Signal quality metrics design for qualifying data for a physiological monitor

• US 20040138540A1
• Filed: 01/10/2003
• Published: 07/15/2004
• Est. Priority Date: 01/10/2003
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Baker, Clark R. Jr., Richards, Edward M.
• Granted Patent: US 7,006,856 B2
• Time in Patent Office: Days
• US Class Current: 600/336
• CPC Class Codes: A61B 5/024 Detecting, measuring or recording pulse rate or heart rate A61B5/0205, A61B5/021 take precedence
• CPC Class Codes: A61B 5/145 Measuring characteristics of blood in vivo, e.g. gas concentration, pH value; Measuring characteristics of body fluids or tissues, e.g. interstitial fluid, cerebral tissuemeasuring of blood pressure or blood flow A61B5/02; non-radiation detecting or locating of foreign bodies in blood A61B5/06
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method and a device for determining the quality of signal used for measuring a physiological parameter. One embodiment of the present invention is directed towards a pulse oximeter, where the measured physiological parameter includes a patient'"'"'s pulse rate and blood oxygen saturation. The signal quality, which is indicative of the accuracy and reliability of the measured physiological parameter, is calculated by combining a plurality of signal quality indicators, each of which is an indicator of a quality of the measured signal. The value of the signal quality metric is compared to a threshold and based on this comparison various decisions are made by the medical device. One decision is directed towards deciding whether or not to display the measured physiological parameter, to ensure that only accurate measured values are displayed. Another decision is directed towards providing feedback to guide the clinician to adjust the location of the sensor to a more suitable tissue location.

Claims

1. A method of controlling a display of a measured value for a physiological parameter in a medical diagnostic apparatus, comprising:

measuring a plurality of signal quality indicators;

processing said plurality of signal quality indicators, to form a plurality of processed signal quality indicators;

combining said plurality of processed signal quality indicators to form a combination of said plurality of processed signal quality indicators;

calculating a signal quality metric, wherein said signal quality metric comprises said combination of said plurality of processed signal quality indicators;

establishing a signal quality threshold;

comparing said signal quality metric to said signal quality threshold; and

displaying said measured value only if said signal quality metric exceeds said signal quality threshold.

2. The method of claim 1 wherein said measured value is an oxygen saturation.

3. The method of claim 1 wherein said measured value is a pulse rate.

4. The method of claim 1 wherein said apparatus comprises a pulse oximeter.

5. The method of claim 1 wherein said apparatus comprises a perinatal pulse oximeter.

6. The method of claim 1 wherein said apparatus comprises a perinatal pulse oximeter having a sensor configured to be placed at a tissue location which is not observable during said measuring.

7. The method of claim 1 wherein said plurality of signal quality indicators are selected from a group consisting of:

a signal measure indicative of the degree of similarity of an infrared and red waveforms,

a signal measure indicative of a low light level,

a signal measure indicative of an arterial pulse shape,

a signal measure indicative of the high frequency signal component in said measure value,

a signal measure indicative of infrared light modulation,

a signal measure indicative of red light modulation,

a signal measure indicative of a consistency of a pulse shape,

a signal measure indicative of an arterial pulse amplitude,

signal measure indicative of modulation ratios of red to infrared modulations and

a signal measure indicative of a period of an arterial pulse.

8. The method of claim 1 wherein said plurality of signal quality indicators comprise:

a signal measure indicative of the degree of similarity of an infrared and red waveforms,

a signal measure indicative of a low light level,

a signal measure indicative of an arterial pulse shape and

a signal measure indicative of the high frequency signal component in said measure value.

9. The method of claim 7 or 8 wherein said plurality of signal quality indicators are derived after a signal processing, wherein said signal processing is one of low pass filtering, high pass filtering, comb filtering, or a combination thereof.

10. The method of claim 7 or 8 wherein said plurality of signal quality indicators are derived from a frequency domain analysis.

11. The method of claim 1 wherein said processing comprises scaling and clipping.

12. The method of claim 1 wherein said calculating further comprises averaging said signal quality over a period of time.

13. The method of claim 1 wherein said calculating further comprises conditioning said signal quality metric by operating on said signal metric using a combination of proportional, integral and derivative control operations.

14. The method of claim 1 wherein said signal quality metric is calculated periodically at a rate between 0.1 and 5 seconds.

15. The method of claim 1 wherein said signal quality metric is calculated periodically at a rate between 0.1 and 1.0 seconds.

16. The method of claim 1 wherein said signal quality metric is calculated at a fixed time interval, said time interval being similar to one to several typical pulse periods.

