An implantable barometric pressure sensor (220) coupled with an implantable medical device (IMD) provides a barometric pressure related, referenced pressure value for use in combination with an absolute pressure value measured by an implantable absolute pressure sensor (20) coupled to the IMD. In one embodiment, the barometric pressure sensor (220) is formed as part of a connector module (180) of the IMD or extends from the connector module (180). A percutaneous access device (360) is implanted to extend through the skin and subcutaneous tissue layer of the patient and is coupled with the barometric pressure sensor (220). The barometric pressure sensor (220) is preferably enclosed within an air chamber (170) of the implantable medical device, and a catheter (310) extends between the air chamber (170) of the implantable medical device and the percutaneous access device (360). Or the barometric pressure sensor (220) is enclosed within an air chamber (368) of the percutaneous access device, and a lead extends between the barometric pressure sensor (220) and the implantable medical device.