Blood and Absorption
I've been thinking about this a little bit lately, and it stems from an experience I had during a research study at the University of Minnesota.
I had a visit planned for this study where I was to stay there all day hooked up to a couple IV's and basically reading, napping or watching garbage on TV. I was to be fasting when I arrived in the morning.
For some reason, I figured that if I had to fast after a certain time of the evening that I was going to go out with a bang! I had a HUGE bowl of ice cream. Now, for me, ice cream is one of those problem foods that is a bit harder to bolus for. I goofed it up a bit and my blood sugar was in the high 300's when I woke up the next morning. I corrected for it, but when I wake up real high like that, the rest of the day is a bitch and I fight the BG's all day long.
When I checked in for the study, and after getting the IV's hooked up, I was still in the low to mid 300's. The study coordinator needed me to be below 200 before starting the tests. I filled them in on my correction bolus and how much insulin I had on board. They checked with the docs and said that they were going to inject Regular insulin into my bloodstream via the IV.
I thought they were nuts! Regular insulin?! That would take HOURS before anything would happen! They went ahead and put it in the IV. 10 minutes later I was down to target. I just about fell over because I was so surprised. We watched my BG as the rest of my Humalog slowly absorbed it's way into my system from the early correction bolus, but we were far enough out that the effect was very small.
Little did I know that once the insulin is in the bloodstream, it's effect is immediate and it has a half-life of about 9 minutes before it's done and out of the system. Apparently what makes the insulins work faster or slower is the stuff that determines how fast it's absorbed through the subcutaneous tissue.
The other thing I thought strange was the fact that I did not feel any ill effects of a rapid drop of BG. I suspect (contrary to this experience), that our bodies just don't like rapid changes.
Same theory with the implantable pumps that have been talked about in the past - from what I remember the insulin is delivered directly into the bloodstream (the portal vein near the liver?).
Can you imagine having insulin that worked right when you bolused? A high blood sugar that was corrected within minutes rather than hours? A meal bolus that could exactly match your digestion?
On the flip side of that coin is a more immediate risk of low blood sugars - say your digestion is delayed due to higher fat or protein content than you expected - your insulin curve would be ahead of your digestion/BG curve. That sounds scary and very dangerous.
If I'm not mistaken, the non-diabetic body releases insulin into the bloodstream based mostly on blood sugar. Trying to dose directly into the bloodstream based on anticipated digestions rates would be dangerous. But, with something like a CGMS, you could get pretty darn close, keeping a post meal spike under a really tight threshold and immediately correcting high BGs.
For those of us using a pump - imagine being able to adjust basal rates in real time! Or even better, use temporary rates right before you need them! For a basal rate change to actually do anything to my blood sugars, I have to make the adjustment at least an hour before I want to see that change. For example, I have to start a temp rate about 1.5 hours before I start playing basketball. I have often times forgotten to start my temp rate, then I'm hustling to keep up with my blood sugars. It would be much easier to make that change 10 minutes before I start.
I wonder if this is the direction that insulin delivery will move towards as the CGMS's hit the market and start to mature?