Artificial Pancreas 2

What are some monitoring and treatment considerations

• By the time symptoms of T1DM nearly 90% of the b cells have been destroyed

• Immediate treatment with insulin is started and needs to be maintained for life

• For glucose control we need to be aware of blood glucose levels to know how much insulin to deliver

What are some things to consider in blood glucose monitoring

Spot test vs continuous

Manual vs dynamic and responsive

What until recently does a diabetic patient had to do

Take blood sample consider the result

• Calc insulin needed and consider what type

• Inject required amount of insulin

• Check blood glucose levels

• Account for any unexpected changes in glucose

What are the components for a glucose biosensor

analyte: glucose

bioreceptor: e.g. enzyme “recognises” analyte

transducer: converts response into a signal

display: shows signal on meter

What are monitoring considerations

• Who needs to know glucose level

  • Why? how often

• What else needs monitoring

  • HbA1c, other biomarkers, physical signs of complications

• Data access and role of AI in developing better treatment responses

  • Can we make unpredictable humans more predictable

  • Can we be spontaneous

  • We will return to this in next lecture

What are some classic complications of diabetes

retinopathy- can lead to blindness

neuropathy- nerve damage

nephropathy- can lead to kidney failure

How is HbA1c is monitored

HbA1C is a useful tool in monitoring for patient and clinician needs a blood sample. Measured using immunoassay, ion-exchange high-performance liquid chromatography, boronate affinity and enzymatic assays

What are some clinical measures needed for good quality control considerations

inter/intra assay variation, “drift”, non-specific binding, sensitivity, precision

Sampling errors

What is the Dexcom usage story

Auto-applicator inserts sensor just beneath the skin

Every 5 minutes sensor measures glucose and sends data to transmitter worn as a stick-on patch

Transmitter sends glucose readings to Dexcom receiver or smartphone

Why is CGM better than finger prick

CGM is superior to finger-prick monitoring because it provides near-continuous glucose readings, trend information, and alerts for hypo-and hyperglycaemia, allowing better day-to-day glucose control with fewer finger pricks

How does a CGM sensor work?

• Sensor- has filament coated in glucose sensing enzymes- detects glucose in interstitial fluid

• Sensor worn for number of days before being replaced and available for 24 hours a day

• Implantable sensors can be used for longer- consist of a larger capsule compared to thin filaments in other CGMs

• Sensor interacts with transmitter above skin to sends data to the receiver or smartphone app

What does regular frequent monitoring and crafty algorithms do

Allows for good BG estimates and insulin requirements

How does calibration work in CGM

Now perform the first calibration a few hours after sensor insertion, when the sensor warm-up period has completed, and subsequent ones every 12-14h, employing a simple first-order time-independent linear function as the calibration law

How does a CGM measure glucose

in ISF ie different compartment to blood need to account for the gradient between BG and IG

What did original CGM devices do for calibration

Initially CGM devices had to be calibrated daily with a capillary reading. Newer CGMs no longer need calibration and remove need for calibration

Long term benefits of CGM

• Mortality stats are improving with advances in monitoring and treatment but still early

• Mortality and side-effects data over next 20 years will give a better reflection of benefits of CGMs and insulin advances

What have been considerations for a wearable CGM

• Accuracy

• How would you improve CGM currently available in UK?

• Algorithms