Implantable Pressure Sensor Research Articles

PD24-08 WIRELESS IMPLANTABLE RECHARGEABLE BLADDER PRESSURE SENSOR: CYSTOSCOPIC IMPLANTATION AND AMBULATORY DATA COLLECTION

You have accessJournal of UrologyUrodynamics/Incontinence/Female Urology: Incontinence: Evaluation (Urodynamic Testing)1 Apr 2015PD24-08 WIRELESS IMPLANTABLE RECHARGEABLE BLADDER PRESSURE SENSOR: CYSTOSCOPIC IMPLANTATION AND AMBULATORY DATA COLLECTION Iryna Makovey, Steve Majerus, Robert Karam, Brett Hanzlicek, Matthew Streicher, Hui Zhu, and Margot Damaser Iryna MakoveyIryna Makovey More articles by this author , Steve MajerusSteve Majerus More articles by this author , Robert KaramRobert Karam More articles by this author , Brett HanzlicekBrett Hanzlicek More articles by this author , Matthew StreicherMatthew Streicher More articles by this author , Hui ZhuHui Zhu More articles by this author , and Margot DamaserMargot Damaser More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.1463AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES There is a need for a minimally invasive chronic bladder pressure-monitoring sensor both for better diagnosis of voiding dysfunction and to be used as a feedback mechanism for neurostimulation. We have developed a miniature wireless implantable micromanometer (WIMM) system designed for cystoscopic sub-mucosal implantation. This system is capable of wireless real time data transmission, wireless battery recharging, and ambulatory bladder pressure data collection. METHODS A WIMM device measuring 6.8 × 3.0 × 15 mm was cystoscopically implanted into a sub-urothelial pocket posterior to the trigone in a female calf model. Cautery was used to nick the mucosa and 1.5 cc 5Fr arterial embolectomy catheter was used to develop the sub-urothelial plane. The WIMM was inserted through the 26Fr rigid cystoscope sheath directly into the pocket. Catheter based urodynamic study was performed while data was recorded simultaneously from the WIMM sensor via wireless data transmission to an external receiver. Manual compressions were conducted during bladder filling as an additional test for the implanted device. Post-operatively data was collected with the WIMM sensor while calves were conscious and standing, laying down, ambulating, or experiencing bladder contractions. Implanted WIMM devices were recharged wirelessly every few days via an external charger. RESULTS Device placement was successfully performed in two female calves. A CT cystogram was performed prior to and after device placement. No contrast extravasation was observed and device location was confirmed posterior to the trigone. We achieved device retention at least 2 weeks after implantation. Data was collected wirelessly with the WIMM device in both anesthetized and conscious ambulatory situations. The correlation coefficient to reference catheter based pressure recording was 0.82. The implanted WIMM pressure sensor was able to detect bladder events such as manual compressions, position changes, movement artifact, and bladder contractions. CONCLUSIONS We have demonstrated the safety and feasibility of minimally invasive cystoscopic implantation of a miniature implantable wireless bladder pressure sensor. Data was successfully collected from anesthetized urodynamics and ambulatory recordings in a calf animal model using the WIMM sensor. This device has the potential for use both for chronic bladder monitoring and for wireless feedback to an electrical stimulation system. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e489 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Iryna Makovey More articles by this author Steve Majerus More articles by this author Robert Karam More articles by this author Brett Hanzlicek More articles by this author Matthew Streicher More articles by this author Hui Zhu More articles by this author Margot Damaser More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

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.

Development of clinically relevant implantable pressure sensors: perspectives and challenges.

