OPTICAL INSTRUMENT WITH AMBIENT LIGHT REMOVAL

• US 20130324811A1
• Filed: 05/31/2012
• Published: 12/05/2013
• Est. Priority Date: 05/31/2012
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Lisogurski, Daniel
• Granted Patent: US 9,220,409 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• CPC Class Codes: A61B 5/00 Measuring for diagnostic purposes radiation diagnosis A61B6/00; diagnosis by ultrasonic, sonic or infrasonic waves A61B8/00; Identification of persons
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• 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 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• 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 5/7203 for noise prevention, reduction or removal
• 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

Abstract

Processing circuitry may process a physiological signal such as a light signal attenuated by a subject. The physiological signal may include a desired component and an undesired component. A first filtering operation may be performed to remove at least a portion of the undesired component and a second filtering operation may be performed to reduce an undesired distortion introduced by the first filter. The transfer function of the second filter may be substantially the inverse of the transfer function of the first filter. One or more physiological parameters may be determined based on the filtered physiological signal.

Claims

1. A method of processing a physiological signal, the method comprising:

detecting a light signal attenuated by a subject, wherein the light signal comprises a first component corresponding to a desired component and a second component corresponding to an undesired component;

performing a first filtering operation based on the light signal to remove at least a portion of the undesired component using a first filter having a first transfer function to generate a first filtered signal; and

performing a second filtering operation based on the filtered signal using a second filter having a second transfer function to generate a second filtered signal, wherein the second transfer function is substantially an inverse of the first transfer function.

2. The method of claim 1, wherein the second transfer function includes at least one pole whose position is adjusted in order to stabilize the second filter.

3. The method of claim 1, wherein the first filtering operation introduces an overshoot or droop to the first filtered signal.

4. The method of claim 3, wherein the second filtering operation at least partially removes the overshoot or droop introduced by the first filtering operation.

5. The method of claim 1, wherein the undesired component comprises ambient light noise.

6. The method of claim 1, further comprising generating a photonic signal comprising at least one wavelength of light, wherein the desired component of the detected light signal corresponds to the photonic signal, wherein the photonic signal comprises a plurality of first segments and a plurality of second segments, wherein light is transmitted during the first segments and no light is transmitted during the second segments, and wherein the first segments and the second segments alternate.

7. The method of claim 1, wherein the first filter comprises an analog high pass filter.

8. The method of claim 1, wherein the second filter comprises a digital inverse high pass filter.

9. The method of claim 8, wherein the first filter comprises an analog high pass filter.

10. The method of claim 1, further comprising determining one or more of a pulse rate, a respiration rate, and a blood oxygen saturation of the subject based on the second filtered signal.

16. The system of claim 1, further comprising a light source configured to generate a photonic signal comprising at least one wavelength of light, wherein the desired component of the detected light signal corresponds to the photonic signal, wherein the photonic signal comprises a plurality of first segments and a plurality of second segments, wherein light is transmitted during the first segments and no light is transmitted during the second segments, and wherein the first segments and second segments alternate.

11. A system for processing a physiological signal, the system comprising:

a detector configured to receive a light signal attenuated by a subject, wherein the light signal comprises a first component corresponding to a desired component and a second component corresponding to an undesired component;

a first filter having a first transfer function, wherein the first filter is configured to perform a first filtering operation based on the light signal to remove at least a portion of the undesired component to generate a first filtered signal; and

a second filter having a second transfer function, wherein the second filter is configured to perform a second filtering operation based on the filtered signal to generate a second filtered signal, wherein the second transfer function is substantially an inverse of the first transfer function.

12. The system of claim 11, wherein the second transfer function includes at least one pole whose position is adjusted in order to stabilize the second filter.

13. The system of claim 11, wherein the first filter is configured to introduce an overshoot or droop to the first filtered signal.

14. The system of claim 13, wherein the second filter is configured to at least partially remove the overshoot or droop introduced by the first filter.

15. The system of claim 11, wherein the undesired component comprises ambient light noise.

17. The system of claim 11, wherein the first filter comprises an analog high pass filter.

18. The system of claim 11, wherein the second filter comprises a digital inverse high pass filter.

19. The system of claim 18, wherein the first filter comprises an analog high pass filter.

20. The system of claim 11, further comprising processing equipment configured to determine one or more of a pulse rate, a respiration rate, and a blood oxygen saturation of the subject based on the second filtered signal.

21. A method of processing a physiological signal, the method comprising:

detecting a light signal attenuated by a subject, wherein the light signal comprises a first component corresponding to a desired component and a second component corresponding to an undesired component;

performing a first filtering operation based on the light signal to remove at least a portion of the undesired component using a first filter to generate a first filtered signal, wherein the first filtering operation introduces a distortion to the first filtered signal; and

performing a second filtering operation based on the filtered signal to remove at least a portion of the distortion using a second filter to generate a second filtered signal.