Measurement of EEG Reactivity

• US 20080194981A1
• Filed: 02/14/2007
• Published: 08/14/2008
• Est. Priority Date: 02/14/2007
• Status: Active Grant

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Virtanen, Juha, Salmi, Tapani, Viertio-Oja, Hanna E., Sarkela, Mika
• Granted Patent: US 7,844,324 B2
• Time in Patent Office: Days
• US Class Current: 600/544
• CPC Class Codes: A61B 5/377 using evoked responses
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: G16H 10/60 for patient-specific data, e.g. for electronic patient records

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 valid signal model is constructed for an EEG signal obtained from the subject. A time reference corresponding to a stimulus is applied and further signal data is obtained from the time series, the further signal data being subsequent to the time reference. By employing the further signal data, the method tests whether the signal model remains to be a valid signal model for the EEG signal also after the stimulus, and indicates, based on the test, whether reactivity is present in the physiological signal.

Claims

1. A method for assessing physiological signal reactivity of a subject, the method comprising:

constructing, based on a time series of a physiological signal obtained from a subject, a signal model for the physiological signal;

applying a time reference corresponding to a stimulus;

obtaining further signal data from the time series, the further signal data being subsequent to the time reference;

testing, whether the signal model is a valid signal model for the physiological signal, wherein the testing includes employing the further signal data; and

indicating, based on the testing, whether reactivity is present in the physiological signal.

2. A method according to claim 1, wherein the constructing includes constructing the signal model based on the time series of the physiological signal, in which the physiological signal is an EEG signal.

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

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

5. A method according to claim 1, wherein the constructing includes constructing the signal model based on the time series of the physiological signal, in which the signal model is an autoregressive model.

6. A method according to claim 1, wherein the testing includes

calculating a prediction value based on the signal model;

and

defining a prediction error based on the further signal data and the prediction value.

7. A method according to claim 6, wherein the indicating includes comparing the prediction error with a predetermined threshold value and deciding, based on the comparing, whether reactivity is present in the physiological signal.

8. A method according to claim 6, wherein the defining includes defining the prediction error, in which the prediction error is dependent on the difference between the prediction value and a value obtained in the further signal data.

9. A method according to claim 1, wherein

the constructing includes deriving the signal model based on a first time window of the time series and first data based on the signal model;

and

the testing includes deriving (i) a further signal model based on a second time window of the time series and second data based on the further signal model, wherein the second time window includes the further signal data, and (ii) an error value dependent on the difference of the first and second data.

10. A method according to claim 1, wherein the constructing includes deriving the first data based on the signal model and the testing includes deriving the second data based on the further signal model, in which the signal model and the further signal model are dependent on an autocorrelation function.

11. A method according to claim 4, wherein the supplying includes supplying the stimulus to the subject, in which the stimulus is a selected stimulus in a sequence comprising a plurality of stimuli in ascending order of intensity.

12. A method according to claim 11, further comprising repeating the constructing, applying, obtaining, and testing for the next stimulus in the sequence, wherein the repeating is performed as long as the testing indicates that reactivity is present in the physiological signal.

13. A method according to claim 12, wherein the indicating further includes determining, based on the intensity of a stimulus, a numeric value for the reactivity, in which the stimulus is the first stimulus in the sequence for which the determining indicates that reactivity is present in the physiological signal.

14. An apparatus for assessing physiological signal reactivity of a subject, the apparatus comprising:

a calculation unit configured to construct, based on a time series of a physiological signal obtained from a subject, a signal model for the physiological signal;

a control unit configured to apply a time reference corresponding to a stimulus;

a reception unit configured to receive further signal data from the time series, the further signal data being subsequent to the time reference;

a test unit configured to test, through employment of the further signal data, whether the signal model is a valid signal model for the physiological signal; and

an indicator unit, responsive to the test unit, configured to indicate, whether reactivity is present in the physiological signal.

15. An apparatus according to claim 14, wherein the physiological signal is an EEG signal.

16. An apparatus according to claim 14, wherein the control unit is configured to apply a time instant that corresponds to the stimulus.

17. An apparatus according to claim 14, further comprising a stimulation unit configured to supply the stimulus to the subject.

18. An apparatus according to claim 14, wherein the calculation unit is configured to construct an autoregressive model.

19. An apparatus according to claim 14, wherein the test unit is configured to

calculate a prediction value based on the signal model and

define a prediction error based on the further signal data and the prediction value.

20. An apparatus according to claim 19, wherein the test unit is configured to compare the prediction error with a predetermined threshold value.

21. An apparatus according to claim 19, wherein the prediction error is dependent on the difference between the prediction value and a value obtained in the further signal data.

22. An apparatus according to claim 14, wherein

the calculation unit is configured to derive the signal model based on a first time window of the time series and first data based on the signal model, and

the test unit is configured to define (i) a further signal model based on a second time window of the time series and second data based on the further signal model, wherein the second time window includes the further signal data, and (ii) an error value dependent on the difference of the first and second data.

23. An apparatus according to claim 22, wherein the signal model and the further signal model are dependent on an autocorrelation function.

24. An apparatus according to claim 17, wherein the stimulus is a selected stimulus in a sequence comprising a plurality of stimuli in ascending order of intensity.

25. An apparatus for assessing physiological signal reactivity of a subject, the apparatus comprising:

calculation means for constructing, based on a time series of a physiological signal obtained from a subject, a valid signal model for the physiological signal;

control means for applying a time reference corresponding to a stimulus;

reception means for receiving further signal data from the time series, the further signal data being subsequent to the time reference;

testing means for testing, through employment of the further signal data, whether the signal model is a valid signal model for the physiological signal; and

indicator means, responsive to the test unit, for indicating, whether reactivity is present in the physiological signal.

26. A computer program product for assessing physiological signal reactivity of a subject, the computer program product comprising:

a first program code portion configured to construct, based on a time series of a physiological signal obtained from a subject, a valid signal model for the physiological signal;

a second program code portion configured to apply a time reference corresponding to a stimulus;

a third program code portion configured to test, through employment of further signal data of the time series, whether the signal model is a valid signal model for the physiological signal, wherein the further signal data is subsequent to the time reference; and

a fourth program code portion, responsive to the third program code portion, configured to indicate whether reactivity is present in the physiological signal.