This post is inspired by Anna in Montréal, who is adjusting her basal rates.
A Side-effect of Exercise
I have a bike. This shouldn’t be a big surprise, as I’ve written about my border-to-border and Quabbin Reservoir rides recently.
I love riding my bike, and during the warm months with lots of sunshine I rode it almost everyday. I like the sensation of rolling along, with the wind whistling in my ears and the scenery blurring by. I don’t even mind the hills anymore, even though the wind stops whistling as I crawl along.
All of that riding has been great at lowering my blood glucose reading. In fact, it’s worked a little too well. Insulin — the enzyme that helps transport glucose into your cells for energy — becomes much more effective when you exercise. And when your muscle cells slide past each other, they basically act as pumps and can work (almost) without insulin. (But not completely without.)
When I ride, I carry a waterbottle full of sports drink — Gatorade if you care to know — but I was still having hypoglycemia more often than I’d like. If you don’t have diabetes, this is commonly referred to as “cracking,” “bonking,” or “hitting the wall.” Your muscles have spent their glycogen (a form of glucose usually found inside of muscles), and your body can’t convert enough fatty acids into energy. You feel tired and find it hard to keep going.
If you have diabetes, hypoglycemia has all of these same attributes. Of course, for us it also means that our brains don’t get enough glucose either. So we’re not just tired, we can also pass out. And stopping for a little while doesn’t fix the problem. We have to replace it right away. So I try really hard not to have hypoglycemia. And as someone trying to take off a few pounds — which is going quite well, thank you very much — I want my body to turn fat into fatty acids and leave my blood glucose more or less alone. And I don’t like to drink a lot when I run, which I’m doing now that it’s dark in the evening. But, as I said on Halloween, hypos scare me.
Time to Fix the Basals
So I pulled out my copy of Smart Pumping. “Oh look! I should probably fix my basal rates as a first step.” Well, it was time to do that anyway.
For those of us with insulin pumps, basal insulin is the continuous trickle of background insulin that keeps our blood glucose in the happy/normal range of 80-150 mg/dL, counteracting the steady release of blood glucose from the liver. Why the liver does this, I don’t know. I read in my book that basal insulin should be about 40-50% of your average total daily dose (basal + food/correction boluses). Mine was about 55-60%. A sign of problems. Fixing these rates requires skipping meals and testing every couple hours. Skipping meals is hard. And if one reading is too much different than the one before, you have stop, make adjustments, and start another day.
But I wanted exercise to be easier (and last longer). And (more importantly) I was coming up on my 10-year anniversary with diabetes and had told myself that I wasn’t going to go five or ten more years just “getting by.” I was starting to be quite unhappy about all of my hypos and high readings. And I had a supportive, active new endocrinologist who wanted to help me improve my readings and my ability to predict them.
After figuring out my morning basal rates — which involved about four or five skipped breakfasts — I began my afternoon tests in late September. When I started, I was getting 22.0 units per day. (A unit is 1/100 of a mL. A vial of insulin has 1000 units.)
Four weeks, seven tests and seven adjustments later, I think I’ve figured it out. I have just one more afternoon test to go — I hope — but I think my new rates are correct. For the curious people with diabetes out there, here’s a bit of the data.
Numbers and stuff
On 26 September, my basal rates were
00:00 - 07:00 = 0.9 u/hr
07:00 - 09:00 = 1.0
09:00 - 20:00 = 0.9
20:00 - 00:00 = 1.0
(22 units per day)
The first or second test:
6 October 2009
Last basal: 4.0u at 7:42 (active insulin at 12:30 is 0.4u)
11:39 - 143
12:54 - 79
Stopped
8 October 2009 - Attempt #2 or 3
Last basal: 4.3u at 7:22
11:20 - 155
12:56 - 97
Stopped
I was checking more often than required in those early tests, because I could actually feel my blood sugar moving. I kid you not, and I had suspicious that I was going a scary place.
By 12 October, I had changed my rates to
00:00 - 0.9 u/hr
07:00 - 1.0
09:00 - 0.7
15:00 - 0.8
20:00 - 1.0
13 October 2009 - Attempt #4
11:38 - 133
13:00 - 93
14:00 - 78
Stopped
19 October 2009 - Attempt #5
11:27 - 216
12:54 - 188
14:45 - 138
15:47 - 111
Stopped
After this, I was feeling close to being there, and before my last test had already knocked off a lot of insulin.
00:00 - 0.9 u/hr
07:00 - 1.0
09:00 - 0.7
11:00 - 0.5
15:00 - 0.6
27 October 2009 - Attempt #7
Previous bolus - 07:51
10:44 - 256
11:53 - 234 (Active insulin 1.1u)
13:36 - 226
16:01 - 180
18:01 - 153
I know that last test started out with high readings, but I just wanted to get the damned thing done, and I knew that having higher readings would give me a good cushion for seven hours of testing.
Currently, here’s where I am:
00:00 - 0.9 u/hr
07:00 - 1.0
08:00 - 0.8
09:00 - 0.7
11:00 - 0.5
20:00 - 1.0
(18 units per day)
These basal tests are all about gradual refinements. If your BG readings change by more than 30 mg/dL up or down over any two hour period, adjust +/- 0.1 unit/hour starting 2-3 hours before the dip/bump. The Pumping Insulin authors also recommend redoing all of your basal tests (overnight, morning, afternoon, and evening) whenever you change exercise patterns, your weight changes 5-10%, or you suspect they’re wrong because of fasting highs or lows.
