What are Flow Limitations and Variable Breathing?

What are Flow Limitations and Variable Breathing?
I see these reported in Encore Pro Analyzer and really don't know the significance, or even what is being measured. Anyone got a handle on this? I have between 2 and 14 flow limitations per night.

To put this very simply ...

1) Obstructive apnea is where the airflow gets blocked by constriction in the throat usually when the back of the tongue plugs the airway

2) Hypopneas on a cpap machine, are scored when air flow drops by 50% for more than 10 secs (this varies a bit between brands)

3) Flow LImitations are similar to hypopneas but didn't get scored as one but are still very relevant (maybe the drop only lasted 6 secs)

For variable breathing, the issues get complex - I am happy to let SWS or some other person describe them as there is likely to be quite a bit of debate on what it really means.

DSM

Thanks for the insights. I was just trying to determine if variable breathing was a significant factor and if so, how its mitigated.

I did some homework on the Respironics Variable Breathing aspect & from the patent got this ....

#2
(originally all the below data was posted in a thread on bilevels - once I determined this info applied to a std Auto I shifted it here) ...

#3
Just adding as a summary, the main way this patent describes how it corrects 'Variable Breathing' is mentioned in paras 177 & 178 & one para says that if pressure has been rising (due to other events) and VB occurs, the machines will start to lower pressure in 0.5 CMs increments & the other action occurs when pressure was going down and VB is detected, then the machine will start raising pressure in 0.5 increments - it seems CMs will go down or up depending what was happening prior to VB being detected.

#4 Variable Breathing is 'erratic' breathing that is the person's rate and volume fluctuates erratically. This is different to 'Periodic Breathing' which is usually defined as 'cyclic' changes to volume - Cheynes-Stokes Respiration is a classic form of 'Periodic Breathing'. The sleeper's airflow volume steadily grows over a few minutes (waxes) then drops steadily for a few minutes (wanes) in a 'cyclic' fashion - a pattern of waxing & waning. Cheynes-Stokes is associated with CHF (Congestive Heart Failure).


D

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This is from the Respironics patent - Variable Breathing & how it is dealt with (see highlighted italic text for the main description of VB) ...

"3. ... a variable breathing control layer that monitors the flow signal to determine whether the patient is experiencing erratic breathing, and causes the pressure generating system to adjust the pressure of the flow of breathing gas responsive to detection of erratic breathing;" ...

"
18. An auto-titration pressure support system comprising: a pressure generating system adapted to generate a flow of breathing gas at a selectable pressure level and to change the pressure level from a base pressure during a respiratory cycle; a patient circuit having a first end adapted to be coupled to the pressure generating system and a second end adapted to be coupled to an airway of a patient; a monitoring system associated with the patient circuit or the pressure generating system and adapted to measure a parameter indicative of a flow of gas in such a patient's airway and to output a flow signal indicative thereof; and a controller coupled to the monitoring system and the pressure generating system, for controlling the base pressure based on the output of the monitoring system, wherein the controller determines a breathing parameter from the flow signal, and wherein the controller analyzes a variability of the breathing parameter and controls the pressure generating system based on a result of the variability analysis.

19. The system of claim 18, wherein analyzing the variability of the breathing parameter includes calculating a weighted peak flow and a best-fit trend line for the weighted peak flow over a plurality of breathing cycles, and calculating a variable breathing number (VB#) as follows: 9 VB # = standard deviation adjusted mean flow ,wherein the standard deviation is calculated as a standard deviation of the weighted peak flows over a plurality of breathing cycles from the best-fit trend line, and wherein the adjusted mean flow is determined based on an actual patient flow determined from the flow signal."


Variable Breathing is though one of the low priority aspects of the algorithm ...