This review describes different aspects to consider when developing implantable pressure sensor systems. Measurement of pressure is in general highly important in clinical practice and medical research. Due to the small size, light weight and low energy consumption Micro Electro Mechanical Systems (MEMS) technology represents new possibilities for monitoring of physiological parameters inside the human body. Development of clinical relevant sensors requires close collaboration between technological experts and medical clinicians. Site of operation, size restrictions, patient safety, and required measurement range and resolution, are only some conditions that must be taken into account. An implantable device has to operate under very hostile conditions. Long-term in vivo pressure measurements are particularly demanding because the pressure sensitive part of the sensor must be in direct or indirect physical contact with the medium for which we want to detect the pressure. New sensor packaging concepts are demanded and must be developed through combined effort between scientists in MEMS technology, material science, and biology. Before launching a new medical device on the market, clinical studies must be performed. Regulatory documents and international standards set the premises for how such studies shall be conducted and reported.

Quality Factor Optimization of Inductive Antennas for Implantable Pressure Sensors

Inductive antenna design for passive wireless implantable use presents several challenges not currently addressed. A small form factor is desired for minimally invasive implantation and monitoring, and a low frequency is necessary for effective through-body power transfer. However, a small inductor limits sensitivity to changes in capacitance at low-frequency operation. It is thus necessary to optimize the inductor for maximal sensitivity while satisfying tight area and low frequency constraints. Here, a design methodology is presented for planar circular spiral inductors used with capacitive pressure sensors to form a passive wireless implantable pressure sensor. Several analytical expressions are collected to find the optimal geometric parameters that maximize the quality factor and sensitivity of the sensor frequency response. The analysis is validated through comparison with field solvers and wireless measurements of fabricated devices.

An implantable pressure sensing system with electromechanical interrogation scheme.

In this paper, we report on the development of an implantable pressure sensing system that is powered by mechanical vibrations in the audible acoustic frequency range. This technique significantly enhances interrogation range, alleviates the misalignment issues commonly encountered with inductive powering, and simplifies the external receiver circuitry. The interrogation scheme consists of two phases: a mechanical vibration phase and an electrical radiation phase. During the first phase, a piezoelectric cantilever acts as an acoustic receiver and charges a capacitor by converting sound vibration harmonics occurring at its resonant frequency into electrical power. In the subsequent electrical phase, when the cantilever is not vibrating, the stored electric charge is discharged across an LC tank whose inductor is pressure sensitive; hence, when the LC tank oscillates at its natural resonant frequency, it radiates a high-frequency signal that is detectable using an external receiver and its frequency corresponds to the measured pressure. The pressure sensitive inductor consists of a planar coil (single loop of wire) with a ferrite core whose distance to the coil varies with applied pressure. A prototype of the implantable pressure sensor is fabricated and tested, both in vitro and in vivo (swine bladder). A pressure sensitivity of 1 kHz/cm H2O is achieved with minimal misalignment sensitivity (26% drop at 90° misalignment between the implanted device and acoustic source; 60% drop at 90° misalignment between the implanted device and RF receiver coil).

Plasma Enhanced Hydrophobicity of Parylene-C Surfaces for a Blood Contacting Pressure Sensor

A bio- and haemocompatible packaging strategy is proposed for an implantable pressure sensor for continuous direct blood pressure monitoring. A commercial sub-millimeter piezoresistive sensor was attached to an alumina substrate and a double coating of PDMS and parylene-C was applied. The packaged device has dimensions of 2.6x3.6x1.8mm. A surface modification technique using O2 and SF6 plasma has been employed to tune the haemocompatibility of the packaged sensor. By enhancing the intrinsic hydrophobicity of parylene it is possible to increase plasma proteins adsorption and minimize platelets adhesion on the surface. Contact angle measurements were performed on parylene-coated PDMS samples after plasma treatment, using water and whole pig blood. A maximum contact angle of 134° has been achieved. The influence of different plasma exposure times on the surface wettability has been investigated. To study the stability of the plasma treated surfaces, the contact angle was measured immediately and at regular intervals.

Nanoscale displacement sensing using microfabricated variable-inductance planar coils

Microfabricated spiral inductors were employed for nanoscale displacement detection, suitable for use in implantable pressure sensor applications. We developed a variable inductor sensor consisting of two coaxially positioned planar coils connected in series to a measurement circuit. The devices were characterized by varying the air gap between the coils hence changing the inductance, while a Colpitts oscillator readout was used to obtain corresponding frequencies. Our approach shows significant advantages over existing methodologies combining a displacement resolution of 17 nm and low hysteresis (0.15%) in a 1 × 1 mm2 device. We show that resolution could be further improved by shrinking the device's lateral dimensions.

