Pulse oximeter with parallel saturation calculation modules

• US 20060183988A1
• Filed: 04/18/2006
• Published: 08/17/2006
• Est. Priority Date: 08/07/1995
• Status: Active Grant

• Current Assignee: Clark R. Baker Jr, Thomas J. Yorkey
• Original Assignee: Clark R. Baker Jr, Thomas J. Yorkey
• Inventors: Yorkey, Thomas J., Baker, Clark R. Jr.
• Granted Patent: US 7,336,983 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/0075 by spectroscopy, i.e. measuring spectra, e.g. Raman spectroscopy, infrared absorption spectroscopy A61B5/0071 takes precedence
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• 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 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: H03H 21/003 KALMAN filters

Abstract

A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The method and apparatus of the invention take into account the physical limitations on various physiological parameters being monitored when weighting and averaging a series of measurements. Varying weights are assigned different measurements, measurements are rejected, and the averaging period is adjusted according to the reliability of the measurements. Similarly, calculated values derived from analyzing the measurements are also assigned varying weights and averaged over adjustable periods. More specifically, a general class of filters such as, for example, Kalman filters, is employed in processing the measurements and calculated values. The filters use mathematical models which describe how the physiological parameters change in time, and how these parameters relate to measurement in a noisy environment. The filters adaptively modify a set of averaging weights to optimally estimate the physiological parameters.

Claims

1. A method for determining oxygen saturation, the method comprising:

determining a first oxygen saturation value based upon signals received from a patient using a first saturation calculation algorithm;

determining a second oxygen saturation value based upon signals received from the patient using a second saturation calculation algorithm; and

arbitrating between the first and second oxygen saturation values based on a saturation confidence associated with the first and second oxygen saturation values to determine a final oxygen saturation value based on the first oxygen saturation value and the second oxygen saturation value.

2. The method, as set forth in claim 1, wherein arbitrating comprises selecting either the first oxygen saturation value or the second oxygen saturation value as the final oxygen saturation value.

3. The method, as set forth in claim 2, wherein arbitrating comprises selecting either the first oxygen saturation value or the second oxygen saturation value as the final oxygen saturation value if the saturation confidence associated with the selected oxygen saturation value is greater than a given percentage above the saturation confidence associated with the unselected oxygen saturation value.

4. The method, as set forth in claim 3, wherein the given percentage is at least 10%.

5. The method, as set forth in claim 1, wherein arbitrating comprises calculating the final oxygen saturation value based on an interpolation between the first and second oxygen saturation values.

6. The method, as set forth in claim 1, wherein arbitrating comprises calculating the final oxygen saturation value based on an interpolation between the first and second oxygen saturation values if the saturation confidence associated with the first oxygen saturation value differs from the saturation confidence associated with the second oxygen saturation value by less than a given percentage.

7. The method, as set forth in claim 6, wherein the given percentage is 10% or less.

8. The method, as set forth in claim 1, wherein the final oxygen saturation value corresponds to the most accurate of the first and second oxygen saturation values.

9. The method, as set forth in claim 1, comprising:

determining a first pulse rate value using a first pulse rate calculation algorithm applied to the electronic signals;

determining a second pulse rate value using a second pulse rate calculation algorithm applied to the electronic signals; and

arbitrating between the first and second pulse rate values based on a pulse rate confidence associated with the first and second pulse rate values to determine a final pulse rate value based on the first pulse rate value and the second pulse rate value.

10. The method, as set forth in claim 9, wherein arbitrating between the first and second pulse rate values comprises selecting either the first pulse rate value or the second pulse rate value as the final pulse rate value.

11. The method, as set forth in claim 10, wherein arbitrating between the first and second pulse rate values comprises selecting either the first pulse rate value or the second pulse rate value as the final pulse rate value if the pulse rate confidence associated with the selected pulse rate value is greater than a given percentage above the pulse rate confidence associated with the unselected pulse rate value.

12. The method, as set forth in claim 11, wherein the given percentage is at least 10%.

13. The method, as set forth in claim 9, wherein arbitrating between the first and second pulse rate values comprises calculating the final pulse rate value based on an interpolation between the first and second pulse rate values.

14. The method, as set forth in claim 13, wherein arbitrating between the first and second pulse rate values comprises calculating the final pulse rate value based on an interpolation between the first and second pulse rate values if the pulse rate confidence associated with the first pulse rate value differs from the pulse rate confidence associated with the second pulse rate value by less than a given percentage.

15. The method, as set forth in claim 14, wherein the given percentage is 10% or less.

16. The method, as set forth in claim 3, wherein the final pulse rate value corresponds to the most accurate of the first and second pulse rate values.

17. The method, as set forth in claim 1, wherein determining the first oxygen saturation value comprises performing adaptive filtering.

18. The method, as set forth in claim 1, wherein determining the second oxygen saturation value comprises performing a ratio of ratios calculation.

19. The method, as set forth in claim 9, wherein determining the first pulse rate value comprises analyzing a waveform associated with the patient signals.

20. The method, as set forth in claim 9, wherein determining the second pulse rate value comprises analyzing a frequency associated with the patient signals.

21. The method, as set forth in claim 1, wherein the saturation confidence is based on noise characteristics of the patient signals.

22. The method, as set forth in claim 9, wherein the pulse rate confidence is based on noise characteristics of the patient signals.

