After using the 670G auto-mode for a few weeks now and looking over my Carelink data, I realized that the insulin pump pauses the background “microbolusing” for about 1.5 hours after a large meal bolus. Because my body still needs “background” insulin during this time, now some of my meal bolus is being consumed as “basal”.
Now my meal-boluses have to do double-duty; Bolus for carbs, AND cover background insulin needs, so using my manual-mode carb ratios, I don’t get enough insulin to cover my carbs, which has lead to post-meal blood-glucose spikes.
Okay, so I can adjust my carb-ratios to compensate for this, but the 670G only stores one set of carb-ratios (different ratios for different times of the day), and shares the same carb-ratios between manual-mode and auto-mode. So, when you get kicked out of auto-mode (for whatever reason), guess what? Your carb-ratios are now causing the pump to deliver too much carb bolus. Surprise!
I suspect this is how Medtronic got this pump approved by the FDA; by deliberately conflating meal-bolus insulin with background “basal” insulin, and hiding it with carb-ratio adjustments.
The real kicker is that they system didn’t need to be designed this way. A control algorithm could have been designed so that it maintained carb-ratio equivalance between manual-mode and auto-mode. Medtronic choose to make things more difficult for us.
“Thank you for choosing Medtronic.” I guarantee you, this will be the LAST TIME I choose Medtronic.