say, maybe around 8cm in significant numbers warranting design observances by manufacturers. There's a viable incentive to deploy FOT-based central differentiation below 10cm ...

I agree. That's why I find it puzzling that we have no evidence supporting ResMed's use of either FOT or cardiac sensing in the Autoset.

The sequence of patents is such that sonic bursting and cardiac sensing were described in the original patent application. (1994) Then, just a few years later (1998) the patent application covering the A10 algorithm was introduced. (At least I think the quad of patents I discussed yesterday relate to the A10, but correct me if I'm wrong here, please.) That suggests (to me at least) that ResMed likely found that leveling pressure increases off at 10 cm was more useful for effective therapy than distinguishing central from obstructive events. The newer patent application even indicates significant obstacles to general usage of the FOT technique.

The only piece which doesn't fit in with ResMed abandoning FOT altogether is the fact that FOT was included in the Continuation-In-Part patent application ResMed filed in 2000, two years after disclosing the limitations of FOT in 1998. If they weren't abandoning FOT then why include it in the CIP? Perhaps they still had hopes for it, or somebody wasn't absolutely convinced that FOT wasn't viable. it is also worth noting that FOT was not included in the most recent Continuation-In-Part application filed in 2003. Only cardiac sensing was included in that application for Central Apnea determination.

Just some thoughts. Not sure I have too much of a point to make.

Regards,
Bill

NightHawkeye wrote:The only piece which doesn't fit in with ResMed abandoning FOT altogether is the fact that FOT was included in the Continuation-In-Part patent application ResMed filed in 2000, two years after disclosing the limitations of FOT in 1998. If they weren't abandoning FOT then why include it in the CIP?

I agree, Bill. That's the intriguing part that still puts that ever-so-slight doubt in the back of my mind that maybe, just maybe, Resmed hasn't abandoned FOT altogether.

And the only theory that I could personally think of was that A10 refrains from all apnea response at 10cm---while employing FOT-based differentiation to cope with the lesser 8cm-to-10cm statistical margin (with this extremely basic FOT method being highly imprecise---and therefore not used at the more menacing 10cm statistical margin). And I still have my serious doubts about that theory.

Resmed's 2 Hz FOT really shouldn't be that hard to observe during a PSG. The fact that I don't recall any posts or articles ever having mentioned seeing this highly basic 2Hz FOT also makes me truly doubt that FOT is part of A10.

I'm about ready to boot FOT with either foot. Still a very interesting subtopic to have pondered IMHO!