Apparatus, software, and methods for cardiac pulse detection using a piezoelectric sensor

• US 20060167515A1
• Filed: 07/22/2005
• Published: 07/27/2006
• Est. Priority Date: 09/30/1999
• Status: Active Grant

• Current Assignee: Physio-Control Incorporated (Stryker Corporation)
• Original Assignee: Medtronic Emergency Response Systems Incorporated
• Inventors: Lank, Paula, Kelly, Patrick F., Nova, Richard C., O'Hearn, Patricia, Jayne, Cynthia P., Stickney, Ronald E., Joo, Tae H., Hampton, David R., Saltzstein, William E.
• Granted Patent: US 8,160,703 B2
• Time in Patent Office: Days
• US Class Current: 607/17
• CPC Class Codes: A61B 2560/0412 Low-profile patch shaped housings
• CPC Class Codes: A61B 2562/02 Details of sensors specially adapted for in-vivo measurements
• CPC Class Codes: A61B 5/1102 Ballistocardiography
• CPC Class Codes: A61B 5/1107 Measuring contraction of parts of the body, e.g. organ, muscle apparatus for measuring work or force in general G01L
• CPC Class Codes: A61B 5/361 Detecting fibrillation
• CPC Class Codes: A61B 5/7264 Classification of physiological signals or data, e.g. using neural networks, statistical classifiers, expert systems or fuzzy systems neural networks per se G06N3/00; expert systems per se G06N5/00
• CPC Class Codes: A61N 1/3712 Auto-capture, i.e. automatic adjustment of the stimulation threshold
• CPC Class Codes: A61N 1/3925 Monitoring; Protecting

Abstract

Signal data obtained from a piezoelectric sensor placed on a patient'"'"'s body is used to detect the presence of a cardiac pulse. The piezoelectric sensor has a transducing element adapted to sense movement due to a cardiac pulse and produce piezoelectric signal data in response thereto. Processing circuitry analyzes the piezoelectric signal data for a feature indicative of a cardiac pulse and determines whether a cardiac pulse is present in the patient based on the feature. In one aspect, the feature may be a temporal feature such as a relative change in energy. In another aspect, the feature may be a spectral feature such as the energy or frequency of a peak in the energy spectrum of the signal. In yet another aspect, the feature may be obtained by comparing the piezoelectric signal data with a previously-identified pattern known to predict the presence of a cardiac pulse. Multiple features may also be obtained from the piezoelectric signal data and classified to determine the presence of a cardiac pulse.

Claims

1. A medical device for detecting the presence of a cardiac pulse, comprising:

a piezoelectric sensor having a transducing element configured for placement on the surface of a patient'"'"'s body, the transducing element being adapted to sense movement in the patient'"'"'s body due to a cardiac pulse and produce piezoelectric signal data in response thereto; and

processing circuitry configured to analyze the piezoelectric signal data for a feature indicative of the presence of a cardiac pulse and determine whether a cardiac pulse is present based on the feature.

3. The medical device of claim 1, further comprising a display, in which the processing circuitry is configured to automatically report via the display whether a cardiac pulse is present in the patient.

4. The medical device of claim 1, further comprising a display, in which the processing circuitry is configured to automatically prompt via the display the application of chest compressions or cardiopulmonary resuscitation if the processing circuitry determines that a cardiac pulse is not present in the patient.

5. The medical device of claim 1, further comprising a defibrillation pulse generator in communication with the processing circuitry for delivering a defibrillation pulse to the patient if the processing circuitry determines that a cardiac pulse is not present in the patient.

9. The medical device of claim 1, in which the processing circuitry is configured to determine the feature indicative of a cardiac pulse from a temporal parameter in the piezoelectric signal data.

10. The medical device of claim 9, in which the feature indicative of a cardiac pulse is an amplitude of the piezoelectric signal data, the processing circuitry being configured to compare the amplitude to a threshold to determine whether a cardiac pulse is present.

11. The medical device of claim 9, in which the feature indicative of a cardiac pulse is an energy in the piezoelectric signal data, the processing circuitry being configured to compare the energy to a threshold to determine whether a cardiac pulse is present.

12. The medical device of claim 9, in which the feature indicative of a cardiac pulse is a derivative of the piezoelectric signal data, the processing circuitry being configured to compare the derivative to a threshold to determine whether a cardiac pulse is present.

