Determination of clinical stress of a subject in pulse oximetry

• US 20060217615A1
• Filed: 03/24/2005
• Published: 09/28/2006
• Est. Priority Date: 03/24/2005
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Huiku, Matti, Takala, Panu
• Granted Patent: US 7,635,337 B2
• Time in Patent Office: Days
• US Class Current: 600/484
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/4824 Touch or pain perception evaluation A61B5/4821 takes precedence

Abstract

The invention relates to the determination of the clinical stress of a subject. In order to bring about an uncomplicated and cost-effective method for monitoring the stress status of a subject, plethysmographic signal data is acquired from the subject and a first measurement signal is derived, which is indicative of a predetemined feature of the respiration modulation appearing in the said signal data. An index signal is then formed based on the first measurement signal and the index signal is employed as an index indicative of the clinical stress of the subject.

Claims

1. A method for determining clinical stress of a subject, the method comprising the steps of:

acquiring plethysmographic signal data from a subject;

deriving a first measurement signal indicative of a predetermined feature of respiration modulation appearing in the plethysmographic signal data;

forming an index signal based on the first measurement signal; and

employing the index signal as an index indicative of the clinical stress of the subject.

2. A method according to claim 1, wherein the deriving step includes deriving the first measurement signal indicative of the predetermined feature, in which the predetermined feature is one feature from a group including respiration rate, respiration rate variability, and respiration amplitude.

3. A method according to claim 1, wherein the forming step includes forming the index signal, in which the index signal is indicative of a change in the first measurement signal.

4. A method according to claim 1, wherein the forming step includes applying a first normalization transform to the first measurement signal, the first normalization transform being dependent on predetermined first history data, whereby a first normalized measurement signal having a predetermined value range is obtained, the first normalized measurement signal being the index signal.

5. A method according to claim 2, wherein

the deriving step includes deriving the first measurement signal indicative of the predetermined feature, in which the predetermined feature is the respiration rate;

and

the forming step includes a sub-step of generating a second measurement signal indicative of variability in the first measurement signal.

6. A method according to claim 5, wherein the forming step further includes applying a second normalization transform to the second measurement signal, the second normalization transform being dependent on predetermined second history data, whereby a second normalized measurement signal having a predetermined value range is obtained, the second normalized measurement signal being the index signal.

7. A method according to claim 5, wherein the forming step includes forming the index signal, in which the index signal is indicative of a change in the second measurement signal.

8. A method according to claim 5, wherein the forming step further includes a sub-step of calculating a weighted average of the first measurement signal and the second measurement signal, the weighted average forming the index signal.

9. A method according to claim 5, further comprising the steps of:

applying a first normalization transform to the first measurement signal, the first normalization transform being dependent on predetermined first history data, whereby a first normalized measurement signal having a predetermined value range is obtained; and

applying a second normalization transform to the second measurement signal, the second normalization transform being dependent on predetermined second history data, whereby a second normalized measurement signal having a predetermined value range is obtained.

10. A method according to claim 9, wherein the forming step further comprises a sub-step of calculating a weighted average of the first normalized measurement signal and the second normalized measurement signal, the weighted averave forming the index signal.

11. A method according to claim 1, further comprising a step of producing at least one further measurement signal from the plethysmographic signal data, wherein the at least one further measurement signal belongs to a group of signals including a first signal indicative of respiration amplitude, a second signal indicative of variability in the respiration amplitude, a third signal indicative of pulse amplitude in the plethysmographic signal data, a fourth signal indicative of pulse-to-pulse interval in the plethysmographic signal data, and a fifth signal indicative of variability in one of the third and fourth signals.

12. A method according to claim 5, further comprising a step of producing at least one further measurement signal from the plethysmographic signal data, wherein the at least one further measurement signal belongs to a group of signals including a first signal indicative of respiration amplitude, a second signal indicative of variability in the respiration amplitude, a third signal indicative of pulse amplitude in the plethysmographic signal data, a fourth signal indicative of pulse-to-pulse interval in the plethysmographic signal data, and a fifth signal indicative of variability in one of the third and fourth signals.

