Here is a screen shot from Tandem’s t:Connect doing its job.
on the left, CIQ saw the CGM curve dive in a COMPRESSION LOW (CL). It turned off the basal appropriately and resumed when the CGM was seeing again. I might point out, I did not do a finger stick because I recognized the shape of the CL curve and waited for the CGM to also wake up.
from the middle to the right edge, CIQ is feathering my basal as the CGM sees slight changes in by glucose level in the interstitial fluid where the sensor wire is sampling my glucose level.
I have seen many discussions about CIQ & CGM here at JDRF and believe this will be a good information and talking point.
@joe, @wadawabbit, @Dennis, I am tagging you fine people so you may make direct comments and help this discussion.
Hope this helps. Belated Holiday Wishes to one and all.
J @987jaj, I have a couple of observations. In no particular order:
The episode at about 4:30 AM may or may not have been a compression low, but rather the precursor to a “sensor error” that appears to have extended for 40 minutes. I’ve experienced this phenomenon on several occasions when there was not a possibility for compression - like when walking. I’ve had a couple of long discussions with Dexcom technical sharing my observations. The “shut-off” is a safety, in my interpretation, [called sensor error] when it appears that readings are not reliable.
It appears that your basal rate is constantly set at 3.0 uph [at least from 3:30 until 9:21 AM] and that you do not step up basal flow to account for the body’s natural somogyi. You are depending solely on CIQ to manage your body’s background insulin needs.
You are still sleeping at 9:21 AM; although you did awaken to take a 4.01 unit manual bolus of which 1.6 units are still active. If you are keeping “sleep mode” operative continuously, you are locking-out a major function of CIQ - automatic bolus corrections.
The only job t-Connect is doing [your opening statement] is displaying an historical report; Control IQ is doing the job of maintaining your BGL within a desired range. CIQ is awesome! I really like having the t:Connect app on my phone; all necessary data is right at hand and easier for me yo see than my pump when I’m out-n-about in bright sun.
J, this three-hour picture of your life, although just a small gymslip, says quite a bit, and shows a steady glucose level. Thanks for sharing. What I’m NOT seeing, is any indicator that you “touched” your t-Slim or made any entries - such as that 4.01 Bolus about three hours ago.
@Dennis. Hey Dennis, I have access to the Dexcom regional nurse. She is the one who confirmed my call of Compression Low. Her conjecture was the sensor/receiver had to take extra time to confirm a valid reading (like three readings nearly the same after the dive) after the compression low.
The bolus in question of 4.01 was coverage of bedside snack I chomped upon awakening& because it was in progress when I did the screen shot, it was not yet recorded. Many days I am asleep until 11AM or later. My sleep mode is set from 2:30 AM bedtime until 11:00AM.
Yes my basal at that time is 3.0… I am nearly bullet proof with insulin resistance.
Thanks again, I thought the group here would like the graph.
I always appreciate Dennis’s incredible analytics and can’t add anything at the moment. All I will say is this: when I started CIQ my hope and goal was for my patterns to resemble a ride in a park: there would be a few inclines (where my numbers rise a bit) and declines (where they dropped slightly); rather than a climb up and down Everest with steep rises and drops.
Presumably any major outliers are due to user error. Sometimes I forget to bolus prior to my meal, or fail to turn on/off my Active mode.
We have a couple of long flights of stairs to get to the car, and just the stair climb can cause a drop, so I go into Active mode before driving. Right now I’m trying to figure out how best to combine Active with my meal bolus if I eat right before going out, or plan to stop for a bite en route. But so long as I do what I should be doing I find it works very well.
Hi @987jaj I don’t have much to add to what @Dennis said except it seems you handled the CGM well. Judging by the graph if I connect the dots, it appears as “ no harm, no foul” to me. Cheers and I wish you continued good luck
Hi @RMcM. When you press on the G6. Such as when you are lying on it. It squishes out the interstitial fluid and the CGM reads low. Nicknamed “Compression Low” in the dexcom community.
It has had this name since the Dexcom 7 was out 20+ years ago. The neighborhood DexCom rep warned me about it and it’s characteristic curve back about 2000-2002.
I was asked to put something together about COMPRESSION LOWs recently. Here is what I pulled together along with an article from the US National Library of Medicine.
Compression Low
BACKGROUND: Compression lows are caused by the person’s body pressing against the mattress, pinning the CGM sensor/transmitter (CGM) between the person’s body and the mattress during sleep. First, the interstitial fluid (IF) is the fluid around body cells. Most of the time IF is exchanged with fluids in the blood vessels. During this exchange, IF glucose is enriched and cellular waste products are removed from the IF all over the body.
THE PROBLEM: When a person is in sound sleep and is mashing the CGM into the mattress, the IF is also mashed. It is this mashing or compressing of the IF that causes the IF not to exchange as it normally does. Since the cells around the CGM sensor wire continue to consume (eat) the glucose available in the compressed area around the sensor wire the glucose in the area drops.
OBSERVATION: It is this low reading in the CGM data is usually seen as a nearly level data graph and then a sudden drop of the glucose level. Because it is a low brought about by the pressure on the CGM, the term COMPRESSION LOW has been offered in pumping circles. Because the Compression Low is a low glucose only in the area of the CGM, a finger stick performed in response to a LOW alarm will show NORMAL. The variation between the finger stick and the CGM data leads to frustration and bewilderment, believing technology is the source of the error.
The next observation is the blood sugar measured by the CGM will return to a value near where the CGM line was before the drop in CGM value. The near level line, the drop & alarm, the finger stick of different reading, and the return to the near pre-alarm value is the full picture of the COMPRESSION LOW.
Here is a link to Susceptibility of Interstitial Continuous Glucose Monitor Performance to Sleeping Position
Sleeping on my stomach hurts my back, so I wear my sensr on my abdomen, upper thigh or upper arm. I’ve unwittingly gotten an Out of Range alarm because my pump somehow found its way under me while I was sleeping, or because I rolled into my side when my sensor was on my arm. I don’t think I’ve experienced compression lows but am wondering if they start before the OOR alert sounds? If so perhaps a sooner notification would be in order during Sleep mode for those using BIQ/CIQ. Just a thought.
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