Objective pain measurement system and method

• US 20020107434A1
• Filed: 07/05/2001
• Published: 08/08/2002
• Est. Priority Date: 07/06/2000
• Status: Active Grant

• Current Assignee: Algodyne Limited
• Original Assignee: Algodyne Limited
• Inventors: Lewinsky, Reuven, Lange, Daniel H.
• Granted Patent: US 6,757,558 B2
• Time in Patent Office: Days
• US Class Current: 600/301
• CPC Class Codes: A61B 5/1106 to assess neuromuscular blockade, e.g. to estimate depth of anaesthesia
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]
• CPC Class Codes: A61B 5/4824 Touch or pain perception evaluation A61B5/4821 takes precedence
• CPC Class Codes: A61B 5/483 by thermal stimulation
• CPC Class Codes: A61B 5/6833 Adhesive patches

Abstract

Methods, apparatuses and systems relating to the objective measurement of the subjective perception of pain in a subject are disclosed. In one aspect, a system for objectively measuring a subjective perception of pain by a subject comprises a plurality of electrodes, including a left channel electrode and a right channel electrode. The plurality of electrodes measures electrical activity at a respective plurality of sites on the subject to generate at least two sets of electrical activity measurements. The system further comprises a processor for processing the at least two sets of electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other to identify the presence of pain in the subject.

Claims

1. A system for objectively measuring a subjective sensation of pain by a subject comprising:

(a) a plurality of sensors for measuring electrical activity at a respective plurality of sites on the subject to generate a set of electrical activity measurements; and

(b) a processor connected to the plurality of sensors for processing the set of electrical activity measurements into a normalized signal, determining a level value for the normalized signal within a predetermined range of frequencies, and scaling the level value for the signal into an objective pain measurement.

2. The system of claim 1, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

3. The system of claim 1, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

4. The system of claim 3, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

5. The system of claim 1, wherein the processor processes the electrical activity measurements by normalizing the set of electrical activity measurements into a set of normalized values, applying digital filtering to the set of normalized values, and specifying the normalized signal from the set of normalized values.

6. The system of claim 5, wherein the processor normalizes the set of electrical activity measurements into a set of normalized values by subtracting a mean of the electrical activity measurements and dividing by a standard deviation of the electrical activity measurements from the electrical activity measurements.

7. The system of claim 6, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

8. The system of claim 7, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

9. The system of claim 1, wherein the processor comprises an analog processor.

124. The system as in claim 1, 2, 5, 6, 7 or 9, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

10. A method of objectively measuring a level of pain subjectively perceived by a subject comprising the steps of:

(a) selecting a plurality of sites on the subject for sensing electrical activity;

(b) making electrical activity measurements for the plurality of sites;

(c) processing the electrical activity measurements into a normalized signal; and

(d) determining a level value for the normalized signal within a predetermined range of frequencies.

11. The method of claim 10, further comprising a step of scaling the level value for the normalized signal into an objective pain measurement.

12. The method of claim 10, wherein steps (b) through (d) are performed by analog processing.

13. The method of claim 10, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

14. The method of claim 10, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

15. The method of claim 14, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

16. The method of claim 10, wherein the processing step is performed by normalizing the set of electrical activity measurements into a set of normalized values, applying digital filtering to the set of normalized values, and specifying the normalized signal from the set of normalized values.

17. The method of claim 16, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

18. The method of claim 17, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

20. The computer-readable medium of claim 19, further comprising a step of scaling the level value for the normalized signal into an objective pain measurement.

21. The computer-readable medium of claim 19, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

22. The computer-readable medium of claim 19, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

23. The computer-readable medium of claim 22, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

24. The computer-readable medium of claim 19, wherein the processing step is performed by normalizing the set of electrical activity measurements into a set of normalized values, applying digital filtering to the set of normalized values, and extracting the normalized signal from the set of normalized values.

25. The computer-readable medium of claim 24, wherein the level value for the normalized signal comprises a measurement of the power spectrum of the normalized signal.

26. The computer-readable medium of claim 25, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

28. The system of claim 27, further comprising means for scaling the value for the signal into an objective pain measurement.

30. The system of claim 29, the processor comparing the at least two normalized signals by measuring linearity and correlation between the at least two normalized signals.

31. The system of claim 30, the processor measuring linearity between the at least two normalized signals by determining a coherence value between the at least two normalized signals, and measuring correlation between the at least two normalized signals by determining a correlation coefficient for the at least two normalized signals.

