Wireless less-invasive blood pressure sensing microsystem for small laboratory animal in vivo real-time monitoring

Abstract

A novel wireless less-invasive implantable blood pressure sensing system is developed for advanced biological research. The system employs a miniature instrumented elastic cuff, wrapped around a blood vessel, for small animal real-time blood pressure monitoring. The elastic cuff is made of bio-compatible soft silicone material by a molding process and is filled by insulating silicone oil with an immersed MEMS capacitive pressure sensor interfaced with low power integrated electronics. This technique avoids vessel penetration and substantially minimizes vessel restriction due to the soft cuff elasticity, thus attractive for long-term implant. The MEMS pressure sensor detects the coupled blood pressure waveform caused by the vessel expansion and contraction, followed by amplification, digitization, and wireless FSK data transmission to an external receiver. The integrated electronics are designed with capability of receiving RF power from an external power source and converting the RF signal to a stable 2V DC supply in an adaptive manner to power the overall implant system, thus enabling a realization of stand-alone battery-less implant microsystem. The electronics are fabricated in a 1.5 μm CMOS process and occupies an area of 2 mm × 2 mm. The prototype monitoring cuff is wrapped around the right carotid artery of a laboratory rat to measure real-time blood pressure waveform. The measured in vivo blood waveform is compared with a reference waveform recorded simultaneously by using a commercial catheter-tip transducer inserted into the left carotid artery. Two measured waveforms are closely matched with a constant scaling factor. The ASIC is interfaced with a 5 mm-diameter RF powering coil and four surface-mount components (one inductor and three capacitors) over a thin flexible substrate via bond wires, followed by silicone coating and packaging with the prototype blood pressure monitoring cuff. The overall system exhibits a weight of 280 mg, representing an order of magnitude mass reduction compared to state-of-the-art commercial technology.