Signal processing apparatus and method
DCFirst Claim
1. In a signal processor, a method of analyzing a measurement condition of 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;
electronically transforming the first and second intensity signals into the frequency domain;
electronically representing the first and second intensity signals mathematically in a manner which corresponds to graphically representing values of the first intensity signal with values of the second intensity signal on axes of a graph, wherein the mathematical representation comprises a plurality of ratios of values of the transformed first intensity signal to values of the transformed second intensity signal;
electronically determining, based at least in part upon the plurality of ratios, one or more values of the transformed first and second intensity signals at nonzero frequencies that correspond to patient motion-induced noise and one or more values that correspond to physiological information;
electronically calculating a blood parameter estimate using the one or more values that correspond to physiological information; and
electronically determining, using one or more physiologically-based rules, a confidence level representing a degree of confidence in the accuracy of the blood parameter estimate.
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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.
991 Citations
31 Claims
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1. In a signal processor, a method of analyzing a measurement condition of a blood parameter of pulsing blood, the method comprising:
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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; electronically transforming the first and second intensity signals into the frequency domain; electronically representing the first and second intensity signals mathematically in a manner which corresponds to graphically representing values of the first intensity signal with values of the second intensity signal on axes of a graph, wherein the mathematical representation comprises a plurality of ratios of values of the transformed first intensity signal to values of the transformed second intensity signal; electronically determining, based at least in part upon the plurality of ratios, one or more values of the transformed first and second intensity signals at nonzero frequencies that correspond to patient motion-induced noise and one or more values that correspond to physiological information; electronically calculating a blood parameter estimate using the one or more values that correspond to physiological information; and electronically determining, using one or more physiologically-based rules, a confidence level representing a degree of confidence in the accuracy of the blood parameter estimate. - View Dependent Claims (2, 3, 4)
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5. In a signal processor, a method of analyzing a measurement condition of a blood parameter of pulsing blood, the method comprising:
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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; electronically transforming the first and second intensity signals into the frequency domain; electronically calculating a plurality of ratios of values of the transformed first intensity signal to values of the transformed second intensity signal; electronically determining, based at least in part upon the plurality of ratios, one or more values of the transformed first and second intensity signals at nonzero frequencies that correspond to patient motion-induced noise and one or more values that correspond to physiological information; electronically calculating a blood parameter estimate using the one or more values that correspond to physiological information; and electronically determining, using one or more physiologically-based rules, a confidence level representing a degree of confidence in the accuracy of the blood parameter estimate. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. An apparatus for analyzing a measurement condition of a blood parameter of pulsing blood, the apparatus comprising:
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an input port configured to accept 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; a processor configured to perform a method comprising; transforming the first and second intensity signals into the frequency domain; calculating a plurality of ratios of values of the transformed first intensity signal to values of the transformed second intensity signal; determining, based at least in part upon the plurality of ratios, one or more values of the transformed first and second intensity signals at nonzero frequencies that correspond to patient motion-induced noise and one or more values that correspond to physiological information; calculating a blood parameter estimate using the one or more values that correspond to physiological information; and determining, using one or more physiologically-based rules, a confidence level representing a degree of confidence in the accuracy of the blood parameter estimate; and an output port configured to output the blood parameter estimate. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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Specification