Methods and systems for qualifying a correlation lag value based on skewness

• US 9,186,076 B2
• Filed: 09/11/2012
• Issued: 11/17/2015
• Est. Priority Date: 09/11/2012
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Covidien LP (Medtronic Plc)
• Inventors: Rodriguez-Llorente, Fernando, Engelbrecht, Pirow, Wooder, Nicholas James
• Primary Examiner(s): Le, Long V
• Assistant Examiner(s): Negarestan, Farshad
• Application Number:
  US13/609,468
• Publication Number:
  US 20140073942A1
• Time in Patent Office: 1,162 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• 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 5/7246 using correlation, e.g. template matching or determination of similarity
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

A physiological monitoring system may determine physiological information, such as physiological rate information, from a physiological signal. The system may determine a skew metric based on the physiological signal. The system may also determine a correlation lag value corresponding to a peak in a correlation sequence derived from the physiological signal. The system may qualify or disqualify the correlation lag value based on the skew metric. The system may, for example, compare the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values to determine whether to qualify or disqualify the correlation lag value.

Claims

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

a pulse oximetry sensor configured to generate a physiological signal, wherein the pulse oximetry sensor is configured to detect light attenuated by the subject; and

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

determine a skew metric value based on the physiological signal;

determine a correlation lag value corresponding to a peak in a correlation sequence derived from the physiological signal;

determine an expected correlation lag value based on the skew metric value; and

qualify or disqualify the correlation lag value based on a comparison between the correlation lag value and the expected correlation lag value;

determine a physiological rate of the subject based on the correlation lag value when the correlation lag value is qualified; and

display the physiological rate of the subject on a display.

2. The system of claim 1, wherein the pulse oximeter is further configured to compare the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values.

3. The system of claim 2, wherein the pulse oximeter is further configured to:

identify the expected correlation lag value from the reference set that most closely matches the determined skew metric value;

determine a difference value indicative of a difference between the determined correlation lag value and the expected correlation lag value; and

compare the difference value to a threshold.

4. The system of claim 3, wherein the threshold is based on the determined correlation lag value.

5. The system of claim 1, wherein the pulse oximeter is further configured to compare the skew metric to a threshold.

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

receive a physiological signal derived from a detector output of a pulse oximetry sensor, wherein the pulse oximetry sensor is configured to detect light attenuated by the subject;

determine a skew metric value based on the physiological signal;

determine a correlation lag value corresponding to a peak in a correlation sequence derived from the physiological signal;

determine an expected correlation lag value based on the skew metric value; and

qualify or disqualify the correlation lag value based on a comparison between the correlation lag value and the expected correlation lag value;

determine a physiological rate of the subject based on the correlation lag value when the correlation lag value is qualified; and

display, on a display of the pulse oximeter, the physiological rate of the subject.

7. The processing module of claim 6, further configured to compare the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values.

8. The processing module of claim 7, further configured to:

identify the expected correlation lag value from the reference set that most closely matches the determined skew metric value;

determine a difference value indicative of a difference between the determined correlation lag value and the expected correlation lag value; and

compare the difference value to a threshold.

9. The processing module of claim 8, wherein the threshold is based on the determined correlation lag value.

10. The processing module of claim 6, further configured to compare the skew metric to a threshold.

11. A method for processing physiological information of a subject by a pulse oximeter, comprising:

receiving, using the pulse oximeter, a physiological signal derived from a detector output of a pulse oximetry sensor, wherein the pulse oximetry sensor is configured to detect light attenuated by the subject;

determining, using the pulse oximeter, a skew metric value based on the physiological signal;

determining, using the pulse oximeter, a correlation lag value corresponding to a peak in a correlation sequence derived from the physiological signal;

determining, using the pulse oximeter, an expected correlation lag value based on the skew metric value;

qualifying or disqualifying, using the pulse oximeter, the correlation lag value based on a comparison between the correlation lag value and the expected correlation lag value;

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

displaying, on a display of the pulse oximeter, the physiological rate of the subject.

12. The method of claim 11, wherein qualifying or disqualifying the particular value comprises comparing the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values.

13. The method of claim 12, wherein comparing the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values comprise:

identifying the expected correlation lag value from the reference set that most closely matches the determined skew metric value;

determining a difference value indicative of a difference between the determined correlation lag value and the expected correlation lag value; and

comparing the difference value to a threshold.

14. The method of claim 13, wherein the threshold is based on the determined correlation lag value.

15. The method of claim 11, wherein qualifying or disqualifying the particular value comprises comparing the skew metric to a threshold.

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

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

receive a physiological signal derived from a detector output of a pulse oximetry sensor, wherein the pulse oximetry sensor is configured to detect light attenuated by the subject;

determine a skew metric value based on the physiological signal;

determine a correlation lag value corresponding to a peak in a correlation sequence derived from the physiological signal;

determine an expected correlation lag value based on the skew metric value;

qualify or disqualify the correlation lag value based on a comparison between the correlation lag value and the expected correlation lag value;

determine a physiological rate of the subject based on the correlation lag value when the correlation lag value is qualified; and

display, on a display of the pulse oximeter, the physiological rate of the subject.

17. The non-transitory computer-readable medium of claim 16, further comprising computer program instructions recorded thereon for causing the pulse oximeter to compare the skew metric and the correlation lag value to a reference set of skew metric values and correlation lag values.

18. The non-transitory computer-readable medium of claim 17, further comprising computer program instructions recorded thereon for causing the pulse oximeter to:

identify the expected correlation lag value from the reference set that most closely matches the determined skew metric value;

determine a difference value indicative of a difference between the determined correlation lag value and the expected correlation lag value; and

compare the difference value to a threshold.

19. The non-transitory computer-readable medium of claim 18, wherein the threshold is based on the determined correlation lag value.

20. The non-transitory computer-readable medium of claim 16, further comprising computer program instructions recorded thereon for causing the pulse oximeter to compare the skew metric to a threshold.