83 - Nitrogen in our Lungs

KYJ 83 - Nitrogen in lungs

I was asked ....  "In air we breathe, does nitrogen have a role"?

Let's recap. Air is 21% oxygen and 78% nitrogen (the other 1% is water, argon, and traces of many gases including CO2).

When we breath in, oxygen in air diffuses into the blood across the respiratory membrane. This occurs because blood in the lung is low in oxygen, so there is a one way flow from high oxygen concentration in alveoli, to low concentration in blood.

As arterial blood rich in oxygen perfuses tissues, cells consume oxygen depleting it. Hence it needs constant replacement.

Nitrogen is not consumed by tissues so it's blood concentration is consistent.  It is called an "inert gas" meaning no physiological role.

Nitrogen in the alveoli doesn't diffuse into the blood because it's concentration in blood and in alveoli is the same.   It is not being used by calls nor created by cells.  The only way we can really remove it from blood is to reduce the concentration of it in the air we breathe... Remember that point.

Now back to the alveoli. That air sac with nitrogen and oxygen in it. Oxygen is leaking out, nitrogen is staying in the sac.
The sac collapses slightly. No big deal. Nitrogen's role in the lung is therefore to splint the alveoli open so they can't fully collapse but they do shrink a little.

Exercise:  do this!
Take the deepest breath you can and hold it for 15 sec. At the 10-15second mark, just try and breathe in some more. ....
I bet you could.  By loosing oxygen into your blood, you made a bit more space inside your lungs. Cool hey!!

Now, what do you suppose happens when you breathe in less nitrogen?  We do this to a patient when we put on oxygen. Someone on a face mask at 8 lpm is breathing 50% oxygen, but by pure mathematics they are also breathing about 50% nitrogen.

Oxygen diffuses into blood, and as it does less nitrogen in the alveoli causes less splinting and more alveolar collapse- this is called atelectasis.   The higher the O2 a person breathes, the greater is this atelectasis, and it can be bad.

As someone breathes high oxygen therapy, their blood nitrogen (now relatively higher than lung nitrogen), starts to drop. This off gassing of nitrogen is one of the mechanisms by which hyperbaric therapy works on divers with the Bends, but in others, the longer they breathe oxygen in high concentrations, the lower their blood nitrogen becomes.

Eventually you will take them off O2.  Now both blood oxygen and nitrogen levels are reduced, meaning that when a person breathes in, the diffusion of both nitrogen and oxygen occurs... Collapsing the alveoli even worse than oxygen alone.

This is one reason that weaning off O2 slowly is needed. Widespread collapse leads to pneumonia.

Summary: the more oxygen you put on your patient, the more lung collapse you cause.
Oxygen is a potentially dangerous and, at times, toxic gas, use it wisely, never routinely.