"The system of claim 3, wherein: (1) the flow limit control layer has a higher priority than the snore control layer, the big leak control layer, the apnea/hypopnea control layer, the variable breathing control layer, and the auto-CPAP control layer; (2) the snore control layer has a higher priority than the big leak control layer, the apnea/hypopnea control layer, the variable breathing control layer, and the auto-CPAP control layer and has a lower priority than the flow limit control layer; (3) the big leak control layer has a higher priority than the apnea/hypopnea control layer, the variable breathing control layer, and the auto-CPAP control layer and has a lower priority than the flow limit control layer and the snore control layer; (4) the apnea/hypopnea control layer has a higher priority than the variable breathing control layer, and the auto-CPAP control layer and has a lower priority than the flow limit control layer, the snore control layer, and the big leak control layer; and (5) the variable breathing control layer has a higher priority than the auto-CPAP control layer and has a lower priority than the flow limit control layer, the snore control layer, the big leak control layer, and the apnea/hypopnea control layer."



Here is a very detailed description of Variable Breathing from the patent ...

[0159] H. Variable Breathing Control Layer

[0160] The Auto-CPAP controller, which is described in the next section, relies on the ability to trend the steady rhythmic breath patterns associated with certain stages of sleep. When a patient is awake, in REM sleep, or in distress, breathing tends to be more erratic and the Auto-CPAP trending becomes unstable. It is, therefore, important to interrupt the Auto-CPAP controller if the patient's breathing pattern becomes too variable. In essence, the variable breathing control layer keeps the Auto-CPAP control layer from being too erratic.

[0161] Referring back to FIG. 2, the variable breathing control layer, which is assigned a seventh (7th) priority, includes a variable breathing detector 270, a variable breathing monitor 272, and a variable breathing controller 274. As described in greater detail below, the variable breathing control layer performs statistical analysis on the scatter of the trended weighted peak flow data to detect unstable breathing patterns or abrupt changes in patient response. When activated, variable breathing control module 274 takes priority over the auto-CPAP controller, so that when a valid variable breathing indication is provided by variable breathing monitor 272, control of the pressure support system is turned over to the variable breathing controller. In short, activation of variable breathing control module 274 interrupts the operation of the auto-CPAP controller when breathing becomes unstable and appropriately manages any necessary pressure changes.

[0162] 1. Variable Breathing Detection and Monitoring

[0163] Variable breathing detection module 270 monitors the weighted peak flows Q.sub.Wpeak over a moving window, which in a presently preferred embodiment, is a four (4) minute window. The detection module in essence trends four minutes worth of weighted peak flow information to determine whether this information is becoming too erratic. FIGS. 10A and 10B are graphs illustrating examples of the scatter of weighted peak flows. In FIGS. 10A and 10B, the weighted peak flows are relatively closely bunched around a trend line 276 in area 278 and is relatively scattered from the trend line in area 280. Trend line 276 is a best-fit line determined using any conventional statistical analysis technique based on the weighted peak flows data collected during the current 4 minute window. The primary difference between FIGS. 10A and 10B is that the trend line in FIG. 10B is shown with a non-zero slope. This is done to highlight the fact that the trend line is a best-fit line based on the collected data points.

[0164] Variable breathing detection module 270 determines the standard deviation of the weighted peak flow data collected during the monitoring window as indicated by dashed lines 282. It should be noted that the standard deviation is calculated based on the best-fit trend line 276. It can be further appreciated that a standard deviation 284 is less in region 278 than a standard deviation 286 in region 280, indicating that the weighted peak flow data is more variable in region 280.

[0165] The present inventors appreciated that using the standard deviation alone as a measure of the degree of variation in the weighted peak flow data may not produce consistently correct results. This is so, because the standard deviation of the weighted peak flow data when the mean patient flow is relatively low is not exactly comparable to the same standard deviation for a higher mean patient flow. The present invention, therefore, seeks to normalize the standard deviation to the mean patient flow, and then takes the mean flow into consideration when analyzing the variation in the data.

[0166] FIG. 11 is a chart illustrating a normalization curve 290 that describes the relationship between the mean patient flow and an adjusted mean patient flow. It can be appreciated from reviewing this figure that there is a linear region 292 in which the adjusted mean flow (vertical axis) has a one-to-one match with the actual mean flow (horizontal axis). If the patient's mean flow for the 4 minute window is within region 292, no adjustment to this mean flow is made. There is also a first region 294 having a 1/2 to one relationship between the adjusted mean flow and the actual mean flow. Thus, if the actual mean flow falls within region 294, which is between 15 and 25 liters per minute (lpm), then an adjusted mean flow is calculated based on curve 290. There is also a flat region 296 where the adjusted mean flow is clamped to a baseline value even if the actual mean flow is decreased. Thus, if the actual mean flow is less than 15 lpm, the adjusted mean flow is clamped at 20 lpm.

