High frequency impedance measurements from implanted unipolar pacing leads

Impedance measurements using frequencies up to 500 MHz were used along with time domain reflectometry techniques to investigate respiration sensing using standard unipolar pacemaker leads. The results have demonstrated the unique nature of these impedance sensing methods versus traditional lower frequency impedance methods. Experimental evidence includes: separation in frequency (or time and thus distance along the lead) of the cardiac stroke volume signal from the respiration signal and respiration sensing using a fully insulated tip unipolar pacing lead