An implantable barometric pressure sensor coupled with an implantable medical device (IMD) provides a barometric pressure related, reference pressure value for use in combination with an absolute pressure value measured by an implantable absolute pressure sensor coupled to the IMD. In one embodiment, the barometric pressure sensor is implanted under the skin and subcutaneous tissue layer at or near the implant site of the IMD. In variations of this embodiment, the barometric pressure is formed as part of a connector module of the IMD or extends from the connector module. In a further embodiment, a percutaneous access device is provided which is adapted to be implanted to extend through the skin and subcutaneous tissue layer of the patient and is coupled with the barometric pressure sensor to provide for an air chamber extending between the atmosphere and the barometric pressure sensor. The barometric pressure sensor is preferably enclosed within an air chamber of the implantable medical device, and a catheter extends between the air chamber of the implantable medical device and the percutaneous access device. Or the barometric pressure sensor is enclosed within an air chamber of the percutaneous access device, and a lead extends between the barometric pressure sensor and the implantable medical device.