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RE: [IP] CGMS and falling BGs

Hi Cynthia,

 > [...] what can be done to increase the
 > value of the isig?

The sensor measures glucose concentration by applying a voltage
across a little cavity filled with fluid (blood) that has an
enzyme dissolved in it (also supplied by the sensor). The enzyme
converts glucose and produces some free ions in the process, which
make the fluid more conductive to electricity. The voltage applied
therefore results in a higher current flowing if the reaction is
more intense, and lower if it is less intense. This current is the
"Isig" -- "I" being the international symbol for an electric
current, and "sig" standing, presumably, for "signal".

The Isig depends, primarily, on three things:

- Voltage applied across the reaction cavity. As I recently
learned, to my chagrin, a Minilink transmitter may have the
battery going bad without loudly yelling about this fact.

- Amount of enzyme available to keep the reaction going. If
nothing else, this will eventually cause a sensor to peter out.
Also, higher BGs cause a more intense reaction, using up more of
the supply.

- Amount of blood, and of glucose n that blood, entering the
reaction chamber. Some of us scar easily, and nothing can keep a
sensor going beyond three days -- simply because it gets walled
off by tissue.

You have already figured out what I am driving at: Beyond making
sure that your transmitter is in good shape, there is nothing you
can do to increase the Isig without increasing your blood sugar.
And like you, I find that with an Isig below 5 (sometimes 6), the
sensor fails to track -- the sensor BG flatlines and no longer
goes up and down with the BG level.

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