Signal component processor

• US 20030055325A1
• Filed: 06/26/2002
• Published: 03/20/2003
• Est. Priority Date: 06/29/2001
• Status: Active Grant

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Cazzoli, Lorenzo, Weber, Walter M., Al-Ali, Ammar
• Granted Patent: US 6,850,787 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• 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 5/02433 for infrared radiation
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• 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 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence

Abstract

A signal processor generates basis functions and identifies at least one basis function component of a sensor signal in order to calculate a physiological measurement. The signal processor is advantageously applied to pulse oximetry so as to directly calculate oxygen saturation and so as to calculate a robust oxygen saturation measurement. In particular, a signal component transform may be calculated within a window around a derived pulse rate estimate. A signal component transform may also utilize sinusoidal basis functions, and an optimization of a signal component transform may occur at a particular frequency or a set of frequencies. A sinusoidal waveform or waveforms at that frequency or set of frequencies is generated to select associated red and infrared components of the sensor signal, and an oxygen saturation is calculated from a magnitude ratio of these components.

Claims

1. A signal processor comprising:

a physiological signal;

a basis function index determined from said signal;

a basis function waveform generated according to said index;

a component derived from said sensor signal and said waveform; and

a physiological measurement responsive to said component.

2. The signal processor according to claim 1 wherein said component is responsive to the inner product of said sensor signal and said waveform.

3. The signal processor according to claim 1 wherein:

said index is a frequency; and

said waveform is a sinusoid at said frequency.

4. The signal processor according to claim 3 further comprising a pulse rate estimate derived from said signal wherein said frequency is selected from a window including said pulse rate estimate.

5. The signal processor according to claim 3 wherein said physiological measurement is an oxygen saturation value responsive to a magnitude of said component.

6. A signal processor comprising:

a signal input;

a basis function indicator derived from said signal input;

a plurality of basis functions generated according to said indicator;

a plurality of characteristics of said signal input corresponding to said basis functions; and

an optimization of said characteristics so as to identify at least one of said basis functions.

7. The signal processor according to claim 6 wherein said indicator is a pulse rate estimate and said processor further comprises:

a window configured to include said pulse rate estimate; and

a plurality of frequencies selected from within said window.

8. The signal processor according to claim 6 wherein said characteristic comprises:

a plurality of signal remainders corresponding to said basis functions; and

a plurality of magnitudes of said signal remainders;

and wherein said optimization comprises a minima of said magnitudes.

9. The signal processor according to claim 7 wherein said characteristic comprises:

a plurality of signal components corresponding to said basis functions; and

a plurality of magnitudes of said components;

and wherein said optimization comprises a maxima of said magnitudes.

10. A signal processing method comprising the steps of:

receiving a sensor signal;

calculating an estimated pulse rate;

determining an optimization of said sensor signal proximate said estimated pulse rate;

defining a frequency corresponding to said optimization; and

outputting a physiological measurement responsive to a component of said sensor signal at said frequency.

11. The signal processing method according to claim 10 wherein said determining step comprises the substeps of:

transforming said sensor signal to a frequency spectrum encompassing said estimated pulse rate; and

detecting an extrema of said spectrum indicative of said frequency.

12. The signal processing method according to claim 11 wherein said transforming step comprises the substeps of:

defining a window including said estimated pulse rate;

defining a plurality of selected frequencies within said window;

canceling said selected frequencies, individually, from said sensor signal to generate a plurality of remainder signals; and

calculating a plurality of magnitudes of said remainder signals.

13. The signal processing method according to claim 12 wherein said detecting step comprises the substep of locating a minima of said magnitudes.

14. The signal processing method according to claim 10 wherein said outputting step comprises the substeps of:

inputting a red (RD) portion and an infrared (IR) portion of said sensor signal;

deriving a RD component of said RD portion and an IR component of said IR portion corresponding to said frequency; and

computing an oxygen saturation based upon a magnitude ratio of said RD component and said IR component.

15. The signal processing method according to claim 14 wherein said deriving step comprises the substeps of:

generating a sinusoidal waveform at said frequency; and

selecting said RD component and said IR component utilizing said waveform.

16. The signal processing method according to claim 15 wherein said selecting step comprises the substep of calculating the inner product between said waveform and said RD portion and the inner product between said waveform and said IR portion.

17. The signal processing method according to claim 16 wherein said selecting step comprises the substeps of:

canceling said waveform from said RD portion and said IR portion, leaving a RD remainder and an IR remainder; and

subtracting said RD remainder from said RD portion and said IR remainder from said IR portion.

18. A signal processor comprising:

a first calculator means for deriving an optimization frequency from a pulse rate estimate and a sensor signal; and

a second calculator means for deriving a physiological measurement responsive to a sensor signal component at said frequency.

19. The signal processor according to claim 18 wherein said first calculator means comprises:

a signal component transform means for determining a plurality of signal values corresponding to a plurality of selected frequencies within a window including said pulse rate estimate; and

a detection means for determining a particular one of said selected frequencies corresponding to an optimization of said sensor signal.

20. The signal processor according to claim 19 wherein said second calculator means comprises:

a waveform means for generating a sinusoidal signal at said frequency;

a frequency selection means for determining a component of said sensor signal from said sinusoidal signal; and

a calculator means for deriving a ratio responsive to said component.