Comparative Pathology of an Implantable Left Atrial Pressure Sensor

A left atrial pressure (LAP) monitoring system was developed for guiding the management of patients with heart failure. The LAP sensor is implanted into the left atrium via transseptal catheterization and affixed to the interatrial septum by nitinol anchors. The long-term safety of permanent implantation of the LAP sensor in patients was evaluated based on the comparative pathology in animals. Tissue specimens of the LAP sensor from 7 patients, 49 canines, and 14 ovine were examined for thrombosis and tissue overgrowth. Implant duration ranged from 22 to 1,686 days. Gross examination showed minimal-to-moderate tissue overgrowth with no evidence of migration, erosion, or perforation. There was no excessive host-to-device reaction or active thrombogenesis in any of the subjects that followed the antithrombotic therapy protocol. Micro-computed tomography scanning confirmed the structural integrity of the device. Low vacuum scanning electron microscopy and histology showed neoendocardial tissue overgrowth with no inflammation or fibrin. The pathology of both animal models was found to closely approximate the pathology in humans and favorably supports the long-term safety of the device.

Integrated microscopy techniques for comprehensive pathology evaluation of an implantable left atrial pressure sensor

The safety and efficacy of an implantable left atrial pressure (LAP) monitoring system is being evaluated in a clinical trial setting. Because the number of available specimens from the clinical trial for histopathology analysis is limited, it is beneficial to maximize the usage of each available specimen by relying on integrated microscopy techniques. The aim of this study is to demonstrate how a comprehensive pathology analysis of a single specimen may be reliably achieved using integrated microscopy techniques. Integrated microscopy techniques consisting of high-resolution gross digital photography followed by micro-computed tomography (micro-CT) scanning, low-vacuum scanning electron microscopy (LVSEM), and microground histology with special stains were applied to the same specimen. Integrated microscopy techniques were applied to eight human specimens. Micro-CT evaluation was beneficial for pinpointing the location and position of the device within the tissue, and for identifying any areas of interest or structural flaws that required additional examination. Usage of LVSEM was reliable in analyzing surface topography and cell type without destroying the integrity of the specimen. Following LVSEM, the specimen remained suitable for embedding in plastic and sectioning for light microscopy, using the positional data gathered from the micro-CT to intersect areas of interest in the slide. Finally, hematoxylin and eosin (H&E) and methylene blue staining was deployed on the slides with high-resolution results. The integration of multiple techniques on a single specimen maximized the usage of the limited number of available specimens from the clinical trial setting. Additionally, this integrated microscopic evaluation approach was found to have the added benefit of providing greater assurance of the derived conclusions because it was possible to cross-validate the results from multiple tests on the same specimen.

인체 삽입용 LC 공진형 혈압 센서 디자인 및 제작

In this paper, we present a MEMS (micro-electro-mechanical system) implantable blood pressure sensor which has designed and fabricated with consideration of size, design flexibility, and wireless detection. Mechanical and electrical characterizations of the sensor were obtained by mathematical analysis and computer aided simulation. The sensor is composed of two coils and a air gap capacitor formed by separation of the coils. Therefore, the sensor produces its resonant frequency which is changed by external pressure variation. This frequency movement is detected by inductive coupling between the sensor and an external antenna coil. Theoretically analyzed resonant frequency of the sensor under 760 mmHg was calculated to 269.556 MHz. Fused silica was selected as sensor material with consideration of chemical and electrical reaction of human body to the material. <TEX>$2mm{\times}5mm{\times}0.5mm$</TEX> pressure sensors fitted to radial artery were fabricated on the substrates by consecutive microfabrication processes: sputtering, etching, photolithography, direct bonding and laser welding. Resonant frequencies of the fabricated sensors were in the range of 269~284 MHz under 760 mmHg pressure.

