A Scientist's Life on the Medtronic MiniMed 670G Insulin Pump and More.

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Category: Auto Mode

Shortcomings of the medtronic minimed 670g, automode and guardian sensors

From the onset let me say I love the Medtronic MiniMed 670G and the Auto Mode setting. Closed loop insulin pump technology is the technology of the future. Personally I foresee the insulin pump becoming an install-and-forget type of medical device in the near-future. While in no way perfect, the first iteration of the MiniMed 670G was a great step forward in this direction.

Here are some design issues that make the pump not as user-friendly:

no SEPARATE delivery settings for manual mode and AUTO MODE

At this time with the MiniMed 670G, if you would like to interchange between Auto Mode and Manual Mode, you have to pay very careful attention to making sure you adjust the carb ratios and the active insulin time (AIT) under OPTIONS>DELIVERY SETTINGS>BOLUS ESTIMATE SETUP every time you toggle between the two modes. Since Auto Mode settings are more aggressive, this could spell disaster when one returns to manual mode from auto mode and forgets to dial back the carb ratio or the AIT. It would be great to see an option for separate delivery settings tailored for each mode in the next iteration of the pump. Since we know the AIT setting in manual mode has a completely different meaning as that on Auto Mode, it only makes sense to separate the settings.


I have written a lot on this topic and what I think causes it, but this is a major flaw that needs to be addressed by Medtronic. No only is it irritating but it a shame that this happens since the Guardian Sensor is a great improvement in terms of accuracy and stability over the Enlite Sensor. I personally think that it is time Medtronic started working on an improvement of the Contour next Link 2.4 meter, since I think the precision (or lack thereof) of this meter is at the heart of the “ENTER BG LOOP” flaw.

navigating the useR menu

Although the user interface is a big improvement in terms of aesthetics, navigating around the Medtronic Minimed 670G is not as easy as it was with the Medtronic Minimed 530G. My major issue is that it takes more than 2 or 3 buttons steps to get to the most basic of functions. For example, if you forget to calibrate the pump using the BOLUS or ENTER BG menu item, you have to browse through OPTIONS > UTILITIES> SENSOR SETTINGS>CALIBRATE SENSOR to be able to calibrate you sensor. A second example,  to change the basal or bolus settings, you have to browse to OPTIONS>DELIVERY SETTINGS

black box AND CONSERVATIVE nature of the auto mode settings

There is a lot that we do not know about the way Auto Mode works and the underlying algorithm. Probably it is a good thing not overload the user with too much information. But only being able to only control 2 or 3 settings in Auto Mode leaves the user feeling helpless especially when they know the suggested bolus by Auto Mode won’t get me to where I need to be. Granted that the FDA approved the closed loop pump on the basis that it was conservative enough not to plunge the user into an irreversible low, so I understand Medtronic’s hands were tied.

But the fact that it is not as easy to achieve the advertised target of 120 mg/dL means that insulin delivery is throttled well above this target. But a target of 150 mg/dL is easily achievable.

Talking about conservative, I have noticed that there is a larger discrepancy in sensor and meter BG readings especially with morning fasting numbers which in many cases put me close to 150 mg/dL while the sensor hovers around 120 mg/dL. Not sure about what is going on, but I get to wonder whether the predictive algorithm is weighted to be more conservative for certain times of the day.

It would also be nice for a user to see the basal rates being used in Auto Mode and the breakdown between the actual basal rate and the microbolus used by the pump to get to the target BG. I do not see why the user cannot use successful Auto Mode basal rates to tune Manual basal rates.

spike control not as easy on auto mode

Once again, due to the conservative nature of Auto Mode, spike control is not as effective as when you are in manual mode. It gets better as Auto Mode continues to learn but it is very had to achieve small spikes or even stay flat post meal time. I was able to do this with ease on manual mode.

Spike control is less effective because the pump stops dispensing basal/microbolus insulin for 15 minutes after one applies a bolus. According to Medtronic, this is done so that the algorithm can see the direction of BG readings after a bolus to avoid lows. But that in itself is counterproductive since it is taking the microbolus away from you when you need it most. Even if you wait for 15 minutes before eating as recommended, there is no way the basal/microbolus can catch up to the spike.

In most cases, with an aggressive carb ratio I am able to keep the spike below 180 mg/dL but I prefer not having to hit 140 mg/dL, which I am able to do on manual mode.

Notice Breakfast Spike and no micro-bolus/basal between 8:05 to 8:30. Also see the dip that occurred when I bolused for a second cup of tea with milk and then over-corrected for the low. Yikes.

I find myself more hesitant to eat high glycemic index foods on Auto Mode as compared to when I am in manual mode where I have honed in my basals over time to cover for spikes.

transmitter range

Sleep in the wrong position, then you will be woken up by the pump alerting you that the communication between the Guardian sensor transmitter and pump has been lost. This happened a lot for the Enlite Sensor too but it rarely happened for the Dexcom 5. There seems to be even a more dangerous flaw when the Guardian sensor loses communication with the pump while in Auto Mode. A couple times, I have slept through a lost sensor with no alert only to be woken up with an alert that the pump has exited Auto Mode.  The only way you realize that is was a lost sensor that caused the Auto Mode exit is by looking at the BG reading graph and you see a long blank period of no sensor BG signal.


morning fasting glucose not exactly where i want them to be

As you can see my morning fasting glucose numbers are running higher than I would like them. I feel well rested in the morning if my numbers are below 120. Above that I wake up feeling tired. I have also noticed that it is in the morning that I get the biggest differences in reading between the Minimed 670G pump Guardian sensor and my BG meter (during other times the readings are within 10 mg/dL of each other but in the morning closer to 20 mg/dL ). Not sure why the sensor consistently under-reports my BG readings, but it is at this time that I would love my sensor to be the most accurate! Most probably it might have to do with the fact that the Auto Mode algorithm is likely most conservative at night.