13. The medical device of claim 9, in which the temporal parameter is an energy in the piezoelectric signal data, the processing circuitry being configured to determine a relative change in energy between an estimated first energy in the piezoelectric signal data and an estimated second energy in the piezoelectric signal data, and use the relative change in energy as the feature indicative of a cardiac pulse.

14. The medical device of claim 13, in which the first energy is estimated using a first set of piezoelectric signal data and the second energy is estimated using a second set of piezoelectric signal data, and in which the second set of piezoelectric signal data is obtained prior to the first set of piezoelectric signal data.

15. The medical device of claim 1, in which the processing circuitry is configured to determine the feature indicative of a cardiac pulse from a spectral parameter in the piezoelectric signal data.

16. The medical device of claim 15, in which the processing circuitry is configured to calculate an energy spectrum of the piezoelectric signal data and locate a peak energy in the energy spectrum, and in which the processing circuitry uses the energy value of the located peak energy as the feature indicative of a cardiac pulse.

17. The medical device of claim 15, in which the processing circuitry is configured to calculate an energy spectrum of the piezoelectric signal data and locate a peak energy in the energy spectrum, and in which the processing circuitry uses the frequency at which the located peak energy occurs as the feature indicative of a cardiac pulse.

18. The medical device of claim 1, in which the feature indicative of the presence of a cardiac pulse is first feature, and in which the processing circuitry is further configured to analyze the piezoelectric signal data for a second feature indicative of the presence of a cardiac pulse, the processing circuitry being configured to determine the presence of a cardiac pulse by evaluating the first and second features.

21. The medical device of claim 1, further comprising an electrode adapted to sense an electrocardiogram (ECG) signal in the patient and communicate ECG signal data to the processing circuitry, the processing circuitry being configured to analyze the ECG data in connection with the piezoelectric signal data to determine the feature indicative of a cardiac pulse.

22. The medical device of claim 21, in which the processing circuitry is further configured to determine the presence of a ventricular complex in the ECG data and determine the presence of a cardiac pulse in the patient if a ventricular complex occurs in the ECG data within an expected time period in relation to a feature in the piezoelectric signal data that indicates a cardiac pulse.

23. The medical device of claim 21, in which the processing circuitry is configured to analyze the ECG data and determine the presence of a ventricular complex in the ECG data, the processing circuitry being further configured to use the occurrence of a ventricular complex to identify the piezoelectric signal data to be used in determining the presence of a cardiac pulse.

24. The medical device of claim 21, further comprising a display, in which the processing circuitry is configured to prompt a message via the display recommending application of chest compressions or cardiopulmonary resuscitation to the patient if the processing circuitry determines that a cardiac pulse is not present in the patient and the ECG data obtained from the patient does not indicate a cardiac rhythm appropriate for immediate treatment by defibrillation therapy.

25. The medical device of claim 21, further comprising a defibrillation pulse generator, in which the processing circuitry is configured to instruct the defibrillation pulse generator to generate a defibrillation pulse if the processing circuitry determines that a cardiac pulse is not present in the patient and that ECG data obtained from the patient indicates a cardiac rhythm appropriate for treatment by defibrillation therapy.

27. The medical device of claim 21, further comprising a display, in which the processing circuitry determines whether the patient is in a state of pulseless electrical activity (PEA) by determining whether a ventricular complex is found in the ECG data and a cardiac pulse is not detected in the piezoelectric signal data, and prompts a message via the display reporting whether the patient is in a state of PEA based on the determination.

29. The medical device of claim 27, in which the processing circuitry is further configured to analyze the patient'"'"'s ECG data for at least ventricular fibrillation (VF), ventricular tachycardia (VT), and asystole, and if the patient is determined to be pulseless and not in a VF, VT, or asystole condition, the processing circuitry then prompting the message reporting that the patient is in a state of PEA.

31. The medical device of claim 1, in which the processing circuitry is configured to analyze the piezoelectric signal data for a feature indicative of the presence of a cardiac pulse by comparing the piezoelectric signal data to a previously-identified piezoelectric signal data pattern known to predict the presence of a cardiac pulse.

32. The medical device of claim 31, in which the comparison produces a pattern match statistic that is the feature indicative of the presence of a cardiac pulse, the processing circuitry being further configured to compare the feature to a predetermined pattern match threshold to determine whether a cardiac pulse is present in the patient.

36. The medical device of claim 1, further comprising:

an electrotherapy generator adapted for delivering electrotherapy to the patient,

wherein the processing circuitry being is further configured to prompt the delivery of an electrotherapy to the patient based on the presence of a cardiac pulse.

