Patent ID: 8306621

Claim:
A cardiac management system comprising: an implantable device, including: a memory circuit; an intrinsic cardiac signal sensor; an impedance measurement circuit configured for generating a sampled transthoracic impedance signal; and a processor, coupled to the intrinsic cardiac signal sensor and the impedance measurement circuit, the processor configured to: initiate sampling of a transthoracic impedance signal substantially at an instance of a fiducial marker in a sensed intrinsic cardiac signal, the sampling to attenuate or remove a cardiac stroke component from the transthoracic impedance signal and to preserve a respiratory component of the transthoracic impedance signal; and measure a time interval between successive occurrences of the fiducial marker indicative of a cardiac cycle and to store a value in the memory circuit representative of the sampled measured transthoracic impedance in correspondence with an indication of the measured time interval; and determine lung information using the sampled measured transthoracic impedance in correspondence with an indication of the measured time interval.