An implantable ZigBee ready telemetric platform for in vivo monitoring of physiological parameters

This paper presents a multiple channel, bidirectional and implantable biotelemetric platform, suitable for real time in vivo monitoring of several physiological parameters. This system consists of an implantable unit, an external host and a user terminal. The ZigBee wireless technology, functioning as telemetric link, enables long battery lifetime and offers the opportunity to build up complex wireless networks of implantable and wearable sensors. A smart Analog Front End, that allows a real time optimization of the signals output dynamics, is also described. Different kinds of sensors, ranging from resistive to current or voltage output sensors, can be directly connected to the front end. The firmware code of the implanted unit can be reprogrammed through the telemetric link, thus enabling active interactions between the system and the end user. For the code development, particular attention was devoted to reducing power consumption: a theoretical maximum battery life of several years, suitable for chronic implants, can be achieved. In order to validate the platform, a ZigBee point to point wireless connection between the implant and the external unit was implemented. Two different sensors were used, i.e. a temperature sensor and a pressure transducer. The system performances were assessed through several in vivo tests. In particular, aortic and ventricular real time pressure and temperature monitoring are reported with the system implanted in farm pigs. Data acquisition was validated by comparison with medical golden standard for pressure monitoring. Finally, the lowest level of transmission power required to establish a reliable communication by using a ZigBee compliant hardware implanted under skin has been quantified as 13.33 mu W during an in vivo experiment in an anesthetized pig. This value is fully compliant with the reference level for general public exposure to time varying electric and magnetic fields. (c) 2007 Elsevier B.V. All rights reserved.