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[IP] Re: Avoiding Bubbles

I certainly agree that the usual cause of bubbles is poor technique.  it is
also the cause of the largest bubbles.

As for the airliner scenario:

If there is a pre-existing bubble in the reservoir and the external pressure
drops by 1/3 there will be a volumetric increase in the size of that bubble
by 1/3.  The expansion of that bubble will be compensated for by pushing
more insulin down the tube and into you.

The plunger is not moving, the walls are not moving, the fluid in the tube
and in you is moving.  There is nothing to stop it.  After some period of
time there will be no difference in pressure from inside to outside the
pump.  A bubble of 1 U will become a bubble of 1.3U and you will get a 0.3U
bolus.  A 1U bubble is a very small bubble.  The volume of the bolus will
increase with the volume of the bubble.  Such that, a 6U bubble will give a
2U bolus with a 1/3 atmospheric pressure decrease.

This will happen because you are not much more than (in StarTrek terms) an
ugly bag of mostly water.  Don't take that personally!!!!  You are the
piston on the other end of the pump. (OK, you can take that personally)
When the lower pressure sucks on everything it sucks on you and you suck on
the tube and the tube sucks on the bubble. (no comment on how you should
take that)

if there are no bubbles then there is no expansion of the fluid, well not
much.  Any bubble that forms from degassing will displace an equal volume of
fluid into you.  I am not saying there will be a lot.

Should we worry about this?  I don't think so.  Unless someone is doing the
"I am out of insulin trick" of putting air into the reservoir to be able to
use the insulin in the tubing as an emergency back up.  Then they could have
20U in the reservoir and get a real bolus.

I am willing to listen to any reasoning that will explain what is keeping
the newly formed or expanding bubbles from pushing insulin down the tube.

I hope you find this exchange fun, I do.

Curtis Lomax

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