13. A method according to claim 12, wherein the forming step includes calculating a weighted average of the first measurement signal, the second measurement signal, and the at least one further measurement signal, the weighted averave forming the index signal.

14. A method according to claim 12, further comprising the steps of:

applying a first normalization transform to the first measurement signal, the first normalization transform being dependent on predetermined first history data, whereby a first normalized measurement signal having a predetermined value range is obtained;

applying a second normalization transform to the second measurement signal, the second normalization transform being dependent on predetermined second history data, whereby a second normalized measurement signal having a predetermined value range is obtained; and

applying a dedicated normalization transform to each of the at least one further measurement signal, each dedicated normalization transform being dependent on predetermined history data specific to the dedicated normalization transform concerned, whereby at least one further normalized measurement signal having a predetermined value range is obtained.

15. A method according to claim 14, wherein the forming step includes calculating a weighted average of the first normalized measurement signal, the second normalized measurement signal, and the at least one further normalized measurement signal, the weighted averave forming the index signal.

16. A method according to claim 12, wherein the acquiring step includes measuring the plethysmographic signal data from an ear and from a finger of the subject, whereby the plethysmographic signal data comprises ear originated signal data and finger originated signal data.

17. A method according to claim 16, further comprising the steps of:

comparing the ear originated signal data with the finger originated signal data; and

selecting whether the ear originated signal data or the finger originated signal data is to be employed for the first measurement signal and whether the ear originated signal data or the finger originated signal data is to be employed for at least one of the third, fourth, and fifth signals.

18. A method according to claim 16, further comprising a step of determining a transit time difference indicative of the time difference between corresponding signal peaks in the ear originated signal data and in the finger originated signal data.

19. A method according to claim 1, further comprising a step of controlling administration of at least one drug to the subject, wherein the controlling step is performed based on the index signal and the at least one drug is selected from a group of drugs including at least one analgesic drug and at least one sedative drug.

20. An apparatus for determining clinical stress of a subject, the apparatus comprising:

emitter means for emitting radiation at at least one wavelength,

detector means for receiving said radiation at the at least one wavelength and producing at least one electrical output signal,

first signal processing means for processing the at least one electrical output signal to obtain at least one plethysmographic signal;

second signal processing means for deriving a first measurement signal indicative of a predetermined feature of respiration modulation appearing in at least one of the at least one plethysmographic signal;

third signal processing means for forming an index signal based on the first measurement signal; and

indicator means for indicating the index signal as an indicator of the clinical stress of the subject.

21. An apparatus according to claim 20, wherein the predetermined feature is one feature from a group including respiration rate, respiration rate variability, and respiration amplitude.

22. An apparatus according to claim 20, wherein the index signal is indicative of a change in the first measurement signal.

23. An apparatus according to claim 20, wherein the third signal processing means are configured to apply a first normalization transform to the first measurement signal, the first normalization transform being dependent on predetermined first history data, to obtain a first normalized measurement signal having a predetermined value range, the first normalized measurement signal being the index signal.

24. An apparatus according to claim 21, wherein the predetermined feature is the respiration rate and the third signal processing means are configured to generate a second measurement signal indicative of variability in the first measurement signal.

25. An apparatus according to claim 24, wherein the third signal processing means are configured to form the index signal by applying a second normalization transform to the second measurement signal, the second normalization transform being dependent on predetermined second history data, to obtain a second normalized measurement signal having a predetermined value range, where the second normalized measurement signal is the index signal.

26. An apparatus according to claim 24, wherein the third signal processing means are configured to generate a signal indicative of a change in the second measurement signal, said signal being the index signal.

27. An apparatus according to claim 24, wherein the third signal processing means are configured to calculate a weighted average of the first measurement signal and the second measurement signal, the weighted average forming the index signal.

