Yep! It should be so observable that nearly everyone with a ResMed machine would likely comment on the funny quivering that wakes 'em up sometimes. ResMed even admits that's an issue.-SWS wrote: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.
-SWS wrote: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.".Snoredog wrote:http://erj.ersjournals.com/cgi/content/ ... /22/6/1026Abstract
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.
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.
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.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.
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. .
I don't think this is strictly accurate, particularly since there are a number of semantic niceties involved.Snoredog (page 25 ) wrote: For example, AutoSet Spirit doesn't record snores or Flow Limitations yet they claim it is their main preemptive response criteria. It reports Hypopnea count from its LCD display and Rescan reports yet it doesn't detect or respond to them according to their website specs.
It is interesting that "hypopnea" as such, which IS detected and measured and reported by ResMed, nevertheless, as you point out, does not explicitly play a part in the ResMed algorithm, nor is it part of their concept of "flow limitation" as they describe it in their literature. I am curious how "flow limitation" (which I would otherwise have assumed would follow in a straightforward manner from direct measurement of output airflow volume over time - which obviously is available to ResMed machines since it defines hypopnea and apnea) is defined for reporting and algorithm utilization by other machines.ResMed AutoSet Spirit Clinical Manual wrote: Inspiratory flow limitation indicates silent partial obstruction. When your patient is breathing normally, the inspiratory flow measured by the unit as a function of time shows a typically rounded curve for each breath. As the upper airway begins to collapse, the shape of the inspiratory flow/time curve changes and the central section flattens. The AutoSet algorithm analyzes the shape of the central part of the curve for each breath and assigns a value as the amount of flattening. Inspiratory flow limitation, or partial airway closure, usually precedes snoring and obstruction. Detection of this flow limitation enables the unit to increase the pressure before obstruction occurs, making treatment pre-emptive. The Flattening Index is a measure of silent inspiratory airflow limitation. Flow limitation with loud snoring is handled by the snore detector. When a patient snores, sound is generated and the inspiratory flow/time curve is distorted by the frequency of the sound. .... In order to avoid falsely responding to central hypopneas, the AutoSet algorithm does not respond to hypopneas but rather to the associated snore or flow limitation.
Okay. I can see you weren't BS'ing after all. Your statement above seems to imply that you honestly but mistakenly thought that FOT implies exactly one method applied by everyone.Snoredog wrote:If their technique differs from FOT as you say it does then it is not FOT
Velbor - good points - my Reslink shows this dataVelbor wrote:
<snip>
However, when "night detail data" is captured by their ResLink add-on module, these parameters (subject to my next point) are displayed. The ResLink is not a sensor (other than in its guise as a pulse-oximeter); it captures "live" (on its own memory card, and with a faster sampling rate) more information than the blower RAM otherwise retains for transmission to the software.
<snip>
-SWS wrote:Okay. I can see you weren't BS'ing after all. Your statement above seems to imply that you honestly but mistakenly thought that FOT implies exactly one method applied by everyone.Snoredog wrote:If their technique differs from FOT as you say it does then it is not FOT
All FOT is not created equal. There are various FOT implementations kicking around out there. Some use a single fixed frequency while others use a selection of multiple frequencies that are intermixed. But that's not where FOT differences end. Varying pressure magnitudes are employed, depending on who's endeavoring forced oscillation and for what purpose. Forced oscillation has been attempted for these tasks: 1) ascertaining sum-total airway impedance, 2) mapping more localized impedances, 3) ascertaining respiratory airway mechanics (as you pointed out), 4) attempted apnea treatment (highly questionable IMHO), and 5) central-versus-obstructive differentiation.
Better argue with Resmed if you don't think their method qualifies as forced oscillation. They clearly refer to it as "forced oscillation" in their most recent patent continuation.
You're absolutely right, Doug.dsm wrote:Wasn't there a paper on how one company were using forced osc as a way to tickle the airway open during an occlusion ? - IIRC it was Sullivan himself who was doing major research in this area ?
-SWS wrote:That pretty much settles the matter in my mind: "FOT is for naught" where A10 is concerned.
