Signal processing apparatus and method

• US 20040204637A1
• Filed: 05/04/2004
• Published: 10/14/2004
• 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 7,499,741 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 determining a blood parameter of pulsing blood, the method comprising:

receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood;

representing the first and second intensity signals mathematically in a manner which corresponds to graphically representing magnitudes of ones of the first intensity signals with magnitudes of ones of the second intensity signals on axes of a graph; and

determining blood oxygen saturation of the pulsing blood using the representation.

2. The method of claim 1, further comprising determining a pulse rate of the pulsing blood using the representation.

3. In a signal processor for processing first and second intensity signals generated by a light-sensitive detector that detects light of at least a first and second wavelength attenuated by body tissue carrying pulsing blood, a method comprising:

sampling at least red and infrared intensity signals over a period to obtain a first series of data points representing said red intensity signal over said period and a second series of data points representing said infrared intensity signal over said period;

transforming said first and second series of data points from time domain data to frequency domain data to obtain a first transformed series of points and a second transformed series of points, said first and second transformed series of points having at least magnitude component and an index;

utilizing the magnitude component to establish a relationship between the red and infrared signal for a plurality of data points along the index; and

determining a resulting blood oxygen saturation from the relationship.

4. The method of claim 3, further comprising determining a pulse rate using the relationship.

5. A method determining motion artifacts in the signals from a light-sensitive detector, the method comprising:

receiving first and second intensity signals from a light-sensitive detector which detects light of at least first and second wavelengths attenuated by body tissue carrying pulsing blood;

representing the first and second intensity signals mathematically in a manner which corresponds to diagramming magnitudes of ones of the first intensity signals with magnitudes of ones of the second intensity signals on axes of a graph; and

detecting motion artifacts in the first and second intensity signals using the representation.