Impedance cardiograph and method of operation utilizing peak aligned ensemble averaging

An impedance cardiograph comprising:

• means for applying an excitation signal to the thorax of an animal;
• means, responsive to the excitation signal, for producing an electrical signal which varies with thoracic impedance changes of the animal;
• means for producing an electrocardiogram signal containing a cardiac QRS wave;
• means for determining a heart rate of the animal from the electrocardiogram signal;
• means for selecting segments of the electrical signal for which a predefined point of a segment occurs within a given interval from an occurrence of a predetermined point on a cardiac QRS wave, said means for selecting including means for determining the given interval;
• and
• means, responsive to said first means for selecting, for computing a cardiac performance parameter value from the selected segments of the electrical signal.

An impedance cardiograph comprising:

• means for applying an excitation signal to the thorax of an animal;
• means, responsive to the excitation signal, for producing a first electrical signal which varies with thoracic impedance changes of the animal;
• means for producing a second signal corresponding to the first derivative of the first electrical signal;
• means for producing an electrocardiogram signal having a QRS wave during each cardiac cycle;
• means for generating a plurality of periodic samples of the first electrical signal, second electrical signal and the electrocardiogram signal, the samples of each signal being divided into a number of groups with the samples in each group representing the respective signal during a different cardiac cycle of the animal;
• means for averaging the samples of the first electrical signal to produce an average thoracic impedance value;
• means for ensemble averaging the groups of the samples of the second electrical signal to produce a first set of ensemble averaged signal samples, said means for ensemble averaging aligning each group of samples of the second electrical signal about a sample in each group which occurs during a cardiac ejection interval and which corresponds to the smallest rate of change of the thoracic impedance;
• means for ensemble averaging the groups of the samples of the electrocardiogram signal to produce a second set of ensemble averaged signal samples;
• and
• means for computing cardiac stroke volume from the first set of ensemble averaged signal samples and the average thoracic impedance value.

A method of measuring cardiac activity in an animal comprising:

• applying an excitation signal to the thorax of the animal;
• producing a first electrical signal which varies with thoracic impedance changes of the animal;
• producing a second electrical signal corresponding to a first derivative of the first electrical signal;
• generating a plurality of periodic samples of the second electrical signal, the samples being divided into a number of groups with the samples in each group representing the second electrical signal during a different cardiac cycle of the animal;
• identifying in each group a signal sample which occurs during a cardiac ejection interval and which corresponds to the smallest rate of change of the thoracic impedance;
• aligning each group of samples of the second electrical signal about a sample in each group which occurs during a cardiac ejection interval and which corresponds to the smallest rate of change of the thoracic impedance, and ensemble averaging the aligned groups of the samples of the second electrical signal to produce a set of ensemble averaged signal samples;
• and
• computing a cardiac performance parameter value from the ensemble averaged signal samples.

An impedance cardiograph comprising:

• means for applying an excitation signal to the thorax of an animal;
• means, responsive to the excitation signal, for producing an electrical signal which varies with thoracic impedance changes of the animal;
• means for producing an electrocardiogram signal containing a cardiac QRS wave;
• means for determining a heart rate of the animal from the electrocardiogram signal;
• means for measuring an interval between two predefined points within a segment of the electrical signal;
• means for selecting segments of the electrical signal, a given segment being selected in response to a measurement of the interval of the segment being within a given range of values;
• and
• means, responsive to said first means for selecting, for computing a cardiac performance parameter value from the selected segments of the electrical signal.