Patent ID: 8688214

Claim:
A system comprising implantable device, the implantable medical device including: an intrinsic cardiac signal sensor; an impedance measurement circuit configured to apply a specified current to a transthoracic region of a subject and to sample a transthoracic voltage resulting from the specified current, wherein the impedance measurement circuit is configured to measure the transthoracic voltage using a transthoracic measurement vector that includes a ventricle of the subject; and a processor, coupled to the intrinsic cardiac signal sensor and the impedance measurement circuit, the processor configured to initiate sampling of a transthoracic voltage signal synchronous to an occurrence of a fiducial marker in a sensed intrinsic cardiac signal to preserve a respiratory component of the transthoracic signal and to determine lung ventilation using the respiratory component of the transthoracic voltage signal, wherein the sampling attenuates or removes variation with cardiac stroke volume from the transthoracic voltage signal.