Signal processing apparatus

• US 7,215,984 B2
• Filed: 05/04/2004
• Issued: 05/08/2007
• Est. Priority Date: 03/07/1991
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Elfadel, Ibrahim M., Weber, Walter M., Diab, Mohamed K., Kiani-Azarbayjany, Esmaiel, Smith, Robert A., McCarthy, Rex J.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US10/838,593
• Publication Number:
  US 20040204636A1
• Time in Patent Office: 1,099 Days
• Field of Search: 600/310, 600/322, 600/323, 600/330, 600/336, 600/502
• US Class Current: 600/323
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02154 by optical transmission
• 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 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• 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 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7253 characterised by using transforms
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 6/00 : Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment instruments measuring radiation intensity for application in the field of nuclear medicine, e.g. in vivo counting, G01T1/161; apparatus for taking X-ray photographs G03B42/02
• CPC Class Codes: A61B 8/00 : Diagnosis using ultrasonic, sonic or infrasonic waves imaging of objects using sonar G01S15/00
• CPC Class Codes: A61B 8/5276 : due to motion
• CPC Class Codes: G01N 2021/3144 : for oxymetry
• CPC Class Codes: G06F 2218/04 : Denoising
• CPC Class Codes: H04B 1/123 : using adaptive balancing or compensation means adaptive filter circuits and algorithms H03H

Abstract

The present invention involves method and apparatus for analyzing measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, the present invention involves utilizing a transformation which evaluates a plurality of possible signal coefficients in order to find appropriate coefficients. Alternatively, the present invention involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to two measured signals. Use of this invention is described in particular detail with respect to blood oximetry measurements.

Claims

1. A physiological monitoring system including an optical probe configured to output one or more intensity signals representative of at least one physiological characteristic of body tissue, and a signal processing device configured to accept the one or more intensity signals and configured to determine a resulting value indicative of the at least one physiological characteristic, the physiological monitoring system comprising:

an optical probe including a light-sensitive detector configured to detect light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood and configured to output one or more intensity signals based on the detected light; and

a signal processing device including;

a first calculator capable of utilizing a first calculation technique to determine at least a first ratio representative of at least one physiological characteristic of the pulsing blood based on at least one of the one or more intensity signals generated from said detection of said light at said at least first and second wavelengths,

a second calculator capable of utilizing a second calculation technique different from the first calculation technique, to determine at least a second ratio representative of the at least one physiological characteristic based on at least one of the one or more intensity signals generated from said detection of said light at said at least first and second wavelengths, and

a processing module configured to utilize at least one of the first and second calculators to determine a resulting value indicative of the at least one physiological characteristic.

2. The physiological monitoring system of claim 1, wherein the at least one physiological characteristic comprises a blood constituent level.

3. The physiological monitoring system of claim 2, wherein the blood constituent level comprises blood oxygen saturation.

4. The physiological monitoring system of claim 3, wherein the resulting value comprises a ratio.

5. The physiological monitoring system of claim 3, wherein the resulting value of the blood oxygen saturation is significantly free of an influence of motion induced noise.

6. The physiological monitoring system of claim 1, wherein at least one the physiological characteristic comprises a pulse rate.

7. The physiological monitoring system of claim 6, wherein the resulting value of the pulse rate is significantly free of an influence of motion induced noise.

8. The physiological monitoring system of claim 1, wherein the resulting value comprises a plethysmographic waveform.

9. The physiological monitoring system of claim 8, wherein the plethysmographic waveform is significantly free of an influence of motion induced noise.

10. The physiological monitoring system of claim 1,

wherein the first calculator is capable of determining characteristics of at least one of the one or more intensity signals;

and

wherein the processing module is configured to utilize the characteristics in the determination of the resulting value.

11. The physiological monitoring system of claim 10, wherein the characteristics comprise a model of at least one of the one or more intensity signals.

12. The physiological monitoring system of claim 11, wherein the model comprises a physiological model.

13. The physiological monitoring system of claim 11, wherein the model comprises a mathematical model.

14. The physiological monitoring system of claim 10, wherein the characteristics comprise statistics.

15. The physiological monitoring system of claim 1, wherein said utilization of said at least one of the first and second calculators is based at least in part on a property of the one or more intensity signals.

