Integrating bioimpedance measurement into an implantable pulse generator for heart rate and respiratory detection

An implantable medical system comprising:

• a lead comprising a proximal end and a distal end;
• a plurality of distal electrodes coupled to the distal end of the lead;
• and
• a medical device coupled to the proximal end of the lead, the medical device comprising:
• a housing;
• at least one surface electrode on the housing;
• an AC current source in the housing;
• a multipole analog switch in the housing coupled to the AC current source;
• a voltmeter in the housing, the voltmeter comprising a first input coupled to a first distal electrode of the plurality of distal electrodes via the lead, and a second input coupled to the at least one surface electrode on the housing;
• and
• a controller in the housing coupled to the multipole analog switch, the controller being configured to operate the multipole analog switch to selectively change the implantable medical system between a neurostimulation mode and a bioimpedance measurement mode,
• wherein in the neurostimulation mode, AC current is delivered from the AC current source and through the lead to a first distal electrode of the plurality of distal electrodes and returned from a second distal electrode of the plurality of distal electrodes to the medical device through the lead, and
• wherein in the bioimpedance measurement mode, AC current is delivered from the AC current source through the lead to a third distal electrode of the plurality of distal electrodes and the voltmeter measures a voltage between the third distal electrode and the at least one surface electrode on the housing.