5. no insulin production
insufficient insulin production
resistance to insulin‟s effects
No insulin to move glucose from blood into cells:
high blood glucose means:
fuel loss. cells starve
short and long-term complications
6. • People with diabetes cannot make their own
insulin, a hormone that is normally secreted by the
pancreas. Insulin is essential to metabolise sugar and
hence generate energy
• Currently most diabetics inject insulin 2 or more
times per day, with the dose injected based on
readings of their blood sugar level
• However, this results in artificial blood sugar
fluctuations as it does not reflect the on-demand
insulin production of the pancreas
8. • Unsafe
A very low level of sugar (arbitrarily, we will call this 3 units) is
dangerous and can result in hypoglaecemia which can result in a
diabetic coma and ultimately death.
• Safe
Between 3 units and about 7 units, the levels of sugar are „safe‟ and
are comparable to those in people without diabetes. This is the ideal
band.
• Undesirable
Above 7 units of insulin is undesirable but high levels are not
dangerous in the short-term. Continuous high-levels however can
result in long-term side-effects.
9. • Simulation of an Automated Insulation
Pump which would check glucose levels at
regular intervals and inject the required
insulin
10. •Design validation
Checking the design to ensure that hazards do not
arise or that they can be handled without causing an
accident.
•Code validation
Testing the system to check the conformance of the
code to its specification and to check that the code is a
true implementation of the design.
•Run-time validation
Designing safety checks while the system is in
operation to ensure that it does not reach an unsafe
state.
11. • System testing of the software has to rely on
simulators for the sensor and the insulin delivery
components.
• Test for normal operation using an operational
profile. Can be constructed using data gathered
from existing diabetics
• Testing has to include situations where rate of
change of glucose is very fast and very slow
Test for exceptions using the simulator
12. • A personal insulin pump is an external device that
mimics the function of the pancreas
• It uses an embedded sensor to measure the blood
sugar level at periodic intervals and then injects
insulin to maintain the blood sugar at a „normal‟
level.
13. “Insulin pump therapy is considered as a treatment
option for people with Type1 diabetes for whom
multiple dose insulin therapy has failed and who
have the commitment and competence to use CSII
therapy effectively”
Feb 2003
14. • Availability
-It is important that the system should be available to deliver insulin
when required
• Reliability
-It is important that the system performs reliably and delivers the
correct amount of insulin to compensate for the current level of
blood sugar
• Safety
-A system failure that resulted in excessive doses of insulin being
delivered could threaten the life of the user
15. • Data flow model of software-controlled insulin
pump
16. • Using readings from the embedded sensor, the
system automatically measures the level of glucose
in the sufferer‟s body
• Consecutive readings are compared and, if they
indicate that the level of glucose is rising (see next
slide) then insulin is injected to counteract this rise
• The ideal situation is a consistent level of sugar
that is within some „safe‟ band
17. Level of sugar is increasing
Reading in unsafe band
No injection.
Reading in safe band
Inject only if the rate of increase is constant or
increasing. If constant, inject standard amount; if
increasing, compute amount based on increase.
Reading in unsafe band
Inject constant amount if rate of increase is constant or
decreasing.
Inject computed amount if rate of increase is increasing
18. Basal rates changed half hourly
Adjusted in 0.05 unit increments
Temporary basal feature
Boluses calculated on BG level, CHO, insulin
sensitivity, active insulin
Boluses -immediate or protracted
Can be adjusted in 0.1unit increments
19. Provide adjustable, constant, SQ insulin
infusion via a small plastic cannula which is
left in place under the skin for several days.
Are a pager-sized device which is worn on the
outside of the body
20. Safe state is a shutdown state where no insulin is
delivered
If hazard arises,shutting down the system will prevent an
accident
Software may be included to detect and prevent
hazards such as power failure
Consider only hazards arising from software failure
Arithmetic error The insulin dose is computed incorrectly
because of some failure of the computer arithmetic
Algorithmic error The dose computation algorithm is incorrect
21. insulin overdose or underdose (biological)
power failure (electrical)
machine interferes electrically with other medical
equipment such as a heart pacemaker (electrical)
parts of machine break off in patient‟s
body(physical)
infection caused by introduction of machine (biol.)
allergic reaction to the materials or insulin used in
the machine (biol).
22. Predicates included in the program indicating
conditions which should hold at that point.
May be based on pre-computed limits e.g.
number of insulin pump increments in
maximum dose.
Used in formal program inspections or may be
pre-processed into safety checks that are
executed when the system is in operation.
23. Safety proofs are intended to show that the
system cannot reach in unsafe state
Weaker than correctness proofs which must
show that the system code conforms to its
specification
Generally based on proof by contradiction
Assume that an unsafe state can be reached
Show that this is contradicted by the program code
24. Fairly recent technology
Generally fairly easy to use
Requires close patient involvement
More thinking and monitoring than insulin by
syringe
300,000 users worldwide
25. Open loop: user gathers sugar data and adjusts
flow rates for activity, diet, other changes in
sugar
Closed loop: the device checks sugar and
adjusts insulin infusion
26. Difficult to control diabetes
Active lifestyle/no time for injections
Committed to tight glucose control
Able to recognize and manage problems with
device
Willing to monitor sugars closely and adjust
insulin and diet
27. Blood sugar level is higher than it should be,
for no apparent reason.
Failure of sugar to respond when bolus dose
given
28. Out of insulin?
Is the pump leaking?
Is the connection between the tubing and the
pump cartridge tight?
Is the hub connection cracked?
Can you smell insulin anywhere? (hint: Insulin
smells like Band Aids)
Can you see insulin drip from the end of the
infusion set if you disconnect and do a bolus?
29. Lack of problem with device.
Tissue abnormality
Redness/pain/heat
Hard tissue/scarring
Kinked cannula
Old site
Improper depth/too near muscle/wrong angle
Air in line
Tube disconnected
