ASV settings and tips

[stevew168]

You're someone here we can all hope to emulate.  Not only did you get the perfect bipap for your requirements, you got it for a great price, and set it up optimally.

Here's a pretty good explanation of Adaptive Servo Ventilation (ASV):  https://www.sleepfoundation.org/sleep-ap...v-machines

[jcp519]

So I have a few questions about using the ASV and how its dropping my respiratory rate when the PS increases.

So I have areas of my sleep where the PS remains high, which causes my respiratory rate to drop quite a bit, usually around 7 bpm and my tidal volume will increase to maintain the minute vent that the machine wants. You can also see when zoomed in the machine maintains this very steady breath waveforms with the low bpm. I also included the area where one of the low bpm areas go away.

I'm wondering if this is normal while using an ASV or if my PS is set too high? Would dropping the PS range be worth trying to keep this from happening? Is this even a problem to begin with?

           

[Jay51]

I'll take a shot at it.  My ASV charts look similar to yours.  Similar I:E ratio (roughly a little over 2 seconds inspiration and a little over 2 expiration).  Also similar tidal volume (actually mine is a little larger.  My respiratory rate actually stays above 12 all the time with ASV (but yours doesn't - and in my PSG and Capnography tests mine dropped as low as 5 and 6 breaths per minute.  Tidal volume got very low at times also - double digits and 100's, 200's, 300's, etc. - but I also had high tidal volume of 750 or more.  Tremendous variability.  

Great question you are asking.  I tried a similar experiment (lowering PS) and found that I need the higher PS for a sustained minute ventilation.  You can try lowering your PS and see if you can maintain a similar minute vent.  If you can't, I would suggest keeping the higher PS range you have now (as long as you can fall asleep and stay asleep with it).  If you can lower PS and still have the same minute vent average, then you can get away with keeping the PS lower.  

It is normal for a person's tidal volume to increase as respiratory rate decreases; and vice versa.  Minute vent. is the key that dictates things though.  When my tidal volume went up, respiratory rate came down; and vice versa.  

Great questions and great thoughts.  Your ASV therapy looks good IMO.  You can try the experiment though if you want.  In my experiment, lowering PS dropped my minjute vent too much (my tidal volume didn't raise enough to compensate).  Your results could be different though.

[jcp519]

Thanks for the input Jay!

I changed my PS range to 3-8 and honestly I can't really tell much of a difference in my data. Seems like my tidal volume increased some, but overall seems like it hardly changed anything. Still getting those periods of low deep breaths when the PS is high. Overall I feel the same too, so looks like the lower PS range might be fine for me.

   

[robbob2112]

Fiddling with PS while on ASV is how you can reduce you flow limits.  Higher PS for me means lower amount and size of flow limits which in turn means a better nights sleep in the end.    I can go 9 hours at a stretch with good sleep.  Main thing is everyone is different and what works for me may not work for you

[jcp519]

Seems like lowering the PS didn't really affect my flow limits at all. I get very few on ASV, and usually they are those huge spikes that are expected.

The nice thing is when I'm using ASV, is my sleep schedule is very regular. I go to bed at 10:30-11 and wake up at 7-7:30. Once I get at least 7-8 hours of sleep I wake up without my alarm clock.

[robbob2112]

Sorry, I thought one thing and typed the opposite.... meant to say higher PS made for lower flow limits and better sleep

[Jay51]

Great points by Robert (robbob2112).  One other major thing I forgot to mention also is "respiratory drive".  It is a person's innate "drive" and "ability" to breathe normally.  It looks like yours is pretty good jcp519.  It sounds like Robert's is good also.  If you would have lowered PS and your minute vent went down significantly, you could have had problems with respiratory drive (and your chart was absent of lots of new flow limits).  Normal respiratory rate + normal tidal volume = a normal minute vent.  People with a poorer respiratory drive (from the brain, CNS, etc.) will  have reduced minute vent because either their respiratory rate is insufficiently low; or their tidal volume is insufficiently low to maintain a normal minute vent.

[jcp519]

That definitely makes sense. I'm in my mid 20s and relatively fit and healthy so I'd assume my respiratory drive is pretty good. The main reason I got the ASV is because my body seems to be very sensitive to blood CO2 changes which would cause me to have centrals/periodic breathing while on CPAP. I had my CPAP for almost 6 months and still had a some centrals that were making me tired from disrupted sleep.

I do feel like I could have gotten away with a VAuto with high trigger sensitivity, but the ASV I found was cheaper than all the VAuto's I was seeing.

[stevew168]

Minute ventilation = tidal volume X respiratory rate. So if minute ventilation stays the same and tidal volume goes up, respiratory rate will decrease. This is normal and desirable with an ASV. Minute ventilation is what counts regarding SpO2 and elimination of CO2.