28. An apparatus according to claim 24, wherein the third signal processing means are configured to apply a first normalization transform to the first measurement signal, the first normalization transform being dependent on predetermined first history data, whereby a first normalized measurement signal having a predetermined value range is obtained, and a second normalization transform to the second measurement signal, the second normalization transform being dependent on predetermined second history data, whereby a second normalized measurement signal having a predetermined value range is obtained.

29. An apparatus according to claim 28, wherein the third signal processing means are configured to calculate a weighted average of the first and second normalized measurement signals, the weighted average forming the index signal.

30. An apparatus according to claim 24, further comprising fourth signal processing means for producing at least one further measurement signal from the plethysmographic signal data, wherein the at least one further measurement signal belongs to a group of signals including a first signal indicative of respiration amplitude, a second signal indicative of variability in the respiration amplitude, a third signal indicative of pulse amplitude in the plethysmographic signal data, a fourth signal indicative of pulse-to-pulse interval in the plethysmographic signal data, and a fifth signal indicative of variability in one of the second and third signals.

31. An apparatus according to claim 28, further comprising fourth signal processing means for producing at least one further measurement signal from the plethysmographic signal data, wherein the at least one further measurement signal belongs to a group of signals including a first signal indicative of respiration amplitude, a second signal indicative of variability in the respiration amplitude, a third signal indicative of pulse amplitude in the plethysmographic signal data, a fourth signal indicative of pulse-to-pulse interval in the plethysmographic signal data, and a fifth signal indicative of variability in one of the second and third signals.

32. An apparatus according to claim 30, wherein the third signal processing means are configured to calculate a weighted average of the first measurement signal, the second measurement signal, and the at least one further measurement signal, the weighted averave forming the index signal.

33. An apparatus according to claim 31, wherein the third signal processing means are configured to apply a dedicated normalization transform to each of the at least one further measurement signal, each dedicated normalization transform being dependent on predetermined history data specific to the dedicated normalization transform concerned, whereby at least one further normalized measurement signal having a predetermined value range is obtained.

34. An apparatus according to claim 33, wherein the third signal processing means are configured to calculate a weighted average of the first normalized measurement signal, the second normalized measurement signal, and the at least one further normalized measurement signal, the weighted averave forming the index signal.

35. An apparatus according to claim 20, wherein the emitter and detector means comprise first emitter and detector means to be attached on an ear of the subject and second emitter and detector means to be attached on a finger of the subject.

36. An apparatus according to claim 30, wherein

the emitter and detector means comprise first emitter and detector means to be attached on an ear of the subject and second emitter and detector means to be attached on a finger of the subject;

and

the first emitter and detector means are configured to supply at least one of the at least one plethysmographic signal to the second signal processing means for deriving the first measurement signal; and

the second emitter and detector means are configured to supply at least one of the at least one plethysmographic signal to the fourth signal processing means for producing at least one of the third, fourth, and fifth signals.

37. An apparatus according to claim 20, further comprising drug administration means for administering at least one drug to the subject, the drug administration means being responsive to the third signal processing means.

38. An apparatus for determining clinical stress of a subject, the apparatus comprising:

a light source configured to emit radiation at at least one wavelength;

a detector unit configured to receive said radiation at the at least one wavelength and to produce at least one electrical output signal,

a first signal processing unit configured to process the at least one electrical output signal to obtain at least one plethysmographic signals;

a second signal processing unit configured to derive a first measurement signal indicative of a predetermined feature of respiration modulation appearing in at least one of the at least one plethysmographic signal;

a third signal processing unit configured to form an index signal based on the first measurement signal; and

a display unit configured to indicate the index signal as an indicator of the clinical stress of the subject.

39. A computer program product for determining clinical stress of a subject in a pulse oximeter, the computer program product comprising:

a first program code portion configured to receive plethysmographic signal data;

a second program code portion configured to derive a first measurement signal from the plethysmographic signal data, the first measurement signal being indicative of a predetermined feature of respiration modulation appearing in the plethysmographic signal data; and

a third program code portion configured to form an index signal based on the first measurement signal, the index signal being indicative of the clinical stress of the subject.