32. The system of claim 31, the processor registering the subjective perception of pain by the subject when the coherence value exceeds a predetermined linearity threshold and the correlation coefficient exceeds a predetermined correlation threshold.

33. The system of claim 32, the processor determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

34. The system of claim 33, wherein the level value comprises a measurement of the power spectrum.

35. The system of claim 34, wherein the left channel electrode is for positioning on a left side of the subject'"'"'s forehead and the right channel electrode is for positioning on a right side of the subject'"'"'s forehead.

36. The system of claim 35, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

37. The system of claim 29, the processor determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

38. The system of claim 37, wherein the level value comprises a measurement of the power spectrum.

39. The system of claim 37, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

40. The system of claim 29, wherein the left channel electrode is for positioning on a left side of the subject'"'"'s forehead and the right channel electrode is for positioning on a right side of the subject'"'"'s forehead.

125. The method as in claim 10, 11, 12, 13, 16 or 17, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

126. The computer-readable medium as in claim 19, 20, 21 or 24, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

127. The system as in claim 29, 30, 31, 32, 33, 34, 35, 37, 38 or 40, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

128. The method as in claim 40, 41, 42, 43, 44, 45, 46, 47, 49, 50 or 52, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

19. A computer-readable medium having stored therein one or more sequences of instructions for objectively measuring a subjective perception of pain in a subject, said one or more sequences of instructions causing one or more processors to perform a plurality of acts, said acts comprising:

(a) reading electrical activity measurements from a plurality of sites on the subject;

(b) processing the electrical activity measurements into a normalized signal; and

(c) determining a level value for the normalized signal within a predetermined range of frequencies.

27. A system for objectively measuring a subjective sensation of pain in a subject comprising:

(a) means for measuring electrical activity at a respective plurality of sites on the subject to generate a set of electrical activity measurements; and

(b) processing means for processing the set of electrical activity measurements into a normalized signal, and determining a level value for the normalized signal within a predetermined range of frequencies.

29. A system for objectively measuring a subjective sensation of pain by a subject comprising:

(a) a plurality of sensors comprising a left channel electrode and a right channel electrode, for measuring electrical activity at a respective plurality of sites on the subject to generate at least two sets of electrical activity measurements; and

(b) a processor connected to the plurality of sensors for processing the at least two sets of electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other to detect the sensation of pain experienced by the subject.

41. A method of objectively measuring pain subjectively experienced by a subject, the method comprising the steps of:

(a) selecting a plurality of sites on the subject for sensing electrical activity;

(b) making electrical activity measurements for the plurality of sites;

(c) processing the electrical activity measurements into at least two normalized signals; and

(d) comparing the at least two normalized signals to each other to identify a presence of pain in the subject.

42. The method of claim 41, the comparing step being performed by measuring linearity and correlation between the at least two normalized signals.

43. The method of claim 42, wherein the linearity between the at least two normalized signals is measured by determining a coherence value between the at least two normalized signals, and wherein the correlation between the at least two normalized signals is measured by determining a correlation coefficient for the at least two normalized signals.

44. The method of claim 43, wherein a subjective perception of pain by the subject is registered when the coherence value exceeds a predetermined linearity threshold and the correlation coefficient exceeds a predetermined correlation threshold.

45. The method of claim 44, further comprising a step of determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

46. The method of claim 45, wherein the level value comprises a measurement of the power spectrum.

47. The method of claim 46, wherein one of the at least two normalized signals relates to electrical activity measurements on a left side of the subject'"'"'s forehead and a second of the at least two normalized signals related to electrical activity measurements on a right side of the subject'"'"'s forehead.

48. The method of claim 47, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

49. The method of claim 41, further comprising a step of determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

50. The method of claim 49, wherein the level value comprises a measurement of the power spectrum.

51. The method of claim 49, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

52. The method of claim 41, wherein one of the at least two normalized signals relates to electrical activity measurements on a left side of the subject'"'"'s forehead and a second of the at least two normalized signals related to electrical activity measurements on a right side of the subject'"'"'s forehead.

53. A computer-readable medium having stored therein one or more sequences of instructions for objectively evaluating a subjective sensation of pain in a subject, said one or more sequences of instructions causing one or more processors to perform a plurality of acts, said acts comprising:

(a) reading electrical activity measurements from a plurality of sites on the subject;

(b) processing the electrical activity measurements into at least two normalized signals; and

(c) comparing the at least two normalized signals to each other to identify a presence of pain in the subject.