17. The method of claim 1 wherein said signal quality metric is calculated once for each qualified pulse.

18. A method of guiding a user of a pulse oximeter apparatus to properly place the pulse oximeter sensor at a sensing location, comprising:

initially placing said sensor at a sensing location;

measuring a plurality of signal quality indicators;

processing said plurality of signal quality indicators, to form a plurality of processed signal quality indicators;

combining said plurality of processed signal quality indicators to form a combination of said plurality of processed signal quality indicators;

calculating a signal quality metric, wherein said signal quality metric comprises said combination of said plurality of processed signal quality indicators;

establishing a signal quality threshold;

comparing said signal quality metric to said signal quality threshold; and

informing said user to adjust the location of said sensor when said signal quality metric is lower than said signal quality threshold.

19. The method of claim 18 wherein said apparatus comprises a perinatal pulse oximeter.

20. The method of claim 18 wherein said sensor is configured to be placed at a tissue location which is not observable during said measuring.

21. The method of claim 18 wherein said plurality of signal quality indicators are selected from a group consisting of:

a signal measure indicative of the degree of similarity of an infrared and red waveforms,

a signal measure indicative of a low light level,

a signal measure indicative of an arterial pulse shape,

a signal measure indicative of the high frequency signal component in said measure value,

a signal measure indicative of infrared light modulation,

a signal measure indicative of red light modulation,

a signal measure indicative of a consistency of a pulse shape,

a signal measure indicative of an arterial pulse amplitude,

signal measure indicative of modulation ratios of red to infrared modulations and

a signal measure indicative of a period of an arterial pulse.

22. The method of claim 18 wherein said plurality of signal quality indicators comprise:

a signal measure indicative of the degree of similarity of an infrared and red waveforms,

a signal measure indicative of a low light level,

a signal measure indicative of an arterial pulse shape and

a signal measure indicative of the high frequency signal component in said measure value.

23. The method of claim 21 or 22 wherein said plurality of signal quality indicators are derived after a signal processing, wherein said signal processing is one of low pass filtering, high pass filtering, comb filtering or comb filtering with boxcar filtering.

24. The method of claim 21 or 22 wherein said plurality of signal quality indicators are derived from a frequency domain analysis.

25. The method of claim 18 wherein said processing comprises scaling and clipping.

26. The method of claim 18 wherein said calculating further comprises averaging said signal quality over a period of time.

27. The method of claim 18 wherein said calculating further comprises conditioning said signal quality metric by operating on said signal metric using a combination of proportional, integral and derivative control operations.

28. The method of claim 18 wherein said signal quality metric is calculated periodically at a rate between 0.1 and 5 seconds.

29. The method of claim 18 wherein said signal quality metric is calculated periodically at a rate between 0.1 and 1.0 seconds.

30. The method of claim 18 wherein said signal quality metric is calculated at a fixed time interval, said time interval being similar to one to several typical pulse periods.

31. The method of claim 18 wherein said signal quality metric is calculated once for each qualified pulse.

32. The method of claim 18 wherein said informing comprises visually indicating on a display monitor a command indicative of a need to adjust said sensor location.

33. The method of claim 18 wherein said informing comprises an audible notification indicative of a need to adjust said sensor location.

34. A pulse oximeter, comprising:

a display monitor for displaying a measured value;

means for measuring a plurality of signal quality indicators;

means for processing said plurality of signal quality indicators, to form a plurality of processed signal quality indicators;

means for combining said plurality of processed signal quality indicators to form a combination of said plurality of processed signal quality indicators;

means for calculating a signal quality metric, wherein said signal quality metric comprises said combination of said plurality of processed signal quality indicators;

means for establishing a signal quality threshold;

means for comparing said signal quality metric to said signal quality threshold; and

means for displaying said measured value on said monitor, only if said signal quality metric exceeds said signal quality threshold.

35. The pulse oximeter of claim 34 wherein said sensor is configured to be placed at a tissue location which is not observable during said measuring.

36. The pulse oximeter of claim 34 wherein said plurality of signal quality indicators are selected from a group consisting of:

a signal measure indicative of the degree of similarity of an infrared and red waveforms,

a signal measure indicative of a low light level,

a signal measure indicative of an arterial pulse shape,

a signal measure indicative of the high frequency signal component in said measure value,

a signal measure indicative of infrared light modulation,

a signal measure indicative of red light modulation,

a signal measure indicative of a consistency of a pulse shape,

a signal measure indicative of an arterial pulse amplitude,

signal measure indicative of modulation ratios of red to infrared modulations and

a signal measure indicative of a period of an arterial pulse.

37. The pulse oximeter of claim 34 further comprising means for guiding a user of said oximeter to adjust the location of said sensor when said signal quality metric is lower than said signal quality threshold.

38. The pulse oximeter of claim 37 wherein said means for guiding comprises visually indicating on said display monitor a command indicative of a need to adjust said sensor location.

39. The pulse oximeter of claim 37 wherein said means for guiding comprises an audible notification indicative of a need to adjust said sensor location.