Nitrogen bubbles and air bubbles

[triswebb]

Hi all,

I have had a question on my mind for some time and thought this was the best place to ask it!

My question concerns air bubbles and nitrogen bubbles. I understand that DCS is caused by the formation of nitrogen bubbles in the blood and that this can lead to varying degrees of severity for the diver. My question is why is it that air bubbles in the blood are so much more severe than nitrogen bubbles and can cause death so quickly i.e. AGE?

Any help with this much appreciated.

Thanks,

Tristan

 

[DA Aquamaster]

I'm not a doctor and I don't even play one on TV. But I was advised at one point in my previous criminal justice career that killing someone by injecting air would take approximamtley 300 CC of gas to accomplish the job.

On the other hand, I think what makes arterial gas embolism potentially fatal is where the air enters the system and where it can potentially go from there.

 

[triswebb]

I'm not a doctor and I don't even play one on TV. But I was advised at one point in my previous criminal justice career that killing someone by injecting air would take approximamtley 300 CC of gas to accomplish the job.

On the other hand, I think what makes arterial gas embolism potentially fatal is where the air enters the system and where it can potentially go from there.

So... Its more that Nitrogen bubbles will restrict the flow of blood to the brain and other vital tissues, where as Air bubbles will travel to the brain? I.E If someone was injected with gas in the arm...(this is a pleasent conversation )

Thanks,

tristan

 

[jonnythan]

As I understand it, the problem is with where the bubbles are, not what gas is in them. I would think that regular bubbles in the blood from improper decompression almost exclusively form in the venous system, where they're generally easily handled. However, getting gas bubbles in an artery can lead to major problems, especially if the bubble travels to the heart or brain.

 

[jonnythan]

Remember... as blood travels through arteries, the vessels get smaller and smaller. So if you have a bubble in an artery going to the brain.. it will keep going until it gets shoved into a vessel that's too small to hold it, and that can cause a blockage. However, in the venous system, vessels get bigger and bigger until you move through the heart and go to the lungs, which (correct me if I'm wrong) are a pretty good filter for bubbles.

 

[Marek K]

Hmmm...

The question I asked during a scuba class once was, why isn't there a problem with oxygen bubbles forming during decompression? I think the answer was that oxygen gets harmlessly absorbed much more quickly into tissues than nitrogen. (I also think whoever it was said that this was because nitrogen is an inert gas. Except that it isn't.)

Plus the fact that there's up to four times more nitrogen in air than oxygen could have to do with this...

 

[triswebb]

Exellent, this is really helping, thanks. Just a couple more questions. You say that:

"regular bubbles in the blood from improper decompression almost exclusively form in the venous system"

Why is this? And in what situation can they form outside of the Venous system?

Thanks again for all your help.

Tristan

 

[jonnythan]

Exellent, this is really helping, thanks. Just a couple more questions. You say that:

"regular bubbles in the blood from improper decompression almost exclusively form in the venous system"

Why is this? And in what situation can they form outside of the Venous system?

Thanks again for all your help.

Tristan

I said I think it's the case, as it makes intuitive sense to me, but I really have no idea what I'm talking about

The venous system tends to operate at a much lower pressure than the arterial side.. hopefully someone who actually knows what's going on will come set us straight soon

 

[MookieMoose]

Exellent, this is really helping, thanks. Just a couple more questions. You say that:

"regular bubbles in the blood from improper decompression almost exclusively form in the venous system"

Why is this? And in what situation can they form outside of the Venous system?

Thanks again for all your help.

Tristan

OK, here's the simple version of what happens, from a physiologic standpoint. As previously mentioned, what gas forms an embolism is irrelavent, WHERE the bubble goes is what is important. In the case of DCS bubbles form almoast exculsively in the venous circulation becuase the gas that forms them is comming out of tissue like muscle, or fat, and blood leaving these tissues enters the venous circulation. The lungs are pretty good at filtering out most bubbles - up to a point. DCS happens when the bubble load in your venous circulation either exceeds the lungs ability to filter, or the bubbles find another way into arteries. Once in the arterial circulation bubbles are forced into ever smaller vessels, ultimately into capillaries where gas exchage with tissues takes place. Sometimes bubbles get stuck here, but not usually. What happens is the bubbles change shape so they can fit through the small capillaries - you end up with thin, VERY long bubbles that interupt the oxygen and nutirient supply of vulnerable tissues like nerves for such a long period (becuase the bubble is so long) that the tissue begins to starve and suffocate (sort-of).

I'll try to attach a picture here to explain things a little better. If this works, it is a photo of blood vessels in the retina of the eye. All the bright white areas are bubbles

Cam

 

[jonnythan]

For those of you who don't have PowerPoint, here is that angiogram as a jpg: