Pulse detection method and apparatus using patient impedance

Abstract

The presence of a cardiac pulse in a patient is determined by evaluating fluctuations in an electrical signal that represents a measurement of the patient's transthoracic impedance. Impedance signal data obtained from the patient is analyzed for a feature indicative of the presence of a cardiac pulse. Whether a cardiac pulse is present in the patient is determined based on the feature in the impedance signal data. Electrocardiogram (ECG) data may also be obtained in time coordination with the impedance signal data. Various applications for the pulse detection of the invention include detection of PEA and prompting PEA-specific therapy, prompting defibrillation therapy and/or CPR, and prompting rescue breathing depending on detection of respiration.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A method of determining the presence of a cardiac pulse in a patient, comprising: 
 (a) obtaining impedance signal data from the patient;    (b) analyzing the impedance signal data for a feature indicative of the presence of a cardiac pulse; and    (c) determining whether a cardiac pulse is present in the patient based on the feature in the impedance signal data.    
     
     
         2 . The method of  claim 1 , wherein analyzing the impedance signal data includes evaluating an amplitude of the impedance signal data.  
     
     
         3 . The method of  claim 2 , wherein evaluating the amplitude of the impedance signal data includes: 
 (a) locating low and high peak amplitude values in the impedance signal data; and    (b) calculating a peak-to-peak change in amplitude using the low and high peak amplitude values.    
     
     
         4 . The method of  claim 3 , wherein the peak-to-peak change in amplitude is the feature indicative of the presence of a cardiac pulse, the method further comprising comparing the feature to a predetermined threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         5 . The method of  claim 1 , wherein analyzing the impedance signal data includes evaluating energy in the impedance signal data.  
     
     
         6 . The method of  claim 5 , wherein evaluating the energy in the impedance signal data includes: 
 (a) selecting impedance signal data for an energy calculation; and    (b) calculating the energy in the selected impedance signal data.    
     
     
         7 . The method of  claim 6 , wherein the calculated energy is the feature indicative of the presence of a cardiac pulse, the method further comprising comparing the calculated energy to a predetermined threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         8 . The method of  claim 1 , wherein analyzing the impedance signal data includes comparing impedance signal data to a previously identified impedance signal pattern known to predict the presence of a cardiac pulse.  
     
     
         9 . The method of  claim 8 , wherein 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 threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         10 . The method of  claim 1 , further comprising analyzing the impedance signal data for two or more features indicative of the presence of a cardiac pulse, the two or more features being determined from two or more analyses that evaluate (a) an amplitude of the impedance signal data, (b) energy in the impedance signal data, or (c) a comparison of impedance signal data with a previously identified impedance signal pattern known to predict the presence of a cardiac pulse.  
     
     
         11 . The method of  claim 1 , further comprising prompting application of defibrillation electrodes to the patient if a cardiac pulse is determined not present in the patient.  
     
     
         12 . A method of determining the presence of a cardiac pulse in the patient, comprising: 
 (a) obtaining impedance signal data from the patient;    (b) obtaining electrocardiogram (ECG) data from the patient;    (c) determining the presence of a QRS complex in the ECG data;    (d) analyzing the impedance signal data for a feature indicative of the presence of a cardiac pulse based on a relationship between the presence of a QRS complex in the ECG data and amplitude changes in the impedance signal data; and    (e) determining whether a cardiac pulse is present in the patient based on the feature in the impedance signal data.    
     
     
         13 . The method of  claim 12 , further comprising locating a QRS complex in the ECG data and selecting a segment of the impedance signal data for the analysis based on the located QRS complex.  
     
     
         14 . The method of  claim 12 , wherein analyzing the impedance signal data includes evaluating an amplitude of the impedance signal data.  
     
     
         15 . The method of  claim 13 , wherein evaluating the amplitude of the impedance signal data includes: 
 (a) locating low and high peak amplitude values in the impedance signal data; and    (b) calculating a peak-to-peak change in amplitude using the low and high peak amplitude values.    
     
     
         16 . The method of  claim 14 , wherein the peak-to-peak change in amplitude is the feature indicative of the presence of a cardiac pulse, the method further comprising comparing the feature to a predetermined threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         17 . The method of  claim 12 , wherein analyzing the impedance signal data includes evaluating energy in the impedance signal data.  
     
     
         18 . The method of  claim 17 , wherein evaluating the energy in the impedance signal data includes: 
 (a) selecting impedance signal data for an energy calculation; and    (b) calculating the energy in the selected impedance signal data.    
     
     
         19 . The method of  claim 18 , wherein the calculated energy is the feature indicative of the presence of a cardiac pulse, the method further comprising comparing the calculated energy to a predetermined threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         20 . The method of  claim 12 , wherein analyzing the impedance signal data includes comparing impedance signal data to a previously identified impedance signal pattern known to predict the presence of a cardiac pulse.  
     
     
         21 . The method of  claim 20 , wherein 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 threshold to determine whether a cardiac pulse is present in the patient.  
     
     
         22 . The method of  claim 12 , further comprising analyzing the impedance signal data for two or more features indicative of the presence of a cardiac pulse, the two or more features being determined from two or more analyses that evaluate (a) an amplitude of the impedance signal data, (b) energy in the impedance signal data, or (c) a comparison of impedance signal data with a previously identified impedance signal pattern known to predict the presence of a cardiac pulse.  
     
     
         23 . A medical device, comprising: 
 (a) electrodes adapted to communicate an impedance-sensing signal through a patient;    (b) a conversion circuit in communication with the electrodes for converting the impedance-sensing signal received from the patient into digital impedance signal data; and    (c) a processing unit in communication with the conversion circuit for processing the impedance signal data, wherein the processing unit is configured to analyze the impedance signal data for a feature indicative of the presence of a cardiac pulse in the patient and determine the presence of a cardiac pulse in the patient based on the feature in the impedance signal data.    
     
     
         24 . A medical device, comprising: 
 (a) electrodes adapted to communicate an impedance-sensing signal through a patient and further to sense electrocardiogram (ECG) signals in the patient;    (b) a conversion circuit in communication with the electrodes for converting the impedance-sensing signal and ECG signal received from the patient into digital impedance signal data and ECG data, respectively; and    (c) a processing unit in communication with the conversion circuit for processing the impedance signal data, wherein the processing unit is configured to analyze the ECG data, determine the presence of a QRS complex in the ECG data, and select a segment of impedance signal data corresponding in time with the QRS complex, the processing unit further configured to analyze the segment of impedance signal data for a feature indicative of the presence of a cardiac pulse in the patient and determine the presence of a cardiac pulse in the patient based on the feature in the impedance signal data.