23. The method, as set forth in claim 1, comprising displaying the final oxygen saturation value.

24. The method, as set forth in claim 1, comprising displaying the final oxygen saturation value if the final oxygen saturation value is not older than a certain limit.

25. The method, as set forth in claim 23, comprising blanking a previously displayed final oxygen saturation value if the final oxygen saturation value does not meet certain criteria.

26. The method, as set forth in claim 23, comprising performing processing subsequent to arbitrating to determine the final oxygen saturation value and prior to displaying the final oxygen saturation value.

27. The method, as set forth in claim 9, comprising displaying the final pulse rate value.

28. The method, as set forth in claim 9, comprising displaying the final pulse rate value if the pulse rate confidence is above a certain limit.

29. The method, as set forth in claim 27, comprising blanking a previously displayed final pulse rate value if the final pulse rate value does not meet certain criteria.

30. The method, as set forth in claim 27, comprising performing processing subsequent to arbitrating to determine the final pulse rate value and prior to displaying the final pulse rate value.

31. A method for measuring a blood constituent, the method comprising:

determining a plurality of possible blood constituent values using a plurality of blood constituent value calculators, wherein each of the possible blood constituent values have a respective confidence level associated therewith; and

arbitrating between the plurality of possible blood constituent values based on the respective confidence levels to determine a final blood constituent value.

32. The method, as set forth in claim 31, wherein arbitrating comprises selecting between the plurality of possible blood constituent values to determine the final blood constituent value.

33. The method, as set forth in claim 32, wherein arbitrating comprises selecting between the plurality of possible blood constituent values to determine the final blood constituent value if the confidence level associated with the selected blood constituent value is greater than a given percentage above the confidence levels associated with the unselected blood constituent values.

34. The method, as set forth in claim 33, wherein the given percentage is at least 10%.

35. The method, as set forth in claim 31, wherein arbitrating comprises calculating the final blood constituent value based on an interpolation between at least a portion of the plurality of possible blood constituent values.

36. The method, as set forth in claim 35, wherein arbitrating comprises calculating the final blood constituent value based on an interpolation between at least a portion of the plurality of possible blood constituent values if the confidence levels associated with the plurality of possible blood constituent values differ from one another by less than a given percentage.

37. The method, as set forth in claim 36, wherein the given percentage is 10% or less.

38. The method, as set forth in claim 31, wherein the final blood constituent value corresponds to the most accurate of the plurality of possible blood constituent values.

39. The method, as set forth in claim 31, wherein the blood constituent comprises oxygen saturation.

40. The method, as set forth in claim 31, wherein the blood constituent comprises pulse rate.

41. The method, as set forth in claim 31, comprising displaying the final blood constituent value.

42. The method, as set forth in claim 31, comprising displaying the final blood constituent value if the final blood constituent value is not older than a certain limit.

43. The method, as set forth in claim 41, comprising blanking a previously displayed final blood constituent value if the final blood constituent value does not meet certain criteria.

44. The method, as set forth in claim 41, comprising performing processing subsequent to arbitrating to determine the final blood constituent value and prior to displaying the final blood constituent value.

45. A method for determining oxygen saturation, the method comprising:

determining a first value correlative to a first oxygen saturation value based upon signals received from a patient using a first saturation calculation algorithm;

determining a second value correlative to a second oxygen saturation value based upon signals received from the patient using a second saturation calculation algorithm; and

arbitrating between the first and second values based on a respective confidence level associated with the first and second values to determine a final oxygen saturation value.

46. The method, as set forth in claim 45, wherein arbitrating comprises selecting either the first value or the second value to determine the final oxygen saturation value.

47. The method, as set forth in claim 46, wherein arbitrating comprises selecting either the first value or the second value to determine the final oxygen saturation value if the confidence level associated with the selected value is greater than a given percentage above the confidence level associated with the unselected value.

48. The method, as set forth in claim 47, wherein the given percentage is at least 10%.

49. The method, as set forth in claim 45, wherein arbitrating comprises calculating the final oxygen saturation value based on an interpolation between the first and second values.

50. The method, as set forth in claim 45, wherein arbitrating comprises calculating the final oxygen saturation value based on an interpolation between the first and second values if the confidence level associated with the first value differs from the confidence level associated with the second value by less than a given percentage.

51. The method, as set forth in claim 50, wherein the given percentage is 10% or less.

52. The method, as set forth in claim 45, wherein the final oxygen saturation value corresponds to the most accurate of the first and second values.

53. The method, as set forth in claim 45, wherein the saturation confidence is based on noise characteristics of the patient signals.

54. The method, as set forth in claim 45, comprising displaying the final oxygen saturation value.

55. The method, as set forth in claim 45, comprising displaying the final oxygen saturation value if the final oxygen saturation value is not older than a certain limit.

56. The method, as set forth in claim 54, comprising blanking a previously displayed final oxygen saturation value if the final oxygen saturation value does not meet certain criteria.

57. The method, as set forth in claim 54, comprising performing processing subsequent to arbitrating to determine the final oxygen saturation value and prior to displaying the final oxygen saturation value.

58. The method, as set forth in claim 57, wherein the processing comprises averaging the final oxygen saturation value with previously determined final oxygen saturation values to adjust the final oxygen saturation value prior to display.

59. The method, as set forth in claim 58, wherein the averaging comprises cardiac gated averaging.