Thoracic or intracardiac impedance detection with automatic vector selection

A system comprising:

• an implantable medical device (IMD), the IMD comprising:
• an impedance detector circuit, including inputs configured to receive impedance signals from different electrode configurations in a subject's thorax;
• a cardiac stroke signal filter circuit, coupled to the impedance detector circuit to receive the impedance signals and extract therefrom corresponding cardiac stroke signals;
• a respiration signal filter circuit, coupled to the impedance detector circuit to receive the impedance signals and to extract therefrom corresponding respiration signals;
• a cardiac stroke amplitude measurement circuit, coupled to the cardiac stroke signal filter circuit to receive the cardiac stroke signals and to extract therefrom corresponding cardiac stroke amplitudes;
• a respiration amplitude measurement circuit, coupled to the respiration signal filter circuit to receive the respiration signals and to extract therefrom corresponding respiration amplitudes;
• and
• a processor circuit, including instructions executable or otherwise interpretable to compute a comparative measurement between each cardiac stroke amplitude and each corresponding respiration amplitude from the same electrode configuration, and based on relative values of the comparative measurement associated with each electrode configuration to select a particular electrode configuration for use in obtaining at least one of a cardiac stroke signal and a respiration signal for use in a diagnostic or therapeutic algorithm.