Intracranial pressure measurement with a miniature passive implanted pressure transensor

Intracranial pressure monitoring in neurosurgery: the present situation and prospects

Intracranial pressure (ICP) is one of the most important indexes in neurosurgery. It is essential for doctors to determine the numeric value and changes of ICP, whether before or after an operation. Although external ventricular drainage (EVD) is the gold standard for monitoring ICP, more and more novel monitoring methods are being applied clinically.Invasive wired ICP monitoring is still the most commonly used in practice. Meanwhile, with the rise and development of various novel technologies, non-invasive types and invasive wireless types are gradually being used clinically or in the testing phase, as a complimentary approach of ICP management. By choosing appropriate monitoring methods, clinical neurosurgeons are able to obtain ICP values safely and effectively under particular conditions.This article introduces diverse monitoring methods and compares the advantages and disadvantages of different monitoring methods. Moreover, this review may enable clinical neurosurgeons to have a broader view of ICP monitoring.

Telemetric Intracranial Pressure Monitoring: A Systematic Review

Telemetric intracranial pressure (ICP) monitoring is a new method of measuring ICP which eliminates some of the shortcomings of previous methods. However, there are limited data on specific characteristics, including the advantages and disadvantages of this method. The main aim of this study was to demonstrate the indications, benefits, and complications of telemetric ICP monitoring. PubMed, MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched for relevant studies without language or date restriction in May 2019. Human studies in which telemetric ICP monitoring was the main subject of the study were included. Our initial search resulted in 1650 articles from which 50 studies were included. There were no randomized controlled trials. The majority of the studies were case reports or case series (68%). The most common aim of studies was testing of the device (52%), and monitoring the disease progression or recovery (46%). The most common indications for telemetric ICP monitoring in these studies were testing cerebrospinal fluid shunt function (46%), ICP control after the procedure (36%), and diagnosing intracranial hypertension (22%) and hydrocephalus (12%). In total, 1423 brain disease patients had been monitored in studies. The possibility of long-term ICP monitoring as the main benefit was reported in 38 (76%) studies. The associated complication rate was 7.1%. Despite the increasing application of telemetric monitoring devices, studies to evaluate specific characteristics of this method have been infrequent and inadequate. Future research using a higher level of scientific methods is needed to evaluate advantage and disadvantages.

Characteristics of an Implantable Blood Pressure Sensor Packaged by Ultrafast Laser Microwelding

We propose a new packaging process for an implantable blood pressure sensor using ultrafast laser micro-welding. The sensor is a membrane type, passive device that uses the change in the capacitance caused by the membrane deformation due to applied pressure. Components of the sensor such as inductors and capacitors were fabricated on two glass (quartz) wafers and the two wafers were bonded into a single package. Conventional bonding methods such as adhesive bonding, thermal bonding, and anodic bonding require considerable effort and cost. Therefore CO₂ laser cutting was used due to its fast and easy operation providing melting and bonding of the interface at the same time. However, a severe heat process leading to a large temperature gradient by rapid heating and quenching at the interface causes microcracks in brittle glass and results in low durability and production yield. In this paper, we introduce an ultrafast laser process for glass bonding because it can optimize the heat accumulation inside the glass by a short pulse width within a few picoseconds and a high pulse repetition rate. As a result, the ultrafast laser welding provides microscale bonding for glass pressure sensor packaging. The packaging process was performed with a minimized welding seam width of 100 μm with a minute. The minimized welding seam allows a drastic reduction of the sensor size, which is a significant benefit for implantable sensors. The fabricated pressure sensor was operated with resonance frequencies corresponding to applied pressures and there was no air leakage through the welded interface. In addition, in vitro cytotoxicity tests with the sensor showed that there was no elution of inner components and the ultrafast laser packaged sensor is non-toxic. The ultrafast laser welding provides a fast and robust glass chip packaging, which has advantages in hermeticity, bio-compatibility, and cost-effectiveness in the manufacturing of compact implantable sensors.

Design and Simulation of an Integrated Wireless Capacitive Sensors Array for Measuring Ventricular Pressure

This paper reports the novel design of a touch mode capacitive pressure sensor (TMCPS) system with a wireless approach for a full-range continuous monitoring of ventricular pressure. The system consists of two modules: an implantable set and an external reading device. The implantable set, restricted to a 2 × 2 cm² area, consists of a TMCPS array connected with a dual-layer coil, for making a reliable resonant circuit for communication with the external device. The capacitive array is modelled considering the small deflection regime for achieving a dynamic and full 5⁻300 mmHg pressure range. In this design, the two inductive-coupled modules are calculated considering proper electromagnetic alignment, based on two planar coils and considering the following: 13.56 MHz frequency to avoid tissue damage and three types of biological tissue as core (skin, fat and muscle). The system was validated with the Comsol Multiphysics and CoventorWare softwares; showing a 90% power transmission efficiency at a 3.5 cm distance between coils. The implantable module includes aluminum- and polyimide-based devices, which allows ergonomic, robust, reproducible, and technologically feasible integrated sensors. In addition, the module shows a simplified and low cost design approach based on PolyMEMS INAOE^® technology, featured by low-temperature processing.

Chronically implanted pressure sensors: challenges and state of the field

Several conditions and diseases are linked to the elevation or depression of internal pressures from a healthy, normal range, motivating the need for chronic implantable pressure sensors. A simple implantable pressure transduction system consists of a pressure-sensing element with a method to transmit the data to an external unit. The biological environment presents a host of engineering issues that must be considered for long term monitoring. Therefore, the design of such systems must carefully consider interactions between the implanted system and the body, including biocompatibility, surgical placement, and patient comfort. Here we review research developments on implantable sensors for chronic pressure monitoring within the body, focusing on general design requirements for implantable pressure sensors as well as specifications for different medical applications. We also discuss recent efforts to address biocompatibility, efficient telemetry, and drift management, and explore emerging trends.

Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care

Continuous monitoring of internal physiological parameters is essential for critical care patients, but currently can only be practically achieved via tethered solutions. Here we report a wireless, real-time pressure monitoring system with passive, flexible, millimetre-scale sensors, scaled down to unprecedented dimensions of 1 × 1 × 0.1 cubic millimeters. This level of dimensional scaling is enabled by novel sensor design and detection schemes, which overcome the operating frequency limits of traditional strategies and exhibit insensitivity to lossy tissue environments. We demonstrate the use of this system to capture human pulse waveforms wirelessly in real time as well as to monitor in vivo intracranial pressure continuously in proof-of-concept mice studies using sensors down to 2.5 × 2.5 × 0.1 cubic millimeters. We further introduce printable wireless sensor arrays and show their use in real-time spatial pressure mapping. Looking forward, this technology has broader applications in continuous wireless monitoring of multiple physiological parameters for biomedical research and patient care.

Clinical and radiological findings in long-term intracranial pressure monitoring

BACKGROUND

Advantages of telemetric devices for long-term intracranial pressure (ICP) measurement have been mentioned several times in the literature. However, descriptions of associated complications are lacking. Therefore, the presented observational study focused on clinical and radiological findings after insertion of an intraparenchymal telemetric ICP monitor.

METHODS

Between April 2010 and February 2013, 185 telemetric ICP catheters were implanted for diagnostic purposes. All patients were clinically followed. Radiological, microbiological and clinical data were analysed.

RESULTS

One brain abscess (0.5 %) and two cutaneous infections (1.1 %) occurred in 185 patients. Staphylococcus spp. could be detected in all cases. Six patients (3.2 %) suffered from single new-onset seizures and one patient (0.5 %) from a temporary hemiparesis. Intracerebral haemorrhages occurred in 15.6 %, most of the time as small punctate bleedings. Perifocal oedematous reactions surrounding inserted telemetric catheters could be observed in 46.9 %. Multiple imaging studies revealed a tendency of complete oedema resolution over time.

CONCLUSIONS

Infectious as well as haemorrhagic complication rates are well comparable with the common literature. The long-term implantation of an ICP probe does not seem to increase the risk of wound infections or brain abscess formation. Surprisingly, very high numbers of oedematous reactions after insertion of the intraparenchymal ICP monitor were seen. Reasons therefore could only be speculated upon.

Design challenges of implantable pressure monitoring system

Pressure in various organs and body parts, such as blood vessels, heart, brain, eyes, bladder and GI tracts, is an important indication of health. Long term, continuous pressure monitoring is critically needed for a number of applications. When combined with existing neuro-prosthetics devices, they may provide better solutions to many neural disorders. First efforts toward a long-term implantable pressure monitoring system were initiated more than 40 years ago. However, a reliable, safe and implantable pressure sensor for long-term applications is not yet commercially available. This paper attempts to reveal the design challenges associated with the development of a long-term implantable pressure sensor.

Long term, implantable blood pressure monitoring systems

An overview of implantable measurement systems suitable for the long-term, continuous monitoring of blood pressure is presented in this paper. The challenges, design considerations and tradeoffs inherent in these systems are overviewed and implantable sensors from both industrial and research environments are reviewed. The paper is concluded with an outlook of future directions for implantable blood pressure monitoring systems.

An improved method for detecting passive pills

One of the principal disadvantages of the passive pill as a telemetric method for measuring various physiological parameters has been its resticted range. The reasons for the restricted range with existing detection methods are discussed. An improved method using a locking spectrometer based on third-order phase-sensitive detection is described and its performance is assessed. A significant increase in the usable range of a high sensitivity passive pill is obtained.

Chronic measurement of epidural pressure with an induction-powered oscillator transducer

An induction-powered oscillator transducer (IPOT) was designed for the chronic measurement of epidural pressure. The transducer was completely implantable so all pressure measurements were made through the intact skin. The IPOT had a linear pressure range from -50 to +200 cm H2O, was sensitive to 1 mm H2O and had a zero drift of less than 1 mm H2O/day under full load. Zero drift was minimized by using a hermetically-sealed metal bellows transducing element which was chemically treated to prevent corrosion and creep. The correlation between epidural pressure and intraventricular pressure was determined during the first 24 hours after implantation in six dogs. Epidural pressure was found to be a linear function of intraventricular fluid pressure. Epidural pressure and intraventricular pressure were essential equal provided the epidural wedge pressure was minimized by proper insertion of the transducer. The correlation between epidural pressure and intraventricular pressure was determined after chronic implantation in five dogs. Epidural pressure was a linear function of intraventricular pressure in the chronically implanted dogs, but epidural pressure was not equal to intraventricular pressure. After chronic implantation, the epidural pressure transducer was not responsive to changes in intraventricular pressure because of mechanical changes in the dura. The dura became stiff and non-compliant. Maximum correlation between epidural pressure and intraventricular fluid pressure in chronic implantations will depend on judicious material selection and mechanical design at the transducer-dura interface.

Telemetry of intracranial pressure

A new technique is described for telemetric measurement of intracranial pressure in man using an external energy source and a small pressure transducer, called a TELECEPTOR, implanted in the skull. The method presents advantages, especially for long term recordings.