Breathing with low inspiration amplitude / negative flow rate

[GinoIT]

I am new and learning. I don't see this pattern all the time but I am curious what it means when the amplitude of flow rate is low above the zero line compared to below the zero line.

Also, for this span of 3 mins, what does a negative flow rate of -5.3 imply? I would guess it somehow means that I exhaled more than I inhaled. I might want to get an O2 sensor that can track data all night. That's how my sleep study was done.

Thanks

[PeterFD]

Air flow rate means air volume velocity. The important word is velocity. The word volume is required because air is a fluid with no defined size or shape like a motor car. When the graph is above the line you are inhaling and when below the line you are exhaling. If you hold your breath, whether your lungs are full or empty, the volume VELOCITY will be zero.

If you have learnt calculus, you will know that if you integrate velocity with respect to time (calculate the area under the velocity versus time curve), you will get distance (plus some unknown constant) and if you differentiate distance (calculate the slope or gradient of the curve) as a function of time, you will get velocity as a function of time. In our case, if you integrate volume velocity, you will get volume (plus an unknown constant).

If you visually try to estimate the area under the inhale part of the flow rate curve for one breath, you will get the volume of air you inhaled, while the area under the exhale part is the volume of air you exhaled. These two quantities may differ slightly for one breath cycle but the long-term average of each must be the same or your lungs would eventually explode or implode. However, the peak volume velocity of the inhale and exhale parts can be any value in principle so long as you are physically able to breath that fast. 

       "what does a negative flow rate of -5.3 imply?"

The units of flow rate (volume velocity) are litres per minute. -5.3 means at that instant of time you were breathing out at a rate of 5.3 litres per minute.

[PeterFD]

Sorry, I think I missed the point of the last question.

The reading you have circled in green is the current value of the plot where the green vertical line cursor was located. When you copy the page, the cursor doesn't get copied.



Your post reminds me that I had already been thinking that it would be nice if OSCAR included a plot of air volume in the lungs (relative to some arbitrary level) as a function of time. Since the volume velocity is already known at equally spaced intervals of time, in principle all that would be required is to continually sum the volume velocity values.

I can see a possible fly in the ointment with that apparent simplicity, however. Due to accumulation of slight round off error (quantization) and sensor read error in each sample value, there is a danger of the errors gradually accumulating and the plot could gradually drift up and/or down the page. This could be corrected, however, by adding a filter that continuously computed the moving average of each breath cycle (or several breath cycles), say, and forcing the average back to zero.

[jdougc]

Welcome to the forum, 
Please post a copy of your sleep report with your info redacted. 

We would like to see the following graphs, (in their order of importance) But the whole charts, even the bottom of the flow limit chart
1.Event Flags
2.Flow rate
3.Pressure
4.Leak rate
5.Flow limits

The statistics and device settings on the left side should be fully visible.

Use the F12 key or FnF12 for a mac to take screenshots. You can attach the .png file and insert in in your post

You had flow limitations, see the tops of your breaths are not rounded. Your airway was restricted, not fully blocked.
That is why your flow rate had little positive values here.
You had a large recovery breath around 4:42, followed by more flow limitations.

[2SleepBetta]

Welcome to the Forum GinoT. Others will want organized OSCAR graphs and then share therapy insights on how to reduce your flow limitations. 

Having done some work with matters PeterFD raised in your thread, I'll chime in here. 

OSCAR provides a moving average of inhaled air volumes for a number of breaths in the Tidal Volume (TV) graph. Similarly, OSCAR provides a moving average of the inhaled volume each minute (or is it a moving average of N minutes?—I forget, but think not) in the Minute Volume (MV) graph.

My avatar is a crude representation of a few of my breaths, their TV's and TV shortfalls.  Each inspiration has a green bar graph of tidal volume. In an actual analysis I obtained those bar values by integration of the data for the area enclosed by the axis and curve at left and above the axis. Matching descending red bars crudely represent how much less TV than, say, 0.5 liters the green bars indicate. (Values and accuracy of illustrative bar lengths vary in the avatar. I did not look, until posting just now see poor agreement, of bar lengths with curve shapes as I drafted this post.) 

Green bar value + Red bar value = 0.5 L a single TV's illustrated value. 

For my home PAP study and some posted graphs of those: The red bar values very crudely represents TV "shortfalls" that arise from flow limitations in the airway, normal changes in TV and changes in respiration rate. The green and red bar values vary. Expediently, I sometimes used my best straight line, "visual curve fitting" for episodes of red and green values and or used a fixed green TV "pseudo constant" (standard value) usually 5.0 L/TV. This stuff is far from exact.

If a person inspires 0.5 L/breath (single tidal volume)  and his respiration rate is 15, his MV = 0.5 x 15 = 7.5 L/min. Somewhere at AB I posted more illustration of this, but the attachment has likely been deleted to release server storage. Each point on the plotted flow rate curve represents a liters per second rate of volume flow as PeterFD indicated.

Using ApneaBoard's search feature (from Menu at top of the Forum page) I searched my handle "2Sleepbetta" using the word "integration" and found several of my related posts but not the one I was thinking of with my integration of flow rate data and more. I didn't take time to look at more.

