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[IP] Re: Avoiding Bubbles
Well Curtis, we may want to continue this off the list, but your argument
won't hold water (so to speak :-). If the plunger is not moving and the
walls are not moving, then there's no way for the bubble to grow or even
see the drop in ambient pressure. Pressure inside a sealed rigid container
doesn't change with surrounding pressure. For the bubble to expand the
volume of the chamber must expand.
If you think that the lowered prssure around your body will "suck" the
bubble bigger, this might possibly occur, but if it did, then it would also
be able to "suck" insulin to a similar degree without any bubbles at all.
But the interstitial liquid around the catheter is not "free" water and
likely transmits pressure poorly. We rarely hear of people getting too much
extra bolus on air flights. Usually its the opposite problem, with BGs
rising off scale.
So th bottom line is that when pressure around a person and his/her pump
falls, bubbles might possibly enlarge somewhat, but there will be no change
in the insulin delivery. Ergo, Not to worry when flying
<<<<<<<<<<<<<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
I am willing to listen to any reasoning that will explain what is
the newly formed or expanding bubbles from pushing insulin down the tube.
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