Combining measurements from different sensors

• US 20030187337A1
• Filed: 04/10/2003
• Published: 10/02/2003
• Est. Priority Date: 06/16/2000
• Status: Active Grant

• Current Assignee: Oxford University Innovation Limited (University of Oxford)
• Original Assignee: Isis Innovation Limited
• Inventors: Tarassenko, Lionel, Townsend, Neil William, Price, James David
• Granted Patent: US 7,647,185 B2
• Time in Patent Office: Days
• US Class Current: 600/300
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: G06F 18/256 of results relating to different input data, e.g. multimodal recognition

Abstract

A method for combining physiological measurements from two or more independent measurement channels, particularly physiological measurements such as heart rate. Independent measurements of heart rate, for instance by ECG and pulse oximetry, can be combined to derive an improved measurement eliminating artefacts on one channel. A model of the process generating the physiological parameter, e.g. the heart rate, is constructed and is run independently for each channel to generate predictions of the parameter. The model may be a Kalman filter. The measured values are compared with the predicted values and the differences is used as an indication of the confidence in the measurement, the higher the difference the lower the confidence. The measurements from the two channels are combined using weights calculated from the respected differences.

Claims

1. A method of measuring a parameter comprising the steps of:

predicting the value of each of two independent measurements of the parameter, making two independent measurements of the parameter to produce two measured values of the parameter, calculating the respective differences between the predicted values and the measured values, and combining the two measured values with weights determined by said differences.

2. A method according to claim 1 in which the steps of prediction, measurement, calculation and combination are repeated continuously, the predicted value for each of the two independent measurements being based on the preceding predicted value and the difference between the preceding predicted value and the preceding measurement.

3. A method according to claim 2 in which the predicted value for each of the two independent measurements is calculated by using a linear predictive model.

4. A method according to claim 2 in which the predicted value for each of the two independent measurements is calculated by using a non-linear predictive model.

5. A method according to claim 3 or 4 in which the model is adaptive, and it adapts in dependence upon the amount of process noise in the measurements.

6. A method according to any one of the preceding claims in which in the step of combining the two measured values the weight of each value varies inversely with the square of the difference between the predicted value and the measurement.

7. A method according to claim 6 in which the two measured values are combined according to the formula:

8. A method according to any one of the preceding claims in which the predicted values for the respective measurements are based on respective models of the system.

9. A method according to claim 8 in which the models of the system include estimates for process noise and sensor noise.

10. A method according to claim 8 or 9 in which the respective models of the system are mutually independent.

11. A method according to claim 10 in which the respective models of the system include the same estimates for process noise and sensor noise.

12. A method according to claim 8, 9, 10, or 11 in which the respective models of the system are Kalman filters.

13. A method according to any one of the preceding claims further comprising the step of discarding series of measurements for which the differences between both measured values and their predicted values exceed a predetermined threshold for a predetermined period of time.

14. A method according to any one of the preceding claims in which the parameter is the heart rate.

15. A method according to claim 14 in which the two independent measurements are made from an electrocardiograph and a pulse oximetry waveform.

16. A method according to claim 14 in which the two measurements are made from a multiple lead ECG recording.

17. A method according to any one of the preceding claims in which there are more than two measurements.

18. A method according to any one of the preceding claims further comprising the step of identifying movement artefacts based on the values of the differences between both measured values and their predicted values.

19. A computer program comprising program code means for executing the method of any one of the preceding claims.

20. Apparatus constructed and arranged to execute the method of any one of claims 1 to 18.