Method and apparatus for estimating a physiological parameter
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Abstract
A method and apparatus for reducing the effects of noise on a system for measuring physiological parameters, such as, for example, a pulse oximeter. The method and apparatus of the invention take into account the physical limitations on various physiological parameters being monitored when weighting and averaging a series of measurements. Varying weights are assigned different measurements, measurements are rejected, and the averaging period is adjusted according to the reliability of the measurements. Similarly, calculated values derived from analyzing the measurements are also assigned varying weights and averaged over adjustable periods. More specifically, a general class of filters such as, for example, Kalman filters, is employed in processing the measurements and calculated values. The filters use mathematical models which describe how the physiological parameters change in time, and how these parameters relate to measurement in a noisy environment. The filters adaptively modify a set of averaging weights to optimally estimate the physiological parameters.
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Citations
48 Claims
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1-17. -17. (canceled)
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18. A physiological monitor for monitoring a pulserate of a living being, said monitor comprising a signal processor configured to:
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transform a time-domain plethysmograph dataset into a spectral-domain dataset;
identify three or more spectral peaks at non-zero frequencies in said spectral domain dataset; and
sort said three or more spectral peaks according to one or more rules into one or more spectral peaks corresponding to a fundamental frequency and one or more harmonics of said fundamental frequency, and estimate a pulserate from said fundamental frequency and said one or more harmonics. - View Dependent Claims (19)
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20. In a physiological monitor for measuring a pulserate of a living being, said monitor having a detector producing a detector output waveform corresponding to a time-domain plethysmograph waveform, a method comprising:
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transforming a time-domain plethysmograph waveform into a spectral domain waveform;
identifying three or more spectral peaks at non-zero frequencies in said spectral domain waveform;
classifying said three or more spectral peaks into a first group comprising one or more spectral peaks corresponding to a fundamental frequency and a second group comprising one or more harmonics of said fundamental frequency; and
estimating a pulserate from at least said first group.
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21. In a physiological monitor for measuring a pulserate of a living being, said monitor having a detector producing a detector output waveform corresponding to a time-domain plethysmograph waveform, a method comprising:
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transforming a time-domain plethysmograph waveform into a spectral domain waveform;
identifying a plurality of spectral peaks in said spectral domain waveform;
classifying said plurality of spectral peaks into a first group comprising one or more spectral peaks corresponding to a fundamental frequency and a second group comprising one or more harmonics of said fundamental frequency; and
estimating a pulserate from at least said first group, wherein said plurality of spectral peaks are classified according to ratios.
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22. In a physiological monitor for measuring a pulserate of a living being, said monitor having a detector producing a detector output waveform corresponding to a time-domain plethysmograph waveform, a method comprising:
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transforming a time-domain plethysmograph waveform into a spectral domain waveform;
identifying a plurality of spectral peaks in said spectral domain waveform;
classifying said plurality of spectral peaks into a first group comprising one or more spectral peaks corresponding to a fundamental frequency and a second group comprising one or more harmonics of said fundamental frequency, and estimating a pulserate from at least said first group, wherein said spectral domain waveform comprises a first component corresponding to a first frequency of light passed through a portion of said living being, and a second component corresponding to a second frequency of light passed through a portion of said living being, and wherein said plurality of spectral peaks are classified at least in part according to one or more ratios, said one or more ratios corresponding to ratios of at least one or more portions of said first component with at least one or more portions of said second component - View Dependent Claims (23)
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24. An apparatus for monitoring physiological parameters of a living organism having a pulserate, said apparatus comprising:
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means for producing a time-domain plethysmograph waveform;
means for transforming said time-domain plethysmograph waveform into a spectral domain waveform having a fundamental spectral peak corresponding to said pulserate and two or more ancillary spectral peaks, and classifying said fundamental spectral peak and said ancillary spectral peaks to estimate said pulserate.
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25. A physiological monitor for monitoring a living being having a pulserate, said monitor comprising a signal processor configured to:
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transform a time-domain plethysmograph dataset into a spectral-domain dataset;
classify spectral lines in said spectral-domain dataset into a group of spectral values corresponding to a fundamental and oft two or more harmonics of said fundamental; and
estimate a pulserate from said group of spectral values according to one or more rules.
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26. A physiological monitor comprising a signal processor configured to:
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transform a time-domain plethysmograph dataset into a spectral-domain dataset;
classify at least three spectral lines in said spectral-domain dataset into a group of spectral values corresponding to a first group of one or more spectral lines and at least one second group of spectral lines, said second group of spectral lines comprising at least one harmonic of said first group; and
estimate said pulserate from said first group and at least one of said second group.