38. The medical device of claim 36, further comprising an electrode adapted to sense an electrocardiogram (ECG) signal in the patient and communicate ECG signal data to the processing circuitry, the processing circuitry being further configured to analyze the patient'"'"'s ECG signal data for ventricular tachycardia and prompt the delivery of defibrillation therapy to the patient if the patient is determined to be pulseless and experiencing ventricular tachycardia.

40. The medical device of claim 36, further comprising an electrode adapted to sense an electrocardiogram (ECG) signal in the patient and communicate ECG signal data to the processing circuitry, the processing circuitry-being further configured to analyze the patient'"'"'s ECG signal data for at least ventricular fibrillation (VF), ventricular tachycardia (VT), and asystole, and if the patient is determined to be pulseless and not in a VF, VT, or asystole condition, the processing circuitry then being configured to prompt delivery of electrotherapy designed specifically for pulseless electrical activity (PEA).

41. The medical device of claim 36, the processing circuitry being further configured to report the return of spontaneous circulation in the patient if a cardiac pulse is determined present in the patient after delivery of electrotherapy to the patient.

46. The medical device of claim 1, further comprising:

an electrotherapy generator for delivering pacing stimuli to the patient,

wherein the processing circuitry analyzes the piezoelectric signal data to determine whether a cardiac pulse occurred in the patient following the delivery of a pacing stimulus to the patient.

47. The medical device of claim 46, in which the processing circuitry is configured to increase the current of further pacing stimuli to be delivered to the patient if a cardiac pulse did not occur in the patient following the delivery of the pacing stimulus.

49. The medical device of claim 46, wherein the processing circuitry is configured to prompt a user of the device to increase the pacing stimuli current based on the determination.

2. (canceled)

6-8. -8. (canceled)

19-20. -20. (canceled)

26. (canceled)

28. (canceled)

30. (canceled)

33-35. -35. (canceled)

37. (canceled)

39. (canceled)

42-45. -45. (canceled)

48. (canceled)

50-86. -86. (canceled)

87. A method of determining the presence of a cardiac pulse, comprising:

obtaining piezoelectric signal data from a sensor having a piezoelectric transducing element placed on the surface of a patient'"'"'s body;

analyzing the piezoelectric signal data for a feature indicative of the presence of a cardiac pulse; and

determining whether a cardiac pulse is present in the patient based on the feature in the piezoelectric signal data.

88. The method of claim 87, in which analyzing the piezoelectric signal data includes evaluating a temporal parameter in the piezoelectric signal data.

89. The method of claim 88, in which evaluating a temporal parameter in the piezoelectric signal data includes:

estimating an instantaneous energy in the piezoelectric signal data;

estimating a background energy in the piezoelectric signal data; and

comparing the instantaneous energy with the background energy to produce the feature indicative of the presence of a cardiac pulse.

90. The method of claim 87, in which analyzing the piezoelectric signal data includes evaluating a spectral parameter in the piezoelectric signal data.

91. The method of claim 90, in which evaluating a spectral parameter in the piezoelectric signal data includes calculating an energy spectrum of the piezoelectric signal data and evaluating the energy spectrum to locate a peak energy value, in which the located peak energy value is used as the feature indicative of the presence of a cardiac pulse, and in which determining whether a cardiac pulse is present in the patient includes comparing the located peak energy value with a threshold energy value.

92. The method of claim 90, in which evaluating a spectral parameter in the piezoelectric signal data includes calculating an energy spectrum of the piezoelectric signal data, evaluating the energy spectrum to locate a peak energy value, and determining the frequency at which the peak energy value occurs, in which the frequency of the peak energy value is used as the feature indicative of the presence of a cardiac pulse, and in which determining whether a cardiac pulse is present in the patient includes comparing the frequency of the peak energy value with a threshold frequency.

93. The method of claim 87, further comprising:

repeating the steps of obtaining piezoelectric signal data, analyzing the piezoelectric signal data for a feature, and determining whether a cardiac pulse is present based on the feature, to produce two or more preliminary determinations of the presence of a cardiac pulse; and

determining whether a cardiac pulse is present in the patient based on the number of preliminary determinations indicating the presence of a cardiac pulse.

94. The method of claim 87, in which analyzing the piezoelectric signal data includes comparing the piezoelectric signal data to a previously-identified piezoelectric signal data pattern known to predict the presence of a cardiac pulse.

95. The method of claim 94, in which the comparison produces a pattern match statistic that is the feature indicative of the presence of a cardiac pulse, the method further comprising comparing the feature to a predetermined pattern match threshold to determine whether a cardiac pulse is present in the patient.

