The Medtronic 670G does not function as a closed loop for 3 reasons.
- In auto mode it does not supply accurate data. Nearly 100% of the time a finger stick will give a reading 15-35% higher than what shows on the pump. (Medtronic claims 35% is 'accurate'). BG by finger stick is so rarely lower than what the pump tells you the sensor is reading as to be a statistical impossibility. I would love to hear some data analysis form other users but I was told by someone on the tech support line that this was intentional. When not in auto mode the finger stick readings are very accurate to what the pump shows and average less than 5% off plus or minus. This shows the sensor itself to be very accurate but the pump skews data when in auto mode.
- When in auto mode the pump will stop all basal delivery for an extended period of time anytime you bolus. This means that using accurate mealtime carb calculations for a bolus will not be enough to prevent an unwarranted rise in BG. Because there are always other elements to a meal besides carbs that a basal should be covering your readings will start going up anytime you have anything to eat or drink. I am unaware of any other insulin protocol that stops basal delivery when logically you need it the most. All of the different endocrinologist I have ever used have recommended a the basal and bolus delivery average should ideally be about 50-50. This is impossible in the 670G auto mode. It really makes no sense to stop basal every time you eat or drink. This is one of the reasons people complain about how their BG rises so high when using the 670G in auto mode. Whenever I eat I have to take it out of auto mode, use a higher than normal programed basal delivery and bolus accurately. Then when BG is stable I can put it back into auto mode preventing the absurd and unnecessary rise. Again Medtronics tech support tells me this feature is intentional. What they are saying is that auto mode works excellent provided you eat or drink nothing, ever.
- You are unable to set a reasonable target using the 670G in auto mode. It does not use any target you set but rather some internal calculation that they can claim is 'accurate' even if it is intentionally off by 35%. I understand legally they want to avoid people having dangerous lows but their target range is so 'safe' as to be ineffective especially when combined with the inaccurate data discussed above. This is another reason why they have so many complaints about excessive highs. To be effective, auto mode should control highs as well as lows, if not, it's just a marketing ploy calling it auto mode. Additionally for safety reasons it will not increase delivery enough when BGs do start to rise. Again they claim this is a safety feature and the pump will 'learn' the user over time. There is no AI in the 80's pager tech they call a pump. It simply averages insulin use over a period of time. Medtronic tech support told me this is 48 hours but they told my endo this is 6 days. Either way it doesn't work simply because you can not set a target, it doesn't set a reasonable target on its own, and it will not deliver enough inulin to reach a reasonable target for 'safety' reasons.
If I had known you could hack an older Medtronic device to create a functioning auto mode I might have tried that. If I had know 'Auto Mode' was little more than a marketing ploy I would have kept my Tandem device which recently had a soft wear upgrade they call safe basal that is pretty much the same as 'auto mode'. To me it is disappointing that I can buy a watch for a few hundred dollars that can pinpoint my location within a few feet anywhere in the world while the tech on this much more expensive medical device has nowhere near the same functionality. Literally I consider my pump to be little more than a pager as far as a piece of tech. No normal consumer would settle for this in todays market, why should we? When will a company come up with pump tech that compares to todays phones? Recent FDA changes to hearing aid rules will allow cheaper, substantially better tech to come into the marketplace. Something similar may be the only solution to the dismal state of insulin pumps.
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