16. The physiological monitoring system of claim 15, wherein said property comprises a correlation between at least two of said intensity signals.

17. The physiological monitoring system of claim 1, wherein the first calculation technique utilizes an adaptive algorithm.

18. The physiological monitoring system of claim 17, wherein at least one of the one or more intensity signals is effected by the adaptive algorithm.

19. The physiological monitoring system of claim 1, wherein the processing module is programmed to evaluate at least one of the one or more intensity signals to obtain an indication of reliability for at least one of the first and second calculation techniques.

20. The physiological monitoring system of claim 1, wherein the processing module is programmed to qualify at least one of the first and second ratios as usable to determine the resulting value.

21. The physiological monitoring system of claim 1, wherein the first and second calculators are capable of relying on at least partially differing assumptions relating to at least one of the one or more intensity signals.

22. The physiological monitoring system of claim 1, wherein the first and second calculators are capable of relying on at least partially differing strengths in processing at least one of the one or more intensity signals.

23. The physiological monitoring system of claim 1, wherein the first and second ratios are different for the same intensity signals.

24. The physiological monitoring system of claim 1, wherein the processing module is programmed to reduce an effect of motion induced noise, on the resulting value.

25. The physiological monitoring system of claim 1, wherein one of the first and second calculators are capable of utilizing an algorithm that adjusts itself in response to changes in the one or more intensity signals and that adjusts itself in response to an error signal to optimize at least one of the one or more intensity signals.

26. A patient monitoring apparatus comprising:

a light-sensitive detector configured to detect light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood and configured to output one or more output signals based on the detected light; and

an electronic processing system (i) programmed to be capable of utilizing a first calculation technique adapted to remove motion induced noise from one of the one or more output signals, and (ii) programmed to be capable of utilizing a second calculation technique different from the first calculation technique, wherein the electronic processing system determines a value indicative of a physiological parameter through utilization of at least one of the first and second calculation techniques.

27. The patient monitoring apparatus of claim 26, wherein the physiological parameter comprises a blood constituent level.

28. The patient monitoring apparatus of claim 27, wherein the blood constituent level comprises blood oxygen saturation.

29. The patient monitoring apparatus of claim 28, wherein the value comprises a ratio.

30. The patient monitoring apparatus of claim 28, wherein the value of the blood oxygen saturation is significantly free of an influence of motion induced noise.

31. The patient monitoring apparatus of claim 26, wherein the physiological parameter comprises a pulse rate.

32. The patient monitoring apparatus of claim 31, wherein the value of the pulse rate is significantly free of an influence of motion induced noise.

33. The patient monitoring apparatus of claim 26, wherein the value comprises a plethysmographic waveform.

34. The patient monitoring apparatus of claim 33, wherein the plethysmographic waveform is significantly free of an influence of motion induced noise.

35. The patient monitoring apparatus of claim 26,

wherein the first calculation technique is capable of determining characteristics of at least one of the one or more output signals;

and

wherein the electronic processing system is programmed to utilize the characteristics in the determination of the value.

36. The patient monitoring apparatus of claim 35, wherein the characteristics comprise a model of at least one of the one or more output signals.

37. The patient monitoring apparatus of claim 36, wherein the model comprises a physiological model.

38. The patly monitoring apparatus of claim 36, wherein the model comprises a mathematical model.

39. The patient monitoring apparatus of claim 35, wherein the characteristics comprise statistics.

40. The patient monitoring apparatus of claim 26, wherein said electronic processing utilizes said at least one of the first and second calculation techniques based at least in part on a property of one or more of said output signals.

41. The patient monitoring apparatus of claim 40, wherein said properly comprises a correlation between at least two of said output signals.

42. The patient monitoring apparatus of claim 26, wherein the first calculation technique utilizes an adaptive algorithm.

43. The patient monitoring apparatus of claim 42, wherein at least one of the one or more output signals is effected by the adaptive algorithm.

