Signal processing apparatus and method

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.

What is claimed is: 
     
         1 . A noninvasive physiological monitor comprising:
 a first input for receiving an output waveform from a detector responsive light attenuated by body tissue, the output waveform including at least a first waveform corresponding to a first wavelength of light attenuated by body tissue and a second waveform corresponding to a second wavelength of light attenuated by body tissue;   a signal processor configured to transform said first and second waveforms into spectral domain waveforms, the processor further configured to select spectral data based on predetermined criteria, the signal processor further configured to determine a physiological, indication of the patient based on the selected spectral data.   
     
     
         2 . The noninvasive physiological monitor of  claim 1 , wherein the physiological indication is pulse rate. 
     
     
         3 . The noninvasive physiological monitor of  claim 1 , wherein the criteria is largest spectral peak. 
     
     
         4 . The noninvasive physiological monitor of  claim 1 , wherein the criteria is a peak with corresponding harmonics. 
     
     
         5 . The noninvasive physiological monitor of  claim 1 , wherein the criteria is a spectral peak in a predetermined range. 
     
     
         6 . A method of determining physiological, information noninvasively based on optical measurements, the method comprising:
 receiving, from a detector, a waveform indicative of tissue attenuated light detected by the detector, the waveform including at least a first waveform corresponding to a first a wavelength of light attenuated by body tissue and a second waveform correspond to a second wavelength of light attenuated by body tissue;   transforming said first and second waveforms into spectral domain waveforms, the processor further configured to select spectral data based on predetermined criteria;   determining, using one or more processors, a physiological indication of the patient based on the selected spectral data.   
     
     
         7 . The method of  claim 6 , wherein the physiological indication is pulse rate. 
     
     
         8 . The method of  claim 6 , wherein the criteria is largest spectral peak. 
     
     
         9 . The method of  claim 6 , wherein the criteria is a peak with corresponding harmonics. 
     
     
         10 . The method of  claim 6 , wherein the criteria is a spectral peak in a predetermined range.