[0167] It is to be expressly understood that the specific shape of curve 290 and the delineations between the various regions is subject to variation. For example, although not illustrated, the present invention further contemplates providing this clamping feature if the mean flow exceeds a predetermined value, such as in region 298.

[0168] A variable breathing number (VB#) is calculated as follows: 1 VB # = standard deviation adjusted mean flow . ( 1 )

[0169] The end result of the variable breathing detection process carried out by variable breathing detection module 270 is this variable breathing number. The higher the VB#, the more variable the weighted peak flow data.

[0170] The variable breathing number is provided by variable breathing detection module 270 to variable breathing monitoring module 272, which compares this number to threshold values to determine when to request that variable breathing controller 274 take control from the auto-CPAP controller. FIG. 12 is a chart illustrating the hysteresis threshold criteria for declaring that the patient is experiencing variable breathing and, hence for requesting control of the pressure support system.

[0171] As shown in FIG. 12, an upper threshold 300 and a lower threshold 302 are set in advance. Preferably, the values of these thresholds are determined from empirical data. Variable breathing monitor 274 declares there to be variable breathing and issues a request for control to request processor 106, when the variable breathing number (VB#), represented by line 304, exceeds upper threshold 300. This occurs at point 306 in FIG. 12. Variable breathing monitor 274 will continue to deem there to be variable breathing, and, hence, continue to request control, even if the VB# falls below upper threshold 300. In short, a variable breathing active indication is turned on at point 306 and remains on over region 308, until the VB# falls below lower threshold 302 at point 310. While the variable breathing active indication is on, variable breathing monitor 274 issues a request for control of the pressure support from request processor 106.

[0172] Similarly, variable breathing monitor 274 will continue to deem there to be no variable breathing, and, hence, will not request control, even if the VB# rises above lower threshold 302. That is, the variable breathing active indication is turned off at point 310 and remains off over region 312, until the VB# exceeds upper threshold 300, which occurs at point 314.

[0173] 2. Variable Breathing Pressure Control

[0174] Once variable breathing controller 274 has been granted control of the pressure support system, it takes some initial action based on that action the auto-CPAP controller discussed below is taking. After this initial action, it performs an independent pressure control operation. FIG. 13 is a chart illustrating the pressure control operation of the variable breathing control module of the present invention.

[0175] As shown in FIG. 13, the pressure control operation performed by variable breathing controller 274 is subdivided into the following three regions: a) an active response region 320, b) a pressure hold region 322, and c) a slow ramp region 324. The pressure control performed by variable breathing controller 274 in each of these regions is discussed in turn below. It is to be understood that even though there appears to be discontinuities in the delivered pressure in FIG. 13, this is only due to the manner in which each region is illustrated. In practice, the pressure at the end of region 320 is the start pressure for the pressure control that takes place in region 322. Similarly, the pressure at the end of region 322 is the start pressure for the pressure control that takes place in region 324.

[0176] In region 320, column A illustrates the possible prior pressure curves, i.e., the possible pressure control actions being taken by the pressure support system before operation of the system was handed over to variable breathing controller 274. Column B illustrates the corresponding pressure control curves that are produced by variable breathing controller 274 based on the prior curves. In case #1, a prior pressure 326 is flat (not increasing, not decreasing). In which case, variable breathing controller 274 will cause the pressure delivered to the patient to remain at this level, as indicated by pressure curve 328.

[0177] In case #2, a prior pressure 330 is increasing. In which case, variable breathing controller 274 initially decreases the pressure delivered to the patient at a rate of 0.5 cmH.sub.2O per minute, as indicated by pressure curve 332. The magnitude of the decrease is dependent on the magnitude of the increase in prior pressure 330. Pressure decrease 332 is intended to erase the prior pressure increase 330 that possibly caused the variable breathing. However, the total decrease in pressure drop 332 is limited to 2 cmH.sub.2O. After pressure decrease 332, variable breathing controller 274 holds the pressure steady, as indicated by pressure curve 334.