44. The patient monitoring apparatus of claim 26, wherein the electronic processing system is programmed to evaluate at least one of the one or more output signals to obtain an indication of reliability for at least one of the first and second calculation techniques.

45. The patient monitoring apparatus of claim 26, wherein the first and second calculation techniques rely on at least partially differing assumptions relating to at least one of the one or more output signals.

46. The patient monitoring apparatus of claim 26, wherein the first and second calculation techniques rely on at least partially differing strengths in processing at least one of the one or more output signals.

47. The patient monitoring apparatus of claim 26, wherein the first and second calculation techniques are capable of producing values that are different from each other for the same output signals.

48. The patient monitoring apparatus of claim 47, wherein said values comprise ratios.

49. The patient monitoring apparatus of claim 26, wherein the electronic processing system is programmed to reduce an effect of motion induced noise on the value.

50. The patient monitoring apparatus of claim 26, wherein one of the first and second calculation techniques utilizes an algorithm that adjusts itself in response to changes in the one or more output signals and in response to an error signal to optimize at least one of the one or more output signals.

51. A method of determining a physiological characteristic of pulsing blood, the method comprising:

receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths transmitted through body tissue carrying pulsing blood;

providing at least first and second calculation techniques, wherein each calculation technique is capable of generating at least one ratio representative of the physiological characteristic of the pulsing blood based upon at least one of the first and second intensity signals; and

utilizing at least one of the first and second calculation techniques to determine a resulting value indicative of the physiological characteristic, wherein each calculation technique relies on at least partially differing strengths associated with that calculation technique, and wherein the first calculation technique is different from the second calculation technique.

52. A method of determining a physiological characteristic of pulsing blood, the method comprising:

receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths transmitted through body tissue carrying pulsing blood; and

utilizing at least one of at least first and second calculation techniques to determine a value indicative of the physiological parameter based upon at least one of the first and second intensity signals, wherein the utilizing comprises qualifying the value for inclusion, depending upon different conditions of the first and second intensity signals, and wherein the first calculation technique is different from the second calculation technique.

53. A physiological monitoring system comprising:

a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood and outputs one or more intensity signals based on the detected light, the one or more intensity signals representative of at least one physiological characteristic of the body tissue; and

a signal processing device which accepts the one or more intensity signals and determines a resulting value indicative of the at least one physiological characteristic, the signal processing device including;

a first calculator capable of utilizing at first calculation technique to determine at least a first value representative of the at least one physiological characteristic of the pulsing blood, a second calculator capable of utilizing a second calculation technique different from the first calculation technique, to determine at least a second value representative of the at least one physiological characteristic, and

a processing module which utilizes at least one of the first and second calculators to determine a resulting value indicative of the at least one physiological characteristic, said utilization based at least in part on a property of the one or more intensity signals.

54. The patient monitoring apparatus of claim 53, wherein said property comprises a correlation between at least two of said intensity signals.

55. The patient monitoring apparatus of claim 53, wherein said first calculation technique is adapted to remove motion induced noise from one of the one or more intensity signals.

56. The patient monitoring apparatus of claim 53, wherein at least one of said first and second values comprise a ratio.

57. A patient monitoring apparatus comprising:

a light-sensitive detector configured to detect light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood and configured to output one or more output signals based on the detected light; and

an electronic processing system (i) programmed to be capable of utilizing a first calculation technique to determine at least a first value representative of the at least one physiological characteristic of the pulsing blood based on at least one of the one or more output signals, (ii) programmed to be capable of utilizing a second calculation technique different from the first calculation technique, and (iii) programmed to utilize at least one of the first and second calculation techniques based at least in pat on a property of the one or more output signals to determine a value indicative of the at least one physiological characteristic.

58. The patient monitoring apparatus of claim 57, wherein said property comprises a correlation between at least two of said output signals.

59. The patient monitoring apparatus of claim 57, wherein said first calculation technique is adapted to remove motion induced noise from one of the one or more output signals.

60. The patient monitoring apparatus of claim 57, wherein the first and second calculation techniques are capable of producing one or more ratios.