Variable indication estimator

• US 6,999,904 B2
• Filed: 08/05/2002
• Issued: 02/14/2006
• Est. Priority Date: 06/05/2000
• Status: Expired due to Term

• Current Assignee: Masimo Corporation
• Original Assignee: Masimo Corporation
• Inventors: Weber, Walter M., Al-Ali, Ammar, Cazzoll, Lorenzo
• Primary Examiner(s): Tsai, Carol S. W.
• Application Number:
  US10/213,270
• Publication Number:
  US 20030101027A1
• Time in Patent Office: 1,289 Days
• Field of Search: 702/189, 702/190, 702/191, 702193-197, 702/199, 702/104, 702/109, 702/110, 702134-135, 702156-157, 702159-160, 702FOR 164-171, 600309-311, 600322-326, 600330-331, 600/336, 600/473, 600/476, 356/39, 356/40, 356/41
• US Class Current: 702/189
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6829 Foot or ankle
• CPC Class Codes: A61B 5/6838 Clamps or clips
• CPC Class Codes: A61B 5/72 Signal processing specially adapted for physiological signals or for diagnostic purposes character recognition, recognising digital ink, document-oriented image-based pattern recognition G06V30/00; recognition or understanding of postal images G06V30/424
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/7271 Specific aspects of physiological measurement analysis A61B5/316, A61B5/349 and A61B5/374 take precedence
• CPC Class Codes: G06F 2218/04 Denoising

Abstract

A variable indication estimator which determines an output value representative of a set of input data. For example, the estimator can reduce input data to estimates of a desired signal, select a time, and determine an output value from the estimates and the time. In one embodiment, the time is selected using one or more adjustable signal confidence parameters determine where along the estimates the output value will be computed. By varying the parameters, the characteristics of the output value are variable. For example, when input signal confidence is low, the parameters are adjusted so that the output value is a smoothed representation of the input signal. When input signal confidence is high, the parameters are adjusted so that the output value has a faster and more accurate response to the input signal.

Claims

1. A signal processor capable of reducing unwanted fluctuations in oxygen saturation values while substantially tracking the occurrence and severity of desaturation events, wherein the oxygen saturation values were derived by processing absorption signals representative of light attenuated by body tissue carrying pulsing blood, the signal processor comprising:

a buffer capable of storing a plurality of input oxygen saturation values corresponding to a plurality of time values;

a signal confidence indicator;

a selected time value based upon said signal confidence indicator; and

an estimator capable of determining an oxygen saturation output value at the selected time value, said oxygen saturation output value comprising an estimate for the plurality of input oxygen saturation values;

wherein the estimator is an oxygen saturation versus time curve fit to the input oxygen saturation values within the buffer;

wherein the oxygen saturation output value is a point along said curve fit at the selected time value; and

wherein the selected time value is between an average of the time values and a maximum of the time values.

2. The signal processor of claim 1,

wherein the curve fit is a least-mean-square linear fit;

wherein a slope of the least-mean-square linear fit corresponds to a ratio of a crossvariance of the plurality of input oxygen saturation values with the plurality of time values and an autovariance of the plurality of time values;

wherein an intercept of the least-mean-square linear fit corresponds to an average of the plurality of input oxygen saturation values.

3. The signal processor of claim 1, wherein the estimator comprises one of a smoother, a filter, a forward predictor, and a backward predictor.

4. The signal processor of claim 1, wherein the estimator comprises a variable mode averager.

5. The signal processor of claim 4, wherein the signal confidence indicator corresponds to a level of confidence that one or more of the oxygen saturation values represent a value of a desired signal.

6. The signal processor of claim 5, wherein the estimator approximates a smoother when the signal confidence indicator is low.

7. The signal processor of claim 5, wherein the estimator approximates a filter when the signal confidence indicator is high.

8. The signal processor of claim 5, wherein the oxygen saturation output value includes a faster response to the oxygen saturation values when the signal confidence indicator is high.

9. The signal processor of claim 5, wherein the oxygen saturation output value includes a more accurate response to the oxygen saturation values when the signal confidence indicator is high.

10. The signal processor of claim 1, wherein the estimator is capable of causing an alarm to be activated when the oxygen saturation output value is below a threshold value, and wherein the estimator lowers an amount of false alarms through adjustment of the signal confidence indicator.

11. The signal processor of claim 1, wherein the oxygen saturation values include a desired signal portion.

12. The signal processor of claim 11, wherein the oxygen saturation values include other signal artifacts.

13. A signal processor capable of reducing unwanted fluctuations in oxygen saturation values while substantially tracking the occurrence and severity of desaturation events, wherein the oxygen saturation values were derived by processing absorption signals representative of light attenuated by body tissue carrying pulsing blood, the signal processor comprissing:

a buffer capable of storing a plurality of input oxygen saturation values corresponding to a plurality of time values;

a signal confidence indicator;

a selected time value based upon said signal confidence indicator; and

an estimator capable of determining an oxygen saturation output value at the selected time value, said oxygen saturation output value comprising an estimate for the plurality of input oxygen saturation values;

wherein the estimator is further capable of segmenting said plurality of said oxygen saturation values;

wherein the estimator is capable of determining a plurality of segment oxygen saturation estimates; and

wherein each segment oxygen saturation estimate is determined from the oxygen saturation values corresponding to a respective segment.

14. The signal processor of claim 13, wherein the oxygen saturation output value corresponds to an interpolation between one or more of the segment oxygen saturation estimates.

15. A method of reducing a time delay in a determination of oxygen saturation when a confidence in the determination is high, the oxygen saturation being determined from one or more signals output from a detector capable of detecting light attenuated by body tissue, the method comprising:

providing a buffer capable of storing a plurality of input values corresponding to a plurality of time values, wherein the input values are indicative of oxygen saturations;

providing a signal confidence indicator; and

providing a signal processor capable of selecting a time value based upon said signal confidence indicator and including an estimator capable of determining an output value at the selected time value, said output value comprising an estimate for the plurality of input values, wherein the estimator comprises an input values to time curve fit to the input values within the buffer, said output value comprising a point along said curve fit at the selected time value, and said selected time value is between an average of the time values and a maximum of the time values.

16. The method of claim 15, wherein the estimator comprises one of a smoother, a filter, a forward predictor, and a backward predictor.

17. The method of claim 15, wherein the estimator comprises a variable mode averager.

18. The method of claim 15, wherein the estimator is capable of causing an alarm to be activated when the output value is below a threshold value, and wherein the estimator lowers an amount of false alarms through adjustment of the signal confidence indicator.

19. The method of claim 15, wherein the input values include a desired signal portion.

20. The method of claim 19, wherein the input values include other signal artifacts.