Method and apparatus for reducing coupling between signals in a measurement system

• US 9,801,588 B2
• Filed: 07/14/2015
• Issued: 10/31/2017
• Est. Priority Date: 07/08/2003
• Status: Expired due to Term

• Current Assignee: Cercacor Laboratories
• Original Assignee: Cercacor Laboratories
• Inventors: Weber, Walter M., Al-Ali, Ammar
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US14/799,357
• Publication Number:
  US 20160007930A1
• Time in Patent Office: 840 Days
• CPC Class Codes: A61B 2562/0238 Optical sensor arrangements for performing transmission measurements on body tissue
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• 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 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• 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

Abstract

A method and an apparatus for separating a composite signal into a plurality of signals is described. A signal processor receives a composite signal and separates a composite signal in to separate output signals. Pre-demodulation signal values are used to adjust the demodulation scheme.

Claims

1. A system which measures one or more physiological characteristics of a living subject non-invasively by measuring pulsing light of two or more wavelengths after attenuation by body tissue, the system comprising:

at least one emitter configured to emit light of at least two or more different wavelengths using a modulation scheme that cycles the at least two or more different wavelengths, the at least one emitter positioned to emit light in the direction of a living subject;

at least one detector configured to detect the light of the at least two or more different wavelengths emitted from the at least one emitter after the light has been attenuated by tissue of the living subject, the detector further configured to generate a detector signal representative of the emitted light;

a demodulation system configured to demodulate the detector signal, the demodulation system comprising an optimizing demodulator configured to reduce crosstalk by calculating updated coefficients that minimize a predetermined error using baseline coefficients,

wherein the demodulation system is configured to use the updated coefficients to determine a plurality of demodulation functions used to demodulate the detector signal.

2. The system of claim 1, the demodulation system is further configured to optimize the demodulation based on previously demodulated signal values.

3. The system of claim 2, wherein the previously demodulated signal values comprises a plurality of demodulated signal values corresponding respectively to the at least two or more different wavelengths.

4. The system of claim 3, wherein each of the plurality of demodulated signal values is determined using a demodulation function.

5. The system of claim 1, wherein the demodulation system is further configured to optimize during an initial calibration period.

6. The system of claim 5, wherein the demodulation system is further configured to optimize during periodic calibration periods during measurement.

7. The system of claim 1, wherein at least one demodulation function is used for each of the at least two or more different wavelengths.

8. A method of demodulating a composite signal generated by applying at least first and second periodic pulses of electromagnetic energy to a system having a physiological parameter to be measured and by non-invasively receiving signals responsive to said electromagnetic energy after attenuation by body tissue of a living subject, said signals received as a composite signal having at least first and second components responsive to said at least first and second pulses respectively, said method comprising:

receiving, at one or more signal processors, a composite signal responsive to electromagnetic energy of at least first and second periodic pulses of electromagnetic energy after attenuation by body tissue;

applying, using the one or more signal processors, a first demodulation scheme to said composite signal to generate at least a first demodulated signal; and

automatically optimizing, using an optimizing demodulator to reduce crosstalk, the first demodulation scheme by determining a plurality of updated coefficients that minimizes a predetermined error using baseline coefficients, the plurality of updated coefficients used to determine a plurality of demodulation functions which are used to demodulate the composite signal.

9. The method of claim 8, wherein the optimizing reduces crosstalk.

10. The method of claim 9, wherein the optimizing occurs continuously.

11. The method of claim 9, wherein the optimizing occurs interspersed with measurements.

12. The method of claim 8, further comprising applying a second demodulation scheme to said composite signal to generate a second demodulated signal and optimizing the second demodulation scheme based at least in part on the second demodulated signal.

13. The method of claim 12, wherein said signal processor is further configured to optimize at least one of the first and second demodulation schemes in the absence of at least one of the first and second periodic pulses of electromagnetic energy.

14. The method of claim 12, wherein said signal processor is further configured to optimize at least one of the first and second demodulation schemes based on the demodulated signals in order to further reduce crosstalk interspersed with measurements.

15. A system for demodulating a composite signal generated by applying at least first and second periodic pulses of electromagnetic energy to a system having a physiological parameter to be measured and by non-invasively receiving signals responsive to said electromagnetic energy after attenuation by body tissue of a living subject, said signals received as a composite signal having at least first and second components responsive to said at least first and second pulses respectively, said system comprising:

means for receiving a composite signal responsive to electromagnetic energy of at least first and second periodic pulses of electromagnetic energy after attenuation by body tissue;

means for applying a first demodulation scheme to said composite signal to generate at least a first demodulated signal; and

means for automatically optimizing the first demodulation scheme by determining a plurality of updated coefficients that minimizes a predetermined error using baseline coefficients, the plurality of updated coefficients used to determine a plurality of demodulation functions which are used to demodulated the composite signal.

16. The system of claim 15, wherein the optimizing reduces crosstalk.

17. The system of claim 15, further comprising applying a second demodulation scheme to said composite signal to generate a second demodulated signal and optimizing the second demodulation scheme based at least in part on the second demodulated signal.

18. The system of claim 17, wherein said signal processor is further configured to optimize at least one of the first and second demodulation schemes in the absence of at least one of the first and second periodic pulses of electromagnetic energy.