Method and apparatus for removing artifact from physiological signals

• US 5,971,930 A
• Filed: 10/17/1997
• Issued: 10/26/1999
• Est. Priority Date: 10/17/1997
• Status: Expired due to Term

• Current Assignee: Draeger Medical Systems Incorporated (Dragerwerk AG)
• Original Assignee: Siemens Medical Systems, Inc. (Siemens AG)
• Inventors: Elghazzawi, Ziad
• Primary Examiner(s): O'Connor, Cary
• Assistant Examiner(s): CARTER, RYAN CHRISTOPHER
• Application Number:
  US08/951,879
• Time in Patent Office: 739 Days
• Field of Search: 600/322-324, 600/364, 600/481, 600/483, 600/454, 600/479, 600/500, 600/513, 600/519, 600/521
• US Class Current: 600/483
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts

Abstract

A heart rate value determined from a first physiological signal that is acquired independently from a second physiological signal, is used to control a band pass filter for controllably bandpass filtering the second physiological signal. In a system having sensors for independently acquiring both electrocardiogram (ECG) and pulse oximetry (SpO2) signals, a heart rate value determined from the ECG signal is used to controllably bandpass filter the red and infrared SpO2 signals, thereby reducing the level of artifact signal in the SpO2 signals.

Claims

1. A method for reducing the level of artifact signal in a physiological signal, comprising the following steps:

acquiring a first physiological signal;

acquiring a second physiological signal using an acquisition technique that is different and independant from the technique used to acquire the first physiological signal;

processing the second physiological signal so as to determine a heart rate value therefrom; and

using said determined heart rate value for controllably bandpass filtering the first physiological signal and developing an AC component thereof having a reduced level of artifact signal therein.

2. The method of claim 1, wherein:

said first-noted acquiring step acquires red and infrared pulse oximetry signals; and

said second-noted acquiring step acquires electrocardiogram signals.

3. The method of claim 2, wherein the processing of the second physiological signal comprises processing electrocardiogram signals for determining a heart rate frequency value.

4. The method of claim 2, including a processing step comprising processing of the red and infrared pulse oximetry signals after being band pass filtered, to develop a measurement of blood oxygenation.

5. The method of claim 4, wherein said processing step processed the red and infrared pulse oximetry signals after being band pass filtered, to develop a measurement of pulse rate.

6. The method of claim 4, wherein the processing step includes processing AC and DC components of the red and infrared pulse oximetry signals in accordance with the following equation:

##EQU4## for developing said measurement of blood oxygenation.

7. The method of claim 4, including a filtering step comprising low pass filtering said red and infrared pulse oximetry signals in parallel with their band pass filtering, to develop DC components thereof.

8. The method of claim 7, wherein said processing step includes processing the AC and DC components of the red and infrared pulse oximetry signals in accordance with the following equation:

##EQU5## for developing said measurement of blood oxygenation.

9. The method of claim 8, wherein said processing step processes the red and infrared pulse oximetry signals after being band pass filtered, to develop a measurement of pulse rate.

10. The method of claim 8, wherein said processing step develops said DC components by determining the mean value of the red and infrared signals over a fixed interval of time.

11. Apparatus for reducing the level of artifact signal in an acquired physiological signal, comprising:

a first sensor arrangement for acquiring a first physiological signal;

a second sensor arrangement for acquiring a second physiological signal using an acquisition technique that is different and independent from the acquisition technique used to acquire the first physiological signal;

a processor responsive to the second physiological signal for determining a heart rate value therefrom; and

a bandpass filter responsive to said determined heart rate value for controllably bandpass filtering the first physiological signal and developing an AC component thereof having a reduced level of artifact signal therein.

12. The apparatus of claim 11, wherein:

said first sensor arrangement acquires red and infrared pulse oximetry signals; and

said second sensor arrangement acquires electrocardiogram signals.

13. The apparatus of claim 12, wherein said processor processes said electrocardiogram signal so as to determine a heart rate frequency value from said electrocardiogram signals.

14. The apparatus of claim 12, wherein said processor is responsive to the red and infrared pulse oximetry signals after they are band pass filtered, for developing a measurement of blood oxygenation.

15. The apparatus of claim 14, wherein said processor is responsive to the red and infrared pulse oximetry signals after they are band pass filtered, for developing a measurement of pulse rate.

16. The apparatus of claim 14, wherein said processor processes AC and DC components of the red and infrared pulse oximetry signals in accordance with the following equation:

##EQU6## for developing said measurement of blood oxygenation.

17. The apparatus of claim 14, further including a low pass filter for filtering said red and infrared pulse oximetry signals in parallel with their band pass filtering, to develop DC components thereof.

18. The apparatus of claim 17, wherein said processor processes AC and DC components of the red and infrared pulse oximetry signals in accordance with the following equation ##EQU7## for developing said measurement of blood oxygenation.

19. The apparatus of claim 18, wherein said processor is responsive to the red and infrared pulse oximetry signals after they are band pass filtered, for developing a measurement of pulse rate.

20. The apparatus of claim 18, wherein said processor develops said DC components by determining the mean value of the red and infrared signals over a fixed interval of time.

21. An oximeter for determining a blood oxygenation level of a patient, comprising:

an oximeter sensor arrangement coupled to the patient for acquiring a blood oxygenation signal having an undesirable artifact signal component;

an additional sensor arrangement coupled to the patient for acquiring an additional signal representative of a physiological condition of the patient using an acquisition technique that is independent of the acquisition technique used to acquire the blood oxygenation signal;

a processor responsive to the additional signal for determining a value therefrom representative of the heart rate of the patient; and

a filter responsive to said determined heart rate value for controllably filtering the blood oxygenation signal in response to changes in the value of the patient'"'"'s heart rate, for developing an AC component for the blood oxygenation signal which has a reduced level of said artifact signal therein.

22. The oximeter of claim 21, wherein said additional sensor arrangement acquires an electrocardiogram signal.

23. The oximeter of claim 21, wherein said filter comprises a bandpass filter having at least one of its filter characteristics controlled by said heart rate value.

24. The oximeter of claim 23, wherein said bandpass filter has its center frequency controlled by said heart rate value.

25. The oximeter of claim 23, wherein said processor is responsive to the blood oxygenation signal after it has been bandpass filtered, for developing a measurement of blood oxygenation of said patient.

26. The oximeter of claim 23, wherein said processor is responsive to the blood oxygenation signal after it has been bandpass filtered, for developing a measurement of pulse rate of said patient.

27. The oximeter of claim 25, wherein:

said first sensor arrangement acquires red and infrared pulse oximetry signals; and

,

said processor processes AC and DC components of the red and infrared pulse oximetry signals in accordance with the following equation;

##EQU8## for developing said measurement of blood oxygenation.

28. The oximeter of claim 27, further including a low pass filter for filtering said red and infrared pulse oximetry signals in parallel with their bandpass filtering, to develop DC components thereof.

29. The oximeter of claim 25, wherein said processor is responsive to the red and infrared signals over a fixed interval of time for determining the mean value of said signals as said DC components.