Signal processing apparatus and method

• US 6,206,830 B1
• Filed: 11/17/1999
• Issued: 03/27/2001
• Est. Priority Date: 03/07/1991
• Status: Expired due to Fees

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Kiani-Azarbayjany, Esmaiel, Diab, Mohamed Kheir
• Primary Examiner(s): O'Connor, Cary
• Assistant Examiner(s): Carter, Ryan
• Application Number:
  US09/441,736
• Time in Patent Office: 496 Days
• Field of Search: 600/485, 600/500-503, 600/561, 600/300, 600/324, 600/364-365, 600/473, 600/476-479, 356/39-41, 379/410-411
• US Class Current: 600/364
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• 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 5/7228 Signal modulation applied to the input signal sent to patient or subject; demodulation to recover the physiological signal modulation H03C
• 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

A signal processor which acquires a first signal, including a first desired signal portion and a first undesired signal portion, and a second signal, including a second desired signal portion and a second undesired signal portion, wherein the first and second desired signal portions are correlated. The signals may be acquired by propagating energy through a sodium and measuring an attenuated signal after transmission or reflection. Alternatively, the signals may be acquired by measuring energy generated by the medium. A processor of the present invention generates a noise reference signal which is a combination of only the undesired signal portions and is correlated to both the first and second undesired signal portions. The noise reference signal is then used to remove the undesired portion of each of the first and second measured signals via an adaptive noise canceler, preferably of the joint process estimator type. The processor of the present invention may be employed in conjunction with an adaptive noise canceler in physiological monitors wherein the known properties of energy attenuation through a medium are used to determine physiological characteristics of the medium. Many physiological conditions, such as the pulse of a patient or the concentration of a constituent in a medium, can be determined from the desired portion of the signal after undesired signal portions, such as those caused by erratic notion, are removed.

Claims

1. A physiological monitoring apparatus comprising:

means for acquiring a first signal comprising a first desired signal portion and a first undesired signal portion and a second signal comprising a second desired signal portion and a second undesired signal portion;

an adaptive canceler having a reference input for receiving a reference signal and a signal input for receiving said first and said second signals, wherein said adaptive canceler generates an output signal which approximates said first desired signal portion and said second desired portion; and

a processor responsive to the output of said adaptive canceler to calculate a physiological parameter.

2. The physiological monitoring apparatus as defined in claim 1 wherein said adaptive noise canceler further comprises a joint process estimator.

3. The physiological monitoring apparatus as defined in claim 2 wherein said joint process estimator further comprises a least-squares lattice predictor in conjunction with a regression filter.

4. A pulse oximeter comprising:

at least first and second light emitting devices;

at least one light detector configured to receive light attenuated by transmission through a living tissue with arterial pulsing blood, the light detector acquiring a first signal based on the first light emitting device comprising a first desired signal portion and a first undesired signal portion and a second signal based on the second light emitting device comprising a second desired signal portion and a second undesired signal portion;

an adaptive filter which filters the first and the second signals through use of an estimate of the first or the second undesired signal portion, wherein the adaptive filter generates an output signal which approximates the first desired signal portion and the second desired signal portion; and

a processor responsive to the output of the adaptive filter to calculate oxygen saturation.

5. The pulse oximeter of claim 4, wherein the adaptive filter uses a least squares algorithm.

6. The pulse oximeter of claim 5, wherein the adaptive filter is an adaptive noise canceler.

7. The pulse oximeter of claim 6, wherein the adaptive filter uses a least squares lattice.

8. The pulse oximeter of claim 7, further comprising a display to display the oxygen saturation.

9. A pulse oximeter comprising:

at least first and second light emitting devices;

at least one light detector configured to receive light attenuated by transmission through a living tissue with arterial blood, the light detector generating a first signal based on the first light emitting device and a second signal based on the second light emitting device;

a filter responsive to signals representing the first and second signals to filter the first and the second signals, wherein the filter adjusts its transfer function in response to changes in at least one of the first and the second signals and in response to an evaluation of an error to optimize at least one of a first and a second filtered output signals; and

a processor calculator responsive to the first and the second filtered output signals to calculate oxygen saturation.

10. The pulse oximeter of claim 9, wherein the filter uses a least squares algorithm to adjust its transfer function.

11. The pulse oximeter of claim 10, wherein the filter is an adaptive noise canceler.

12. The pulse oximeter of claim 11, wherein the filter is a least squares lattice.

13. The pulse oximeter of claim 9, wherein the filter uses a least means squares algorithm.

14. The pulse oximeter of claim 9, further comprising a display to display the oxygen saturation.

15. A method of calculating blood oxygen saturation comprising the steps of:

transmitting light of at least first and second wavelengths through body tissue carrying blood to a light-sensitive detector to generate first and second measured intensity signals;

adaptively filtering representations of the first and second measured intensity signals to provide first and second filtered signals; and

calculating oxygen saturation based upon the first and second filtered signals.

16. The method of claim 15, wherein the adaptive filtering uses a least squares algorithm.

17. The method of claim 15, wherein the adaptive filtering uses a least squares lattice.

18. The method of claim 15, wherein the adaptive filtering uses an adaptive noise canceler.

19. The method of claim 15 further comprising displaying the oxygen saturation.

20. A method of calculating blood oxygen saturation comprising the steps of:

transmitting light of at least first and second wavelengths through body tissue carrying blood to a light-sensitive detector to generate first and second signals;

filtering the first and the second signals, wherein the filtering comprises adjusting a filter transfer function in response to changes in at least one of the first and the second signals and in response to an evaluation of an error, and wherein the filtering optimizes at least one of a first and a second filtered output signal; and

calculating oxygen saturation based upon the first and the second filtered output signals.

21. The method of claim 20, wherein the filtering uses a least squares algorithm to adjust the transfer function.

22. The method of claim 20, wherein the filtering uses a least means squares algorithm to adjust the transfer function.

23. The method of claim 20, wherein the filter is a least squares lattice.

24. The method of claim 20, wherein the filter is an adaptive noise canceler.

25. The method of claim 20, further comprising displaying the oxygen saturation.

26. A pulse oximeter comprising:

a light emitter adapted to emit light of at least first and second wavelengths;

at least one light detector configured to receive light attenuated by transmission through a living tissue with arterial pulsing blood, the light detector acquiring a first signal based on the first wavelength and a second signal based on the second wavelength;

an analog to digital converter that digitizes the first and the second signals to produce digitized first and second signals;

an adaptive signal processor responsive to the first and the second digitized signals to filter the first and the second digitized signals, to produce adaptively filtered first and second signals; and

a processor responsive to the adaptively filtered first and second signals to calculate oxygen saturation.

27. The pulse oximeter of claim 26, wherein the adaptive signal processor uses a least squares algorithm.

28. The pulse oximeter of claim 26, wherein the adaptive signal processor is configured as a least squares lattice.

29. The pulse oximeter of claim 26, wherein the adaptive signal processor is configured as an adaptive noise canceler.

30. The pulse oximeter of claim 26, further comprising a display to display the oxygen saturation.