Signal processing apparatus and method

Abstract

The present invention relates to the field of signal processing. More specifically, the present invention relates to the processing of measured signals to remove undesired portions when little is known about the undesired signal portion. <IMAGE>

What is claimed is:  
     
       1. A method of determining an indication of blood oxygen saturation comprising the steps of: 
       transmitting light of at least first and second wavelengths through body tissue carrying blood to a light-sensitive detector to generate first and second measured intensity signals;  
       filtering at least one of said first and second intensity signals with an adaptive canceler to provide at least one output signal; and  
       calculating oxygen saturation based upon said at least one output signal.  
     
     
       2. The method of  claim 1 , wherein said step of transmitting light comprises the steps of transmitting a first wavelength in the red wavelength range and a second wavelength in the infrared wavelength range. 
     
     
       3. The method of  claim 2 , wherein said first and said second signals have at least a desired physiological component and an artifact component. 
     
     
       4. The method of  claim 3 , wherein said first and second wavelengths are selected based on light absorption characteristics of the physiologic medium, such that a substantially linear relationship exists between the desired physiologic components of said first and second measured signals. 
     
     
       5. The method of  claim 1 , further comprising the step of converting said first and second intensity signals to a digital representation of said first and second intensity signals, and wherein said step of filtering at least one of said first and second intensity signals with said adaptive canceler comprising filtering said digital representation. 
     
     
       6. The method of  claim 1 , further comprising the step of filtering said first and second signals with a predetermined filter prior to said filtering at least one of said first and second intensity signals with an adaptive canceler. 
     
     
       7. The method of  claim 6 , further comprising the step of converting said first and second intensity signals to a digital representation of said first and second intensity signals, and wherein said step of filtering at least one of said first and second intensity signals with an adaptive canceler comprises filtering said digital representation. 
     
     
       8. The method of  claim 6 , further comprising the step of displaying said oxygen saturation on a display. 
     
     
       9. The method of  claim 1 , further comprising the step of displaying said oxygen saturation on a display. 
     
     
       10. The method of  claim 1 , wherein said step of filtering at least one of said first and second intensity signals with an adaptive canceler comprises the steps of: 
       multiplying at least one of said first and second intensity signals by a predetermined constant and subtracting the result from the other of said first and second intensity signals to provide a reference signal; and  
       filtering at least one of said first and second intensity signals based upon said reference signal.  
     
     
       11. The method of  claim 5 , wherein said step of filtering at least one of said first and second intensity signals with an adaptive canceler comprises the steps of: 
       multiplying at least one of the digital representations of said first and second intensity signals by a predetermined constant and subtracting the result from the other of said first and second intensity signals to provide a reference signal; and  
       adaptively  filtering at least one of the digital representations of said first and second intensity signals based upon said reference signal.  
     
     
       12. The method of  claim 11 , further comprising the step of filtering said first and second signals with a predetermined filter prior to filtering at least one of said first and second intensity signals with an adaptive canceler. 
     
     
       13. The method of  claim 5 , where said adaptive canceler is a dynamic multiple notch filter. 
     
     
       14. The method of  claim 13 , wherein said adaptive canceler adjusts its transfer function in accordance with a predetermined algorithm. 
     
     
       15. The method of  claim 14 , wherein said predetermined algorithm is a least-squares algorithm. 
     
     
       16. A pulse oximeter which measures the oxygen saturation of blood in body tissue, said pulse oximeter comprising: 
       a light emitter adapted to emit light of at least first and second wavelengths;  
       a light detector responsive to light from said light emitter which has passed through body tissue having blood, said light detector providing intensity signals;  
       an adaptive filter responsive to said intensity signals to provide at least one filtered signal; and  
       a oxygen saturation module responsive to at least said filtered signal to calculate oxygen saturation of said blood.  
     
     
       17. The pulse oximeter of  claim 16 , further comprising a display coupled to said oxygen saturation module. 
     
     
       18. The pulse oximeter of  claim 16 , wherein said adaptive filter comprises a first predetermined filter and adaptive correlation canceler  an adaptive noise canceler. 
     
     
       19. The pulse oximeter of  claim 16 , further comprising an analog to digital converter in communication with said light detector, said analog to digital converter providing digital representations of said intensity signals, said analog to digital converter providing said digital representations to said adaptive filter. 
     
     
       20. The pulse oximeter of  claim 19 , further comprising a signal conditioner coupled between said light detector and said analog to digital converter. 
     
     
       21. The pulse oximeter of claim  16   18 , wherein said adaptive filternoise canceler is coupled to comprises  a multiplication unit and an adaptive correlation noise canceler . 
     
