some yokel in the peanut gallery wrote:The patent's logic does not preclude ancillary flow-limitation routines/logic from occurring that might be embodied in yet other designs/patent-descriptions
This excerpt adds relevance to the above statement:
patent application WO/2008/138040 wrote:[0076] Although M-shaped breaths may be rare, it may still be desirable to develop further methods and devices for detecting flow-limitation and/or improve existing methods and devices.
Prior-generation ResScan used the nomenclature
"flattening index" for that same ResScan graph line that is currently labeled "
flow limitation". I believe at that time Resmed relied exclusively on what Resmed calls a "flattening index" (but without the "M" shaped FFL analysis occurring) for their pre-S9 flow limitation detection and treatment. Here's how Resmed defines their "flattening index":
patent application WO/2008/138040 wrote: A flattening index is a non-dimensional feature [e.g., a real number) calculated using a patient's inspiration waveform. It attempts to measure essentially how flat-topped the waveform is.
Resmed also offers what they call six "rare" scenarios in which that
flattening index can fall short:
patent application WO/2008/138040 wrote: [0069] While a flattening index is an excellent measure of flow- limitation, it is designed to detect certain situations. However, in some particular implementations it has been observed not to address some rare situations. The following lists areas where we have made such observations:
[0070] 1. A five-breath moving average slows down the detection of flow-limitation. This is illustrated in FIG. 2. In FIG. 2, the top trace shows a plot of a traditional five-breath moving- average flattening index. The bottom trace shows a measure of respiratory flow. The patient begins to obstruct mildly and the flattening trace descends in staircase fashion at 202 due to the five-breath average. To the right of the graph the obstruction becomes more severe and progressively more "M" in shape. As shown, the flattening index eventually starts to reverse direction and increase rather than decrease with worsening obstruction.
[0071] 2. Because different inspiratory shapes can average to give a completely new shape, the five breath moving average can have consequences. This is illustrated in FIG. 3. FIG. 3 shows a sequence of so called, M-shaped obstructed breaths at 302 ending in an arousal at 304 followed by some reasonably normal recovery breaths at 306. As shown in the graph, both single- breath flattening and traditional flattening are high at the end of the sequence of M-breaths (the former getting to the maximum value quicker) and that after the arousal, traditional flattening actually falls below 0.1, not because the breaths are flattened, rather because the M-breaths averaged with the normal breaths to produce a pseudo-flat shape.
[0072] 3. The flattening index is not designed to detect M breaths. In fact, the flattening index goes high when M-shaped breaths occur. This is illustrated in Figs. 2 and 3.
[0073] 4. The flattening index can cause a pressure increase regardless of current ventilation or sleep state of the patient- user of the device.
[0074] 5. The heuristics applied to de-weight flattening might also result in under-treatment in some patients.
[0075] 6. The flattening index is subject to normal random variations that have consequences for the sensitivity and specificity of any algorithm that uses it to detect flow- limitation.
I'm fairly certain "flattening index" is still employed with the S9-generation machines in the real world, but the above "M" and "chair" shaped routines now take algorithmic/preemptive priority (over basic flow-flatness vs flow-roundness) regarding flow-limitation detection and treatment. And that can make for a significantly different machine response to a patient's FL compared to prior-generation AutoSet machines---but especially for patients who present "M" shaped flow limitations in significant numbers (with or without the "chair" shaped augmentation).
Despite the patent emphasis on "M" and "chair" shaped FL, the programming logic can still associate heightened FL severity with a more basic flat-shaped FL (FL without "M" characteristics):
- if (VERY_HIGH_FLATTENING AND LOW_VENTILATION) then FFL is "Mild-to-Moderate"
- if (EXTRA_HIGH_FLATTENING AND Ti-on-T tot _VERY__HIGH) then FFL is Moderate-to-Severe
- if (EXTRA_HIGH_MSHAPE AND Ti-on-T tot _VERY_HIGH) then FFL is Moderate- to-Severe
The red text refers to breaths scored with an extra-high flattening index but no "M" characteristics.
So I believe the "M" shaped FFL routine in this patent serves to preemptively albeit partially address the above 6 shortcomings associated with the "flattening index".
Patent Application WO/2008/138040 under discussion:
http://www.sumobrain.com/patents/wipo/A ... 38040.html
