Pulse oximetry method and system with improved motion correction

• US 6,434,408 B1
• Filed: 09/29/2000
• Issued: 08/13/2002
• Est. Priority Date: 09/29/2000
• Status: Expired due to Term

• Current Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Original Assignee: Datex-Ohmeda Incorporated (General Electric Company)
• Inventors: Heckel, Donald W.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US09/675,596
• Time in Patent Office: 683 Days
• Field of Search: 600/310, 600/323, 600/330, 600/336
• US Class Current: 600/336
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts

Abstract

A pulse oximetry method and system for improved motion correction is disclosed. The method/system provides for the use of a detector output signal to obtain a different plurality of differential absorption data sets in corresponding relation to each of a succession of measurement, wherein each of the data sets includes differential absorption values for light of a first wavelength and light of a second wavelength. The data sets are processed to obtain a relative motion estimate value for each measurement. When the relative motion estimate value for a given measurement falls within a predetermined range (i.e., corresponding with clinical motion), a corresponding blood analyte indicator value is adjusted in a predetermined manner, wherein the corresponding adjusted blood analyte indicator is employable to obtain at least one blood analyte concentration value. In one embodiment, blood analyte indicator values may be readily multiplied by a predetermined adjustment factor (i.e., when clinical motion is identified). The relative motion estimate value for a given measurement Sep. 27, 2000 may be obtained by conducting a principal component analysis of the corresponding plurality of data sets relative to a corresponding best fit function therefor to obtain corresponding variance values V₁, V₂. The variance value V₁, and/or V₂ for a given current measurement may be employed to obtain a current motion estimate value. The current motion estimate value and the relative motion estimate value obtained for a prior low motion measurement (i.e., for which no adjustment was necessary) may be used to compute the relative motion estimate value for the current measurement. The variance values V₁ and/or V₂ are also employable to compute an ongoing, updated motion probability factor, wherein such factor may be used to adjust relative motion estimates values in instances of rapid tissue perfusion changes.

Claims

1. A method for use in a pulse oximetry system which provides a detector output indicative of light absorption by a tissue-under-test at each of a plurality of different light wavelengths, comprising:

utilizing said detector output to (i.) compute blood analyte indicator values for each of a plurality of measurements, and (ii.) obtain a corresponding relative motion estimate value for each of said plurality of measurements; and

,

determining whether the corresponding relative motion estimate value for each of said plurality of measurements is within a first predetermined range, wherein for at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range the corresponding blood analyte indicator value is adjusted utilizing a predetermined adjustment factor that is empirically determined, and wherein said adjusted blood analyte indicator value is employable to obtain a blood analyte concentration value.

2. A method as recited in claim 1, wherein for said at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range said predetermined adjustment manner includes:

adjusting the corresponding blood analyte indicator value utilizing a predetermined adjustment factor.

3. A method as recited in claim 2, wherein said adjusting step includes:

multiplying the corresponding blood analyte indicator value by said predetermined adjustment factor.

4. A method as recited in claim 3, wherein said adjusting step further includes:

comparing the corresponding blood analyte indicator value to a predetermined threshold value, wherein said predetermined adjustment factor is scaled when said blood analyte indicator value exceeds said predetermined threshold value.

5. A method as recited in claim 3, wherein said predetermined adjustment factor is set to a value between about 0.5 and 0.85.

6. A method as recited in claim 1, said utilizing step including:

processing said detector output to obtain a different plurality of data sets corresponding with each of said plurality of measurements, each of said plurality of data sets comprising a first differential absorption value for light at a first wavelength and a second differential absorption value for light at a second wavelength, wherein for each of said plurality of measurements a corresponding best fit function is computed for the corresponding plurality of data sets.

7. A method as cited in claim 6, wherein for each of said plurality of measurements said utilizing step further includes:

performing a statistical analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one statistical variance value indicative of a relative degree of patient motion; and

,

computing said corresponding relative motion estimate value using said corresponding at least one statistical variance value.

8. A method as cited in claim 6, wherein for each of said plurality of measurements said utilizing step further includes:

performing a principal component analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one of a first principal component variance value (V₁) and a second principal component variance value (V₂); and

computing said corresponding relative motion estimate value using at least one of said corresponding first principal component variance value V₁ and said corresponding second principal component value V₂.

