Method and apparatus for estimating pulse rate

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.

What is claimed is: 
     
         1 . A noninvasive physiological monitor comprising: a signal processor communicating with a detector responsive to light attenuated by body tissue, said detector producing a detector output waveform, said signal processor receiving said detector output waveform and configured to transform said detector output waveform into spectral data, said signal processor further configured to identify spectral peaks and frequencies corresponding to said spectral peaks from said spectral data, and configured to apply a plurality of rules to said spectral peaks and said corresponding frequencies in order to determine a pulse rate estimate. 
     
     
         2 . The noninvasive physiological monitor of  claim 1 , wherein at least one of said plurality of rules compares amplitude information and frequency information about said spectral peaks. 
     
     
         3 . The noninvasive physiological monitor of  claim 1 , wherein at least one of said plurality of rules determines whether at least one of the spectral peaks falls within a predetermined range. 
     
     
         4 . The noninvasive physiological monitor of  claim 1 , wherein at least one of said plurality of rules determines whether a frequency corresponding to at least one of the spectral peaks falls within a predetermined range. 
     
     
         5 . A method of electronically calculating a physiological parameter in a patient comprising the steps of:
 transmitting light through tissue having flowing blood;   detecting said light after it has passed through said tissue;   generating an output signal indicative of the intensity of said light after attenuation;   transforming the output signal into spectral data;   identifying spectral peaks and frequencies corresponding the spectral peaks from the spectral data; and   calculating an estimate of pulse rate by applying a plurality of rules to the spectral peaks and the corresponding frequencies.   
     
     
         6 . The method of electronically calculating a physiological parameter of  claim 5  wherein the first wavelength is in a red light spectrum. 
     
     
         7 . The method of electronically calculating a physiological parameter of  claim 5  wherein the second wavelength is in an infrared light spectrum.