Methods and systems for qualifying physiological values based on segments from a cross-correlation sequence

• US 9,392,974 B2
• Filed: 09/11/2012
• Issued: 07/19/2016
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Engelbrecht, Pirow, Rodriguez-Llorente, Fernando, Wooder, Nicholas James
• Primary Examiner(s): Peng, Bo J
• Application Number:
  US13/609,569
• Publication Number:
  US 20140073963A1
• Time in Patent Office: 1,407 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02444 Details of sensor A61B5/02427 takes precedence
• CPC Class Codes: A61B 5/14552 Details of sensors specially adapted therefor
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: G16H 40/63 for local operation
• CPC Class Codes: G16H 50/20 for computer-aided diagnosis, e.g. based on medical expert systems

Abstract

A physiological monitoring system may process a physiological signal such a photoplethysmograph signal from a subject. The system may determine physiological information, such as a physiological rate, from the physiological signal. The system may use search techniques and qualification techniques to determine one or more initialization parameters. The initialization parameters may be used to calculate and qualify a physiological rate. The system may use signal conditioning to reduce noise in the physiological signal and to improve the determination of physiological information. The system may use qualification techniques to confirm determined physiological parameters. The system may also use autocorrelation techniques, cross-correlation techniques, fast start techniques, and/or reference waveforms when processing the physiological signal.

Claims

1. A pulse oximetry system for determining physiological information of a subject, comprising:

a pulse oximetry sensor configured to generate an intensity signal, wherein the pulse oximetry sensor detects light attenuated by the subject; and

a pulse oximeter coupled to the pulse oximetry sensor, wherein the pulse oximeter is configured to;

determine a value indicative of a physiological rate of the subject;

calculate a cross-correlation sequence based on a cross-correlation of the intensity signal and a reference waveform for a plurality of lags, wherein the cross-correlation sequence comprises a plurality of calculated cross-correlation values;

select two segments from the cross-correlation sequence, wherein the two segments are the same size and each comprises a plurality of cross-correlation values, and wherein the starting points of the two segments are offset from each other;

calculate one or more of;

(a) distances based on the two segments and (b) angles based on the two segments;

determine one or more metric values based on the calculated one or more distances and angles, wherein the one or more metric values indicate confidence as to whether the value indicative of the physiological rate of the subject is correct;

determine whether to qualify the value indicative of the physiological rate of the subject based on the one or more metric values;

determine a pulse rate value for the subject based on the value indicative of the physiological rate when the value indicative of the physiological rate is qualified; and

display the pulse rate value for the subject on a display.

2. The system of claim 1, wherein the starting points of the two segments are offset by a quarter of a period, wherein the period is associated with the value indicative of the physiological rate, and wherein the size of the two segments is equal to or greater than the period.

3. The system of claim 1, wherein the calculation of each distance is based on a value from a first of the two segments and a value from a second of the two segments.

4. The system of claim 3, wherein the one or more metric values is determined based on a maximum and a minimum of the distances.

5. The system of claim 1, wherein the calculation of each angle is based on a value from a first of the two segments and a value from a second of the two segments.

6. The system of claim 5, wherein the one or more metric values comprises a sum of the angles.

7. The system of claim 1, wherein the pulse oximeter is further configured to not use the value indicative of the physiological rate in calculating a display rate when the value is not qualified.

8. The system of claim 1, wherein the pulse oximeter is further configured to filter the value indicative of the physiological rate in a rate filter, wherein a filter weight associated with the value is decreased when the value is not qualified.

9. The system of claim 1, wherein the intensity signal is a photoplethysmograph signal.

10. A processing module of a pulse oximeter for determining physiological information of a subject, wherein the processing module is configured to:

receive an intensity signal from a detector of a pulse oximetry sensor, wherein the detector detects light attenuated by the subject;

determine a value indicative of a physiological rate of the subject;

calculate a cross-correlation sequence based on a cross-correlation of the intensity signal and a reference waveform for a plurality of lags, wherein the cross-correlation sequence comprises a plurality of calculated cross-correlation values;

select two segments from the cross-correlation sequence, wherein the two segments are the same size and each comprises a plurality of cross-correlation values, and wherein the starting points of the two segments are offset from each other;

calculate one or more of;

(a) distances based on the two segments and (b) angles based on the two segments;

determine one or more metric values based on the calculated one or more distances and angles, wherein the one or more metric values indicate confidence as to whether the value indicative of the physiological rate of the subject is correct;

determine whether to qualify the value indicative of the physiological rate of the subject based on the one or more metric values;

determine a pulse rate value for the subject based on the value indicative of the physiological rate when the value indicative of the physiological rate is qualified; and

display the pulse rate value for the subject on a display.

11. The processing module of claim 10, wherein the starting points of the two segments are offset by a quarter of a period, wherein the period is associated with the value indicative of the physiological rate, and wherein the size of the two segments is equal to or greater than the period.

12. The processing module of claim 10, wherein the calculation of each distance is based on a value from a first of the two segments and a value from a second of the two segments.

13. The processing module of claim 12, further configured to determine whether to qualify the value indicative of the physiological rate based on a maximum and a minimum of the distances.

14. The processing module of claim 10, wherein the calculation of each angle is based on a value from a first of the two segments and a value from a second of the two segments.

