Flow Rate Value Clarification in OSCAR

[cmpman1974]

I am trying to understand what the number means exactly on the per breath analysis OSCAR does.  I am confused on this.  My understanding it Tidal Volume is literally an every breath number in milliliters.  When I look at a flow rate chart, it shows highest values at inspiration such as 27, 45, 50, or on crazy occasions 120.   I understand CPAP/BPAP pressures are reflected in cm/H2O.  

So what do these 27, 45, etc. numbers truly mean.  if I add up the absolute values for each breath in a minute time period, any meaning at all?  I get consistency is key and low flow rates = apnea/hypopnea, but the question is what is 'low' based on absolute value indicated?  I am also guessing a higher flow rate can be due to increased effort of my own breathing, increased pressure delivered by the BPAP, etc.  I'm looking for a dumbed down explanation if possible.  Thanks in advance.

[cmpman1974]

I think I got my answer here:

http://www.apneaboard.com/wiki/index.php...Rate_graph


I just wanted to say everyone who developed this board and the write-ups did one impressive job.  I am blown away by the level of detail and knowledge people have.  I have never had any physician go into anything more than hours the machine was used and AHI stats.  Even then, the data provided was minimal at best.  It really is a shame there is not more involvement in the whole thing.   I think what blows me away is the lack of concern for O2 stats night to night if that is primarily the whole point of treatment.  I would guess it's not an issue for a lot of people, but to assume a single night of data at a polysomnogram represents the remaining 364 days in a year seems very, very wrong.  Just a few spot checks of different nights seems like it would be of big benefit to assess efficacy of treatment outside of a patient's subjective statements regarding how they feel day to day.

[Sleeprider]

Glad you found a helpful wiki article. I'll just add, while you're in a zoomed view, your cursor location is given by a vertical green line. Where that line intersects through the flow rate chart is the instantaneous flow in milliliters (mL). As you move horizontally along the flow rate, you can watch the flow rate change in the margin at the top-right of the graph from -40 to +40 (or what ever the peak expiratory / inspiratory flow is) and you can see where the flow rate crosses zero, which is the transition between inspiration and expiration. You can also right-click near the title of the graph Flow Rate and pull up a context menu. A helpful tool is that you can change the y-axis range from auto, which is the full range of flow, to a lower +y -y range that better reflects your normal respiratory flow range. Also you can add a dotted line at zero so you can see more easily the inspiration and expiration crossovers.

[Sleeprider]

Here is an example of a chart I used to show the timing of respiratory flow and mask pressure. Here I have attempted to draw a black line over the green cursor line. You can  see the line intersects the Flow rate at 13.44 mL just after peak inspiration, and at that moment, the mask pressure shows 13.44 cm which is the peak IPAP pressure at this time.  A zero line is shown on the flow rate line which ranges from -125 to +125.  These changes to the y-axis and dotted line make the chart more consistent and easier to read.  Moving the cursor horizontally, the relationship between respiratory flow and mask pressure can be analyzed and you should see that where respiratory flow  crosses zero before inspiration is the lowest EPAP pressure of the cycle.  

Have fun!.

[cmpman1974]

Thanks Sleeprider.  Very useful info here.   I've started using the zero line and sometimes median line on charts for better perspective.  I still am trying to fully understand how a ResMed Air Curve 10 ST-A decides when it's time to increase flow rate / IPAP from the min level to a higher stage.  It's kind of hard to grasp the timing.  Not that I have any control over it, but it's more curiosity than anything.

[pholynyk]

Some minor corrections and a clarification...
OSCAR reports the flow rate in millilitres per second, and ResMed machines report the flow rate 25 times per second.
Finally, By default OSCAR does data smoothing on the flow rate, so the displayed value may not match the reported flow rate; this can be defeated by going to Preferences, clicking on the Appearance tab. The second item in the right-hand column 'Square wave plots' should be checked to display the reported values without smoothing.
When you zoom in sufficiently, you will see the stair step effect.

[cmpman1974]

I was looking at a pretty dismal day of BPAP back in Apr-22.  This was not representative of a typical night.  How does one have a decent tidal volume the whole time, no significant leaks, but just this relentless pattern of apneas/hypopneas.  Flow rate is all over the place, but tidal volumes decent.  This was on my old BPAP S at 16 IPAP/8 EPAP.  My day to day results seemed quite unpredictable in general.

[Sleeprider]

We have discussed positional apnea several times. The clusters of OA are characteristic of that problem, and almost nothing else looks like it. http://www.apneaboard.com/wiki/index.php...onal_Apnea

[cmpman1974]

We have discussed positional apnea several times. The clusters of OA are characteristic of that problem, and almost nothing else looks like it. http://www.apneaboard.com/wiki/index.php...onal_Apnea

I was thinking that may be the issue.  I'm learning still obviously.  Fortunately, I don't seem to see those crazy clusters lately.  Maybe I changed my sleep habits some over the years. : The odd thing is I read sleep specialists don't feel positional apnea is a real entity or at least nothing proven.  I don't have a whole lot of faith in many so not a big worry. lol.