54. The computer-readable medium of claim 53, the comparing step being performed by measuring linearity and correlation between the at least two normalized signals.

55. The computer-readable medium of claim 54, wherein the linearity between the at least two normalized signals is measured by determining a coherence value between the at least two normalized signals, and wherein the correlation between the at least two normalized signals is measured by determining a correlation coefficient for the at least two normalized signals.

56. The computer-readable medium of claim 55, wherein a subjective perception of pain by the subject is registered when the coherence value exceeds a predetermined linearity threshold and the correlation coefficient exceeds a predetermined correlation threshold.

57. The computer-readable medium of claim 56, said acts further comprising determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

58. The computer-readable medium of claim 57, wherein the level value comprises a measurement of the power spectrum of the one of the at least two normalized signals.

59. The computer-readable medium of claim 58, wherein one of the at least two normalized signals relates to electrical activity measurements on a left side of the subject'"'"'s forehead and a second of the at least two normalized signals related to electrical activity measurements on a right side of the subject'"'"'s forehead.

60. The computer-readable medium of claim 59, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

61. The computer-readable medium of claim 53, said acts further comprising determining a level value within a predetermined range of frequencies for one of the at least two normalized signals.

62. The computer-readable medium of claim 61, wherein the level value comprises a measurement of the power spectrum of the one of the at least two normalized signals.

63. The computer-readable medium of claim 62, wherein the predetermined range of frequencies is from about 0.1 Hertz to about 5 Hertz.

64. The computer-readable medium of claim 53, wherein one of the at least two normalized signals relates to electrical activity measurements on a left side of the subject'"'"'s forehead and a second of the at least two normalized signals related to electrical activity measurements on a right side of the subject'"'"'s forehead.

129. The computer readable medium as in claim 53, 54, 55, 56, 57, 58, 59, 61, 62 or 64, wherein the predetermined range of frequencies is from about 0.5 Hertz to about 2 Hertz.

65. A system for objectively measuring a subjective sensation of pain by a subject comprising:

(a) means for measuring electrical activity at a respective plurality of sites on the subject to generate at least two sets of electrical activity measurements; and

(b) processing means for processing the at least two sets of electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other to identify the presence of pain in the subject.

66. A network for objectively measuring pain subjectively perceived by subjects comprising:

(a) at least one signal acquisition subsystem for making electrical activity measurements at a respective plurality of sites on each of the subjects;

(b) a signal processing subsystem for analyzing the electrical activity measurements and for determining analysis values representing pain measurements for different periods of time; and

(c) a communication link linking the signal processing subsystem and the at least one signal acquisition subsystem for transmitting the electrical activity measurements of subjects to the signal processing subsystem.

67. The network of claim 66, wherein the signal acquisition subsystem comprises:

(a) a sensor array for obtaining an electrical signal at a site on the subject;

(b) an amplifier connected to the sensor array for amplifying the signal;

(c) a band-pass filter connected to the amplifier for at least partially removing components of the signal below about 0.1 Hertz and above about 5 Hertz; and

(d) an analog-to-digital converter connected to the band-pass filter for converting the signal into a set of discrete values comprising the electrical activity measurements.

68. The network of claim 67, wherein the signal processing subsystem comprises:

(a) a memory for storing the electrical activity measurements; and

(b) a processor connected to the memory for processing the electrical activity measurements into a normalized signal, determining a level value for the normalized signal within a predetermined range of frequencies, and scaling the level value for the signal into an objective pain measurement comprising one of the analysis values.

69. The network of claim 66, wherein the signal processing subsystem comprises:

(a) a memory for storing the electrical activity measurements; and

(b) a processor connected to the memory for processing the electrical activity measurements into a normalized signal, determining a level value for the normalized signal within a predetermined range of frequencies, and scaling the level value for the signal into an objective pain measurement comprising one of the analysis values.

70. The network of claim 66, wherein the communication link is the Internet.

71. A pain measurement report comprising:

(a) a reference to a subject; and

(b) a value representing an objective level of pain subjectively experienced by the subject.

72. The report of claim 71 further comprising a reference to a time to which the value relates.

73. The report of claim 72 further comprising additional values relating to different times.

74. The report of claim 71 further comprising additional values relating to different times.

75. A method of operating a network comprising the steps of:

(a) receiving electrical activity measurements on a subject from a remote location;

(b) analyzing the electrical activity measurements to obtain an objective pain measurement report;

(c) transmitting the objective pain measurement report to the remote location; and

(d) receiving non-medical patient information from the remote location for performing the analyzing step.