15. The processing module of claim 14, wherein the one or more metric values comprises a sum of the angles.

16. The processing module of claim 10, further configured to not use the value indicative of the physiological rate in calculating a display rate when the value is not qualified.

17. The processing module of claim 10, further configured to filter the value indicative of the physiological rate in a rate filter, wherein a filter weight associated with the value is decreased when the value is not qualified.

18. The processing module of claim 10, wherein the intensity signal is a photoplethysmograph signal.

19. A method for processing physiological information of a subject using a pulse oximeter, comprising:

receiving, using the pulse oximeter, an intensity signal from a detector of a pulse oximetry sensor, which detects light attenuated by the subject;

determining, using the pulse oximeter, a value indicative of a physiological rate of the subject;

calculating, using the pulse oximeter, a cross-correlation sequence based on a cross-correlation of the intensity signal and a reference waveform for a plurality of lags, wherein the cross-correlation sequence comprises a plurality of calculated cross-correlation values;

selecting, using the pulse oximeter, two segments from the cross-correlation sequence, wherein the two segments are the same size and each comprises a plurality of cross-correlation values, and wherein the starting points of the two segments are offset from each other;

calculating, using the pulse oximeter, one or more of;

(a) distances based on the two segments and (b) angles based on the two segments;

determining, using the pulse oximeter, one or more metric values based on the calculated one or more distances and angles, wherein the one or more metric values indicate confidence as to whether the value indicative of the physiological rate of the subject is correct;

determining, using the pulse oximeter, whether to qualify the value indicative of the physiological rate of the subject based on the one or more metric values;

determining, using the pulse oximeter, a pulse rate value for the subject based on the value indicative of the physiological rate when the value indicative of the physiological rate is qualified; and

displaying, using the pulse oximeter, the pulse rate value for the subject on a display.

20. The method of claim 19, wherein the starting points of the two segments are offset by a quarter of a period, wherein the period is associated with the value indicative of the physiological rate, and wherein the size is equal to or greater than the period.

21. The method of claim 19, wherein the calculation of each distance is based on a value from a first of the two segments and a value from a second of the two segments.

22. The method of claim 21, wherein the one or more metric values is determined based on a maximum and a minimum of the distances.

23. The method of claim 19, wherein the calculation of each angle is based on a value from a first of the two segments and a value from a second of the two segments.

24. The method of claim 23, one or more metric values comprises sum of the angles.

25. The method of claim 19, further comprising not using the value indicative of the physiological rate in calculating a display rate when the value is not qualified.

26. The method of claim 19, further comprising filtering, using the pulse oximeter, the value indicative of the physiological rate in a rate filter, wherein a filter weight associated with the value is decreased when the value is not qualified.

27. The method of claim 19, wherein the intensity signal is a photoplethysmograph signal.

28. A non-transitory computer-readable medium for use in determining physiological information of a subject, the computer-readable medium comprising:

computer program instructions recorded thereon for causing a pulse oximeter to;

receive an intensity signal from a detector of a pulse oximetry sensor, which detects light attenuated by the subject;

determine a value indicative of a physiological rate of the subject;

calculate a cross-correlation sequence based on a cross-correlation of the intensity signal and a reference waveform for a plurality of lags, wherein the cross-correlation sequence comprises a plurality of calculated cross-correlation values;

select two segments from the cross-correlation sequence, wherein the two segments are the same size and each comprises a plurality of cross-correlation values, and wherein the starting points of the two segments are offset from each other;

calculate one or more of;

(a) distances based on the two segments and (b) angles based on the two segments;

determine one or more metric values based on the calculated one or more distances and angles, wherein the one or more metric values indicate confidence as to whether the value indicative of the physiological rate of the subject is correct;

determine whether to qualify the value indicative of the physiological rate of the subject based on the one or more metric values;

determine a pulse rate value for the subject based on the value indicative of the physiological rate when the value indicative of the physiological rate is qualified; and

display the pulse rate value for the subject on a display.

29. The non-transitory computer-readable medium of claim 28, wherein the starting points of the two segments are offset by a quarter of a period, wherein the period is associated with the value indicative of the physiological rate, and wherein the size of the two segments is equal to or greater than the period.

30. The non-transitory computer-readable medium of claim 28, wherein the calculation of each distance is based on a value from a first of the two segments and a value from a second of the two segments.

31. The non-transitory computer-readable medium of claim 30, wherein the one or more metric values is determined based on a maximum and a minimum of the distances.

32. The non-transitory computer-readable medium of claim 28, wherein the calculation of each angle is based on a value from a first of the two segments and a value from a second of the two segments.

33. The non-transitory computer-readable medium of claim 32, wherein the one or more metric values comprises a sum of the angles.

34. The non-transitory computer-readable medium of claim 28, comprising further computer program instructions recorded thereon for causing the pulse oximeter to not use the value indicative of the physiological rate in calculating a display rate when the value is not qualified.

35. The non-transitory computer-readable medium of claim 28, comprising further computer program instructions recorded thereon for causing the pulse oximeter to filter the value indicative of the physiological rate in a rate filter, wherein a filter weight associated with the value is decreased when the value is not qualified.

36. The non-transitory computer-readable medium of claim 28, wherein the intensity signal is a photoplethysmograph signal.