A multisensor implant for continuous monitoring of intracranial pressure dynamics

In humans, intracranial pressure (ICP) is not only influenced by pathology, but also by orientation in space and body movements. Therefore, it is proposed to measure ICP dynamics and body acceleration simultaneously. An algorithm for acceleration analysis was developed to monitor orientation in space and allow more accurate examination of ICP dynamics during quiet periods. For continuous monitoring, an implant was developed and wireless data transmission was implemented; this prototype was successfully tested in five pigs. Hydrocephalus with increased ICP was experimentally induced in the animals using a surgical kaolin infusion. This model of porcine pathology was then tested with the implant with the aim for eventual use in humans. ICP dynamics and 2D-acceleration data were simultaneously recorded for up to two weeks. This study allowed 24-h monitoring and provided analysable data on porcine ICP dynamics with humanlike ICP waves, the so called B- and P-waves. Results show that acceleration often had a stronger influence on ICP than the amplitudes of the physiological ICP characteristics. With test animals in a standing position, without obvious body movement, ICP varied to an extent that made the characteristic ICP waves difficult to identify. These data allow us to conclude that analysis of both ICP and acceleration may be essential for autonomous implants.