Methods and systems for determining physiological information based on a correlation sequence

• US 9,314,209 B2
• Filed: 09/11/2012
• Issued: 04/19/2016
• 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): Fernandez, Katherine
• Assistant Examiner(s): Negarestan, Farshad
• Application Number:
  US13/609,448
• Publication Number:
  US 20140073938A1
• Time in Patent Office: 1,316 Days
• Field of Search: 600/301, 600/476, 600/479, 600/500
• 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 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• 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 6/5217 extracting a diagnostic or physiological parameter from medical diagnostic data
• CPC Class Codes: A61B 8/5223 for extracting a diagnostic or physiological parameter from medical diagnostic data for algorithms to analyse biomedical images G06T7/0012

Abstract

A physiological monitoring system may determine physiological information, such as physiological rate information, from a physiological signal. The system may generate a correlation sequence between two segments of the physiological signal at multiple correlation lag values. The system may compare the correlation sequence to a predetermined threshold, which may vary as a function of lag. Based on the comparison, the system may determine whether the correlation sequence value exceeds the threshold, and whether the correlation sequence value corresponds to a peak. The system may identify a lag value when the correlation sequence corresponding to the lag value exceeds the threshold and corresponds to a peak. The system may determine physiological rate information based on the identified lag value.

Claims

1. A subject 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 detects light attenuated by the subject; and

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

calculate a correlation sequence corresponding to multiple lag values based on the physiological signal, wherein the correlation sequence comprises a correlation sequence value corresponding to each of the multiple lag values;

for at least one lag value of the multiple lag values;

determine at least one threshold value corresponding to the at least one lag value of the multiple lag values, wherein the at least one threshold value varies as a predetermined function of lag values,

compare the correlation sequence value corresponding to the at least one lag value to a corresponding one of the at least one threshold value,

determine whether the correlation sequence value exceeds the corresponding threshold value, and

determine whether the correlation sequence value corresponds to a peak;

identify a particular lag value of the multiple lag values when the correlation sequence value corresponding to the particular lag value exceeds the corresponding threshold value and corresponds to a peak;

determine a physiological rate of the subject based on the identified particular lag value; and

display the physiological rate of the subject on a display.

2. The system of claim 1, wherein the at least one threshold value is a predetermined square root function of lag values.

3. The system of claim 1, wherein the pulse oximetry processor is further configured to sequentially compare the correlation sequence values corresponding to multiple lag values to corresponding ones of the at least one threshold value in ascending order of lag value until the particular lag value is identified.

4. The system of claim 1, wherein the pulse oximetry processor is further configured to calculate one value of the correlation sequence at a time, and wherein the at least one lag value comprises the most current lag value of the multiple lag values.

5. The system of claim 1, wherein the pulse oximetry processor is further configured to determine whether the correlation sequence value corresponds to a peak by:

determining for a predetermined number of first correlation sequence values adjacent to the correlation sequence value and corresponding to smaller lag values, that the first correlation sequence values are increasing with lag value; and

determining for a predetermined number of second correlation sequence values adjacent to the correlation sequence value and corresponding to larger lag values, that the second correlation sequence values are decreasing with lag value.

6. The system of claim 1, wherein the pulse oximetry processor is further configured to normalize the correlation sequence values to range between an upper value and a lower value.

7. The system of claim 1, wherein the pulse oximetry processor is further configured to normalize at least a portion of the physiological signal.

8. A processing module of a pulse oximeter for processing physiological information of a subject, wherein the processing module comprises a pulse oximetry processor configured to:

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

calculate a correlation sequence corresponding to multiple lag values based on the physiological signal, wherein the correlation sequence comprises a correlation sequence value corresponding to each of the multiple lag values;

for at least one lag value of the multiple lag values;

determine at least one threshold value corresponding to the at least one lag value of the multiple lag values, wherein the at least one threshold value varies as a predetermined function of lag values,

compare the correlation sequence value corresponding to the at least one lag value to a corresponding one of the at least one threshold value,

determine whether the correlation sequence value exceeds the corresponding threshold value, and

determine whether the correlation sequence value corresponds to a peak;

identify a particular lag value of the multiple lag values when the correlation sequence value corresponding to the particular lag value exceeds the corresponding threshold value and corresponds to a peak;

determine a physiological rate of the subject based on the identified particular lag value; and

display the physiological rate of the subject on a display.

9. The processing module of claim 8, wherein the at least one threshold value is a predetermined square root function of lag values.

10. The processing module of claim 8, wherein the pulse oximetry processor is further configured to sequentially compare the correlation sequence values corresponding to multiple lag values to corresponding ones of the at least one threshold value in ascending order of lag value until the particular lag value is identified.

11. The processing module of claim 8, wherein the pulse oximetry processor is further configured to calculate one value of the correlation sequence at a time, wherein the at least one lag value comprises the most current lag value of the multiple lag values.

12. The processing module of claim 8, wherein the pulse oximetry processor is further configured to determine whether the correlation sequence value corresponds to a peak by:

determining for a predetermined number of first correlation sequence values adjacent to the correlation sequence value and corresponding to smaller lag values, that the first correlation sequence values are increasing with lag value; and

determining for a predetermined number of second correlation sequence values adjacent to the correlation sequence value and corresponding to larger lag values, that the second correlation sequence values are decreasing with lag value.