9. A method as recited in claim 8, wherein for each given one of said plurality of measurements said utilizing step further includes:

calculating a corresponding current motion estimate value (CMEV) using at least one of said corresponding V₁ and V₂ values;

establishing a reference motion value (RMV); and

computing said corresponding relative motion estimate value (RMEV) using said corresponding CMEV and said RMV.

10. A method as recited in claim 9, wherein for each of said plurality of measurements:

said CMEV is calculated as follows;

11. A method as recited in claim 10, wherein for at least one of said plurality of measurements said establishing step includes:

$\mathrm{RMV}=\frac{V_1}{V_2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{CMEV}}^{*}<br><br>K,$

wherein V₁, V₂ and CMEV are as determined for said at least one of said plurality of measurements, and wherein K is a constant.

12. A method as recited in claim 9, wherein for at least one of said plurality of measurements said establishing step includes:

setting the RMV equal to a lowest RMEV corresponding with a prior one of said plurality of measurements.

13. A method as recited in claim 12, wherein said establishing step further includes:

computing a motion probability factor (MPF) on an ongoing, updated basis utilizing at least one of said V₁ values and said V₂ values; and

,

using the MPF to adjust said RMV when the MPF exceeds a predetermined threshold.

14. A method as recited in claim 13, wherein said computing step further includes:

determining an average V₂ value in relation to each given one of a series of measurements by averaging a sum of the V₂ value corresponding with the given measurement and the V₂ values corresponding with a predetermined number of prior measurements comprising said series, and,

comparing the average V₂ value corresponding with each given one of the series of measurement periods with the lowest average V₂ value corresponding with any precedent one of said series of measurement periods to obtain a ratio therebetween, wherein said ratio is employable as said MPF.

15. A method as recited in claim 14, wherein in said using step said RMV is adjusted to an adjusted RMV as follows:

16. A method as recited in claim 1, further comprising:

determining whether the relative motion estimate value corresponding with each of said plurality of measurements is within a second predetermined range, non-overlapping with said first predetermined range, wherein for each measurement having a corresponding relative motion estimate value within said second predetermined range the corresponding blood analyte indicator value is employable to obtain at least one blood analyte concentration value free from adjustment.

18. A method as provided in claim 16, wherein said blood analyte indicator values are each defined by a slope value of a regression line computed with respect to the corresponding plurality of data sets for a given measurement, and wherein the predetermined adjustment factor is set to a value between about 0.6 and 0.75.

17. A method for use in pulse oximetry system which provides a detector output indicative of light absorption by tissue under test at each a plurality of different light wavelengths and which employs the detector output to compute blood analyte indicator value for each of the plurality of measurements, comprising:

processing said detector output to obtain a plurality of data sets corresponding with each of said plurality of measurements, each of said plurality of data sets comprising a first differential absorption value for light at a first wavelength and a second differential absorption value light at a second wave wavelength, wherein for each of said plurality of measurements a corresponding best fit function is computed for the corresponding plurality of data sets;

performing for each of said plurality of measurements a statistical analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one statistical variance value;

computing a relative motion estimate value for each of said plurality of measurements using said corresponding at least one statistical variance value; and

,

determining whether the corresponding relative motion estimate value for each of said plurality of said measurements is within a first predetermined range, wherein for at least one of a plurality of measurements having a corresponding relative motion estimate value within the first predetermined range, the corresponding blood analyte indicator value is adjusted utilizing a predetermined adjustment factor, and wherein the adjusted blood analyte indicator value is employable to obtain a blood analyte concentration value.

19. A method as provided in claim 17, wherein for each of said plurality of measurements said performing step further includes:

conducting a principal component analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one of a first principal component variance value (V₁) and a second principal component variance value (V₂); and

,

computing said corresponding relative motion estimate value using at least one of said corresponding first principal component variance value (V₁) and said corresponding second principal component variance value (V₂).

