Signal processing apparatus and method

• US 20060200016A1
• Filed: 05/03/2006
• Published: 09/07/2006
• Est. Priority Date: 04/14/1997
• Status: Active Grant

• Current Assignee: Mohamed K. Diab, Rex J. Mccarthy
• Original Assignee: Mohamed K. Diab, Rex J. Mccarthy
• Inventors: Diab, Mohamed K., McCarthy, Rex
• Granted Patent: US 7,489,958 B2
• Time in Patent Office: Days
• US Class Current: 600/324
• 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 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/02433 for infrared radiation
• 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 5/6826 Finger
• 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 5/7225 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
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/742 using visual displays A61B5/339 takes precedence
• CPC Class Codes: G06F 2218/04 Denoising

Abstract

A method and an apparatus to analyze two measured signals that are modeled as containing desired and undesired portions such as noise, FM and AM modulation. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, a transformation is used to evaluate a ratio of the two measured signals in order to find appropriate coefficients. The measured signals are then fed into a signal scrubber which uses the coefficients to remove the unwanted portions. The signal scrubbing is performed in either the time domain or in the frequency domain. The method and apparatus are particularly advantageous to blood oximetry and pulserate measurements. In another embodiment, an estimate of the pulserate is obtained by applying a set of rules to a spectral transform of the scrubbed signal. In another embodiment, an estimate of the pulserate is obtained by transforming the scrubbed signal from a first spectral domain into a second spectral domain. The pulserate is found by identifying the largest spectral peak in the second spectral domain.

Claims

1. A method of validating a blood parameter measurement of pulsing blood, the method comprising:

receiving a first intensity signal from a light-sensitive detector which detects light of a first wavelength attenuated by body tissue carrying pulsing blood;

receiving a second intensity signal from the light-sensitive detector which detects light of a second wavelength attenuated by body tissue carrying pulsing blood;

determining a plurality of points representing magnitudes of the first intensity signal as a function of magnitudes of the second intensity signal over a period of time;

determining a locus of points that fall within an expected distribution of the points related to normal measurement conditions of the blood parameter; and

determining from the locus of points whether the first and second intensity signals represent desired physiological data.

2. The method of claim 1, wherein the blood parameter is oxygen saturation.

3. The method of claim 1, wherein the blood parameter is pulse rate.

4. The method of claim 1, further comprising detecting motion artifacts in the first and second intensity signals using the locus of points.