13. The processing module of claim 8, wherein the pulse oximetry processor is further configured to normalize the correlation sequence values to range between an upper value and a lower value.

14. The processing module of claim 8, wherein the pulse oximetry processor is further configured to normalize at least a portion of the physiological signal.

15. A method for processing physiological information of a subject, comprising:

receiving, using a pulse oximetry processor, a physiological signal derived from an output of a detector of a pulse oximetry sensor, wherein the detector detects light attenuated by the subject;

calculating, using the pulse oximetry processor, a correlation sequence corresponding to multiple lag values based on the physiological signal, wherein the correlation sequence comprises a correlation sequence value corresponding to each of the multiple lag values;

for at least one lag value of the multiple lag values;

determining, using the pulse oximetry processor, at least one threshold value corresponding to the at least one lag value of the multiple lag values, wherein the at least one threshold value varies as a predetermined function of lag values,

comparing, using the pulse oximetry processor, the correlation sequence value corresponding to the at least one lag value to a corresponding one of the at least one threshold value,

determining, using the pulse oximetry processor, whether the correlation sequence value exceeds the corresponding threshold value, and

determining, using the pulse oximetry processor, whether the correlation sequence value corresponds to a peak;

identifying, using the pulse oximetry processor, a particular lag value of the multiple lag values when the correlation sequence value corresponding to the particular lag value exceeds the corresponding threshold value and corresponds to a peak;

determining, using the pulse oximetry processor, a physiological rate of the subject based on the identified particular lag value; and

displaying the physiological rate of the subject on a display.

16. The method of claim 15, wherein the at least one threshold value is a predetermined square root function of lag values.

17. The method of claim 15, further comprising sequentially comparing the correlation sequence values corresponding to multiple lag values to corresponding ones of the at least one threshold value in ascending order of lag value until the particular lag value is identified.

18. The method of claim 15, wherein calculating the correlation sequence comprises calculating one value of the correlation sequence at a time, and wherein the at least one lag value comprises the most current lag value of the multiple lag values.

19. The method of claim 15, wherein determining whether the correlation sequence value corresponds to a peak comprises:

determining for a predetermined number of first correlation sequence values adjacent to the correlation sequence value and corresponding to smaller lag values, that the first correlation sequence values are increasing with lag value; and

determining for a predetermined number of second correlation sequence values adjacent to the correlation sequence value and corresponding to larger lag values, that the second correlation sequence values are decreasing with lag value.

20. The method of claim 15, wherein calculating the correlation sequence comprises normalizing the correlation sequence values to range between an upper value and a lower value.

21. The method of claim 15, wherein calculating the correlation sequence comprises normalizing at least a portion of the physiological signal.

22. 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 oximetry processor to;

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

calculate a correlation sequence corresponding to multiple lag values based on the physiological signal, wherein the correlation sequence comprises a correlation sequence value corresponding to each of the multiple lag values;

for at least one lag value of the multiple lag values;

determine at least one threshold value corresponding to the at least one lag value of the multiple lag values, wherein the at least one threshold value varies as a predetermined function of lag values,

compare the correlation sequence value corresponding to the at least one lag value to a corresponding one of the at least one threshold value,

determine whether the correlation sequence value exceeds the corresponding threshold value, and

determine whether the correlation sequence value corresponds to a peak;

identify a particular lag value of the multiple lag values when the correlation sequence value corresponding to the particular lag value exceeds the corresponding threshold value and corresponds to a peak;

determine a physiological rate of the subject based on the identified particular lag value; and

display the physiological rate of the subject on a display.

23. The non-transitory computer-readable medium of claim 22, wherein the at least one threshold value is a predetermined square root function of lag values.

24. The non-transitory computer-readable medium of claim 22, further comprising computer program instructions recorded thereon for causing the pulse oximetry processor to sequentially compare the correlation sequence values corresponding to multiple lag values to corresponding ones of the at least one threshold value in ascending order of lag value until the particular lag value is identified.

25. The non-transitory computer-readable medium of claim 22, further comprising computer program instructions recorded thereon for causing the pulse oximetry processor to calculate one value of the correlation sequence at a time, wherein the at least one lag value comprises the most current lag value of the multiple lag values.

26. The non-transitory computer-readable medium of claim 22, further comprising computer program instructions recorded thereon for causing the pulse oximetry processor to determine whether the correlation sequence value corresponds to a peak by:

determining for a predetermined number of first correlation sequence values adjacent to the correlation sequence value and corresponding to smaller lag values, that the first correlation sequence values are increasing with lag value; and

determining for a predetermined number of second correlation sequence values adjacent to the correlation sequence value and corresponding to larger lag values, that the second correlation sequence values are decreasing with lag value.

27. The non-transitory computer-readable medium of claim 22, further comprising computer program instructions recorded thereon for causing the pulse oximetry processor to normalize the correlation sequence values to range between an upper value and a lower value.

28. The non-transitory computer-readable medium of claim 22, further comprising computer program instructions recorded thereon for causing the pulse oximetry processor to normalize at least a portion of the physiological signal.