20. A method as recited in claim 19, wherein said method further includes:

establishing a reference motion value (RMV); and

, wherein for each given one of said plurality of measurements said computing step further includes;

calculating a corresponding current motion estimate value (CMEV) using at least one of said corresponding V₁ and V₂ values; and

,

computing said corresponding relative motion estimate value (RMEV) using said corresponding CMEV and said corresponding RMEV.

21. A method as recited in claim 20, wherein said establishing step further includes:

computing a motion probability factor (MPF) on an updated basis utilizing at least one of said V₁ values and said V₂ values; and

,

adjusting said RMV utilizing said MPF when said MPF exceeds a predetermined threshold.

22. A method for use in a pulse oximetry system which provides a detector output indicative of light absorption by a tissue-under-test at each of a plurality of different light wavelengths and which employs the detector output to compute blood analyte indicator values for each of a plurality of measurements, comprising:

utilizing said detector output to obtain a corresponding relative motion estimate value for each of said plurality of measurements by processing said detector output to obtain a different plurality of data sets corresponding with each of said plurality of measurements, each of said plurality of data sets comprising a first differential absorption value for light at a first wavelength and a second differential absorption value for light at a second wavelength, wherein for each of said plurality of measurements a corresponding best fit function is computed for the corresponding plurality of data sets; and

,

determining whether the corresponding relative motion estimate value for each of said plurality of measurements is within a first predetermined range, wherein for at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range the corresponding blood analyte indicator value is adjusted in a predetermined adjustment manner, and wherein said adjusted blood analyte indicator value is employable to obtain a blood analyte concentration value.

23. A method as cited in claim 22, wherein for each of said plurality of measurements said utilizing step further includes:

performing a statistical analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one statistical variance value indicative of a relative degree of patient motion; and

,

computing said corresponding relative motion estimate value using said corresponding at least one statistical variance value.

24. A method as cited in claim 22, wherein for each of said plurality of measurements said utilizing step further includes:

performing a principal component analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one of a first principal component variance value (V₁) and a second principal component variance value (V₂); and

,

computing said corresponding relative motion estimate value using at least one of said corresponding first principal component variance value V₁ and said corresponding second principal component value V₂.

25. A method as recited in claim 24, wherein for each given one of said plurality of measurements said utilizing step further includes:

calculating a corresponding current motion estimate value (CMEV) using at least one of said corresponding V₁ and V₂ values;

establishing a reference motion value (RMV); and

,

computing said corresponding relative motion estimate value (RMEV) using said corresponding CMEV and said RMV.

26. A method as recited in claim 25, wherein for each of said plurality of measurements:

said CMEV is calculated as follows;

27. A method as recited in claim 26, wherein for at least one of said plurality of measurements establishing step includes:

$\mathrm{RMV}=\frac{V_1}{V_2}<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{CMEV}}^{*}<br><br>K,$

wherein V₁, V₂ and CMEV are as determined for said at least one of said plurality of measurements, and wherein K is a constant.

28. A method as recited in claim 25, wherein for at least one of said plurality of measurements said establishing step includes:

setting the RMV equal to a lowest RMEV corresponding with a prior one of said plurality of measurements.

29. A method as recited in claim 27, wherein said establishing step further includes:

computing a motion probability factor (MPF) on an ongoing, updated basis utilizing at least one of said V₁ values and said V₂ values; and

,

using the MPF to adjust said RMV when the MPF exceeds a predetermined threshold.

30. A method as recited in claim 29, wherein said computing step further includes:

determining an average V₂ value in relation to each given one of a series of measurements by averaging a sum of the V₂ value corresponding with the given measurement and the V₂ values corresponding with a predetermined number of prior measurements comprising said series, and,

comparing the average V₂ value corresponding with each given one of the series of measurement periods with the lowest average V₂ value corresponding with any precedent one of said series of measurement periods to obtain a ratio therebetween, wherein said ratio is employable as said MPF.