96. The method of claim 94, further comprising analyzing the piezoelectric signal data for two or more features indicative of the presence of a cardiac pulse, in which one of the features is determined from the comparison of the piezoelectric signal data with a previously-identified piezoelectric signal data pattern and in which one of the other features is determined from an evaluation of an amplitude of the piezoelectric signal data or an energy in the piezoelectric signal data.

97. The method of claim 87, further comprising obtaining electrocardiogram (ECG) data from the patient, in which analyzing the obtained piezoelectric signal data for a feature indicative of the presence of a cardiac pulse further includes determining whether a ventricular complex occurred in the ECG data.

98. The method of claim 97, further comprising locating a QRS complex in the ECG data and selecting piezoelectric signal data for the analysis based on the location of the ventricular complex.

99. The method of claim 97, further comprising determining whether the patient is in a state of pulseless electrical activity (PEA) based on the determinations of whether a cardiac pulse is present in the patient and whether a ventricular complex occurred in the ECG data.

101. The method of claim 99, further comprising analyzing the patient'"'"'s ECG data for at least ventricular fibrillation (VF), ventricular tachycardia (VT), and asystole, and determining that the patient is in a state of PEA if the patient is determined to be pulseless and not in a VF, VT, or asystole condition.

102. The method of claim 87,

wherein analyzing the piezoelectric signal data for a feature indicative of a cardiac pulse comprises:

estimating a first energy in the piezoelectric signal data;

estimating a second energy in the piezoelectric signal data; and

determining a relative change in energy between the first energy and the second energy, and

wherein determining whether a cardiac pulse is present in the patient comprises determining the presence of a cardiac pulse in the patient based on the determined relative change in energy.

103. The method of claim 102, in which the first energy is estimated using a first set of piezoelectric signal data and the second energy is estimated using a second set of piezoelectric signal data, and in which the second set of piezoelectric signal data is obtained prior to the first set of piezoelectric signal data.

104. The method of claim 102, further comprising:

calculating an energy spectrum of the piezoelectric signal data; and

evaluating the energy spectrum for a spectral energy feature indicative of the presence of a cardiac pulse,

wherein determining whether a cardiac pulse is present in the patient comprises determining the presence of a cardiac pulse in the patient based on the determined relative change in energy and the spectral energy feature.

111. The method of claim 87,

in which analyzing the piezoelectric signal comprises:

calculating an energy spectrum of the piezoelectric signal data; and

evaluating the energy spectrum for first and second spectral energy features indicative of the presence of a cardiac pulse, and

in which determining whether a cardiac pulse is present in the patient comprises determining the presence of a cardiac pulse in the patient is based on the first and second spectral energy features.

112. The method of claim 111, in which the first spectral energy feature is a peak energy value in the energy spectrum, and in which the second spectral energy feature is the frequency at which a peak energy value occurs in the energy spectrum.

114. The method of claim 87, wherein analyzing a piezoelectric signal for a feature indicative of the presence of a cardiac pulse comprises analyzing the piezoelectric signal for a spectral energy feature and a temporal feature, and determining whether a cardiac pulse is present in the patient comprises determining the presence of a cardiac pulse in the patient is based on the spectral energy feature and the temporal feature.

117. The method of claim 114, in which the temporal feature is based on an estimated energy in the piezoelectric signal data, and in which the spectral energy feature is based on a peak energy value in the energy spectrum.

118. The method of claim 114, in which the temporal feature and spectral energy feature are jointly classified in a multi-dimensional classifier to determine whether a cardiac pulse is present in the patient.

100. (canceled)

105-110. -110. (canceled)

113. (canceled)

115-116. -116. (canceled)

119. A method for delivering electrotherapy that provides pacing stimuli and seeks capture of a cardiac pulse in a patient, the method comprising:

delivering a pacing stimulus to the patient;

obtaining piezoelectric signal data from a sensor having a piezoelectric transducing element placed on the surface of the patient'"'"'s body;

analyzing the piezoelectric signal data to determine whether a cardiac pulse occurred in the patient after delivery of the pacing stimulus; and

if a cardiac pulse did not occur in the patient after delivery of the pacing stimulus, increasing the current of further pacing stimuli to be delivered to the patient.

122. The method of claim 119, further comprising prompting a user of the device to increase the pacing stimuli current prior to the current of the pacing stimuli being increased.

120-121. -121. (canceled)

123. (canceled)