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27. In a physiological monitor to monitor pulserate, said monitor having a detector responsive to physiological properties related to light passed through a living being, a method comprising:
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transforming a first time-domain plethysmograph waveform into a first spectral domain waveform, said first time-domain plethysmograph waveform corresponding to a first frequency of light passed through a living being;
transforming a second time-domain plethysmograph waveform into a second spectral domain waveform, said second time-domain plethysmograph waveform corresponding to a second frequency of light passed through said living being;
classify one or more spectral values obtained from a ratio of said first spectral domain waveform and said second spectral domain waveform into a series of spectral peaks comprising a fundamental peak and at least one harmonics of said fundamental peak; and
estimating said pulserate from said series of spectral peaks. - View Dependent Claims (28, 29, 30)
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31. In a physiological monitor attached to a living organism having a pulserate, said monitor having a detector responsive to physiological properties related to pulserate, a method comprising the steps of:
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transforming a time-domain plethysmograph waveform into a spectral domain waveform;
classifying one or more spectral values obtained from said spectral domain waveform; and
using results from a center of mass calculation of at least a portion of said spectral values to estimate said pulserate.
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32. A physiological monitor for monitoring comprising a signal processor configured to:
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transform a time-domain representation of a plethysmograph waveform into a spectral-domain representation of said plethysmograph waveform, said spectral-domain representation having at least three spectral peaks at non-zero frequencies;
select a selected portion of said spectral-domain representation based on one or more rules relating to characteristics of spectral lines in said selected portion and one or more harmonics of spectral lines in said selected portion; and
estimate said pulserate from said selected portion of said spectral-domain representation.
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33. A physiological monitor comprising a signal processor configured to:
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transform a first time-domain representation of a first plethysmograph waveform corresponding to a first optical measurement wavelength into a spectral domain to produce a first spectral-domain representation representing said first plethysmograph waveform and transform a second time-domain representation of a second plethysmograph waveform corresponding to a second optical measurement wavelength into said spectral domain to produce a second spectral-domain representation representing said second plethysmograph waveform;
classify spectral data from said first spectral-domain representation and said second spectral-domain representation at least in part according to a ratio of at least a portion of said first spectral-domain representation and at least a portion of said second spectral-domain representation to identify a series of spectral peaks corresponding to a fundamental and at least one or more harmonics of said fundamental; and
estimate said pulserate from said series of spectral peaks as a function of a center of mass type of calculation of at least a portion of said series of spectral peaks.
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34. A physiological monitor comprising a signal processor configured to:
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transform a first time-domain representation of a first plethysmograph waveform corresponding to a first optical measurement wavelength into a spectral domain to produce a first spectral-domain representation representing said first plethysmograph waveform and a second time-domain representation of a second plethysmograph waveform corresponding to a second optical measurement wavelength into said spectral domain to produce a second spectral-domain representation representing said second plethysmograph waveform;
classify spectral data from said first spectral-domain representation and said second spectral-domain representation at least in part according to a ratio of at least a portion of said first spectral-domain representation and at least a portion of said second spectral-domain representation to identify a series of spectral peaks corresponding to a fundamental and at least one or more additional spectral peaks at frequencies higher than said fundamental; and
compute an estimate of said pulserate from said series of spectral peaks according to said fundamental and at least one of said one or more additional spectral peaks. - View Dependent Claims (35, 36, 37, 38, 39)
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40. A physiological monitor for monitoring a pulse rate of a living being, said monitor comprising a signal processor configured to:
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perform a Fast Fourier Transform on a time-domain plethysmograph waveform, to obtain a power spectrum having multiple peaks corresponding to a fundamental frequency and one or more harmonics of said fundamental frequency;
apply one or more rules to said multiple peaks to identify a fundamental frequency and the one or more harmonics of said fundamental frequency; and
estimate a pulse rate from said fundamental frequency and said one or more harmonics. - View Dependent Claims (41)
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42. A physiological monitor comprising a signal processor configured to:
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perform a transformation on a time-domain plethysmograph waveform, to obtain a power spectrum having multiple peaks corresponding to at least three harmonics of a pulse rate of a living being, said multiple peaks corresponding to a fundamental frequency and one or more harmonics of said fundamental frequency;
classify said fundamental frequency and said one or more harmonics of said fundamental frequency by applying one or more rules to said multiple peaks; and
estimate a pulse rate from said fundamental frequency and said one or more harmonics. - View Dependent Claims (43)
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44. A physiological monitor for monitoring a pulse rate of a living being, said monitor comprising a signal processor configured to:
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perform a transformation on a time-domain plethysmograph waveform, to obtain a power spectrum having multiple peaks corresponding to a fundamental frequency and one or more harmonics of said fundamental frequency;
perform a calculation of a validity metric for said multiple peaks, wherein said validity metric is based in part on the strength of said fundamental frequency and said one or more harmonics; and
estimate a pulse rate using said calculation of said validity metric.
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45. A physiological monitor for monitoring a patient'"'"'s pulse rate using time-domain data corresponding to two wavelengths of electromagnetic energy transmitted through the tissue of the patient, said monitor comprising a signal processor configured to:
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track the pulse rate in the data using an adaptive comb filter;
periodically calculate a frequency power spectrum of one of said wavelengths;
calculate an autocorrelation function of said wavelengths;
identify peaks in said frequency power spectrum and peaks in said autocorrelation function; and
estimate the pulse rate from said peaks in said frequency power spectrum and said peaks in said autocorrelation function using one or more rules. - View Dependent Claims (46, 47, 48)
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Specification