[0178] In case #3, a prior pressure 336 is decreasing. In which case, the variable breathing controller initially increases the pressure delivered to the patient at a rate of 0.5 cmH.sub.2O per minute, as indicated by pressure curve 338. The magnitude of the increase 338 is dependent on the magnitude of the decrease in prior pressure 336. Pressure increase 338 is intended to erase the prior pressure decrease 336 that may have caused the variable breathing. However, the total increase in pressure 338 is limited to 2 cmH.sub.2O. After pressure increase 338, variable breathing controller 274 holds the pressure steady, as indicated by pressure curve 340.

[0179] In a presently preferred embodiment, the duration during which pressure is provided according to the paradigms discussed above for region 320, column B, is set to 5 minutes. Thus, pressure curve 328 (case #1), curve 332-334 (case #2), or curve 338-340 (case #3) is provided for 5 minutes or until the variable breathing condition clears. Thereafter, the pressure is controlled according the pressure operations of region 322. It is to be understood, however, that this duration can be varied over a range of durations.

[0180] In region 322, the pressure is either maintained at a constant value, as indicated by pressure curve 342 (case #4), or it follows a decrease and hold pattern, as indicated by pressure curve 344 (case #5). The decision to hold the pressure (case #4) or to decrease the pressure (case #5) is made by comparing the current pressure, i.e., the patient pressure at the end of region 320, with the snore treatment pressure. This is similar to the pressure control operation of A/H controller 168 discussed above with respect to FIG. 9.

[0181] If there is no snore treatment pressure stored in the system, which will be the case if the snore controller has not been activated, the pressure is held constant as pressure curve 342. If there is a snore treatment pressure, and if the current pressure is more than a predetermined amount above this snore treatment pressure, such as more than 2 cmH.sub.2O above the snore treatment pressure, variable breathing controller 274 decreases the pressure to a level that is a predetermined amount higher than the snore treatment pressure, as indicated by pressure curve 344, and holds the pressure at the lower level, as indicated by line 346, over the duration of region 322. The present invention decreases the pressure during pressure decrease 344 to the snore treatment pressure +1 cmH.sub.2O.

[0182] In a presently preferred embodiment, the duration during which pressure is provided according to the paradigms discussed above for region 322 is set to 15 minutes. Thus, pressure curve 342 (case #4) or curve 344-346 (case #5) is provided for 15 minutes or until the variable breathing condition clears. Thereafter, the pressure is controlled according to the pressure operation of region 324. It is to be understood, however, that this 15 minute duration can be varied over a range of durations.

[0183] In region 324, there is only one pressure control operation. Namely, the pressure delivered to the patient is slowly ramped down, as indicated by pressure curve 348. This downward pressure ramp continues until the minimum system pressure is reached or until the variable breathing condition clears.

DSM

Wow DSM . More than I expected there.
Will read a couple times to try to get my mind around it, but it seems to be one of the fundamental control parameters (algorithms) for pressure adjustment in the APAP.

Thanks for taking the time.

The following is a quote from SAG re a way to look at 'Variable Breathing'.
copied from this page of the other thread ...
viewtopic.php?f=1&t=35298&start=615

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SAG wrote ...

I would like to create a "Living Document" to determine an interpretive strategy for the variable breathing (VB) parameter, and would like to start out with:

< 5.0% Normal
5 - 15% Mild Disturbance
15 - 25% Moderate Disturbance
> 25% Severe Disturbance

I would say the contributors to the VB are:

Normal variation (REM sleep, normal wake periods)
Abnormal variation (insomnia, wake/1 transition, arousals from non-respiratory events)
Whatever the VB criteria actually is.
Criteria when it can't kick in (the algorithm hierarchy seems to say that if there are
leaks, snores, or apnea/hypopnea, you can't enter Variable Breathing Mode (VBM)(I just
made that up, too)(the acronym, not the hierarchy). That's why I believe Periodic Breathing,
when there are apneas, would not be relegated to the VB Bucket.

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DSM, I see where you have Periodic Breathing excluded from the Respironics Variable Breathing control-layer criteria. This doesn't make sense to me. the entire purpose of the VB control layer is to normalize breathing that pressure titration might have caused.