Double arrows pointing down on your pump is never a good thing especially if the number is 65. But towards the end of life the guardian CGM sensor, it is especially important to counter-check this reading against a BG meter reading. It is quite common for the sensor to yo-yo between lows and highs (displaying double arrows due to false positives and negatives in current readings) especially on the last days of its life. In fact, this instability is normally a signal it is time to change your sensor especially if the numbers do not match BG meter readings.

Decided to counter-check sensor BG before treating low .

A Short Article Review – Optimizing Hybrid Closed-Loop Therapy in Adolescents and Emerging Adults Using the MiniMed 670G System

Link to the Article abstract for this article titled Optimizing Hybrid Closed-Loop Therapy in Adolescents and Emerging Adults Using the MiniMed 670G System by Messer Et al. that was published on Diabetes Care in April 2018. Inbox me to see how we can get you a copy of this paper. Disclaimer.

Bottomline: Your Endo might need to really get aggressive in adjusting your carb-ratios for Auto Mode.

This article is probably the most detailed of any Medtronic funded studies out there that actually discusses pump settings used to optimize the Auto Mode settings. It also delves a little and provides references on how the HCL algorithm used in Auto Mode works and the inputs that can be adjusted when it comes to Auto Mode.

In their trials, the authors looked at how to optimize Auto Mode inputs for 31 adolescent and young adult participants (14-26 years old) over a period of 3 months.

It talks of three settings that can be used to tune Auto Mode, namely: carb to insulin ratio, Active Insulin Time (AIT) and Bolus Speed (although this settings is not used or explained for the trial).

The main takeaways from this paper can be summarized as follows:

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Upper Thigh Sensor Insertion Sites Seem to Take Longer to Stabilize

I have noticed that when I am using the outer side of my upper thigh as my sensor site, it takes such a long time for the sensor to stabilize and enter Auto-Mode for the Medtronic MiniMed 670G.

During my pump training, I was told that Medtronic now officially recognizes the outer side of the upper thigh as a good insertion site for the Guardian sensor. This was not the case for the enlite sensor.

However after stabilizing, from my experience, this site gives the some of the best and consistent sensor readings.

TIP: To shorten the time it will take the sensor to stabilize and enter Auto Mode, you can insert the new sensor and leave it in place a couple hours prior to replacing the current sensor.

Solution for the Medtronic 670G AutoMode BG Loop

Couple weeks ago, I could not enter Auto Mode on my 670G for three days due to the dreaded “BG Required Loop.” As a solution, I eventually had to change the sensor to be able to re-enter AutoMode.

God knows I have tried to resolve the issue using every advise given online in forums (including trying to “fake” the system by entering a number just above or below your last entry) but these have only worked only a couple times.

What I think Causes the BG Required Loop

At issue I think is the way that the 670G calibrates the Guardian sensor. It seems to be programmed to validate the BG you’ve entered into the system probably based on the ISIG history and its predictive model of where your BG readings are trending towards.

Sounds complicated?

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Kicked Out of Auto Mode….Again!

Guardian Sensor Stability and Auto Mode

I have been trying to get back to Auto Mode for the better part of the day today.

As you can see my readings in manual mode were not so bad and I would say those were stable sensor readings. I am not sure what reading variance the Auto Mode algorithm considers acceptable to enter Auto Mode.

Variance does not look too shabby but Auto Mode did not like it.

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Review – What I Love (and Hate) about the Minimed 670G Auto Mode Feature

The MiniMed 670G in AutoMode. The blue shield means it is all-systems-go and in AutoMode.

The MiniMed 670G in AutoMode. The blue shield means it is all-systems-go and in AutoMode.

There is a lot to like about the Auto Mode feature for the Medtronic MiniMed 670G. This feature is analogous to self-driving technology where a car employing this technology drives along fine until the camera hits a blind spot. The same happens for Auto Mode, it works fine until an unexpected situation arises and the Auto Mode algorithm cannot handle this sudden change.

The closed-loop hybrid system is ground-breaking technology that as a research scientist I really appreciate. Yes it is a work in progress. But its current intricacies and potential to give people with Diabetes better control of their glucose numbers and more freedom to pursue other important things in their lives is really laudable.

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Tunable Settings in Auto Mode for the MiniMed 670G

Tuning Auto Mode for the Medtronic MiniMed 670G is just like tuning an engine. Changing one setting throws off the other settings

Getting Auto Mode settings just right seems to be a balancing act – more fine tuning than just dialing settings up or down

When it comes to Auto Mode for the MiniMed 670G, tuning the settings to get as close to your sugar targets feels a little more complicated as compared to the manual mode. This is because the closed loop system has a feedback mechanism which will likely throw-off one setting when you change another.

In the course of your day, the system is performing a balancing act between bolus and basal to keep you as close to Auto Mode’s fixed and preset BG target of 120mg/dL by introducing a third input – the micro bolus.

When it is all said and done, the user has control of  two settings only, namely Carb Ratio and Active Insulin time.

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