Method for processing signals, particularly for oximetric measurements on living human tissue

• US 5,113,861 A
• Filed: 04/20/1989
• Issued: 05/19/1992
• Est. Priority Date: 05/09/1988
• Status: Expired due to Fees

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Rother, Peter
• Primary Examiner(s): McGraw, Vincent P.
• Assistant Examiner(s): KEESEE, LACHARLES
• Application Number:
  US07/340,969
• Time in Patent Office: 1,125 Days
• Field of Search: 364/413.09, 364/496, 364/497, 364/498, 364/499, 364/525, 364/571.02, 364/724.01, 364/724.13, 128/633, 128/664, 128/665, 128/666, 356/41, 371/6, 371/64, 328/162, 328/165, 328/167
• US Class Current: 600/322
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor

Abstract

A method is used for processing signals, particularly for oximetric measurements on living human tissue. Spurious signals are suppressed with respect to information signals. The spurious signals have a frequency lying in a first frequency range, and the information signals have a frequency lying in a second frequency range being different from said first frequency range. The signals are conducted over a filter having essentially a blocking characteristic in said first frequency range and having essentially a transmission characteristic in said second frequency range. An output signal of the filter is further processed.

In order to eliminate distorting effects from the filter on the information signal, a first function is determined representing the deviation of the frequency response of the filter in said frequency range from an ideal transmission characteristic. A second function inverted with respect to said first function is generated. The output signal is weighted by the second function to generate a weighted output signal.

Claims

1. A method for deriving output signals from spurious signals having a frequency lying in a first frequency range and n multiplexed information signals having a frequency lying in a second frequency range that is different from said first frequency range, said method comprising the steps of:

passing said signals through a filter having an essentially blocking characteristic in said first frequency range and having an essentially transmitting characteristic in said second frequency range so as to produce a column matrix;

providing a first n² matrix function representing the deviation of the frequency range from an ideal transmission characteristic;

deriving a second n² matrix function inverted with respect to said first matrix function; and

multiplying said column matrix at the output of said filter with said second n² matrix function to generate said output signals.

2. The method of claim 1 further comprising the step of providing said information signal in the form of a multiplexed signal having pulse trains of a pulse frequency that is above the frequency of said spurious signals.

3. The method of claim 2, wherein said inverted function is a first square matrix having a number of lines and columns, each of which is equal to the number of pulses in a pulse train and wherein said signal passed by said filter is represented as a second square matrix of the respective first amplitudes of pulses of pulse trains appearing at the output of said filter, the step of multiplying said first and second matrices by each other to generate a third square matrix of amplitudes of pulses of pulse trains to produce said output signals.

4. The method of claim 3 further comprising the steps of:

determining coefficients of said first square matrix by providing a number of test pulse trains of a predetermined fist amplitude to said filter, the number of test pulse trains and the number of test pulses in each of said test pulse trains corresponding to said number of lines and columns of said first square matrix,

deriving second amplitudes of pulses appearing at the output of said filter in response to said test pulses, and

dividing a fourth matrix defined from said first amplitudes by a fifth matrix defined from said second amplitudes.

5. The method of claim 4 further comprising the step of providing said test pulse trains in such manner that each train has one pulse having a higher amplitude than the other pulses of said train.

6. The method of claim 3 further comprising the steps of:

decreasing the principal diagonal coefficients of said first matrix by unity.

factoring out the value of a n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

7. The method of claim 4 further comprising the steps of:

decreasing the principal diagonal coefficients of said first matrix by unity,

factoring out the value of a n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

8. The method of claim 5 further comprising the steps of:

decreasing the principal diagonal coefficients of said first matrix by unity,

factoring out the value of a n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

9. The method of claim 3 further comprising the steps of:

standardizing the principal diagonal coefficients of said first matrix on unity,

factoring out the value of n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

10. The method of claim 4 further comprising the steps of:

standardizing the principal diagonal coefficients of said first matrix on unity,

factoring out the value of n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

11. The method of claim 5 further comprising the steps of:

standardizing the principal diagonal coefficients of said first matrix on unity,

factoring out the value of n-th power of two, and

digitally multiplying said second matrix by said first matrix using digital words having a number of bits smaller than n.

12. The method of claim 9 further comprising:

weighting an offset-value by said first matrix having its principal diagonal coefficients standardized to unity to generate a sixth matrix of correction values, said correction values being subtracted from said weighted signals generated from pulse trains exhibiting said offset-value.

13. The method of claim 10, further comprising:

weighting an offset-value by said first matrix having its principal diagonal coefficients standardized to unity to generate a sixth matrix of correction values, said correction values being subtracted from said weighted signals generated from pulse trains exhibiting said offset-value.

14. The method of claim 11, further comprising:

weighting an offset-value by said first matrix having its principal diagonal coefficients standardized to unity to generate a sixth matrix of correction values, said correction values being subtracted from said weighted signals generated from pulse trains exhibiting said offset-value.

15. The method of claim 2, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

16. The method of claim 3, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

17. The method of claim 4, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

18. The method of claim 5, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

19. The method of claim 6, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

20. The method of claim 7, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

21. The method of claim 8, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

22. The method of claim 9, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

23. The method of claim 10, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship fist pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

24. The method of claim 11, further comprising the steps of:

using a plurality of light-emitting elements to send in timely spaced relationship first pulsed light beams of different wavelength into a living human tissue supplied with blood, and

directing second light beams that have passed through said tissue on to a light-receiving element so as to generate said multiplexed signal.

25. A method for deriving signals representing blood oxygen saturation comprising:

transmitting successive series of n pulses of light of different wavelengths at a given pulse repetition frequency;

producing electrical signals in response to the passage of said pulses of light through a body member or in response to their reflection from a body member;

applying the electrical signals to a noise-removing filter,

expressing the signals at the output of the filter as a first matrix having a column of n elements;

multiplying said first matrix with a second matrix in n² form having coefficients representing the deviations in the modified signals produced by the filter;

the coefficients of said second matrix being selected such that they represent the values obtained by a matrix division of third and fourth matrices in n² form;

wherein the coefficients in the columns of said third matrix have been obtained, with the filter bypassed, from the responses to n pulse trains, each pulse train consisting of n pulses; and

wherein the coefficients in the columns of said third matrix have been obtained, with the filter active, from the responses to n pulse trains, each pulse train consisting of n pulses.

26. The method of claim 25, wherein:

the principal diagonal coefficients of said second matrix have been decreased by unity;

the value of an m-th power of two has been factored out from the principal coefficients of said second matrix; and

digitally multiplying said first matrix by said second matrix using digital words having a number of bits smaller than m.

27. The method of claim 25 wherein:

the principal diagonal coefficients of said second matrix have been standardized to unity;

the value of an m-th power of two has been factored out from the principal coefficients of said second matrix; and

digitally multiplying said first matrix by said second matrix using digital words having a number of bits smaller than m.

28. The method of claim 25 wherein:

the principal diagonal coefficients of said second matrix have been standardized to unity;

said principal diagonal coefficients have further been decreased to unity;

the value of an m-th power of two has been factored out from the principal coefficients of said second matrix; and

digitally multiplying said first matrix by said second matrix using digital words having a number of bits smaller than m.

29. The method of claim 25 wherein:

the principal diagonal coefficients of said second matrix have been standardized to unity;

an offset value has been multiplied with said second standardized matrix to generate a fifth column matrix with n elements of correction values; and

subtracting said fifth column matrix from the product of said first and said second matrices.