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[IP] Thoughts on a closed loop system from an engineer
1. glucose detection
2. lag time in current detection and delivery system
3. a rule-based system, system calibration
1. Glucose detection. Note that this is a GUESS, but I would suspect that
glucose levels cannot be detected at the absorption site where insulin is
delivered. I would suspect that the fluids used near the delivery site
would have a lower value than the true blood glucose level. There is still
also comfort issues, calibration issues, accuracy issue... Many things to be
2. Lag times...
Let's say you start exercise at 130 and within the first 15 minutes usually
crash to the 40's (with a pump, you gave a reduced basal for two hours in
advance, but we're assuming the system knows all/does all). How fast does
it detect this change? How often does it measure blood glucose values?
Every 3 minutes? Every 5 minutes? Every second (would kill the batteries
Let's assume every 3 minutes... So at time 0, you are 110. At time 3, you
are 90. What constitutes a significant change? Who defines these
constants? What do you do if you DO consider this a significant change?
Does the system suspend as you would like it to? Does it just reduce and on
the next check see if there is another significant change? Is it too late
to recover at this point?? (You might already be 65! and still dropping...)
The *only* way I can see this working is with a intraperitoneal shunt which
eliminates the variable of insulin absorption times. But this increases the
risk of infection so high, I'd much prefer to stick with my infusion sets,
no pun intended. Plus, I can take my pump OFF if I want and use shots. I
did this yesterday for a "vacation" - I did this when I was at the beach,
etc. The shunt is always there, always visible and you bet your a$$ I
would't be caught dead swimming in "icky" waters like I encountered white
water rafting with it!
3. What kind of software drives a system that is dependent on #1 so many
variables and #2 is individualized to the user? Who defines the "rules"
(i.e. If bloodglucose < 70, drop basal by X% else if bloodglucose is > 150
give X as a correction bolus. We all know "X" differs widely from person to
person, depending on height, weight and the hand of God.
What if the factory preset of X units is too much? Is it a learning system
(yes, folks, these do exist - systems do trial and error and set their own
constants (with user feedback, ie. No, bad pump, you got it wrong!!!! But
this takes you back to you, the user, having to be intelligent enough to do
this and the machine "gentle" enough to not hurt you in the process - think
the FDA will approve THAT! ha!)?
What if.... What if the slacker programmer in cube three "forgot" to add a
system command? Ever here of the Therac-25? (search for that on google.com
and you'll get a ton of hits)
We all hope that we design flawless software, but the fact of the matter is,
even with the intense testing that is performed before a release, mistakes,
like daylight savings time, still do slip by. Do you really want a machine
that much in control of you?
As a programmer, I believe heavily in the use of the human brain when it
comes to life-critical systems. I would love very much for a system that
was pseudo-closed loop, where I had to approve certain user-defined commands
(i.e. I want to approve all basal rate changes, all pump suspensions and all
boluses > 5.0 units or something).
But again, I am opposed to implanting an AI machine inside of me and placing
my life in its hands, I am opposed to shunts for the infection risk (ie.
that kind of infection could be fatal guys!). I *like* my pump. Sure it
gets tiring being the brain for it but to me it is a gift from God.
Appreciate what you have today and don't pin your hopes on tomorrow!
I'll use it until I die :)
Susan Fisher, just my $0.02, please dear God, don't flame me. It upsets me
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