That VB criteria should include both hyperventialtion and frank PB that happens to be absent of A or H. So I guess I'm trying to understand how we think the Respironics APAP algorithm will handle frank PB that is absent of A or H if not by suspending titration via the VB control layer.

Respironics wrote:Periodic breathing is defined as alternating periods of hyperventilation with waxing/waning tidal volume and periods of central hypopneas or apneas. There are many forms of periodic breathing, one of which is Cheyne-Stokes Respiration (CSR).

(emphasis mine)

I'm thinking any PB that is absent of A or H will, indeed, get relegated to the VB control layer by definition. No?

-SWS wrote:DSM, I see where you have Periodic Breathing excluded from the Respironics Variable Breathing control-layer criteria. This doesn't make sense to me. the entire purpose of the VB control layer is to normalize breathing that pressure titration might have caused.

That VB criteria should include both hyperventialtion and frank PB that happens to be absent of A or H. So I guess I'm trying to understand how we think the Respironics APAP algorithm will handle frank PB that is absent of A or H if not by suspending titration via the VB control layer.

Respironics wrote:Periodic breathing is defined as alternating periods of hyperventilation with waxing/waning tidal volume and periods of central hypopneas or apneas. There are many forms of periodic breathing, one of which is Cheyne-Stokes Respiration (CSR).

(emphasis mine)

I'm thinking any PB that is absent of A or H will, indeed, get relegated to the VB control layer by definition. No?

SWS,

In the patent description Respironics say that with VB (not covering PB) they are looking for 'erratic' breathing (PB is not erratic but is 'cyclic'). If they detect it, they appear to work on the assumption that the AUTO may have contributed to it so start to either increase or decrease pressure in 0.5 CMs increments in the opposite direction from the one last moved in.

PB is mentioned in the BipapSV literature but only ever as CSR.

I am still trying to find an acceptable definition for both that would avoid confusion. The two (VB & PB) are different.

I am guessing that the AUTO would ignore CSR (cyclic breathing) but is scanning for erratic patterns.

DSM

I have done a little bit of googling for definitions but they tend to be vague - I am wondering if the different manufacturers will also have different thoughts on this but

Periodic Breathing

http://www.medterms.com/script/main/art ... ekey=10902

http://www.thefreedictionary.com/periodic+breathing (associates it with CSR)

http://www.thefreedictionary.com/Cheyne ... espiration

http://www.resmed.com/en-us/clinicians/ ... clinicians



Variable Breathing

Can only find references in sales brochures for the Bipap AUTO & the Patent e.g. ...

Although the present invention contemplates that the information gathered via monitoring system 100 , 100 ′ can be output, displayed, or transmitted in any one of a variety of formats, one example of such an output is shown in FIG. 8. This figure is a graph of breathing frequency recorded over a night derived from the present invention. Five minute averages of minimum and maximum breathing frequency may be plotted to easily identify periods of relatively stable breathing patterns from variable breathing patterns.

Breathing pattern analysis includes the identification of abnormal forms of breathing, such as, but not limited to, Cheyne-Stokes breathing, Kussmaul breathing, apnea, hypopnea, and snoring. Breathing pattern analysis may be performed using the respiratory timing variables derived according to the present invention. Cheynes-Stokes breathing is seen with some central nervous system disorders, uremia, and some sleep patterns and is characterized by repeating cycles of waxing and waning in the depth of breathing including a period of apnea. Kussmaul breathing is seen in coma or diabetic ketoacidosis and is characterized by a deep, rapid respiratory pattern. Any conventional technique for determining these breathing patterns can be used in the present invention.


DSM

Doug, I'm still confused. Are you saying that periodic breathing is explicitly mentioned somewhere in the patent description as being excluded from the VB control layer?

Or are you saying that PB is always highly patterned, never erratic, and therefore logically won't qualify for the VB control layer----specifically because the VB control layer only handles erratic breathing? Thanks.

-SWS wrote:Doug, I'm still confused. Are you saying that periodic breathing is explicitly mentioned somewhere in the patent description as being excluded from the VB control layer?

Or are you saying that PB is always highly patterned, never erratic, and therefore logically won't qualify for the VB control layer----specifically because the VB control layer only handles erratic breathing? Thanks.

