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[IPk] For Melissa?

Hi Melissa,

This might be a question for you. At least, I'm sure you'd be able to point 
me in the right direction on where to look to find out more.

Edward has been using the Medtronic Sensor Pump for just over three months 
now and I want to know more about how the actual sensor  bit of the pump 
works. My understanding so far, is that the inter-stitial glucose is 
measured by the sensor electrode somehow converting glucose into an electric 
current using two marker points to calculate resistance. Presumably when you 
enter the first calibrated BG, the sensor looks at the resistance and 
matches that with the BG to then go on and track the inter-stitial glucose 
values. The pump indicates an ISIG (don't know what that stands for) value 
which I think the manual says is a measurement of nanoamperes and the dsn 
said that the ISIG value needs to be between 10 and 100 for the sensor to 
work. Is it something to do with the density of the fluid between the cells 
and if so, what affects this? Often, when I put a new sensor canula in the 
ISIG is high (over 100) but by the time the two hour initialisation is 
complete it is usually around 20 or 30. So what is this ISIG and what causes 
it to changed? I have noticed that if Ed drops below 4mmol interstitally, 
even though his BG can be ok, that the ISIG is likely to be below 10. If the 
ISIG goes down to 4 then the sensor tends to give up altogether. Is this 
something that is affected by stress/adrenaline? Not surprisingly, Ed isn't 
keen on having the canulas changed and the more worked up he is the higher 
the ISIG.

I know this isn't something I need to know but it's been bugging me for 
weeks now. I just want to understand what is going on. Any ideas? Questions 
to Medtronic and our team at the hospital haven't given any more answers.


Jane. Mum to Ed (4).
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