Estimation of insulin sensitivity from CGM and subcutaneous insulin delivery in type 1 diabetes
In a method of determining insulin sensitivity in a patient, glucose level is sensed continuously. A first area under the curve representing the glucose level over time is calculated. An amount of insulin that has been administered to the patient is sensed. An estimation of insulin on board the patient is calculated based on the glucose level and the amount of insulin administered to the patient. A second area under the curve representing the insulin on board over time is calculated. Patient data indicative of at least one patient physical parameter is received. Information indicative of amount of glucose ingested by the patient during a meal is received. An insulin sensitivity output indicative of ability of insulin to stimulate glucose utilization and inhibit glucose production in the patient based on the first and second area under the curve, the patient data and the meal information is generated.
1. A device for calculating insulin sensitivity in a patient, comprising:
(a) a glucose module that includes a continuous glucose monitoring sensor configured to generate a glucose signal (CGM signal) indicative of a glucose level in the patient and an area under the curve calculator that is responsive to the glucose signal and that generates a first area under the curve signal [AUC(ΔCGM)] indicative of an area under the curve representing the over basal glucose signal and a second area under the curve signal [AUC(|ΔCGM|)] indicative of an area under the curve representing the absolute value of over basal glucose signal over a predetermined period of time;
(b) an insulin module that is responsive to the glucose signal and to an insulin input from an insulin infusion device, the insulin input indicative of an amount of insulin that has been administered to the patient by the insulin infusion device, the insulin module also including an area under the curve calculator that generates an insulin module area under the curve [AUC(I)] indicative of an area under a curve representing the insulin signal over a predetermined period of time. the insulin module also including an insulin on board (IOB) module that is responsible for adding a contribution of onboard still active insulin administered before the predetermined period of time and subtracting the contribution of still active insulin at the end of the predetermined period of time;
(c) a patient module that generates a patient data signal indicative of at least one patient physical parameter and a meal information signal indicative of an amount of glucose ingested by the patient during a meal; and
(d) an insulin sensitivity calculator that generates an insulin sensitivity output that is indicative of an ability of insulin to stimulate glucose utilization and inhibit glucose production in the patient based on the first area under the curve [AUC(ΔCGM)] and the second area under the curve [AUC(|ΔCGM|)] signals generated by the glucose module, the insulin module area under the curve [AUC(I)], the patient data signal and the meal information signal, wherein the insulin sensitivity output (SI) is calculated as follows:
SI
=
D
·
f
BW
-
GEZI
·
AUC
(
Δ
CGM
)
-
V
G
·
[
CGM
(
t
end
)
-
CGM
(
t
meal
)
]
AUC
(
I
)
·
[
AUC
(
Δ
CGM
)
(
t
end
-
t
meal
)
]
where:
D=amount of glucose ingested during the meal (in mg);
f=0.9;
BW=patient's body weight (in kg);
GEZI=a population parameter fixed to 0.01 dL/kg/min;
V G =1.48 dL/kg;
t end =ending time of study;
t meal =starting time of study corresponding to time of the patient's last meal;
CGM(t end )=value of CGM signal at ending time of study; and
CGM(t meal )=value of CGM signal at starting time of study corresponding to time of last meal.
2. The device of claim 1 , wherein the continuous glucose monitoring sensor comprises a self-monitoring blood glucose device.
3. The device of claim 2 , wherein the continuous glucose monitoring sensor further comprises a calibration module configured to combine data from both the self-monitoring blood glucose device and the continuous glucose monitoring sensor so as to generate the glucose signal.
4. The device of claim 1 , further comprising a bolus calculator module that is responsive to the insulin sensitivity output and that is configured to generate an estimated bolus dosage of insulin to be administered to the patient.
5. The device of claim 4 , wherein the bolus calculator module comprises:
(a) a carbs ratio calculator configured to calculate a carbs ratio representing a total amount of glucose entering the patient after a meal to the total amount of glucose cleared due to a pre-meal bolus;
(b) a correction factor calculator configured to calculate a correction factor representing a decrease in glucose in the patient caused by an insulin bolus; and
(c) an adding circuit that adds the carbs ratio to the correction factor and that subtracts an estimated insulin on board to generate an estimated bolus dosage value.
6. A system for calculating an estimated bolus dosage of insulin to be administered to a patient, comprising:
(a) a continuous glucose monitoring sensor configured to generate a glucose signal (CGM signal) indicative of a glucose level in the patient and an area under the curve calculator that is responsive to the glucose signal and that generates a first area under the curve signal [AUC(ΔCGM)] indicative of an area under the curve representing the over basal glucose signal and a second area under the curve signal [AUC(|ΔCGM|)] indicative of an area under the curve representing the absolute value of over basal glucose signal over a predetermined period of time;
(b) an insulin infusion device, responsive to the basal glucose signal and to an insulin input from an insulin infusion device, the insulin input indicative of an amount of insulin that has been administered to the patient by the insulin infusion device, the insulin module also including an area under the curve calculator that generates an insulin module area under the curve [AUC(I)] indicative of an area under a curve representing the insulin signal over a predetermined period of time. the insulin module also including an insulin on board (IOB) module that is responsible for adding a contribution of onboard still active insulin administered before the predetermined period of time and subtracting the contribution of still active insulin at the end of the predetermined period of time;
(c) a patient module that generates a patient data signal indicative of at least one patient physical parameter and a meal information signal indicative of an amount of glucose ingested by the patient during a meal;
(d) an insulin sensitivity calculator that generates an insulin sensitivity output that is indicative of an ability of insulin to stimulate glucose utilization and inhibit glucose production in the patient based on the first area under the curve [AUC(ΔCGM)] and the second area under the curve [AUC(|ΔCGM|)] signals generated by the glucose module, the insulin module area under the curve [AUC(I)], the patient data signal and the meal information signal, wherein the insulin sensitivity output (SI) is calculated as follows:
SI
=
D
·
f
BW
-
GEZI
·
AUC
(
Δ
CGM
)
-
V
G
·
[
CGM
(
t
end
)
-
CGM
(
t
meal
)
]
AUC
(
I
)
·
[
AUC
(
Δ
CGM
)
(
t
end
-
t
meal
)
]
where:
D=amount of glucose ingested during the meal (in mg);
f=0.9;
BW=patient's body weight (in kg);
GEZI=a population parameter fixed to 0.01 dL/kg/min;
V G =1.48 dL/kg;
t end =ending time of study;
t meal =starting time of study corresponding to time of the patient's last meal;
CGM(t end )=value of CGM signal at ending time of study; and
CGM(t meal )=value of CGM signal at starting time of study corresponding to time of last meal; and
(e) a bolus calculator that is responsive to the insulin sensitivity output and that is configured to generate the estimated bolus dosage of insulin to be administered to the patient.
7. The system of claim 6 , wherein the continuous glucose monitoring sensor comprises a self-monitoring blood glucose device.
8. The system of claim 7 , wherein the continuous glucose monitoring sensor further comprises a calibration module configured to combine data from both the self-monitoring blood glucose device and the continuous glucose monitoring sensor so as to generate the glucose signal.
9. The system of claim 6 , wherein the bolus calculator comprises:
(a) a carbs ratio calculator configured to calculate a carbs ratio representing a total amount of glucose entering the patient after a meal to the total amount of glucose cleared due to a pre-meal bolus;
(b) a correction factor calculator configured to calculate a correction factor representing a decrease in glucose in the patient caused by an insulin bolus; and
(c) an adding circuit that adds the carbs ratio to the correction factor and that subtracts the estimated insulin on board to generate an estimated bolus dosage value.