Measurement of EEG reactivity

Abstract

The invention relates to a method and apparatus for assessing the reactivity observable in a certain physiological signal, especially the EEG signal, of a comatose subject. In order to obtain an objective and a reliable measure of the reactivity automatically and without the presence of a trained EEG specialist, a time reference corresponding to a stimulus is detected and the physiological signal data obtained from the subject is aligned with the time reference. Two sets of values are determined for a measure indicative of the amount of irregularity in the physiological signal data, both sets including at least one value of the said measure and having defined positions with respect to the time reference in time domain. Based on the two sets, the apparatus determines whether reactivity is present in the physiological signal data.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention and its preferred embodiments are described more closely with reference to the examples shown in FIG. 1 to 6 in the appended drawings, wherein:

FIG. 1 is a flow diagram illustrating one embodiment of the method of the invention;

FIG. 2 illustrates the time windows used for determining the EEG reactivity;

FIG. 3 is a flow diagram illustrating one embodiment for the reactivity determination in the embodiment of FIG. 1;

FIG. 4 a is a flow diagram illustrating another embodiment of the method of the invention;

FIG. 4 b is a flow diagram illustrating still another embodiment of the method of the invention;

FIG. 5 illustrates one embodiment of the apparatus/system of the invention; and

FIG. 6 illustrates another embodiment of the apparatus of the invention.

Claims

1. A method for assessing physiological signal reactivity of a subject, the method comprising the steps of: receiving physiological signal data obtained from a subject;applying a time reference corresponding to a stimulus;aligning the physiological signal data temporally with the time reference;deriving a first set of values for a first measure indicative of irregularity in the physiological signal data, the first set including at least one value of the first measure;producing a second set of values for the first measure, the second set being subsequent to the first set and including at least one value of the first measure; anddetermining, based on the first set and the second set, whether reactivity is present in the physiological signal data,wherein the first and second sets have defined positions with respect to the time reference in time domain.

2. A method according to claim 1, wherein the receiving step includes receiving EEG signal data from the subject.

3. A method according to claim 1, wherein the applying step includes applying the time reference, in which the time reference is a time instant corresponding to the stimulus.

4. A method according to claim 1, further comprising a step of supplying the stimulus to the subject.

5. A method according to claim 3, wherein the deriving step includes the sub-steps of defining N consecutive time windows preceding the time instant; anddetermining the first measure for each of the N time windows, whereby N values of the first measure are obtained for the first set.

6. A method according to claim 3, wherein the producing step includes the sub-steps of defining M consecutive time windows subsequent to the time instant; anddetermining the first measure for each of the M time windows, whereby M values of the first measure are obtained for the second set.

7. A method according to claim 3, wherein the deriving step includes the sub-steps of defining N consecutive time windows preceding the time instant step and determining the first measure for each of the N time windows, whereby N values of the first measure are obtained for the first set; andthe producing step includes the sub-steps of defining M consecutive time windows subsequent to the time instant and determining the first measure for each of the M time windows, whereby M values of the first measure are obtained for the second set.

8. A method according to claim 7, wherein the determining step includes the sub-steps of: determining a second measure indicative of a standard deviation of the N values of the first measure;defining a third measure indicative of an average of the N values of the first measure;defining a fourth measure indicative of a maximum deviation of the M values from the average;comparing the fourth measure with the second measure; andgenerating, based on the comparing sub-step, a reactivity indicator indicating whether reactivity is detected in the physiological signal data.

9. A method according to claim 7, wherein the determining step includes the sub-steps of: defining a second measure indicative of an average of the N values of the first measure;defining a third measure indicative of a maximum deviation of the M values from the average;comparing the third measure with a predetermined limit value; andgenerating, based on the comparing sub-step, a reactivity indicator indicating whether reactivity is detected in the physiological signal data.

10. A method according to claim 8, wherein the generating sub-step includes generating the reactivity indicator, in which the reactivity indicator indicates a numeric reactivity value.

11. A method according to claim 10, wherein the generating sub-step includes generating the reactivity indicator indicating the numeric reactivity value, in which the numeric reactivity value is proportional to the maximum deviation.

12. A method according to claim 1, further comprising a step of defining an intensity of the stimulus, and wherein the determining step includes determining a numeric reactivity value based on the intensity of the stimulus.

13. A method according to claim 2, wherein the deriving step includes deriving the first set of values for the first measure and the producing step includes producing the second set of values for the first measure, in which the first measure is indicative of spectral entropy of the EEG signal data.

14. A method according to claim 2, wherein the deriving step includes deriving the first set of values for the first measure and the producing step includes producing the second set of values for the first measure, in which the first measure is one of the indicators in a set including an indicator of approximate entropy, an indicator of Shannon entropy, an indicator of Lempel-Ziv complexity, an indicator of irregularity obtained by spectral analysis, an indicator of irregularity obtained by a fractal spectral analysis, an indicator of irregularity obtained by a bispectral analysis, an indicator of irregularity obtained by a multispectral analysis, and an indicator of irregularity obtained by a stationarity analysis.