But I still wonder why Resmed has continued this highly basic FOT patent for so many years. Perhaps the decision is based on nothing more than a "FOT because we ought" philosophy.
Well, darned if FOT didn't crop up again in 2006 Patent 6,988,498, filed in 2002 and Continuation-In-Part from the 1998 application.Snoredog wrote:Fact is you don't know for sure if they have used it or not. If their technique differs from FOT as you say it does then it is not FOT it is something else like IOS or some other technique.
There are plenty of papers on FOT and xpap therapy, only thing is not many with Resmeds name on it.
Just a couple of things worth mentioning about this:Patent 6,988,498 wrote:As previously discussed, one prior art method for avoiding unnecessary increases in pressure in response to open airway apneas is to determine the conductance of the airway during an apnea using the forced oscillation method, and only increase mask pressure if the conductance is less than a threshold. However, if the nasal airway is narrow or if the subject has lung disease, the airway conductance may be low even in the presence of an open airway and the forced oscillation method may still falsely increase pressure in response to open airway apneas. Conversely, the combination of the forced oscillation method with embodiments of the present invention has the added advantage that in most cases open airway apneas are correctly detected by the 'forced oscillation method', but in those cases where the forced oscillation method falsely reports a closed airway, the mask pressure will not increase above 10 cm H2O, thus preventing run-away increases in pressure. This is demonstrated in a third embodiment using the following pseudocode:
It is also worth noting that the methods in these claims evaluate snoring, flow limitations, flow vs time, and cardiogenic activity to determine a suitable response to apnea. Hypopneas, per se, are not a component of the ResMed algorithm, just as Velbor (I think) pointed out.Claims in Patent 6,988,498 wrote:1. A method for the administration of CPAP treatment pressure comprising the steps of: supplying breathable gas to a patient's airway at an initial treatment pressure, and repeatedly: determining a measure of respiratory airflow; determining the occurrence of an apnea from a reduction in said measure of respiratory airflow below a threshold; determining the duration of said apnea; and increasing the treatment pressure by an amount which is an increasing function of the duration of said apnea, and a decreasing function of the treatment pressure immediately before said apnea.
2. CPAP treatment apparatus comprising: a controllable flow generator operable to produce breathable gas at a pressure elevated above atmosphere; a gas delivery tube coupled to the flow generator; a patient mask coupled to the tube to receive said breathable gas from the generator and provide said gas, at a desired treatment pressure, to the patient's airway; a controller operable to receive input signals and to control operation of said flow generator and hence the treatment pressure; and sensor means located at the flow generator, in the delivery tube or at the mask that generates a signal input to said controller from which patient respiratory airflow is determined; and wherein said controller is operable to determine the occurrence of an apnea from a reduction in said respiratory airflow, determine the duration of said apnea, and cause said flow generator to increase CPAP treatment pressure by an increment that is an increasing function of said apnea duration and a decreasing function of the treatment pressure immediately prior to said apnea.
3. The CPAP treatment apparatus of claim 2, wherein there is a further determination of the occurrence of at least partial upper airway obstruction by the controller being further operable to detect the presence of characteristic changes in shape of an inspiratory flow versus time curve indicative of inspiratory airflow limitation.
4. A method for the administration of CPAP treatment pressure comprising the steps of: supplying breathable gas to the patient's airway at a treatment pressure; determining a measure of respiratory airflow; and determining the occurrence of an apnea from a reduction in the measure of respiratory airflow below a threshold, and, if having occurred, (i) determining the duration of the apnea; and (ii) increasing the treatment pressure by an amount which is an increasing function of the duration of the apnea, and a decreasing function of the treatment pressure immediately before the apnea.
5. The method of claim 4, wherein the increase in treatment pressure is substantially zero if the treatment pressure before the apnea exceeds a pressure threshold.
6. The method of claim 5, wherein the increase in pressure below the pressure threshold is an increasing function of the duration of the apnea, multiplied by the difference between the pressure threshold and the current treatment pressure.
