Method and apparatus for determining physiological characteristics

• US 20010037059A1
• Filed: 03/23/2001
• Published: 11/01/2001
• Est. Priority Date: 03/29/2000
• Status: Active Grant

• Current Assignee: Kinderlife Instruments, Inc., Woolsthorpe Technologies Corporation
• Original Assignee: Woolsthorpe Technologies Corporation
• Inventors: Mills, Alex K., Stone, Robert T.
• Granted Patent: US 6,594,511 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 5/0006 ECG or EEG signals
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• 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

Abstract

A method for determining physiological characteristics comprising the steps of (a) acquiring a first blood oxygen signal from a subject, the blood oxygen signal having an undesirable artifact signal component; (b) acquiring an additional physiological signal having a heart rate component using an acquisition technique that is different and independent from the first acquiring step; (c) processing the first blood oxygen signal and the physiological signal to provide a first waveform having a reduced level of the artifact signal component therein; (d) processing the first waveform and the physiological signal to provide a reference waveform; and (e) processing the reference waveform and the physiological signal to provide a second blood oxygen saturation signal corresponding to the blood oxygen saturation level of said subject.

Claims

1. A method for determining the blood oxygen saturation level of a subject, comprising the steps of:

acquiring a first blood oxygen signal from the subject, said blood oxygen signal having an undesirable artifact signal component;

acquiring an additional physiological signal having a heart rate component, said second acquiring step using an acquisition technique that is different and independent from said first acquiring step;

processing said first blood oxygen signal and said physiological signal to provide a first waveform signal having a reduced level of said artifact signal component therein;

processing said first waveform and said physiological signal to provide a reference waveform; and

processing said reference waveform and said physiological signal to provide a second blood oxygen signal corresponding to the blood oxygen saturation level of said subject.

2. The method of

claim 1

, wherein said first waveform includes a plurality of quasi-stationary heartbeat spaces.

3. The method of

claim 2

, wherein said heart rate component comprises plurality of first r-wave signals corresponding to first r-wave events.

4. The method of

claim 3

, wherein said second waveform includes said plurality of quasi-stationary heartbeat spaces and a plurality of second r-wave events substantially corresponding to said first r-wave events.

5. 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.

6. The method of

claim 1

, wherein said first-noted processing step comprises synchronous averaging.

7. The method of

claim 1

, wherein said first-noted processing step comprises binomial averaging.

8. The method of

claim 1

, wherein said first-noted processing step comprises ranked order averaging.

9. The method of

claim 1

, wherein said second-noted processing step comprises correlation canceling.

10. A method for determining the blood oxygen saturation level of a subject, said subject having a tissue region and a heart, comprising;

passing first and second lights through said subject'"'"'s tissue region, said first light being substantially in a red light range and said second light being substantially in an infrared light;

detecting the light absorbed by said tissue region and providing a first signal corresponding to said absorbed light;

processing said first signal to provide a second signal corresponding to at least one red light signal component and a third signal corresponding to at least one infrared light signal component, each of said first and second signals including a noise component;

detecting the electrical potential generated by said subject'"'"'s heart and providing an ECG signal corresponding to said electrical potential, said ECG signal including a plurality of first r-wave components corresponding to first r-wave events;

processing said first, second and ECG signals to provide a first waveform, said first waveform having a reduced level of said noise component, said first waveform including a plurality of quasi-stationary heartbeat spaces;

processing said first waveform and said ECG signal to provide a second waveform, said second waveform including said plurality of quasi-stationary heartbeat spaces and a plurality of second r-wave events substantially corresponding to said first r-wave events; and

processing said third signal and said second waveform to provide a fourth signal, said fourth signal substantially corresponding to the blood oxygen saturation level of said subject.

11. The method of

claim 10

, wherein said first-noted processing step comprises synchronous demodulation.

12. The method of

claim 10

, wherein a wireless ECG monitor is used to detect said electrical potential.

13. The method of

claim 10

, wherein said first-noted processing step comprises synchronous averaging.

14. The method of

claim 10

, wherein said first-noted processing step comprises binomial averaging.

15. The method of

claim 10

, wherein said first-noted processing step comprises ranked order averaging.

16. The method of

claim 10

, wherein said third-noted processing step comprises correlation canceling.

17. An apparatus for determining the blood oxygen saturation level of a subject, comprising:

an oximeter sensor arrangement coupled to said subject for acquiring a first blood oxygen signal, said first blood oxygen signal having an artifact component;

an ECG detector coupled to said subject for acquiring an ECG signal, said ECG signal including a plurality of first r-wave components substantially corresponding to first r-wave events;

first processing means for processing said first blood oxygen signal and said ECG signal to provide a first waveform, said first waveform having a reduced level of said artifact component, said first waveform including a plurality of quasi-stationary heartbeat spaces;

second processing means for processing said first waveform and said ECG signal to provide a second waveform, said second waveform including said plurality of quasi-stationary heartbeat spaces and a plurality of second r-wave events substantially corresponding to said first r-wave events; and

third processing means for processing said first blood oxygen signal and said second waveform, said third processing means being adapted to provide a second blood oxygen signal substantially corresponding to the blood oxygen saturation level of said subject.

18. The apparatus of

claim 17

, wherein said third processing means comprises a correlation canceler.

19. The apparatus of

claim 17

, wherein said apparatus includes memory means adapted to record said first and second blood oxygen signals, said ECG signal and said first and second waveforms.

20. An apparatus for determining the blood oxygen saturation level of subject, said subject having a tissue region and a heart, comprising;

a plurality of light means for passing first and second lights through said subject'"'"'s tissue region, said first light being substantially in a red light range and said second light being substantially in an infrared range;

a photo detector adapted to detect the light absorbed by said tissue region, said photo detector being further adapted to provide at least a first signal corresponding to said absorbed light;

a demodulator in communication with said photo detector, said demodulator being adapted to provide a second signal corresponding to at least one red light signal and a third signal corresponding to at least one infrared signal in response to said first signal, each of said second and third signals including a noise component;

an ECG detector adapted to detect the electrical potential generated by said subject'"'"'s heart, said ECG detector being further adapted to provide an ECG signal corresponding to said electrical potential, said ECG signal including a plurality of first r-wave components corresponding to first r-wave events;

a data acquisition device in communication with said demodulator and ECG detector, said data acquisition device including first processing means for processing said second, third and ECG signals to provide a first waveform, said first waveform having a reduced level of said noise component, said first waveform including a plurality of quasi-stationary heartbeat spaces, and second processing means for processing said first waveform and said ECG signal to provide a second waveform, said second waveform including said plurality of quasi-stationary heartbeat spaces and a plurality of second r-wave events substantially corresponding to said first r-wave events; and

a correlation canceler for processing said second waveform and said third signal to provide a S_pO₂ signal, said S_pO₂ signal substantially corresponding to the blood oxygen saturation level of said subject.