Signal processing apparatus
First Claim
1. A method of calculating oxygen saturation from intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, comprising:
 sampling the intensity signals over a first time period;
performing a Fourier transform on the sampled intensity signals; and
calculating oxygen saturation by including at least a plurality of magnitudes for each of the Fourier transformed intensity signals for nonzero frequencies in the calculation for the first time period.
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Abstract
The present invention involves method and apparatus for analyzing two measured signals that are modeled as containing primary and secondary portions. Coefficients relate the two signals according to a model defined in accordance with the present invention. In one embodiment, the present invention involves utilizing a transformation which evaluates a plurality of possible signal coefficients in order to find appropriate coefficients. Alternatively, the present invention involves using statistical functions or Fourier transform and windowing techniques to determine the coefficients relating to two measured signals. Use of this invention is described in particular detail with respect to blood oximetry measurements.
1027 Citations
35 Claims

1. A method of calculating oxygen saturation from intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, comprising:

sampling the intensity signals over a first time period;
performing a Fourier transform on the sampled intensity signals; and
calculating oxygen saturation by including at least a plurality of magnitudes for each of the Fourier transformed intensity signals for nonzero frequencies in the calculation for the first time period.  View Dependent Claims (2, 3, 4, 5, 6)


7. A method of calculating oxygen saturation from intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, comprising:

sampling the intensity signals over time;
performing a Fourier transform on the sampled intensity signals; and
determining oxygen saturation from at least a plurality of magnitudes of the Fourier transformed intensity signals for nonzero frequencies, wherein the step of determining comprises generating a ratio of the Fourier transformed intensity signals for the plurality of magnitudes and selecting at least one peak of ratios, and wherein the selecting at least one peak comprises evaluating the cross correlation between the intensity signals from the first wavelength and the second wavelength.


8. A method of calculating oxygen saturation from intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood, comprising:

sampling the intensity signals over time;
performing a Fourier transform on the intensity signals; and
determining oxygen saturation from at least a plurality of magnitudes of the Fourier transformed intensity signals for nonzero frequencies, wherein the step of determining comprises averaging the oxygen saturation over time, and wherein the step of averaging comprises altering the averaging depending upon the level of motion noise in the intensity signals.


9. A pulse oximeter comprising:

a detector that generates intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood; and
a processor that samples the intensity signals over a first time, executes a Fourier transform on the sampled intensity signals, and that calculates oxygen saturation from at least a plurality of magnitudes for each of the Fourier transformed intensity signals for nonzero frequencies during the first time period.  View Dependent Claims (10, 11, 12, 13, 14)


15. A pulse oximeter comprising:

a detector that generates intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood; and
a processor that executes a Fourier transform on the intensity signals, and determines oxygen saturation from at least a plurality of magnitudes of the Fourier transformed intensity signals for nonzero frequencies, wherein the processor determines oxygen saturation by selecting at least one peak of ratios of the Fourier transformed intensity signals, and wherein the processor selects at least one peak by evaluating the cross correlation between the intensity signals from the first wavelength and the second wavelength.


16. A pulse oximeter comprising:

a detector that generates intensity signals resulting from light of first and second wavelengths attenuated by body tissue carrying pulsing blood; and
a processor that executes a Fourier transform on the intensity signals, and determines oxygen saturation from at least a plurality of magnitudes of the Fourier transformed intensity signals for nonzero frequencies, wherein the processor averages oxygen saturation over time, and wherein the processor varies its averaging depending upon the level of motion noise in the intensity signals.


17. A method of determining a physiological parameter of pulsing blood, the method comprising:

receiving at least first and second intensity signals from a lightsensitive detector which detects light of at least first and second wavelengths propagated through body tissue carrying pulsing blood;
transforming said first and second intensity signals to obtain frequency domain data indexed by frequency;
selecting a plurality of the frequency domain data corresponding to those nonzero frequencies where the frequency domain data exhibit similar properties; and
calculating a physiological parameter of the pulsing blood using at least two of the selected plurality of the frequency domain data.  View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25)


26. In a signal processor for processing first and second intensity signals generated by a lightsensitive detector that detects light of at least a first and second wavelength propagated through body tissue carrying pulsing blood, a method comprising:

sampling at least first and second intensity signals over a period to obtain a first series of data points representing said first intensity signal over said period and a second series of data points representing said second intensity signal over said period, wherein the first and second intensity signals substantially adhere to a signal model for blood constituent saturation and include a primary signal portion and a secondary signal portion;
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;
determining a plurality of ratios of magnitudes of ones of said first transformed series of points to ones of said second transformed series of points; and
calculating a resulting blood oxygen saturation using at least the plurality of ratios in the calculation.  View Dependent Claims (27)


28. A method of determining blood oxygen saturation, the method comprising:

receiving at least first and second intensity signals from a lightsensitive detector which detects light of at least first and second wavelengths propagated through body tissue carrying pulsing blood;
sampling the first and second intensity signals over a first time period;
transforming the sampled first and second intensity signals into first and second sets of spectral domain data; and
determining oxygen saturation of the pulsing blood based on more than one indication of the oxygen saturation from each of the first and second sets of spectral domain data for the first time period.  View Dependent Claims (29, 30, 31, 32, 33, 34)


35. In a signal processor for processing intensity signals generated by a lightsensitive detector that detects light of at least a first and second wavelength propagated through body tissue carrying pulsing blood, a method comprising:

sampling at least red and infrared intensity signals over a first time 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 a magnitude component and an index for the first time period;
utilizing the magnitude component to establish more than one indication of oxygen saturation for a plurality of data points along the index; and
determining a resulting blood oxygen saturation from the relationship.

1 Specification