US Patent 7988634 Adaptive cancellation of a signal component

A cardiac-related signal such as a cardiogenic impedance signal is derived to obtain cardiac information such as stroke volume information that may be used to evaluate cardiac performance and/or other medical conditions. In some aspects detection of the cardiogenic impedance signal involves adaptively cancelling an unwanted component of a sensed signal. For example, in some embodiments a sensed respiratory signal may be subtracted from a thoracic impedance signal to reduce a respiratory component of the thoracic impedance signal. In this way, a more accurate cardiogenic impedance signal may be derived from the resulting signal.