Method and apparatus for determining the cerebral state of a patient with fast response

• US 6,801,803 B2
• Filed: 04/15/2002
• Issued: 10/05/2004
• Est. Priority Date: 10/16/2000
• Status: Expired due to Term

• Current Assignee: Instrumentarium Dental Incorporated (Envista Holdings Corporation)
• Original Assignee: Instrumentarium Dental Incorporated (Envista Holdings Corporation)
• Inventors: Viertiö-Oja, Hanna Elina
• Primary Examiner(s): Nasser, Robert L.
• Assistant Examiner(s): Mallari, Patricia C.
• Application Number:
  US10/123,056
• Publication Number:
  US 20030055355A1
• Time in Patent Office: 904 Days
• Field of Search: 600/544-546, 600/300-301, 600/508
• US Class Current: 600/544
• CPC Class Codes: A61B 2505/05 Surgical care
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/16 Devices for psychotechnics using teaching or educational appliances G09B1/00 - G09B7/00; Testing reaction times ; Devices for evaluating the psychological state
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/389 Electromyography [EMG]
• CPC Class Codes: A61B 5/4821 Determining level or depth of anaesthesia A61B5/1106 takes precedence
• CPC Class Codes: A61B 5/6814 Head
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06F 2218/08 Feature extraction

Abstract

A method and apparatus for ascertaining the depth of anesthesia of the patient. In one embodiment, the entropy of the patient'"'"'s EEG signal data is determined as an indication of the depth of anesthesia. A frequency domain power spectrum quantity is obtained from the patient'"'"'s EMG signal data. The latter quantity can be updated more frequently than the EEG entropy due to its higher frequency. The EEG entropy indication and the EMG power spectrum indication can be combined into a composite indicator that provides an immediate indication of changes in the state of the patient. In a further embodiment, the frequency range over which the entropy of the biopotential signal from the patient is determined is selected to encompass both EEG signal data and EMG signal data and the entropy so determined used as an indication of the patients state. In addition, entropy of the EEG range alone can be used together with the entropy of the broadened range to indicate separately contributions from EEG and EMG. In a more generalized version of the further embodiment, a set of frequency components obtained from selected frequency ranges is utilized in determining entropy. The patient signal data from which the frequency components are extracted are obtained from time windows of differing lengths so that the resulting entropy indication will have optimally fast response times.

Claims

1. A method for ascertaining the cerebral state of a patient, including a state resulting from the administration of a drug, said method comprising the steps of:

(a) obtaining biopotential signal data from the patient, the biopotential signal data containing EEG signal data and EMG signal data, the EMG signal data being primarily of a higher frequency than the EEG signal data which is primarily of a lower frequency;

(b) collecting the biopotential signal data over a plurality of time periods of differing lengths;

(c) subjecting the biopotential signal data of each of the time periods to spectral decomposition to obtain the frequency components of the collected biopotential signal data;

(d) selecting frequency components in a selected frequency band from the decomposed biopotential signal data for each of the time periods;

(e) analyzing the frequency components of a desired number of the frequency bands to obtain a measure of the complexity of the frequency components over a frequency range formed from the selected frequency bands; and

(f) providing the measure so obtained as an indication of the cerebral state of the patient.

2. The method according to claim 1 further defined as establishing the lengths of the time periods dependent on the frequency band of the frequency components selected in step (d).

3. The method according to claim 2 further defined as establishing the lengths of the time periods to provide a desired minimum number of cycles of biopotential signal data frequency components in the frequency band selected in step (d).

4. The method according to claim 1 further including the step of establishing the lengths of the time periods to produce optimally fast response time in ascertaining the cerebral state of the patient.

5. The method according to claim 1 further defined as utilizing the frequency components of at least two frequency bands.

6. The method according to claim 5 further defined as establishing the frequency bands in accordance with the magnitude of at least one of the EEG and EMG signal data.

7. The method according to claim 1 wherein the frequency bands are selected to include at least one frequency band containing primarily EMG signal data.

8. The method according to claim 5 wherein the frequency bands are selected to include at least one frequency band containing primarily EEG signal data.

9. The method according to claim 8 wherein the frequency bands are selected to include a plurality of frequency bands containing primarily EEG signal data.

10. The method according to claim 1 wherein step (e) is further defined as analyzing frequency components for frequency bands including EEG and EMG signal data.

11. The method according to claim 10 further including the steps of additionally analyzing frequency components for a frequency band or frequency bands including primarily EEG signal data to obtain a measure of the complexity of the frequency components and providing the complexity measure so obtained as a further indication of the cerebral state of the patient.

12. The method according to claim 1 wherein step (d) is further defined as selecting frequency components in two desired frequency bands for the biopotential signal data for at least one of the time periods;

step (e) is further defined as analyzing the frequency components in the two frequency bands to obtain the complexity measure; and

the method includes the step of determining the difference between the two complexity measures and providing the difference for use in the indication of the cerebral state of the patient.

13. The method according to claim 1 further defined as one for ascertaining the hypnotic state of the patient.

14. The method according to claim 1 wherein step (e) is further defined as obtaining a measure of the entropy of the frequency components as the indication.

15. The method according to claim 14 wherein step (e) is further defined as obtaining the spectral entropy of the frequency components as the indication.

16. The method according to claim 14 wherein step (e) is further defined as obtaining the approximate entropy of the frequency components as the indication.

17. The method according to claim 1 wherein step (e) is further defined as obtaining a Lempel-Ziv complexity measure of the frequency components as the indication.

18. A method according to claim 1 wherein step (e) is further defined as obtaining the measure of complexity from fractal spectrum analysis.

