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[IP] Re: Pump/meter connections

Recently Bonnie wrote, regarding the promised connection between the pump 
and a continuous blood-glucose meter:

> I am waiting on that also.   I can't figure
> out why it is taking so long.   We have the infusion set..which should be
> able to handle measuring bg and pumping accordingly....it just doesn't seem
> that diffucult to me.  But than I am not an engineer or a research
> scientist.

Neither am I, but I play one on TV... boy, that dates me, doesn't it? How
long ago was that commercial on?

I wish such a connection existed, too, but I think the idea is more
difficult than it seems at first glance.

Here's how I understand it from a technical type I heard from once. The
meter will be able to take BG readings almost instantaneously. But our pumps
don't change insulin levels fast. Even with Humalog, when you bolus, it may
take 15 to (in my case) 45 minutes before your BG even starts to react, and
longer before the change is significant (YMMV).

So, suppose your meter detects a reading of 150, and your target is 100. It
starts bolusing insulin. Your BG stays the same for a few minutes, so the
pump keeps bolusing. BG starts dropping, to 130 say, but isn't near 100 yet,
so pump keeps bolusing. An hour later, your BG is 100, and your pump finally
stops bolusing... but now you've got maybe three extra units on board, still
active, and your BG keeps dropping into the basement!

Here's a silly analogy. Imagine driving a car around a complicated race
course, with a steering assembly that delays your turns by 10 seconds
whenever you turn the wheel, and a videocam for a window that only shows you
the road _behind_ you!. And a throttle stuck at 50 mph. That's an imprecise
(though entertaining) analogy in some ways, I suppose, but it's similar to
what I'm talking about.

It's a lag-time problem: the pump can't fix things fast enough with simple
infusion to keep up with the meter. There are two ways around this, I guess:
(A) implant the pump, so it can feed more directly into your blood, for
quicker reactions; (2) program the pump cleverly, so it can detect these
trends and bolus properly even via infusion. But the pump programmer would
have to be VERY clever to take into account all the various variables we
have to (exercise, fat consumption, etc.). I'm not saying it's impossible,
but I'm not sure I'd _trust_ a pump-meter connection! unless I knew the
programmer. At least not until at least version 1.3 of the software.   :-)

Keith Johnson
Fleischmann Planetarium
email @ redacted
"Time flies like an arrow; fruit flies like a banana."

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