Method of Calibrating a System for Measuring the Concentration of Substances in Body and an Apparatus for Exercising the Method

• US 20080312859A1
• Filed: 09/05/2005
• Published: 12/18/2008
• Est. Priority Date: 09/03/2004
• Status: Abandoned Application

• Current Assignee: Novo Nordisk A/S
• Original Assignee: Novo Nordisk A/S
• Inventors: Skyggebjerg, Ole, Stjernholm Madsen, Arne, Gerstenberg, Michael
• Application Number:
  US11/661,866
• Publication Number:
  US 20080312859A1
• Time in Patent Office: Days
• US Class Current: 702/85
• CPC Class Codes: A61B 2562/0295 Strip shaped analyte sensors for apparatus classified in A61B5/145 or A61B5/157 disposable multilayered or laminated electrodes G01N27/307; details of handling chemical test elements G01N33/4875
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes

Abstract

This invention relates to procedures for the calibration of systems for continuously measuring the concentration of substances in a body fluid. The system comprises first and second sensors adapted for subcutaneous insertion and an electronic calculator unit adapted for measuring signals from the two sensors. The system is calibrated following the steps of: a) introducing the first sensor subcutaneously, b) calibrating the first sensor, c) obtaining sensor data S₁(t) provided by the first sensor, d) introducing the second sensor subcutaneously, e) obtaining sensor data S₂(t) provided by the second sensor, f) determining the rate of change over time δR(t)/δt, R(t) being a signal which correlates to sensor data S₂(t) over time, and g) performing a calibration of the second sensor when δR(t)/δt is less than a predetermined value, said calibration of the second sensor being performed using sensor data S₁(t) obtained by the first sensor.

Claims

1. A method of initial calibration of a newly mounted sensor for continuous measuring the concentration of substances in body fluid, e.g. the glucose concentration, the system comprising an already mounted and calibrated first subcutaneous sensor, a newly mounted uncalibrated second subcutaneous sensor and an electronic calculator unit adapted for measuring signals from said sensors, said signals being measured over time, said method comprising the steps of:

obtaining sensor data S₁(t) provided by the first sensor,

obtaining sensor data S₂(t) provided by the second sensor,

determining the rate of change over time δ

R(t)/δ

t, R(t) being a signal which correlates to sensor data S₂(t) over time,

performing a calibration of the second sensor when δ

R(t)/δ

t is less than a predetermined value, said calibration of the second sensor being performed using sensor data S₁ (t) obtained by the first sensor.

2. The method as defined in claim 1, wherein R(t) is determined by

3. The method as defined in claim 1, wherein a reference calibration measurement of the body fluid concentration is performed;

and wherein the result is transmitted to the electronic calculator unit.

4. The method as defined in any of claim 1, wherein the electronic calculator unit comprises two transmitter/receiver circuits which are coupled to each their sensor from the time of introducing the second sensor until δ

R(t)/δ

t becomes less than a predetermined value.

5. The method as defined in claim 4, wherein the electronic calculator unit transmits a message to the user when there is sufficient correspondence between the signals from the two sensors.

6. The method as defined in any of claim 3, wherein the electronic calculator unit transmits a message to the user to perform a reference calibration measurement.

7. The method as defined in any of claim 1, wherein a cross-correlation analysis is performed on the signals from the two sensors.

8. The method as defined in claim 7, wherein curves are recorded representing the signals from the two sensors;

and that the respective areas between the curves, measured during predetermined respective periods of time, are compared to each other.

9. The method as defined in any of claim 7, wherein the signals from the second sensor are divided into a number of signals that are mutually time-lagged;

and that each of the time-lagged signals are compared to the signals from the first sensor.

10. The method as defined in any of claim 1, wherein the electronic calculator unit is configured for calculating and displaying the uncertainty interval of the measurement from the sensor.

11. An apparatus for subcutaneous measurement of the concentration of substances in body fluid;

e.g. the glucose concentration, said apparatus being adapted for receiving signals from a first and at least a second sensor, said signals being measured over time, the apparatus having means for obtaining sensor data S₁ (t) obtained by the first sensor and means for obtaining sensor data S₂(t) provided by the second sensor, the apparatus further comprising;

means for determining the rate of change over time δ

R(t)/δ

t, R(t) being a signal which correlates to sensor data S₂(t) over time,

means for evaluating when δ

R(t)/δ

t is less than a predetermined value, indicating that a valid calibration of the second sensor can be carried out.

12. The apparatus as defined in claim 11, wherein the apparatus has means for calibrating the second sensor using sensor data S₁ (t) obtained by the first sensor.

13. The apparatus as defined in claim 11, wherein the apparatus has means for signalling when δ

R(t)/δ

t is less than a predetermined value.

14. The apparatus as defined in any of claim 11, wherein R(t) is determined by

15. The apparatus as defined in any of claim 11, wherein the apparatus is configured for simultaneously receiving, during a calibration period, measurement signals from the two subcutaneous sensors;

and performing sensor calibration by comparison of the signals received from the two sensors.

16. The apparatus as defined in any of claim 11, wherein the apparatus is configured for receiving reference calibration measurements.

17. The apparatus as defined in claim 16, wherein the apparatus comprises a measuring device for measuring the blood-glucose concentration in a blood sample.

18. The apparatus as defined in any of claim 11, wherein the apparatus is configured for calculating and displaying the uncertainty interval of the measurement from the first and/or the second sensor;

and that the apparatus comprises a display configured for displaying the uncertainty interval.

19. The apparatus as defined in claim 18, wherein the display is configured for graphical representation of the uncertainty interval.