7. The method of claim 6, wherein said increasing function of apnea duration is linear on apnea duration.
8. The method of claim 5, in which the pressure threshold is substantially 10 cm H2O.
9. The method of claim 4, wherein the occurrence of an apnea is determined by the steps of: calculating the RMS respiratory airflow over a short time interval; calculating the RMS respiratory airflow over a longer time interval; and determining an apnea if the RMS respiratory airflow over the short time interval is less than a predetermined fraction of the RMS respiratory airflow over the longer time interval.
10. The method of claim 4, comprising the further step of reducing the treatment pressure towards an initial treatment pressure in the absence of a further apnea.
11. The method of claim 4, comprising the further steps of: in the absence of an apnea, determining the presence of partial obstruction; and if present, increasing the treatment pressure.
12. The method of claim 11, in which the presence of partial obstruction is determined from the shape of the patient's inspiratory flow vs time curve.
13. The method of claim 11, in which the presence of partial obstruction is determined from the presence of snoring.
14. The method of claim 11, in which the presence of partial obstruction is determined from both the shape of the patient's inspiratory flow vs time curve, and from the presence of snoring.
15. The method of claim 14, in which the patency of the airway is determined by the presence of a cardiogenic component in the respiratory airflow.
16. The method of claim 14, in which the patency of the airway is determined by the steps of: modulating the treatment pressure at a known frequency; measuring the component of the respiratory airflow at said modulation frequency; calculating the conductance of the airway as the ratio of the amplitude of said component of the respiratory airflow to the amplitude of the mask pressure modulation; and determining that the airway is patent if the conductance exceeds a conductance threshold.
17. The method of claim 4, comprising the further steps of: if an apnea is occurring, determining whether the patient's airway is patent during the apnea; and if the airway is patent, setting the increase in treatment pressure to zero.
Alright... you really got me chuckling pretty hard with that proposed file structure. I tried to match that same theme with equal humor but had to yank it. My humorous attempt fell way short. It happens.Snoredog wrote: Got it, filing this latest under a new folder:
/SWSBS/RJ11_Air_Conditioning
/SWSBS/FOT_Funny_Oscillating_Technique
Interesting that someone else is using it, my guess is Wienmann
http://www.ncbi.nlm.nih.gov/pubmed/1270 ... t=Abstract
http://www.ncbi.nlm.nih.gov/pubmed/1122 ... t=Abstract
http://www.ncbi.nlm.nih.gov/pubmed/1115 ... t=Abstract
The above portion of patent 6,988,498 seems to bear out that AutoSet is the model/modality Resmed has in mind for this technique. The patent text above mentions that the machine will increase treatment pressure (hence Resmed's APAP). The text also states that the machine will not increase pressure beyond 10cm (implicitly in response to all apneas), to cover those cases where this forced oscillation method returns CA false negatives.Resmed Patent 6,988,498 wrote:Conversely, the combination of the forced oscillation method with embodiments of the present invention has the added advantage that in most cases open airway apneas are correctly detected by the 'forced oscillation method', but in those cases where the forced oscillation method falsely reports a closed airway, the mask pressure will not increase above 10 cm H2O, thus preventing run-away increases in pressure.
I was wondering specifically about these cases of expiratory-end-phase airway collapse. In these cases is there a frequent pattern of slight (respiratory cycle) sinusoidal decay leading up to that final expiratory cycle of obstructive collapse?split_city wrote:Rightio, here is a snapshot from a patient showing three obstructive events. It should be pretty obvious that collapse occurs towards the end of expiration and not during inspiration.
First of all, I shouldn't really hijack this thread with data from my current project. I will add some results to an earlier thread I started which talks about my work.-SWS wrote:I was wondering specifically about these cases of expiratory-end-phase airway collapse. In these cases is there a frequent pattern of slight (respiratory cycle) sinusoidal decay leading up to that final expiratory cycle of obstructive collapse?
That hypothetical sinusoidal decay I am wondering about might be reflected by peak pressure and/or flow progressively diminishing (perhaps slightly or even moderately) in previous respiratory cycles.