31. A method as recited in claim 30, wherein in said using step said RMV is adjusted to an adjusted RMV as follows:

32. A method for use in a pulse oximetry system which provides a detector output indicative of light absorption by a tissue-under-test at each of a plurality of different light wavelengths, comprising:

utilizing said detector output to obtain a corresponding relative motion estimate value for each of said plurality of measurements; and

,

determining;

(i.) whether the corresponding relative motion estimate value for each of said plurality of measurements is within a first predetermined range, wherein for at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range the corresponding blood analyte indicator value is adjusted in a predetermined manner, and wherein said adjusted blood analyte indicator value is employable to obtain a blood analyte concentration value; and

,

(ii.) whether the relative motion estimate value corresponding with each of said plurality of measurements is within a second predetermined range, non-overlapping with said first predetermined range, wherein for each measurement having a corresponding relative motion estimate value within said second predetermined range the corresponding blood analyte indicator value is employably to obtain at least one blood analyte concentration value free from adjustment.

33. A method as recited in claim 32, wherein for said at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range said predetermined adjustment manner includes:

adjusting the corresponding blood analyte indicator value utilizing a predetermined adjustment factor.

34. A method as recited in claim 33, wherein said adjusting step includes:

multiplying the corresponding blood analyte indicator value by said predetermined adjustment factor.

35. A method as recited in claim 34, wherein said adjusting step further includes:

comparing the corresponding blood analyte indicator value to a predetermined threshold value, wherein said predetermined adjustment factor is scaled when said blood analyte indicator value exceeds said predetermined threshold value.

36. A method as recited in claim 34, wherein said predetermined adjustment factor is set to a value between about 0.5 and 0.85.

37. A method as recited in claim 32, said utilizing step including:

processing said detector output to obtain a different plurality of data sets corresponding with each of said plurality of measurements, each of said plurality of data sets comprising a first differential absorption value for light at a first wavelength and a second differential absorption value for light at a second wavelength, wherein for each of said plurality of measurements a corresponding best fit function is computed for the corresponding plurality of data sets.

38. A method as cited in claim 37, wherein for each of said plurality of measurements said utilizing step further includes:

performing a statistical analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one statistical variance value indicative of a relative degree of patient motion; and

,

computing said corresponding relative motion estimate value using said corresponding at least one statistical variance value.

39. A method for use in a pulse oximetry system which provides a detector output indicative of light absorption by a tissue-under-test at each of a plurality of different light wavelengths, comprising:

utilizing said detector output to (i.) compute blood analyte indicator values for each of a plurality of measurements, and (ii.) obtain a corresponding relative motion estimate value for each of said plurality of measurements; and

,

determining whether the corresponding relative motion estimate value for each of said plurality of measurements is within a first predetermined range, wherein for at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range the corresponding blood analyte indicator value is adjusted in a predetermined adjustment manner; and

,

separately employing, for each of said plurality of measurements, the corresponding blood analyte indicator value, as adjusted, to obtain a blood analyte concentration value.

40. A method as recited in claim 39, wherein for said at least one of said plurality of measurements having a corresponding relative motion estimate value within the first predetermined range said predetermined adjustment manner includes:

adjusting the corresponding blood analyte indicator value utilizing a predetermined adjustment factor.

41. A method as recited in claim 40, wherein said adjusting step includes:

multiplying the corresponding blood analyte indicator value by said predetermined adjustment factor.

42. A method as recited in claim 41, wherein said adjusting step further includes:

comparing the corresponding blood analyte indicator value to a predetermined threshold value, wherein said predetermined adjustment factor is scaled when said blood analyte indicator value exceeds said predetermined threshold value.

43. A method as recited in claim 41, wherein said predetermined adjustment factor is set to a value between about 0.5 and 0.85.

44. A method as recited in claim 39, said utilizing step including:

processing said detector output to obtain a different plurality of data sets corresponding with each of said plurality of measurements, each of said plurality of data sets comprising a first differential absorption value for light at a first wavelength and a second differential absorption value for light at a second wavelength, wherein for each of said plurality of measurements a corresponding best fit function is computed for the corresponding plurality of data sets.

45. A method as cited in claim 44, wherein for each of said plurality of measurements said utilizing step further includes:

performing a statistical analysis of the corresponding plurality of data sets in relation to the corresponding best fit function to obtain at least one statistical variance value indicative of a relative degree of patient motion; and

,

computing said corresponding relative motion estimate value using said corresponding at least one statistical variance value.