Tidal Volume - a question - (ASV)

[JDS74]

Since switching to a Respironics 960 ASV machine, I have been tracking tidal volume among other parameters to see what is changing, if anything.

My reported tidal volume for the first 8 months has averaged 650 mL.
Now, for the month of May, the average is just above 730 mL.
The change occurred pretty dramatically over a very short period.

I do have an atelectasis(collapsed section) of the base of one lung. Could the ASV machine be correcting this condition?
I won't be seeing my pulmonologist for several months and I will be bringing this up as a question but thought to ask if anyone else has had this kind of change in tidal volume after switching to ASV.

Just curious.

[shortcake]

Hi there. Interesting observation. How did you come up with the 650 mL for the first 8 months? Did you look at the data as one big chunk or did you find an average for each month, then find the average of those 8 averages? That makes a big difference with calculations. (Because taking the average of a value that's already an average of something else will be inaccurate). It's possible that during those 8 months you had some periods with higher tidal volumes, but they got balanced out by periods with lower volumes, so it may not be anything too out of the ordinary.

I am curious what's happening with your RR though. If your RR went down, it's possible your Vt is increasing in order to maintain the same minute ventilation. For instance, my minute ventilation is nearly identical (around 4) whether using my Resmed ASV or Respironics CPAP, even though the machine is getting me there different ways:

Resmed: RR = 12, Vt = 330 mL (MV = 4)
Respironics: RR = 9, Vt = 440 mL (MV = 4)

It's like my body has some sort of regulatory system so I breathe just enough to stay at a minute volume of 4. So maybe something similar is happening with you, that your tidal volume is increasing to compensate for a decrease in RR.

[JDS74]

I did average 8 monthly averages to get the 650 mL figure.
Averages of monthly averages will allow a small error to creep in because the number of days in each month will vary. That aside, the computed number will be close.
The individual months were between 630 and 660 mL each month with only a couple of days above 700 mL.
Contrast that with May when all but a few were above 700 mL.

Since I am using an ASV machine, on the days where the PTB% drops very low (65% or less), the tidal volume on those days is higher. But recently, that is not the case. I will have to look in to effects of PTB% and tidal volume. From my data, it appears that the RR when in ventilator mode is 10 BPM while my "normal" sleeping RR is 16 BPM.

I'll try to post a graph showing the differences as well as a scatter graph showing RR vs Tidal Volume.
Edit: Here they are:
May Tidal Volume and Breathing Rate:

Feb v. May Scatter Graphs:



Thank you for you thoughtful questions.

[shortcake]

The individual months were between 630 and 660 mL each month with only a couple of days above 700 mL.
Contrast that with May when all but a few were above 700 mL.

Gotcha. This gives me a clearer understanding of why the increase seems so sudden (going from a few times in 8 months, to seeing these numbers constantly).

Are your PTB %s dropping lately? I think that would be an interesting correlation to look into, since the machine-initiated breaths appear to increase your Vt. Could your mask be getting older or leaking more than usual? Though I'm not exactly sure if that would cause false increases or decreases in Vt.

I don't know much about atelectasis, but maybe yours is getting better over time and therefore your lungs are able to pull in more air than before? Probably not a bad thing unless the ASV is causing hyper-inflation. You definitely have some great questions to pose to your pulmonologist though

[JDS74]

Check prev. post, the graphs are in it.

[JDS74]

My mask leaks are pretty flat and below the manufacturer's indicated volume. Essentially zero leaks.
In the beginning, my PTB% hovered around 90% and now they hover In the low 80's.
I don't see any correlation between those numbers and the Tidal Volume numbers I'm now getting.

I hope hyperinflation is not going on as that could lead to pneumothorax and that would be bad.
I doubt that the top pressure of 25 cm H2O would cause that without one of the many doc's I've been seeing and who've listened to my lungs commenting on the condition. I blow harder than that to inflate a balloon.

Here is a typical leak profile for me.

The little tiny bumps are when the pressure pops up to 25 cm H2O.

[shortcake]

The scatter graphs are interesting. Your May RR is trending down a bit from Feb but nothing stands out as a definite sign of what's going on. Have you recently started new meds, supplements, upped your exercise, etc? Have you felt worse or better in May? This may be one of those things that remains a mystery but if it makes you feel worse or the trend continues, ask your doc about it, especially since it may impact your lung condition.

[JDS74]

The numbers on the scatter graph in the upper left are the actual averages for the periods named.
The third line is the May average omitting the very low outliers on the Tidal Volume chart.
The difference is almost 85 mL.

No new meds, no new exercises, still feeling about the same (much better than when I was on the BiPap machine) mor energy and less sleepiness.

It may just be pugsy's aliens messing with me