Selection of ensemble averaging weights for a pulse oximeter based on signal quality metrics

• US 20070208242A1
• Filed: 02/01/2007
• Published: 09/06/2007
• Est. Priority Date: 03/08/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Baker, Clark
• Granted Patent: US 7,474,907 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence

Abstract

A method and a system for ensemble averaging signals in a pulse oximeter, including receiving first and second electromagnetic radiation signals from a blood perfused tissue portion corresponding to two different wavelengths of light, obtaining an assessment of the signal quality of the electromagnetic signals, selecting weights for an ensemble averager using the assessment of signal quality, and ensemble averaging the electromagnetic signals using the ensemble averager.

Claims

1-18. -18. (canceled)

19. A method of calculating oxygen saturation, comprising:

receiving first and second electromagnetic radiation signals from a blood perfused tissue portion, the first and second electromagnetic radiation signals corresponding to two different wavelengths of light;

conditioning the first and second electromagnetic signals to generate first and second conditioned signals;

obtaining an assessment of signal quality of the conditioned signals;

calculating weights for an ensemble averager from a continuous weighting function using the assessment of signal quality;

normalizing the first and second conditioned signals to generate first and second normalized signals;

ensemble averaging the normalized signals using the ensemble averager to generate first and second averaged signals;

performing a ratio-of-ratios calculation using averaged signals to generate an averaged ratio-of-ratios calculation; and

calculating oxygen saturation based on the averaged ratio-of-ratios calculation and calibration coefficients.

20. The method of claim 19 wherein obtaining an assessment of signal quality comprises obtaining a measure of the degree of arrhythmia of the conditioned signals.

21. The method of claim 19 wherein obtaining an assessment of signal quality comprises obtaining a measure of the degree of correlation between the first and second conditioned signals.

22. The method of claim 19 wherein obtaining an assessment of signal quality comprises obtaining a measure of the degree of noise present in the conditioned signals.

23. The method of claim 22 wherein obtaining a measure of the degree of noise comprises obtaining a ratio of a current pulse amplitude to the long-term average pulse amplitude of the conditioned signals.

24. The method of claim 19 wherein obtaining an assessment of signal quality comprises obtaining a ratio of a current pulse amplitude to the previous pulse amplitude of the conditioned signals.

25. The method of claim 19 wherein obtaining an assessment of signal quality comprises determining an overall signal quality metric the conditioned signals, wherein the overall signal quality metric is a combination of several other signal quality metrics.

26. The method of claim 19 wherein obtaining an assessment of signal quality comprises obtaining a ratio of a current pulse period to that of an average pulse period of the conditioned signals.

27. The method of claim 19 wherein calculating weights comprises forming a combination of one or more of the following parameters:

a measure of the degree of arrhythmia of the conditioned signals, a measure of the degree of correlation between the first and second conditioned signals, a measure of the degree of noise present in the conditioned signals, a ratio of a current pulse amplitude to a previous pulse amplitude of the conditioned signals, and a ratio of a current pulse period to that of an average pulse period of the conditioned signals.

28. A pulse oximetry system comprising:

a sensor configured to receive first and second electromagnetic radiation signals from a blood perfused tissue portion, the first and second electromagnetic radiation signals corresponding to two different wavelengths of light; and

a pulse oximeter configured to;

condition the first and second electromagnetic signals to generate first and second conditioned signals;

obtain an assessment of signal quality of the conditioned signals;

calculate weights for an ensemble averager from a continuous weighting function using the assessment of signal quality;

normalize the first and second conditioned signals to generate first and second normalized signals;

ensemble average the normalized signals using the ensemble averager to generate first and second averaged signals;

perform a ratio-of-ratios calculation using averaged signals to generate an averaged ratio-of-ratios calculation; and

calculate oxygen saturation based on the averaged ratio-of-ratios calculation and calibration coefficients.

29. The pulse oximetry system of claim 28 wherein the pulse oximeter is configured to obtain the assessment of the signal quality by determining a correlation between the first and second conditioned signals.

30. The pulse oximetry system of claim 28 wherein the pulse oximeter is configured to obtain the assessment of the signal quality by measuring a degree of variability of a ratio-of-ratios of the first and second conditioned signals.

31. The pulse oximetry system of claim 28, wherein the pulse oximeter is configured to filter the conditioned signals based on an ECG signal.

32. The pulse oximetry system of claim 28, wherein the pulse oximeter is configured to calculate the weights based on a variability of a ratio-of-ratios over a time.

33. The pulse oximetry system of claim 28, wherein the pulse oximeter is configured to calculate the weights based on a pulse qualification score of the conditioned signals.