15. A method according to claim 4, further comprising a step of prompting a user to rate subject response based on the stimulus.

16. A method according to claim 4, wherein the supplying step comprises inducing an electromagnetic pulse in the interior of the subject's head.

17. A method according to claim 4, wherein the supplying step comprises supplying the stimulus, in which the stimulus is sensed by the subject's sensory nervous system.

18. An apparatus for assessing physiological signal reactivity of a subject, the apparatus comprising: reception means for receiving physiological signal data obtained from a subject;means for applying a time reference corresponding to a stimulus;alignment means for temporally aligning the physiological signal data with the time reference;first calculation means for deriving a first set of values for a first measure indicative of irregularity in the physiological signal data, the first set including at least one value of the first measure;second calculation means for producing a second set of values for the first measure, the second set being subsequent to the first set and including at least one value of the first measure; andthird calculation means for determining, based on the first set and the second set, whether reactivity is present in the physiological signal data,wherein the first and second sets have defined positions with respect to the time reference in time domain.

19. An apparatus according to claim 18, wherein the reception means are configured to receive EEG signal data from the subject.

20. An apparatus according to claim 18, wherein the means for applying the time reference are configured to apply a time instant corresponding to the stimulus.

21. An apparatus according to claim 18, further comprising stimulation means for generating the stimulus.

22. An apparatus according to claim 20, wherein the first calculation means are configured to define N consecutive time windows preceding the time instant and to determine the first measure for each of the N time windows, thereby to obtain N values of the first measure for the first set; andthe second calculation means are configured to define M consecutive time windows subsequent to the time instant and to determine the first measure for each of the M time windows, thereby to obtain M values of the first measure for the second set.

23. An apparatus according to claim 22, wherein the third calculation means are further configured to determine a second measure indicative of a standard deviation of the N values of the first measure, a third measure indicative of an average of the M values of the first measure, and a fourth measure indicative of a maximum deviation of the M values from the average;the third calculation means comprise comparison means for comparing the fourth measure with the second measure and reactivity indicator means, responsive to the comparison means, for generating a reactivity indicator indicating whether reactivity is detected in the EEG signal data.

24. An apparatus according to claim 22, wherein the third calculation means are further configured to determine a second measure indicative of an average of the M values of the first measure, and a third measure indicative of a maximum deviation of the M values from the average; andthe third calculation means comprise comparison means for comparing the third measure with a predetermined limit value and reactivity indicator means, responsive to the comparison means, for generating a reactivity indicator indicating whether reactivity is detected in the physiological signal data.

25. An apparatus according to claim 23, wherein the reactivity indicator means are configured to generate a numeric value for the reactivity indicator.

26. An apparatus according to claim 24, wherein the reactivity indicator means are configured to generate a numeric value for the reactivity indicator.

27. An apparatus according to claim 21, further comprising means for prompting a user to rate subject response based on the stimulus.

28. An apparatus according to claim 18, further comprising means for defining an intensity of the stimulus, and wherein the third calculation means are configured to determine a numeric reactivity value based on the intensity.

29. An apparatus according to claim 21, wherein the stimulation means are configured to induce an electromagnetic pulse in the interior of the subject's head.

30. An apparatus according to claim 21, wherein the stimulus is sensed by the subject's sensory nervous system.

31. An apparatus for assessing physiological signal reactivity of a subject, the apparatus comprising: a memory unit configured to receive physiological signal data obtained from a subject;a first controller configured to detect a time reference corresponding to a stimulus and to align the physiological signal data temporally with the time reference;a second controller configured to derive a first set of values for a first measure indicative of irregularity in the physiological signal data, the first set including at least one value of the first measure;a third controller configured to produce a second set of values for the first measure, the second set being subsequent to the first set and including at least one value of the first measure after the time instant; anda fourth controller configured to determine, based on the first set and the second set, whether reactivity is present in the physiological signal data,wherein the first and second sets have defined positions with respect to the time reference in time domain.

32. An apparatus according to claim 31, further comprising a stimulator module configured to generate the stimulus, wherein the stimulus is an electromagnetic pulse.

33. An apparatus according to claim 31, further comprising a stimulator module configured to generate the stimulus, wherein the stimulus is sensed by the subject's sensory nervous system.

34. A computer program product for assessing physiological signal reactivity of a subject, the computer program product comprising: a first program code portion configured to apply a time reference corresponding to a stimulus and to align physiological signal data obtained from a subject with the time reference; anda second program code portion configured to derive a first set of values for a first measure indicative of irregularity in the physiological signal data, the first set including at least one value of the first measure;a third program code portion configured to produce a second set of values for the first measure, the second set being subsequent to the first set and including at least one value of the first measure after the time instant; anda fourth program code portion configured to determine, based on the first and second sets, whether reactivity is present in the physiological signal data,wherein the first and second sets have defined positions with respect to the time reference in time domain.