Disolved Gas Content of the Body

[Thalassamania]

Someone asked me, "What is the total approximate dissolved gas content in blood and tissues in an average sized person at one atmosphere ambient (saturated and at 30 min. at 100 feet of water)." Anybody know?

 

[Dr Deco]

The gas content, on average, is one liter per atmosphere at saturation.

 

[Thalassamania]

Thanks, I've passed that value along. Any idea of how much gas at 4 ata for 30 mins?

 

[eponym]

Neat question, Thal.

The gas content, on average, is one liter per atmosphere at saturation.

Thanks, I've passed that value along. Any idea of how much gas at 4 ata for 30 mins?

From a theoretical perspective, that would depend on tissue halftime. For example, a body with an overall average halftime of 30 minutes would be fifty percent saturated after thirty minutes, meaning two litres dissolved. A five-minute compartment would be essentialy fully saturated after thirty minutes (six halftimes), for four litres dissolved.

But I'm sure Thal knows that already . . . is there experimental data on dissolved gas, maybe from chamber work?

-Bryan

 

[Thalassamania]

I could back calculate it based on a 12 tissue model, but I have no idea of what percent of the body to allocate to each tissue. I'd hoped that someone had an easier way, like a number.

 

[eponym]

Yeah, the halftime values in different models go up to, what, two hundred forty minutes? I'm hoping someone's actually done post-chamber-ride tests to measure, for example, breathed-out nitrogen over a period long enough to extrapolate an actual offgassing curve. That could be used to estimate total beginning load, I think.

I searched on Rubicon but saw nothing pertinent. I'll ask Gene via PM. I really like the initial question. I always start the discussion of nitrogen ongassing/offgassing by pointing out that we walk around with a base load of dissolved nitrogen but have not yet been asked to quantify that.

-Bryan

 

[rjack321]

I always start the discussion of nitrogen ongassing/offgassing by pointing out that we walk around with a base load of dissolved nitrogen but have not yet been asked to quantify that.

Knowing the starting 1L, how long does NASA breathe O2 for before 0 ATA space walks? That gives a clue to the length of the curve to eliminate that. Continue that curve in reverse and you could guesstimate to 30 mins at 4 ATA. One way to account for the whole body "net" halftime.

 

[bvanant]

What to me is more interesting and what I tell the kids in my lab is that while 1 liter sounds like a lot, it is less than 2 grams total which makes you think about how little dissolved gas really is around when you try to make devices to measure it in-vivo.
Bill

 

[Gene_Hobbs]

I searched on Rubicon but saw nothing pertinent. I'll ask Gene via PM. I really like the initial question. I always start the discussion of nitrogen ongassing/offgassing by pointing out that we walk around with a base load of dissolved nitrogen but have not yet been asked to quantify that.

The closest "measured" nitrogen volume I can think of included a 100fsw/ 25 minute dive:

Dick, AP; Vann, RD; Mebane, GY; Feezor, MD. Decompression induced nitrogen elimination. Undersea Biomed Res. 1984 Dec;11(4):369-80. RRR ID: 2981

They do a nice job describing their method as well as showing how changes in cardiac output will have an effect on inert gas uptake and elimination.

Some others that might be of interest (from our collection anyway) can be found with the keywords "nitrogen elimination". A PubMed search will also turn up a few others that are interesting reading, keywords "nitrogen elimination diving".



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