Vauto CA Trigger and Cycle

[SevereApnea]

Hi All.

I note from posts on this forum that if one has an increase of CA when using a Resmed VAuto one can opt to lower the IPAP or lower PS.

It is also mentioned that increasing the Trigger Sensitivity helps to reduce the CA.

When I started the Vauto I used:
Min EPAP=6.2-6.8 Max IPAP= 13.0 -14.0 for 3 days with PS 2.6 - 3.2
Trigger Sensitivity=Medium and Cycle Sensitivity= Medium
OA HA CA were 
2,1,10
1,2,6 then
0,2,22 !


Then I increased Trigger Sensitivity to High with similar pressures/PS and resulted in

OA HA CA
1,1,3
2,3,3
0,0,2
1,1,6 etc

Q1: I am interested in how/why this works: 
Do we know how does this help to retain C02? 

Q2: If this still feels uncomfortable, can we alter the Cycle Sensitivity to do something similar? if so, in which direction?

   

[Sleeprider]

I started using high trigger sensitivity with the thought that in a CA events I lacked spontaneous effort to create normal respiratory volume. I don't have any form of respiratory failure or reason for CA to occur, so the idea was to lower the threshold for triggering IPAP. That pressure increase turns out to be enough to awaken the spontaneous effort and a breath usually results where a CA might have happened. Our pressure support is not high enough to result in inspiration without spontaneous effort, so the high trigger sensitivity just serves as a subliminal reminder to increase inspiratory effort, and you don't actually have to be awake or aware to make that happen.

I don't think the higher trigger sensitivity affect CO2, but as you approach the apneic threshold where hypopnea or CA might otherwise occur, the switch to IPAP helps support an otherwise lower-volume breath. Cycle sensitivity, usually in conjunction with a shorter Ti Max, is only used to preserve time for expiration. That is more useful in cases of COPD, asthma and hyperinflation, and I don't think that is applicable for you.

[sheepless]

a related question: how do we interpret and respond to the vauto's spontaneous cycle % statistic?

I've seen mine as low as ~70%; more often in the low 90's%. my cycle is at med but I've tried low and high without noticing any differences. ti is set to 1.0 - 3.0 (I raised max because I felt my inhale was being cut off.) my trigger is very high for mixed apnea.

[Sleeprider]

The spontaneous cycle is simply whether the user cycles to exhale spontaneously before the Ti Max is reached. When you brought this up last time, I moved my Ti Max from 2.2 to 3.0 and have had 100% spontaneous cycle since with no change to my results. I don't think this is a particularly important metric or setting in those of us without respiratory complications that restrict expiration, or experience hyperinflation issues. It is more of an issue where a timed respiratory pace is in use and sufficient time for expiration needs to be preserved.

[sheepless]

thanks Sleeprider. so when I see a low figure like 70%, that means 30% of the time I'm not spontaneously exhaling before my ti max of 3 seconds? idk that this is undesirable - I'm not sure I notice it at all - but if I wanted to address this I'd extend ti max and/or raise cycle to high or very high?

[Sleeprider]

It really depends on why your time of inspiration is so long. If you are awake and taking long slow breaths, that is one thing, but long inspiratory times during sleep is a strong indicator of flow limitation, and a need for pressure support.

[sheepless]

I won't distract any more from this thread other to say that unflagged flow limitations continue to haunt me even at ps 5.2. I only noticed my inhale being cut off when ti max was ~2.5 as I drifted off to sleep; no idea what happens during sleep. with I:E around 1:1.6 or so I don't think my inhales approach 3 seconds very often. I guess that's what the spontaneous cycle % tells us. if this is any use to SevereApnea, great. otherwise, I can repost this stuff in my own thread if there's more to discuss. or mods can move post # 3-7 to my related thread here: http://www.apneaboard.com/forums/Thread-...eous-cycle

thanks.

[Crimson Nape]

Try upping the Ti MAx to 3.0. That should allow a long slow inhale. The IPAP pressure is cutting off while you're still inhaling can cause the Flow Limitations.

[SevereApnea]

@ sleeprider and Sheepless

Really interesting discussion, worth pursuing I think both wrt to Trigger and Cycle.

I am really trying hard to understand this, to make sense of what I am feeling and seeing in my results.
If I am out of line, just shout, no problems, and will let the subject go.

Firstly, from the Vauto Clinician manual: 
The Vauto should not initiate a breath, (unlike the ASV type machine, or a machine with ST mode).

Page 5 from the Clinician Manual " ... the device triggers (initiates IPAP) and cycles (terminates IPAP) and changes to EPAP) as it senses the change in patient flow." [my italics]

From this, as far as I understand it, the Vauto waits for me to initiate a breath, at which point this then triggers the IPAP. Would this be a correct conclusion?

This is in fact, what I see on my OSCAR chart of the 14th Jan.
   

The second CA on the night of 14th January lasted 32 seconds. The Vauto then continues to produce the FOT waiting for me to breathe. It makes no attempt to make me breath. It waits for me to build up my CO2 at which point I make an inspiratory effort and then the IPAP triggers. Have I got that right? (Later on in the sleep session I can see I am getting cyclical breathing as I hover around my apnea threshold.)

   
Important for me to fully understand this because if I can bring the IPAP forward (to the left with higher sensitivity) as per diagram on page 5 am I not also potentially altering I:E ratios, use of ventilatory "dead space" and tinkering with other stuff I don't fully understand?

@sheepless

thank you, no you are not distracting at all, it all helps.

I have noticed that the Vauto shows % spontaneous cycled breaths "live" while you look at the screen: from the manual this is averaged over the last 20 breathes only.
When I switch the machine off, this figure is different and I assume the figure is for the whole night, and closely matches that shown in Statistics in ResScan.

[Sleeprider]

Your understanding of the machine waiting for you to initiate a spontaneous breath is true. You don't need to worry about I:E ratios or any of the other stuff. There really isn't any way to affect that with settings we might suggest here. All we are doing is lowering the threshold of spontaneous inspiratory flow for the machine to trigger IPAP. Sometimes that will kick-start the rest of the breath or come in behind a weak breath and assist. Your cyclical breathing at the apneic threshold is common for CA sufferers. It shows a fluctuating CO2 ranging from hypercapnic which increases respiratory drive to hypocapnic which reduces it. The actual biochemical mechanism is more complex, but you have a very narrow range of optimum PCO3 and even a deep breath or sigh can reduce CO2 and start a cycle like this where as CO2 rises and falls the respiratory drive follows in a feedback loop.

Your best bet is to experiment with smaller levels of EPR to minimize the effects of ventilation on your apneic threshold.