I recommend you read at this link how to present necessary OSCAR graphs with tables of breathing parameters to enable therapy help: OSCAR Chart Organization - Apnea Board Wiki

[Sleeprider]

GinoIT, if you're still out there, try turning on EPR full-time at setting 3. That will give you 3-cm of inspiratory pressure support that will mitigate the flow limits shown in your charts.

[PeterFD]

Sleeprider

If one sets EPR to 3 all that does is set exhale pressure to 3 lower than the set pressure in the menu, and leave inhale pressure as it was (sort of), doesn't it? 


How does that increase inspiratory pressure support? 

In fact, with my ResMed machine at least, inhale pressure ramps up slowly from the exhale pressure value (i.e. set pressure minus EPR) and only reaches the set pressure by about the end of inhalation, so the average inhalation pressure would be lowered by a bigger EPR value. At least that's what the Mask Pressure plot in OSCAR says, anyway.

I always thought that EPR was provided for breathing comfort during exhalation.

[PeterFD]

2SleepBetter

Yes, I do make use of the Tidal Volume plot. As you say, it is a moving average of several breaths. Presumably so that it can be calculated in real time, it only makes use of breaths that have passed and therefore will appear to lag the current time. Averaging several breaths means that it will tend to mask detail mainly confined to one breath. Also, the plot is often jerky, suggesting that all breaths have equal weight. Giving more weight to the most recent breaths would improve that. Deciding when a breath starts and finishes would be a bit tricky when a bit of spluttering is going on at that time.

That is why I proposed an instantaneous relative volume plot from the running sum of the flow rate to help me understand what is going on at a micro level. It would not be of much help if your only concern was minimizing AHI.

[2SleepBetta]

2SleepBetter

Yes, I do make use of the Tidal Volume plot. As you say, it is a moving average of several breaths.

Presumably so that it can be calculated in real time . . .  Please clarify, I don't understand your meaning.

 it only makes use of breaths that have passed and therefore will appear to lag the current time. Averaging several breaths means that it will tend to mask detail mainly confined to one breath. Yes, that is the nature of a moving average and why I integrated the flow rate curve to get individual breath tidal volumes needed for my purposes evaluating flow limitations (as is llustrated poorly by my avatar's mismatching green and red bar lengths vs  their associated inspiration wave areas). 

Also, the plot is often jerky, Yes, the flow rate curves can be highly irregular and individual breath volumes will reflect that

 suggesting that all breaths have equal weight I think you mean a moving average could be misread that way or mean there is a benefit from moving average smoothing as in your next sentence  Giving more weight to the most recent breaths would improve that.

Deciding when a breath starts and finishes would be a bit tricky Yes, cardiogenic oscillations at end of expirations can confuse start and end point of a breath, making Ti and Te hard to determine. But irregular breathing data from my Resmed devices have not posed a problem for my numerical integrations or for OSCAR  when a bit of spluttering is going on at that time.

That is why I proposed an instantaneous relative volume plot from the running sum of the flow rate to help me understand what is going on at a micro level. Again, I don't understand the statement.

It would not be of much help if your only concern was minimizing AHI.

PeterFD

Your text is in blue font, my insertions are in black italic font.

I could attach on-point graphics, but we've gone into hijacking this thread. I do not intend to post more on this TV topic here. In the weeds, it diverts from the OP. If you wish to continue our discussion, I suggest you start another thread about these matters. If you see need, you may want to clarify here what I haven't understood or state where you see things differently.

@jdougc:

We posted within 15 minutes of each other, you the earlier. Regret duplicating some of your call for more info. I was likely in the middle of drafting my post when you posted.

[Sleeprider]

Sleeprider

If one sets EPR to 3 all that does is set exhale pressure to 3 lower than the set pressure in the menu, and leave inhale pressure as it was (sort of), doesn't it? 


How does that increase inspiratory pressure support? 

The Resmed Airsense EPR with EasyBreathe algorithm, which provides the expiratory pressure relief is in fact identical to the Resmed Aircurve pressure support with Easybreathe algorithm, except for being limited to 3-cm.  While it is advertised as a comfort feature (it is), it is also a limited bilevel feature capable of reducing flow limitation, snores, RERA and other problems that arise when pressure support cannot be provided.  With CPAP only one pressure is provided, with bilevel, two pressure channels, IPAP and EPAP are delivered. The CPAP pressure becomes IPAP and EPR subtracts from that pressure to provide EPAP.  As inspiration starts, it triggers IPAP which rises until flow slows to zero and expiration begins where the device cycles to EPAP.  The complication with EPR is that the minimum pressure must be at least the device minimum pressure of 4.0 cm, plus the EPR setting. So with EPR 3, the minimum pressure must be 7.0 or the full EPR will not be delivered and the device becomes less responsive to obstructive events.

In your case, the minimum pressure of 5-17 should be changed to 7 -17 with EPR 3 which will provide pressures of 7/4 to 17/14 (IPAP/EPAP).  To maintain your current minimum pressure during exhale, I would suggest increasing that to 8-17.   The use of EPR as I mentioned results in pressure support during inspiration which mitigates the negative pressure caused by increasing inspiratory flow and can mitigate flow limitation and increase tidal volume in the same manner as a bilevel device with 3-cm of pressure of support.  This is explained in the wiki Flow Limitations with comparisons of CPAP with EPR and the Vauto. https://www.apneaboard.com/wiki/index.ph...limitation