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Tidal Volume Help - chd3143 - 09-18-2014
Would someone be willing to explain tidal volume? Every now and then I have some really erratic fluctuations -- from a normal 475-ish to an up and down spike that lasts about 30 seconds sometimes peaking at 1800. Over this time, exhaling seems to increase from 2 seconds to around 4 seconds. Displacement also increases quite a bit from 10L to 30L. This happens once or twice a night, and I wasn't sure if it could be influenced by something else -- leakage, etc. I'll attach some pics.
Thanks as always!
Oops here's the second capture.
RE: Tidal Volume Help - surferdude2 - 09-18-2014
No doubt it happens in context with something else but we can't correlate it without all the other data.
RE: Tidal Volume Help - justMongo - 09-18-2014
I see the same thing in mine. There is a big breath, then a pause. What causes the big breath, I do not know. The pause makes sense in light of the big breath.
RE: Tidal Volume Help - surferdude2 - 09-18-2014
With the added graph you posted, it looks like it only lasted 10 ~ 12 seconds. I see lots of people partially wake up and take a deep breath and go back to sleep. Mostly that was my kids when they were little ones but I've seen big people do it too. I've seen it on my graphs as well so I'd say, not to worry.
RE: Tidal Volume Help - vsheline - 09-21-2014
(09-18-2014, 07:44 PM)chd3143 Wrote: Would someone be willing to explain tidal volume? Every now and then I have some really erratic fluctuations -- from a normal 475-ish to an up and down spike that lasts about 30 seconds sometimes peaking at 1800. Over this time, exhaling seems to increase from 2 seconds to around 4 seconds. Displacement also increases quite a bit from 10L to 30L. This happens once or twice a night, and I wasn't sure if it could be influenced by something else -- leakage, etc. I'll attach some pics.
I don't know what is the cause of the variations in Flow and Tidal Volume shown in your posted plots. You say these events are fairly rare, occurring just a few times per night. Perhaps these plots are of times when you are changing sleep positions? (Just a guess.)
Tidal Volume (abbreviated Vt or TV) is the machine's estimate for the volume of air we are inhaling (or exhaling) per breath. The number plotted is a moving average across several breaths.
The Flow is the estimated Rate of airflow (the volume of air per unit of time, for example Liters per minute) entering our airway (positive Flow) or exiting our airway (negative Flow).
The Tidal Volume is mathematically derived from the Flow. I think the Vt would be simply the integration of the positive Flow (or negative Flow), averaged across several breaths.
RE: Tidal Volume Help - me50 - 09-21-2014
just curious what an average vt would be....and yea, I know it varies per person but wanted to see what others vt is during sleep
RE: Tidal Volume Help - vsheline - 09-21-2014
(09-21-2014, 02:08 AM)me50 Wrote: just curious what an average vt would be....and yea, I know it varies per person but wanted to see what others vt is during sleep
For someone who is 5 foot 10 inches (70 inches tall), I think ResMed indicates a typical Tidal Volume would be around 500mL, with about 75% of it reaching the alveoli and participating in gas exchange (O2 and CO2 exchange).
ADDED:
I searched more on this topic. Among the articles which turned up was one which states that normal Tidal Volumes are 5 to 7 mL per kg of ideal body weight (NOT actual body weight).
The ideal body weight depends on sex and height.
Here is a link to an online calculator for Tidal Volume. We put in our sex and height and the value we want the calculator to use for the conversion factor (for example, 7 mL/kg).
http://www.mdcalc.com/ideal-body-weight/
Here is the article which includes the "5 to 7 mL/kg" number:
http://rtboardreview.com/public/tables_lists/minute_alveolarventilation.htm
RE: Tidal Volume Help - me50 - 09-21-2014
so when looking at SH, for TV it shows minimum, medium, 95% and maximum. Do I understand that the "average" TV is based on a person's height? Is it problematic if a person is under 500 or that the 95% or maximum is over 500? The TV is something that has always confused me. If there is information here explaining that, if someone could direct me to the info, I would appreciate it
RE: Tidal Volume Help - vsheline - 09-21-2014
(09-21-2014, 08:27 AM)me50 Wrote: so when looking at SH, for TV it shows minimum, medium, 95% and maximum. Do I understand that the "average" TV is based on a person's height? Is it problematic if a person is under 500 or that the 95% or maximum is over 500? The TV is something that has always confused me. If there is information here explaining that, if someone could direct me to the info, I would appreciate it
Hi me50,
I have added more info in my previous post, above, including a link to an online calculator.
What my googling found is there's an appalling degree of misinformation about what the Tidal Volume should be set for when using hospital mechanical ventilators. Apparently, Respiratory Therapists use various values between 4 to 12 mL per kg of body weight, sometimes without realizing that ideal rather than actual body weight should be used AND that forcing high values like 10 or 12 mL/kg sometimes causes lung damage.
In their instructions for Respironics BiPAP AVAPS machines (which are non-invasive ventilator machines which are set up with a target Tidal Volume), I think Respironics suggests targeting 8 mL/kg ideal body weight, but I think this suggestion (using 8 mL/kg of ideal weight) should not be taken at face value because, if memory serves, their machine effectively would target something like only 70% or 80% of that much, because the machine increases the Pressure Support (in order to prevent the Tidal Volume dropping too low) when the Tidal Volume falls to 70% or 80% of the value entered in machine's settings.
I suspect that most adults on PAP therapy have an average Tidal Volume around 6 or 7 mL per kg ideal weight, and the peaks may reach several times that large when we are breathing deeply after an arousal caused by an apnea.
RE: Tidal Volume Help - PaytonA - 09-21-2014
(09-21-2014, 01:36 PM)vsheline Wrote: I suspect that most adults on PAP therapy have an average Tidal Volume around 6 or 7 mL per kg ideal weight, and the peaks may reach several times that large when we are breathing deeply after an arousal caused by an apnea.
I just ran some numbers and I think that is about right. Thanks for the info Vaughn. I have been mildly curious about tidal volume for a while. I am still a little curious why it is measured and kept track of for apnea data. I have similar feelings about respiratory rate.
Best Regards,
PaytonA