SWS,

I am still trying to get a good definition of VB vs PB. For example one book mentions the two and implies that VB is varying rate while PB is varying volume. That sort of fits with what I am reading in other technical journals.

As happens so often in cpaptalk, when a discussion centers on a subject such as Variable Breathing - the discussion can get confused if the participants have different ideas of what it means. I located the Respironics patent that describes VB & posted that here some weeks ago. I am also looking at various descriptions of Periodic Breathing and see that a different description is often used (usually CSR).

So without clarity on what I think you mean by PB or VB, I am not at all clear what we are discussing. The Respironics patent talks of VB in a manner that describes erratic rate but also implies volume . The Respironics & Resmed literature discusses PB as related to CSR with waxing and waning volume.

So I am still seeking agreement as to which is which, then I can look meaningfully into questions on one or the other.

DSM

#2 - read the para on Respiration in this book at this link - they authors talk of PB & VB in the way I am trying to describe above.

http://books.google.com.au/books?id=e9r ... &ct=result

This book also describes Variable Breathing
http://books.google.com.au/books?id=1C8 ... &ct=result

-SWS wrote:Doug, I'm still confused. Are you saying that periodic breathing is explicitly mentioned somewhere in the patent description as being excluded from the VB control layer?

Or are you saying that PB is always highly patterned, never erratic, and therefore logically won't qualify for the VB control layer----specifically because the VB control layer only handles erratic breathing? Thanks.

SWS,

I am not saying that VB excludes PB - I am questioning ...

1) Is there a difference between VB & PB (thus far I am concluding yes based on the patent above & other docs linked to)
2) If there is a difference then what is it ? (erratic rate (VB) vs cyclic volume (PB) ?)
3) Does PB really mean 'periods of breathing' where the patient stops breathing at regular intervals

The literature on respiration implies 3 above but CSR tends to be a clearly seen pattern, not so much stopping breathing as cycling through patterns of volume. If VB is a reference to CSR then that is quite different to the VB described in the patent where they say ...
>>
[0160] The Auto-CPAP controller, which is described in the next section, relies on the ability to trend the steady rhythmic breath patterns associated with certain stages of sleep. When a patient is awake, in REM sleep, or in distress, breathing tends to be more erratic and the Auto-CPAP trending becomes unstable. It is, therefore, important to interrupt the Auto-CPAP controller if the patient's breathing pattern becomes too variable. In essence, the variable breathing control layer keeps the Auto-CPAP control layer from being too erratic.
<<

This is telling me that the machine monitors regular rhythmic breathing patterns BUT only reacts if they become erratic >> "breathing tends to be more erratic and the Auto-CPAP trending becomes unstable" <<

I read the above as saying that VB in the Resp AUTO is the machine looking for patterns of erratic breathing and if that happens it activates the VB adjustments. CSR isn't erratic breathing it is cyclic respiration. CSR is the common form of PB. An AUTO with VB support tries to compensate for it as explained above. I don't believe an AUTO will try to do anything to CSR (thus PB). Thus an AUTO is quite the wrong machine to regulate PB. An SV does have the means to normalize PB. SV Pressure Support is a means to try to correct VB but as we have seen with Bev, perhaps not very well.

DSM

#2 This is one of the references that talks of VB and PB as different effects.

Got it, Doug. Thanks!

Maybe SAG can tell us the correct pressure response to periodic breathing during NPSG.

-SWS wrote:Got it, Doug. Thanks!

Maybe SAG can tell us the correct pressure response to periodic breathing during NPSG.

my guess:

Elimination of the Central Dysregulation that preceded it.

Snoredog wrote:

-SWS wrote:Got it, Doug. Thanks!

Maybe SAG can tell us the correct pressure response to periodic breathing during NPSG.

my guess:

Elimination of the Central Dysregulation that preceded it.

But what if the machine is the guilty party causing that central dysregulation.

Give the patient a central then clear it with cycling ipap-epap plus PS & add a headache in to boot

Actually just joking. PB as defined in CSR gets normalized using Pressure Support in both the Respironics and Resmed SV machines.
If Bev has VB (erratic respiration) then SV PS may not do the job other than give Bev a headache by inducing central dysregulation and hypercapnia.


DSM