Understanding Air Embolus and Blood Circulation

[Charles123]

I have never really thought why an air embolus can restrict the passage of blood, until now, and I don't really understand. Why can't the circulation pressure just push the air embolus forward until it is eventually expelled in the lungs? Or why can't it dissolve the embolus? In a plant is easier the see why it is a problem, there is not a push, but a pull, due to transpiration, the presence of an embolus will interfere with the cohesion attraction that makes possible the transpiration pull. But in blood circulation I am not seeing why is a problem.
Thank you
Regards
João

 

[Borek]

I would guess too low a pressure to push the bubble when it blocks the vessel.

 

[Rooted]

I agree, for a venous air embolus the pressures are unlikely to be great enough to push the air through. For arterial emboli I thought that at the capilllary level the air gets 'trapped' and a secondary response occurred as a direct result of the exposure of the endothelium to air, causing a complement cascade and microinfarcts. I suppose a big enough embolus ending up in the heart would empty it and drop cardiac output.

 

[Charles123]

Thank you both for your answers.
"I agree, for a venous air embolus the pressures are unlikely to be great enough to push the air through." But what makes air more difficult to push?
"For arterial emboli I thought that at the capilllary level the air gets 'trapped' and a secondary response occurred as a direct result of the exposure of the endothelium to air, causing a complement cascade and microinfarcts." Why does it get trapped? How does that secondary response works?
"I suppose a big enough embolus ending up in the heart would empty it and drop cardiac output." I have read about this, but I don’t understand why it is not just a brief transient situation.
Regards

 

[Rooted]

"For arterial emboli I thought that at the capilllary level the air gets 'trapped' and a secondary response occurred as a direct result of the exposure of the endothelium to air, causing a complement cascade and microinfarcts." Why does it get trapped? How does that secondary response works?

I may well be wrong here but I have a feeling it is something to do with hyperoxygenation causing an inflammatory response, and this response causes endothelial damage. I am not sure why the air gets trapped though. Is the pressure at the capillary bed only a fraction of the arterial pressure? I wonder if an increase in resistance due to the presence of an air obstruction would cause incoming blood to be diverted through other vessels, preventing the bubble to be washed through, perhaps? Interesting question.

"I suppose a big enough embolus ending up in the heart would empty it and drop cardiac output." I have read about this, but I don’t understand why it is not just a brief transient situation.
Regards

For the heart full of air, I think purely the contraction of the heart when not filled with blood means the air gets compressed without a significant outgoing pressure, so arterial pressure plummets.

 

[Charles123]

"For the heart full of air, I think purely the contraction of the heart when not filled with blood means the air gets compressed without a significant outgoing pressure, so arterial pressure plummets."

You mean the hear is only able to compress the air, which then expands again, its compressed again, but it never gets expelled from the heart?

 

[Rooted]

Yes I think so. I'm not sure how transient it is though, as you were saying. Out of curiosity what does happen in a plant? Would it stop the flow completely?

 

[Charles123]

I think so... There would be no more cohesion

 

[Borek]

Guess again - we need additional pressure to fight the surface tension.

 

[Charles123]

Borek, how so?
What about what happens in arteries/veins, no more insights?
Regards

 

[Borek]

To squeeze the bubble into a thinner vessel requires changing curvature of the bubble surface. Just like water doesn't drop from a capillary because it is held by the surface tension - it is the same process, only reversed.

 

[Charles123]

Water not falling from a capillary is more capillarity than surface tension, inst it?
And surface tension in the air? Why would you have cohesive forces in air?

 

[Borek]

Surface tension requires a surface, that means phase boundary between liquid and gas in this case, it has nothing to do with forces in the bulk of the bubble.

Perhaps water in a capillary is not the best example, as it wets the glass. Have you ever seen mercury in the capillary? There is (almost) no wetting, but because of strong surface tension mercury doesn't drop, you need some extra pressure to force it out of the tube.

 

[Charles123]

I know it requires an interface between 2 different constituents, but it is as wikipedia puts it - "This property is caused by cohesion of similar molecules, and is responsible for many of the behaviors of liquids.". The boundary causes the difference in attraction that does not exist in the bulk of the liquid as you put it.

 

[Charles123]

How does an air embolus restrict the passage of blood?

I understand that air bubbles clog smaller arteries, surface tension with insufficient time/surface area through which to dissolve, air bubbles maintain themselves, but they are pushed trough, aren`t they? So why don’t they just eventually get dissolved and/or then ultimately expelled by the lungs? Is it a matter of blood clothing in contact with oxygen? How does that work?
Thank you
Regards

 

[Saged]

Any one who's interested (OP posted this elsewhere and got an answer.)

http://en.allexperts.com/q/Physics-1358/2012/9/air-embolism.htm

 

[Evo]

He already got an answer here.

 

[Charles123]

And this is a follow-up: http://en.allexperts.com/q/Physics-1358/2012/9/decompression-sickness.htm

Also, does anyone know how the air-coagulation relation work?

Regards

 

[Evo]

And this is a follow-up: http://en.allexperts.com/q/Physics-1358/2012/9/decompression-sickness.htm

Also, does anyone know how the air-coagulation relation work?

Regards

I think the other poster summed it up when they told you

This is the last time I answer a follow-up on this question and beat this dead horse