SIGNAL DEMODULATION

• US 20120245441A1
• Filed: 06/04/2012
• Published: 09/27/2012
• Est. Priority Date: 12/13/2007
• Status: Abandoned Application

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett LLC (Medtronic Plc)
• Inventors: Petersen, Ethan
• Application Number:
  US13/488,072
• Publication Number:
  US 20120245441A1
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/02028 Determining haemodynamic parameters not otherwise provided for, e.g. cardiac contractility or left ventricular ejection fraction
• 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 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

A method for processing an analog composite signal in a system has the steps of receiving a composite signal with at least one first signal component and at least one interfering signal component; filtering the composite signal with a filter having a transfer function H(s); sampling the filtered composite signal in periodic intervals wherein each periodic interval has n samples; forming a matrix equation representing the composite signal wherein the matrix equation has a signal vector with the at least first one signal component and the at least one interfering signal component and a matrix comprising weighted coefficients; solving the matrix equation to determine the at least one signal component; outputting the at least one signal component.

Claims

1. A system, comprising:

a filter configured to receive a signal from a physiological sensor, wherein the signal comprises a first signal component and a second signal component comprising an interference component, and wherein the filter is configured to output a filtered signal;

an analog-to-digital converter configured to receive the filtered signal and sample the filtered signal in periodic intervals to generate a sampled filtered signal, wherein each periodic interval comprises n samples; and

a processor configured to;

receive the sampled filtered signal;

solve a matrix equation representing the sampled filtered signal for the first signal component, wherein the matrix equation comprises a signal vector comprising the first and second components and a matrix comprising weighted coefficients; and

determine a physiological parameter based on the first signal component and not the second signal component.

2. The system of claim 1, wherein the processor is configured to determine the interference component by a linear approximation between a first and last sample of each periodic interval.

3. The system of claim 1, wherein the filter comprises a variable filter and wherein the processor is configured to determine an inverse of the matrix of coefficients during a start-up phase of the system

4. The system of claim 1, wherein the filter comprises a constant filter and wherein the processor is configured to determine an inverse of matrix of coefficients.

5. The system of claim 1, wherein the filter comprises an adaptive filter and wherein the processor is configured to determine an inverse of the matrix of coefficients after each adaptation of the adaptive filter.

6. The system of claim 1, wherein the physiological sensor comprises a pulse oximetry sensor.

7. The system of claim 1, wherein the second signal component comprises an ambient light signal component.

8. The system of claim 7, wherein the ambient light signal component is approximated by a linear approximation between a first and last sample of each periodic interval.

9. The system of claim 1, wherein the second signal component comprises cable transient components.

10. The system of claim 9, wherein the weighted coefficients of the matrix equation for the cable transients are determined by a transfer function of the filter and a sample position within a periodic interval

11. The system of claim 1, wherein the first signal component comprises a red signal component.

12. The system of claim 1, wherein the first signal component comprises an infrared signal component and a red signal component.

13. The system of claim 1, wherein the red signal component and the IR signal component are timely separated within each periodic interval and the red signal component and the IR signal component each comprise a predetermined signal length having an on and off transient.

14. A method, comprising:

receiving a composite signal comprising a red component, an infrared component, and at least one interfering signal component;

filtering the composite signal with a filter having a transfer function H(s);

sampling the filtered composite signal with an analog to digital converter in periodic intervals wherein each periodic interval comprises n samples; and

using a processor;

solving a matrix equation representing the composite signal for the red component and the infrared component, wherein the matrix equation comprises a signal vector comprising the red component, the infrared component, and the at least one interfering signal component and a matrix comprising weighted coefficients, wherein weighted coefficients for the at least one interfering signal component are based on an impulse response and a magnitude of an impulse;

generating an output based on the red component and the infrared component.

15. The method of claim 14, wherein the red component and the infrared component are represented by an impulse response at a periodic interval multiplied by a measured current.

16. The method of claim 14, wherein the interfering signal component comprises an ambient light signal component and cable transients.

17. The method of claim 16, wherein the weighted coefficients for the cable transients are determined by the transfer function and a sample position within a periodic interval.

18. A system, comprising:

a sensor comprising one or more light emitters and a detector configured to detect light emitted by the one or more light emitter and generate a signal, wherein the signal comprises a primary signal component and at least one of an ambient light component or a cable cross-talk component;

a patient monitor comprising;

a filter configured to receive the signal and outputting a filtered signal;

an analog-to-digital converter configured to receive the filtered signal and sample the filtered composite signal in periodic intervals wherein each periodic interval comprises n samples;

a signal processor configured to;

receive the sampled filtered signal;

solve a matrix equation for the primary signal component, wherein the matrix equation comprises a signal vector comprising the primary signal component and at least one of the ambient signal component or the cable cross-talk component and a matrix comprising weighted coefficients; and

determine a physiological parameter based at least in part on the primary signal component.

19. The system of claim 18, wherein the at least one of an ambient light component or a cable cross-talk component is approximated by a linear approximation between a first and last sample of each periodic interval.

20. The system of claim 18, wherein n is determined based on an accuracy of the physiological parameter.