The Umbrella Effect

While long-acting or basal insulin delivery (insulin degludec [Tresiba], glargine [Lantus], detemir [Levemir], or the basal delivery rate of an insulin pump) is like having a long roof over your glycemic ‘head’. Injections or boluses of rapid acting insulin properties which are more "umbrella"-like.

Consider this image:

Properties of any insulin preparation include:

1) time to onset of sugar lowering effect;

2) duration of peak sugar lowering activity;

3) an effective duration of action; and,

4) day to day inconsistency, which can wobble or vary a bit.

It’s not only helpful, but crucial that a person using insulin have a good working understanding (conceptualization) of these properties of the insulin being taken. Without this understanding, manipulation of sugar levels as I’m about to describe are not possible.

When properly applied, rapid-acting insulin protects the user (like an umbrella) from the ‘shower’ of after meal hyperglycemia that rains down for a certain period of time (as in the image above). It does so by 'disposing' of glucose (sugar) into cells. Extending the metaphor fully, basal insulin acts as a 'roof' with gutters that continually and gradually shunt sugar into cells, but without a great capacity.

So, in a sense insulin has umbrella-like qualities as I show here. I ate late on this evening and chose one of my more challenging foods to manage: fried chicken (b in the image above). It’s a 'favorite' and I don’t eat it regularly for this reason. Nevertheless it was my choice. Fried meals often take more time to digest into blood sugar. That time can extend well beyond the action of the meal time insulin used to cover the meal (i.e., the umbrella), as it did in this case.

As you can see, my CGM device allows me to validate my duration of active insulin time, which for me is around 3 hours (a in the image above). This is the actual span of my insulin 'umbrella' in this case. After that time, the waning insulin effect is no longer able to contain the steady input of sugar coming into my blood stream from my fried meal and the basal insulin in my body can’t properly “cover” this slow influx of sugar. The end result is a slow accumulation of sugar in my blood stream, registered as the rise on my CGM plot shown here (b in the image above). This is a DELTA WAVE.

Well, I awoke and glanced at my sensor and noted I was at 171 mg/dl [9.5 mmol/L] (d in the image above) but the arrow was straight, meaning a gradual upward trend of under 1 mg/dl/minute. Looking at the trend line, recalling what I ate and knowing my prior responses to fried meals, I decided to correct this trend so I would not wake up in the morning with a BG well over 200 mg/dl. Therefore, I took 6 units of insulin to accomplish this. Normally this would take about 3 units since my correction factor is between 1:25 and 1:33 most of the time. But here is another teaching point: my BG was slowly rising and had a form of “momentum” behind it. Had it been trending straight, or even downward, I would have taken very different actions. But since it was trending up, I knew from experience that I needed a greater insulin “force” to neutralize the rise, turn the BG trend downward, and back to my desired target BG of 100 mg/dl. So…I doubled it (6 units).

As illustrated here, there was the customary 20 minute or longer “lag” time before any measurable effect of my correction insulin was seen (c in the image above). After the insulin lowering effect was underway, it took a full two hours to arrive and stabilize at my target (e in the image above).