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The air we breathe consists of about 80% nitrogen and 20% oxygen. The oxygen gets diffused into the blood and CO2 out of it, the nitrogen does mostly nothing, as there isn't a partial pressure of nitrogen between the air and your blood.

In membrane oxygenators the blood flows arround small tubes which contain pure oxygen. The oxygen diffuses in your blood en the CO2 diffuses in the tubes, basically doing the same thing lungs does. However, since it's pure oxygen that flows through those tubes, the nitrogen in your blood should get diffused into the tubes.

So is this what happens? Does the nitrogen simply diffuse untill there's nothing left? Isn't that then bad for your body if all the nitrogen is out? Or can't nitrogen pass through the membrane the tubes are made of? Or does it differ wether you use 'true' membrane of microporous membrane?

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  • $\begingroup$ You are not considering the fact that nitrogen has low solubility in blood. There isn't a lot of nitrogen in the blood anyway and it performs no physiological function. I don't understand why you assume that loss of nitrogen will have any negative effect on the body? $\endgroup$ – WYSIWYG Apr 25 at 12:23
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    $\begingroup$ I was actually asking what happens with the nitrogen in your blood in membrane oxygenators, wether it gets diffused in the tubes or stays in the blood or... The "isn't that bad for your body" is more of a side question which you now answered, for which thank you. $\endgroup$ – user9000 Apr 25 at 15:35
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    $\begingroup$ I wouldn't be so quick to write off the importance of dissolved nitrogen. N2 coming out of solution and forming bubbles is a major contributor to 'the bends' ref $\endgroup$ – user1136 Apr 25 at 17:58
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It gets diffused out, like you expected. Grist (2013) writes about this in relation to "the bends," which has already been mentioned by user1136. He writes:

Cavitation of blood containing normal oxygen and nitrogen levels by mechanical heart valves after implantation generates bubbles that can be detected in the brain using transcranial Doppler ultrasound (2). These bubbles are mainly nitrogenous. Nitrogen is less soluble in water than oxygen. So during excessive turbulence, temperature changes, or pressure changes, nitrogen is the first gas to come out of the solution. (Ask any knowledgeable diver about the physiology of the bends.) We know these bubbles are mainly nitrogen because when the nitrogen in the patient’s blood is off-gassed by breathing 100% oxygen, the cavitated bubbles go away. In one study, the administration of 100% oxygen by facemask reduced the cavitation generation of GME by 98% (3). [Emphasis added]

Can't say it a lot better than that and the rest of the article. When people are breathing de-nitrogenated air, it simply results in nitrogen being diffused out of the blood. So yeah, basically the amount of N2 goes down to 0, at least if they are on it for long enough.

As for it being bad for you, not really, at least not perceptibly: though nitrogen is critical for body function, it's practically useless to the body in the N2 form; it has to be "fixed" to a more reactive form such as ammonia / other nitrogen oxide.


Sources

  • Grist G. 2013. Oxygen or Nitrogen: Which Is the Lesser of Two Evils? J Extra Corpor Technol 45(1): 61-63.

  • Sprent JI, Sprent P. 1990. Nitrogen fixing organisms: Pure and applied aspects.

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    $\begingroup$ Great ref. Anyone who has used an Amicon ultrafiltration apparatus to concentrate an enzyme will be familiar with (unwanted) bubbles forming when the N2 pressure is released. $\endgroup$ – user1136 Apr 25 at 18:38

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