76. A system for acquiring a signal representative of a subjective perception of pain by a subject comprising:

(a) a sensor array for measuring an electrical signal at a site on the subject;

(b) an amplifier for amplifying the signal;

(c) a band-pass filter connected to the amplifier for at least partially removing components of the signal below about 0.1 Hertz and above about 5 Hertz; and

(d) an analog-to-digital converter for converting the signal into a set of discrete values.

77. The system of claim 76, wherein the sensor array is connected to the band-pass filter, and the analog-to-digital converter is connected to the amplifier.

78. The system of claim 76, wherein the sensor array is connected to the amplifier, and the analog-to-digital converter is connected to the band-pass filter.

79. The system of claim 78, further comprising an optical isolator connecting the sensor array and the amplifier.

80. The system of claim 79, further comprising a memory connected to the analog-to-digital converter for storing the set of discrete values.

81. The system of claim 76, further comprising a memory for storing the set of discrete values.

131. The system as in claim 76, 77, 78, 79, 80 or 81 wherein the band-pass filter is for at least partially removing components of the signal below about 0.5 Hertz and above about 2 Hertz.

82. A method of acquiring an electrical signal representative of a subjective perception of pain by a subject comprising the steps of:

(a) detecting an electrical signal at a site on the subject;

(b) amplifying the signal; and

(c) filtering the signal to at least partially remove components of the signal below about 0.1 Hertz and above about 5 Hertz.

83. The method of claim 82 further comprising a step of converting the signal into a set of discrete values.

84. The method of claim 83 further comprising the step of storing the set of discrete values.

85. The method of claim 82 further comprising the step of recording the signal.

130. The method as in claim 82, 83, 84 or 85, wherein the signal is filtered to at least partially remove components of the signal below about 0.5 Hertz and above about 2 Hertz.

86. A system for processing electrical activity measurements taken from a subject comprising:

(a) a memory for storing the electrical activity measurements; and

(b) a processor connected to the memory for processing the electrical activity measurements into a normalized signal, and determining a level value representative of an objective pain measurement for the normalized signal within a predetermined range of frequencies.

87. The system of claim 86, the processor for scaling the level value for the signal into the objective pain measurement.

88. The system of claim 86, the electrical activity measurements comprising at least two sets of electrical activity measurements, and the processor for processing the at least two sets of electrical activity measurements into at least two normalized signals, and for comparing the at least two normalized signals to each other to detect the experience of pain by the subject.

89. The system of claim 88, the processor for determining a confidence value associated with the level value based on the processor comparing the at least two normalized signals.

90. The system of claim 89, the processor for determining a pain value based on the level value and the confidence value.

91. A method of processing electrical activity measurements taken from a subject comprising the steps of:

(a) processing the electrical activity measurements into a normalized signal;

(b) determining a level value for the normalized signal within a predetermined range of frequencies; and

(c) scaling the level value for the signal into an objective pain measurement.

92. A system for processing electrical activity measurements taken from a subject comprising:

(a) a signal preparer for normalizing the electrical activity measurements;

(b) a pain intensity quantifier connected to the signal preparer for processing the normalized signal to determine a pain intensity level;

(c) a pain detector connected to the signal preparer for processing the normalized signal to determine a pain detection level; and

(d) a confidence assessor connected to the pain intensity quantifier and the pain detector for processing the pain detection level and the pain intensity level to determine an output pain level.

93. The system of claim 92, further comprising an output interface connected to the confidence assessor for displaying the output pain level.

94. A sensor array for measuring electrical activity on a forehead of a subject comprising:

(a) a sensor pad;

(b) a left channel electrode positioned proximate to a first edge of the sensor pad;

(c) a right channel electrode positioned proximate to a right edge of the sensor pad;

(d) a common electrode positioned substantially equidistant between the left channel electrode and the right channel electrode; and

(e) filtering circuitry electrically connected to the electrodes for filtering electrical signals from the electrodes in a frequency range between about 0.1 Hertz and about 5 Hertz.

95. The sensor array of claim 94 further comprising a connector grouping electrical connections from the electrodes into a single electrical interface.

