bubbles in the arteries

[beche de mer]

Why don't bubbles form in the arterial circulation?

Is is because of the higher pressure, or are they removed by the lungs before they become evident or measurable? Or some other reason?

 

[The Iceni]

but, as you surmise, brech de mer, the higher arterial pressure means the offgassing pressure in the arteries is far less than in the veins, or indeed within the soft tissues - which is where they must form first - to be mopped up by the lungs if the anatomy is normal.

As deco tables are designed to prevent the formation of significant tissue or venous bubbles, arterial bubbles are seldom found in normal dive profiles.

Hope that helps,

 

[Dr Deco]

Dear B D Mer:

There are several reasons, but probably the best is that there is not any supersaturation in the arteries. If gas exchange in the lungs is normal, there will not be much excess of inert gas in arterial blood. Gas exchange from tissues will not occur until one reaches the capillary level.

At the capillary level, the hydrostatic pressure is low and tissue pressure is high. There are also probably micronuclei present in the capillaries form when they are squeezed (collapsed) and reopened. This is known as viscous adhesion” or Stephan adhesion.

There also do not appear to be micronuclei in arterial blood (or any blood for that matter).

Dr Deco :doctor:

 

[beche de mer]

Thanks doc. Something also that I picked up from another thread is that when gas is dumped from the tissues, it goes straight into the venous circulation and under normal circumstances, would never make it through to the other side. (Which might be what you're saying.)

 

[The Iceni]

Mea culpa.

What Dr Deco confirms is that the lungs are so efficient at gas exchange that they rapidly equalise the blood flowing through them with ambient pressure. Therefore the arterial blood leaving the lungs will rarely, if ever, be in a position of being superstaurated with any gas, which is the prime mover for the formation of micronuclei and bubbles.

The lungs are not the limiting factor in decompression.

On the other hand the tissues are not nearly as efficient and take up inert gas, and subsequently off gas, at a rate determined by their blood flow and physical properties and so are prone to supersaturation (as is the venous blood supplied by them).

The two situations where bubbles are found in arterial blood will be when there is a right to left shunt or an explosive decompression.

I hope this has restored my credibility! :bonk:

 

[Nan]

...we had a diver a few years ago who had an AGE on Grand Cayman. Loss of consciousness (AFTER getting to the platform, thank goodness), GREAT irritability on awakening, residual UE weakness and paresthesias for about 6 mo afterward. Definite spinal cord involvement. He was a long-term heavy smoker, and we always assumed that was the major contributing factor (he had kept to his dive profile but was out of shape and probably dehydrated as well).

Would the right-to-left shunt you mention have operated in this case? I was never very sure about AGE formation--I understand the venous side.

*Maybe this should be in the deco forum. I'll look for it there if it's not here when I get back.

 

[beche de mer]

Nan once bubbled...
... He was a long-term heavy smoker,...he had kept to his dive profile but was out of shape and probably dehydrated as well.

In the situation you describe, I'd be thinking pulmonary barotrauma, possibly related to his smoking.

Localised areas of air trapping causes tearing of the lung tissue, allowing air into the blood which goes back to the left side of the heart, and then up into the cerebral circulation.

Patent ductus arteriorus is a possibility also.

 

[Nan]

Yeah, emphysematous bulla is what I was thinking. It seems intuitively obvious. But when I think about it, wouldn't that just more or less cause a pneumothorax rather than an AGE? I should think a tear would not necessarily introduce enough air into the bloodstream, since you'd have to pressurize bubbles into little teeny capillaries that were oozing blood back-at-ya at the same time. You could get plenty of air into the pleural space to cause a pneumo. But that's a whole different thing.

 

[DocVikingo]

Assuming that you mean patent ductus "arteriosus," how do you see this as possibly contributing to AGE?

Best regards.

DocVikingo

 

[beche de mer]

DocVikingo once bubbled...
Assuming that you mean patent ductus "arteriosus," how do you see this as possibly contributing to AGE.

DocVikingo

Err....yes. Transient dyslexic episode.

I meant patent foramen ovale. :dunce:

I haven't had much personal experience of this type of situation, but could a PFO result in the catastropic type of event described by Nan?

(Note to self: keep away from medical thread after second glass of wine.)