[Symptoms] Hard to Inhale using CPAP

[flyingg103]

Your flow limits indicate you may need a bi-level machine.  You are at the maximum setting an autoset can provide.  A bi-level offers much more pressure support than an autoset.  

Sleep doctors provide very little help to their patients once they are using a machine, less even than a regular doctor.  If your AHI is under five they consider that all is well.  That is simply not true.

OK, so once you are on a cpap machine how do I approach this with a doctor to make the determination a bi level machine is needed. Are they are any resources that can help me better understand the flow limits and why/how mine can be improved. Like I mentioned I have never felt any better after using CPAP over the last 10+ years even though my AHI numbers have always been WAY below 3 every night and honestly if i see 2 on any night I wonder what may be going wrong.

I really appreciate the guidance, and wonder is a bi level machine any sort of risk of moving to compared to cpap?

[flyingg103]

Your flow limits indicate you may need a bi-level machine.  You are at the maximum setting an autoset can provide.  A bi-level offers much more pressure support than an autoset.  

Sleep doctors provide very little help to their patients once they are using a machine, less even than a regular doctor.  If your AHI is under five they consider that all is well.  That is simply not true.

Are there any resources where I can read more about the flow considerations? Since my doctor has not offered any other options how do you get past the " Your numbers look great" comments.

[DaveSkvn]

Hi flyingg103,

Years on CPAP and "NO real relief from daytime sleepiness". Yes, been there. Very much wearing the T-shirt. I've recently found OSCAR and have set out on a voyage of discovery. Flow limits have been mentioned - the following is what I, as a relative noob, currently understand. 

There seems to be two uses of the term "flow limits".

1) OSA/CPAP sense. These are "lesser-hyponeas": like hyponeas but not as bad. The flow in each subsequent breath noticeably decreases but you never get to what would be defined as a Hypopnea. They are associated with RERAs (Respiratory effort related arousals). There is/was a camp that thought RERAs contribute to daytime sleepiness. There is another camp, waving a number of scientific studies, saying RERAs do not lead to daytime sleepiness. You can choose your own side. Spotting lesser-hyponeas is however useful for auto CPAP machines. If you start getting lesser-hyponeas you may well progress to the full hypopnea. If a lesser-hyponeas is spotted it is time to ramp up the pressure. CPAP machines have a flow limitations index you can see in the graph. The index is not a measure of one thing. It is an mix of different measures meant to spot lesser-hyponeas to help CPAP/APAP operate.

2) UARS sense. In UARS your breath is in a steady state - it does not decrease from one breath to the next - but each breath is limited by some "minor" obstruction in your airway. You never stop breathing. You find it more difficult to breathe than you would like and more difficult than when you are awake. This sends some distress signal (normally put down to "respiratory effort") to you brain and you don't enter restful sleep.

Here are 5 of my flow rate graphs from Oscar.

   

• The first is when I've just switched the CPAP machine on. The inspiration (above the mid line) portion are nice and round - see green circles.
  
• The second is a low level UARS-style flow limit. The breaths are at a constant level. The top of inspiration curve has become flat. The flow cannot rise above some level. For some people (me / you?) this could be sending a distress signal to the brain saying something is wrong.
  
• The third is a bit more panicked version of the second. The flat tops have become pitted.
  
• The fourth is from the beginning of the month and was what my breathing was like about half the night - respiration rate recorded between 35 & 50 bpm. AHI recorded around 2.
  
• The fifth is a OSA/CPAP "flow limitation". The top of the inspiration curves are flat. The height is decreasing with each breath. Its looking like its heading to apnea/hyponea but doesn't get there.
  

Only two of these are recorded in the "flow limitation" graph on my Oscar trace. The fourth (catastrophically bad breathing) was given a value of 0.1 - probably because the height was a bit lower at the start. The fifth was given a value of around 0.7. It is the kind of event associated with OSA and is the one that should trigger an APAP to increase pressure to deal with Apnea/Hypopnea.

Graphs 2, 3 and 4 are events that could lead to daytime sleepiness (in me / you?) but not through the mechanism of OSA. They are not visible in AHI. You have to eyeball the flow graph yourself.

The folk wisdom is that flow limits are better handled using a BiLevel machine. They need a larger difference between inspiration / expiration pressures.

Perhaps you want to revisit your flow graph, where the respiration rate looks a bit choppy. Zoom in to one minute's of data and set the y-axis scale to a fixed value (right click to the left of the graph, select y-axis and set mode "override", min -40, max +40 or similar) and upload again.

[flyingg103]

Hi flyingg103,

Years on CPAP and "NO real relief from daytime sleepiness". Yes, been there. Very much wearing the T-shirt. I've recently found OSCAR and have set out on a voyage of discovery. Flow limits have been mentioned - the following is what I, as a relative noob, currently understand. 

There seems to be two uses of the term "flow limits".

1) OSA/CPAP sense. These are "lesser-hyponeas": like hyponeas but not as bad. The flow in each subsequent breath noticeably decreases but you never get to what would be defined as a Hypopnea. They are associated with RERAs (Respiratory effort related arousals). There is/was a camp that thought RERAs contribute to daytime sleepiness. There is another camp, waving a number of scientific studies, saying RERAs do not lead to daytime sleepiness. You can choose your own side. Spotting lesser-hyponeas is however useful for auto CPAP machines. If you start getting lesser-hyponeas you may well progress to the full hypopnea. If a lesser-hyponeas is spotted it is time to ramp up the pressure. CPAP machines have a flow limitations index you can see in the graph. The index is not a measure of one thing. It is an mix of different measures meant to spot lesser-hyponeas to help CPAP/APAP operate.

2) UARS sense. In UARS your breath is in a steady state - it does not decrease from one breath to the next - but each breath is limited by some "minor" obstruction in your airway. You never stop breathing. You find it more difficult to breathe than you would like and more difficult than when you are awake. This sends some distress signal (normally put down to "respiratory effort") to you brain and you don't enter restful sleep.

Here are 5 of my flow rate graphs from Oscar.

• The first is when I've just switched the CPAP machine on. The inspiration (above the mid line) portion are nice and round - see green circles.
  
• The second is a low level UARS-style flow limit. The breaths are at a constant level. The top of inspiration curve has become flat. The flow cannot rise above some level. For some people (me / you?) this could be sending a distress signal to the brain saying something is wrong.
  
• The third is a bit more panicked version of the second. The flat tops have become pitted.
  
• The fourth is from the beginning of the month and was what my breathing was like about half the night - respiration rate recorded between 35 & 50 bpm. AHI recorded around 2.
  
• The fifth is a OSA/CPAP "flow limitation". The top of the inspiration curves are flat. The height is decreasing with each breath. Its looking like its heading to apnea/hyponea but doesn't get there.
  

Only two of these are recorded in the "flow limitation" graph on my Oscar trace. The fourth (catastrophically bad breathing) was given a value of 0.1 - probably because the height was a bit lower at the start. The fifth was given a value of around 0.7. It is the kind of event associated with OSA and is the one that should trigger an APAP to increase pressure to deal with Apnea/Hypopnea.

Graphs 2, 3 and 4 are events that could lead to daytime sleepiness (in me / you?) but not through the mechanism of OSA. They are not visible in AHI. You have to eyeball the flow graph yourself.

The folk wisdom is that flow limits are better handled using a BiLevel machine. They need a larger difference between inspiration / expiration pressures.

Perhaps you want to revisit your flow graph, where the respiration rate looks a bit choppy. Zoom in to one minute's of data and set the y-axis scale to a fixed value (right click to the left of the graph, select y-axis and set mode "override", min -40, max +40 or similar) and upload again.

 Very interesting, I have not zoomed in this far before. I provided a few for example, one where a RERA was indicated. Over time the graph is inconsistent ( not with real flat tops with waves at the peak) but inconsistent over a longer period of time. I am sure you would like to see the same level of breathing over time but maybe not over longer periods of time?

---

 Very interesting, I have not zoomed in this far before. I provided a few for example, one where a RERA was indicated. Over time the graph is inconsistent ( not with real flat tops with waves at the peak) but inconsistent over a longer period of time. I am sure you would like to see the same level of breathing over time but maybe not over longer periods of time?

here is the 4th one

[Sleeprider]

Are there any resources where I can read more about the flow considerations? Since my doctor has not offered any other options how do you get past the " Your numbers look great" comments.

Deborah K who gave you this advise has the best thread on this exact topic, where she needed to move from CPAP to bilevel due to flow limitations. It's a long read, but worth your time and has over 16,645 views. Here is the link: https://www.apneaboard.com/forums/Thread...to-Bilevel

[DaveSkvn]

Looking at the screenshot 1 & 2 I'd say there's no sign of flat tops but as you say the peaks are not very level which is not something I see in my own trace - I wouldn't be surprised if this is linked to the breathing issues you are getting in the daytime (but I have no expertise in this area). On screenshot 3 I'd say there are signs of flat tops in the first half of the trace but are not bad by the end. The fourth is clearly a classic 'OSA flow limitation' with flat tops and a decreasing height. You can see the machine has detected this and is ramping up the pressure. It doesn't seem to have dealt with the issue because the tops remain flat 20+ secs after it has hit your Max pressure of 11. None of this will show up in the AHI.

@Sleeprider You did awesome work there. I particularly like this part.

https://www.apneaboard.com/forums/Thread...#pid497142

I want a BiLevel myself now.