19. The method according to claim 1 further defined as carrying out the spectral decomposition by means of a Fourier transform.

20. The method according to claim 1 further defined as repeating steps (e) and (f) to update the indication.

21. The method according to claim 20 further defined as one for ascertaining the hypnotic state of a patient.

22. A method for ascertaining the cerebral state of a patient, including a state resulting from the administration of a drug, said method comprising the steps of:

(a) obtaining biopotential signal data from the patient, the biopotential signal data containing EEG signal data and EMG signal data, the EMG signal data being primarily of a higher frequency than the EEG signal data which is primarily of a lower frequency;

(b) collecting the biopotential signal data over a plurality of time periods of differing lengths;

(c) subjecting the biopotential signal data of each of the time periods to decomposition to a set of basis functions;

(d) selecting spectral components in a desired class of basis functions for each of the time periods;

(e) analyzing the spectral components of a desired number of the classes of basis functions to obtain a complexity measure of the spectral components from the desired number of classes of basis functions; and

(f) providing the measure so obtained as an indication of the cerebral state of the patient.

23. The method according to claim 22 wherein step (d) is further defined as selecting spectral components in two desired classes of basis function for the biopotential signal data for at least one of the time periods;

step (e) is further defined as analyzing the spectral components in the two classes to obtain the complexity measures; and

the method includes the step of determining the difference between the two complexity measures and providing the difference for use in the indication of the cerebral state of the patient.

24. Apparatus for ascertaining the cerebral state of a patient, including a state resulting from the administration of a drug, said apparatus comprising:

(a) means for obtaining biopotential signal data from the patient, the biopotential signal data containing EEG signal data and EMG signal data, the EMG signal data being primarily of a higher frequency than the EEG signal data which is primarily of a lower frequency;

(b) means for recording the biopotential signal data over a plurality of time periods of differing lengths;

(c) means for spectrally decomposing the biopotential signal data of each of the time periods to obtain the frequency components of the collected biopotential signal data;

(d) means for selecting frequency components in a selected frequency band from the decomposed biopotential signal data for each of the time periods;

(e) means analyzing the frequency components of a desired number of the frequency bands to obtain a measure of the complexity of the frequency components over a frequency range formed from the selected frequency bands; and

(f) means providing the measure so obtained as an indication of the cerebral state of the patient.

25. The apparatus according to claim 24 wherein said recording means is further defined as establishing the lengths of the time periods dependent on the frequency band of the selected frequency components.

26. The apparatus according to claim 24 wherein said analyzing means is further defined as utilizing the frequency components of at least two frequency bands.

27. The apparatus according to claim 24 wherein said selecting means selects frequency bands including at least one frequency and containing primarily EMG signal data.

28. The apparatus according to claim 24 wherein said selecting means selects frequency bands including at least one frequency and containing primarily EEG signal data.

29. The apparatus according to claim 28 wherein said selecting means selects frequency bands including a plurality of frequency bands containing primarily EEG signal data.

30. The apparatus according to claim 24 further including means or additionally analyzing frequency components for a frequency band or frequency bands including primarily EEG signal data to obtain a measure of the complexity of the frequency components and means providing the complexity measure so obtained as a further indication of the cerebral state of the patient.

31. The apparatus according to claim 24 further including means for selecting frequency components in two desired frequency bands for the biopotential signal data for at least one of the time periods;

said analyzing means further analyzes the frequency components in the two frequency bands to obtain the complexity measure;

said apparatus includes means for determining the difference between the two complexity measures and said providing means provides the difference for use in the indication of the cerebral state of the patient.

32. The apparatus according to claim 24 further defined as one for ascertaining the hypnotic state of the patient.

33. The apparatus according to claim 24 wherein said analyzing means is further defined as obtaining a measure of the entropy of the frequency components as the indication.

34. The apparatus according to claim 33 wherein said analyzing means is further defined as obtaining the spectral entropy of the frequency components as the indication.

35. The apparatus according to claim 33 wherein said analyzing means is further defined as obtaining the approximate entropy of the frequency components as the indication.

36. The apparatus according to claim 24 wherein said analyzing means is further defined as obtaining a Lempel-Ziv complexity measure of the frequency components as the indication.

37. A apparatus according to claim 24 wherein said analyzing means is further defined as obtaining the measure of complexity from fractal spectrum analysis.

38. The apparatus according to claim 24 wherein said spectral decomposition means is further defined as carrying out the spectral decomposition by means of a Fourier transform.

39. Apparatus for ascertaining the cerebral state of a patient, including a state resulting from the administration of a drug, said apparatus comprising:

(a) means for obtaining biopotential signal data from the patient, the biopotential signal data containing EEG signal data and EMG signal data, the EMG signal data being primarily of a higher frequency than the EEG signal data which is primarily of a lower frequency;

(b) means for recording the biopotential signal data over a plurality of time periods of differing length;

(c) means for subjecting the biopotential signal data of each of the time periods to decomposition to a set of basis functions;

(d) means for selecting spectral components in a desired class of basis functions for each of the time periods;

(e) means analyzing the spectral components of a desired number of the classes of basis functions to obtain a complexity measure of the spectral components from the desired number of classes of basis functions; and

(f) means for providing the measure so obtained as an indication of the cerebral state of the patient.

40. The apparatus according to claim 39 including means for further selecting spectral components in two desired classes of basis functions for the biopotential signal data for at least one of the time periods;

said analyzing means further analyzes the spectral components in the two classes to obtain the complexity measures;

said apparatus includes means for determining the difference between the two complexity measures and said providing means provides the difference for use in the indication of the cerebral state of the patient.