     
       22. The pulse oximeter of  claim 21  wherein said adaptive filter  noise canceler further comprises a predetermined filter. 
     
     
       23. The pulse oximeter of  claim 16 , wherein said adaptive filter is a dynamic multiple notch filter. 
     
     
       24. The pulse oximeter of  claim 23 , wherein said adaptive filter adjusts its transfer function in accordance with a predetermined algorithm. 
     
     
       25. The pulse oximeter of  claim 24 , wherein said predetermined algorithm is a least squares lattice. 
     
     
       26. A pulse oximeter which measures the oxygen saturation of blood in body tissue, said pulse oximeter comprising: 
       a light emitter adapted to emit light of at least first and second wavelengths;  
       a light detector responsive to light from said light emitter which has passed through body tissue having blood, said light detector providing intensity signals;  
       a digital to analog converter which digitizes the intensity signals from said light detector;  
       a multiple notch filter responsive to said intensity signals after conversion with said digital to analog converter to provide at least one filtered signal; and  
       an oxygen saturation module responsive to at least said filtered signal to calculate oxygen saturation of said blood.  
     
     
       27. The method of  claim 26 , wherein said multiple notch filter adjusts its transfer function based on a predetermined algorithm. 
     
     
       28. A pulse oximeter which measures the oxygen saturation of blood in body tissue, said pulse oximeter comprising: 
       a light emitter adapted to emit light of at least first and second wavelengths;  
       a light detector responsive to light from said light emitter which has passed through body tissue having blood, said light detector providing intensity signals having desired and undesired signal portions;  
       an analog to digital converter which digitizes the intensity signals from said light detector;  
       an adaptive signal processor responsive to  that operates to process said intensity signals to adaptively filter said intensity signals  to provide processed intensity signals; and  
       an oxygen saturation module  routine responsive to at least one signal  said processed intensity signals to calculate oxygen saturation of said blood.  
     
     
       29. The pulse oximeter of  claim 28 , wherein said adaptive signal processor comprises an adaptive noise canceler. 
     
     
       30. The pulse oximeter of  claim 29 , wherein said adaptive noise canceler comprises a joint process estimator with a least-squares lattice predictor. 
     
     
       31. The pulse oximeter of  claim 29 , wherein said adaptive noise canceler operates as a multiple notch filter. 
     
     
       32. The pulse oximeter of  claim 28 , wherein said adaptive signal processor comprises an adaptive filter. 
     
     
       33. A method for determining oxygen saturation of blood in body tissue, the method comprising the steps of: 
       
         emitting light of at least first and second wavelengths;  
       
       
         detecting the light of at least first and second wavelengths that has passed through body tissue including pulsing blood to produce at least one intensity signal;  
       
       
         processing a representation of the at least one intensity signal using an adaptive algorithm to provide at least one output signal; and  
       
       
         calculating an oxygen saturation of the pulsing blood using the at least one output signal.  
       
     
     
       34. The method of  claim 33 , wherein the representation of the at least one intensity signal is a digital representation.  
     
     
       35. The method of  claim 33 , further comprising the step of displaying the calculated oxygen saturation of the blood.  
     
     
       36. The method of  claim 33 , wherein the step of processing comprises processing the representation using a component of an adaptive noise canceler.  
     
     
       37. The method of  claim 33 , wherein the adaptive algorithm is a least squares algorithm.  
     
     
       38. The method of  claim 33 , wherein the adaptive algorithm is a least mean square algorithm.  
     
     
       39. A pulse oximeter comprising: 
       
         light emitters that emit light of at least first and second wavelengths;  
       
       
         a light detector responsive to the light from the light emitters that has passed through body tissue including pulsing blood, the light detector providing at least one intensity signal;  
       
       
         an analog to digital converter that provides a digital representation of the at least one intensity signal;  
       
       
         a processor including a first routine to adaptively process the digital representation of the at least one intensity signal to provide at least one output signal; and  
       
       
         a second routine responsive to the at least one output signal to calculate oxygen saturation of the blood.  
       
     
     
       40. The pulse oximeter of  claim 39 , wherein the first routine comprises an adaptive algorithm.  
     
     
       41. The pulse oximeter of  claim 40 , wherein the adaptive algorithm comprises a least squares algorithm.  
     
     
       42. The pulse oximeter of  claim 40 , wherein the adaptive algorithm comprises a least mean square algorithm.  
     
     
       43. The pulse oximeter of  claim 41 , wherein the adaptive algorithm comprises a least squares lattice algorithm.  
     
     
       44. The pulse oximeter of  claim 39 , wherein the processor comprises a component of an adaptive noise canceler.