Discussion on Tidal Volume

[ajack]

The ASV is a bit different to what is talked about here, the default min PS:3 also has a max setting, usually the default PS:15, unless otherwise indicated. The ASV will work between these numbers to provide the PS needed. Depending if there was a reason to set the PS:3 or if it was just the default, you could as sleeprider said, reduce the PS: down. The machine will ramp it up to the pressure it needs. so min PS:1 and max PS:15 could effectively be the same, in how the machine will automatically adjust the PS between those 2 numbers. It just has to make a bit more change in PS. I think it would depend if the titration determined you needed a PS:3 for a specific reason. This is something you could talk over with your doctor.

sleeprider, I don't know that I see it to be done as a reason for less CA. If that was the case, would be concerned from any rise in EPAP or PS increase for issues other than CA? Would the user even know how many CA they are having a night? The ASV treats every CA, according to resmed. They say the UA are obstructive. They don't have FOT to confirm it every time or that the FOT would work on an ASV, there isn't the time lag of not breathing with a CA

[Sleeprider]

sleeprider, I don't know that I see it to be done as a reason for less CA. If that was the case, would be concerned from any rise in EPAP or PS increase for issues other than CA? Would the user even know how many CA they are having a night?  The ASV treats every CA, according to resmed. They say the UA are obstructive. They don't have FOT to confirm it every time.

I have observed in some members that get ASV for CPAP induced central apnea, that a lower minimum PS sometimes results in a "less busy" machine, which I interpret as more spontaneous breathing.  Results are not consistent, and everyone has to look a t what works best for them.  It certainly is not based on any authoritative information, but you can pretty quickly tell if an ASV is providing a lot of pressure support frequently. I have seen where reducing PSmin has also reduced the need for higher pressure support to address whatever events would otherwise be there.  The other situation it has been useful is if the user is sensitive to higher pressures.  Keeping PSmin lower also seems to result in lower effective maximum pressures.  I think the default of 3-cm is recommended for a good reason or comfort, but those are the specific reasons I sometimes will suggest a trial at lower PSmin.

Along those same lines, I have seen users with higher hypopnea rates respond well to higher EPAP min and sometimes PSmin. It's a bit of trial and error. I see a lot more residual hypopnea events in Philips SV Auto Advanced users than Aircurve ASV users, and don't really know the reason why.

[ajack]

As you know, they work differently, could be one of the reasons. The resmed follows the minute vent, the philips follow peak flow, to shape the breath. Both rely on the backup rate for CA. That may account for some differences on how the algorithm works.

The differences I'm seeing with ASV resmed, they say to titrate both OA and H with EPAP, as you know H is normally done with PS on s/st.
The ASV will still misread a deep breath followed by 'normal' as a H, but isn't a low Vt that follows the high Vt and there wouldn't be the O2 desat that goes with a true H. So that has to be zoomed in on to see what it looks like. I wouldn't trust a H flag without looking.

I find this sort of stuff interesting
https://www.scribd.com/document/36749268...pt-Convert
ASV Therapy
In this context, the term ASV therapy is used to describe a therapy for treating central sleep apnea (CSA) in its various forms. However, ASV, or adaptive servo-ventilation, is actually a generic, descriptive term for the functioning of a control system (and is not specific to CSA at all). ASV devices work by creating an adaptive target, in this case based on the patient’s breathing, and then adjusting a parameter, in this case pressure support, to meet that target

[CB91710]

Data point:
I'm 6'3" about 250, I average about 680
My wife is 5'6", about 280, she averages 320

[ajack]

It doesn't really mean much by itself. you need the minute vent and respiration rate as well. Maths are a guess, You can have 680 with RR12 and minute vent 7 and be fine. You can have 680 rr25 and minute vent 18 and be sick. This may indicate there is a problem with gas transfer between the veins and air sacs in the lung.

[Matt00926]

A backup rate is not only for those with central apneas, or those that stop breathing, or can't trigger a breathe in their sleep. It can also be used for individuals who tend to default to inappropriately low respiration rates while sleeping, which can hamper effective ventilation.

For example, for a person with reduced chest wall compliance, or lung compliance, it can require a lot of pressure support to ventilate the person properly--especially while sleeping. Sometimes you have to choose a strategy of reduced tidal volume (less than 8 mL/KG ideal body weight) and increased respiratory rate to insure adequate minute ventilation rates (blow off of CO2). I've seen IPAP pressures of 25cmH2O or higher required which could obviously be uncomfortable.

Minute Volume is the product of respiratory rate and tidal volume, so manipulating the RR can be an effective option for increasing ventilation. Although increasing tidal volume is usually preferred, as by increasing the RR you also increase the amount of deadspace -- the part of the volume of a breath that doesn't aid in gas exchange.

Oxygen levels alone can't tell you if someone is being effectively ventilated. You would need to monitor carbon dioxide levels.

But anyway, if you don't have a respiratory disease or some other related issue, most likely you don't need to bother looking at tidal volume, minute volume and rr as it's not important. Usually a MV above 10 indicates acute illness of some sort.

[juliomalva61]

From what I'm hearing my normal tidal volume should be above 500 (my weight: 78 kg), but following are my numbers, do you think are normal?

min vent: median 7,63 
resp rate: median 18,8
tidal vol: median 400

In case it helps attached is my flow wave form

[SarcasticDave94]

On Tidal Volume discussion, SleepyHead has my TV, Minute Vent, and Resp Rate as follows:

TV: Min at 0.00 / Med at 620.00 / 95% at 820.00 / Max at 1860.00

Minute Vent: Min at 0.00 / Med at 6.25 / 95% at 8.62 / Max at 27.75

Resp. Rate: Min at 0.00 / Med at 10.00 / 95% at 12.20 / Max at 16.60

These represent last day I've imported data to SH.

[Sleeprider]

Julio, I tend not to worry too much about tidal volume as it varies quite a bit between individuals, and really can't be manipulated with CPAP, particularly the Dreamstation. Increasing minute vent and tidal volume through ventilation would require bilevel pressures. The best diagnostic is a simple "Spirometry Test" that measures the Forced Vital Capacity (FVC). Read this link for more: https://www.spirometry.guru/spirometry.html You can request a spirometry test at your next routine physical from your doctor. The tests are very common and good to have as a baseline. Lots of things can affect tidal volume including smoking, pulmonary restriction and general health.

From what I've seen, Vt of 400 is not unusual here, and it probably does not mean much. Mine consistently averages over 640 and sometimes reaches the 700s, however I have been monitored for FCV for many years due to use in my profession of a respirator, and was always well above average.