96. The sensor array of claim 95 wherein the connector is electrically connected to a ground electrode.

97. The sensor array of claim 96 wherein the left channel electrode and the right channel electrode are substantially elliptical in shape such that the major axis of each of the left channel electrode and the right channel electrode is substantially perpendicular to the orientation of the subject.

98. The sensor array of claim 97 wherein the common electrode is substantially elliptical in shape such that the major axis of the common electrode is substantially perpendicular to the orientation of the subject.

99. The sensor array of claim 98 further including a ground electrode.

100. The sensor array of claim 99 wherein the ground electrode is positioned substantially equidistant from the left channel electrode and the right channel electrode and proximate to an upper edge of the sensor pad, and the common is positioned proximate to a lower edge of the sensor pad.

101. The sensor array of claim 100 wherein the ground electrode and the common electrode are substantially elliptical in shape such that the major axis of each of the common electrode and the ground electrode is substantially parallel to the orientation of the subject.

102. The sensor array of claim 101 wherein electrical connections from the electrodes include signal amplifier circuitry.

103. The sensor array of claim 102 wherein the sensor array comprises a shielding layer, a printed circuit layer beneath the shielding layer, and a foam layer beneath the printed circuit layer.

104. The sensor array of claim 94 wherein the left channel electrode and the right channel electrode are substantially elliptical in shape such that the major axis of each of the left channel electrode and the right channel electrode is substantially perpendicular to the orientation of the subject.

105. The sensor array of claim 94 wherein the common electrode is substantially elliptical in shape such that the major axis of the common electrode is substantially perpendicular to the orientation of the subject.

106. The sensor array of claim 94 further including a ground electrode.

107. The sensor array of claim 106 wherein the ground electrode is positioned substantially equidistant from the left channel electrode and the right channel electrode and proximate to an upper edge of the sensor pad, and the common is positioned proximate to a lower edge of the sensor pad.

108. The sensor array of claim 107 wherein the ground electrode and the common electrode are substantially elliptical in shape such that the major axis of each of the common electrode and the ground electrode is substantially parallel to the orientation of the subject.

109. The sensor array of claim 94 wherein electrical connections from the electrodes include signal amplifier circuitry.

110. The sensor array of claim 94 wherein the sensor array comprises a shielding layer, a printed circuit layer beneath the shielding layer, and a foam layer beneath the printed circuit layer.

132. The sensor array as in any one of claims 94-110, wherein the frequency range is between about 0.5 Hertz and about 2 Hertz.

111. A physiological monitor for measuring vital signs of a subject comprising;

(a) a system for objectively measuring a subjective perception of pain; and

(b) a thermometer.

112. The physiological monitor of claim 111, further comprising a pulse meter.

113. The physiological monitor of claim 112, further comprising a blood pressure gauge.

114. The physiological monitor of claim 113, further comprising a respiratory gauge.

116. The physiological monitor of claim 115, further comprising a blood pressure gauge.

117. The physiological monitor of claim 116, further comprising a respiratory gauge.

119. The physiological monitor of claim 118, further comprising a respiratory gauge.

123. The electrical signal of claim 122, wherein the site on the subject is the forehead.

115. A physiological monitor for measuring vital signs of a subject comprising;

(a) a system for objectively measuring a subjective perception of pain; and

(b) a pulse meter.

118. A physiological monitor for measuring vital signs of a subject comprising:

(a) a system for objectively measuring a subjective perception of pain; and

(b) a blood pressure gauge.

120. A physiological monitor for measuring vital signs of a subject comprising;

(a) a system for objectively measuring a subjective perception of pain; and

(b) a respiratory gauge.

121. A system for delivering medication for reducing pain in a subject comprising:

(a) a reservoir for containing the medication;

(b) a delivery device connected to the reservoir for delivering the medication to the subject;

(c) a delivery counter connected to the reservoir for measuring the medication transferred between the reservoir and the delivery device;

(d) an objective pain measurement device for objectively measuring a subjective perception of the pain in the subject;

(e) a medication delivery controller in communication with the objective pain measurement device, the delivery counter and the delivery device for controlling the amount of medication delivered to the subject by the delivery device based on a delivery rate communicated by the delivery counter and an objective pain measurement communicated by the objective pain measurement device.

122. An electrical signal containing information objectively describing an intensity of a subjective experience of pain in a subject obtained by a process comprising the steps of:

(a) selecting a site on the subject for sensing electrical activity;

(b) detecting electrical activity from the site; and

(c) filtering the electrical activity within a frequency range of about 0.1 Hertz to about 5 Hertz.