An Implantable Left Atrial Pressure Sensor Lead Designed for Percutaneous Extraction Using Standard Techniques

BackgroundAn implantable left atrial pressure (LAP) monitoring system for guiding the management of patients with advanced heart failure has the potential to require extraction, particularly in the setting of infection. The LAP sensor lead was designed to be suitable for ease of percutaneous extraction using standard techniques for extracting pacemaker and defibrillator leads. The clinical experience, to date, with percutaneous extraction of the LAP sensor lead is presented.MethodsA total of 82 patients underwent successful implantation of the LAP sensor lead using transseptal catheterization. Five patients of the 82 patients during a cumulative follow-up period of 267 patient-years (median of 2.9 years/patient) underwent percutaneous extraction using manual traction with a locking stylet and/or an excimer laser sheath to bore through adhesions. The distal fixation anchors of the LAP sensor lead are designed to fold forward during extraction so that the sensor module can easily separate from the interatrial septum.ResultsPercutaneous extraction of the LAP sensor lead was accomplished successfully in all five patients with no embolic events, vascular tears, perforations, or other complications requiring surgical intervention. Manual traction alone was sufficient to detach the LAP sensor lead from the interatrial septum in all cases. Use of the excimer laser sheath was needed in selected cases to bore through scar tissue within the venous insertion site, but not within the heart.ConclusionsThe extraction of the LAP sensor lead was accomplished safely using standard techniques and equipment for percutaneously extracting pacemaker and defibrillator leads.

A SU-8-Based Microfabricated Implantable Inductively Coupled Passive RF Wireless Intraocular Pressure Sensor

With the growing demand in noncontact detection of human diseases, this paper presents an implantable passive wireless pressure sensor using an inductively coupled wireless sensing technique, particularly designed to monitor the intraocular pressure (IOP) of glaucoma patients. The microfabricated IOP sensor consists of a planar spiral gold coil inductor, a two-parallel-gold-plate (metal-insulator-metal) capacitor, and a SU-8 pressure-sensitive diaphragm. The IOP sensor is fully encapsulated inside biocompatible SU-8 stacking layers to isolate the IOP sensor from the biological tissue medium environment. By measuring the impedance phase dip frequency shift from the external coil, the IOP signal can be obtained through the implanted IOP sensor. The optimized size of the manually wound external coil was investigated. The readout distance is up to 6 mm from the implanted sensor. Characterization results show that the microfabricated IOP sensor has relatively high sensitivities-7035 ppm/mmHg in air and 3770 ppm/mmHg in saline medium-with pressure resolution lower than 1 mmHg, which is adequate for IOP monitoring application.

An implantable optical blood pressure sensor based on pulse transit time

An implantable sensor system for long-term monitoring of blood pressure is realized by taking advantage of the correlation between pulse transit time and blood pressure. The highly integrated implantable sensor module, fabricated using MEMS technologies, uses 8 light emitting diodes (LEDs) and a photodetector on chip level. The sensor is applied to large blood vessels, such as the carotid or femoral arteries, and allows extravascular measurement of highly-resolved photoplethysmograms. In addition, spectrophotometric approaches allow measurement of hemoglobin derivatives. For the calibration of blood pressure measurements, the sensor system has been successfully implemented in animal models.

Revolution of Sensors in Micro-Electromechanical Systems

Microsensors realized by micro-electromechanical systems (MEMS) technology play a key role as the input devices of systems. In this report, the following sensors are reviewed: piezoresistive and capacitive pressure sensors, surface acoustic wave (SAW) wireless pressure sensors, tactile sensor networks for robots, accelerometers, angular velocity sensors (gyroscopes), range image sensors using optical scanners, infrared imagers, chemical sensing systems as Fourier transform infrared (FTIR) spectroscopy and gas chromatography, flow sensors for fluids, and medical sensors such as ultrafine optical-fiber blood pressure sensors and implantable pressure sensors.

Revolution of Sensors in Micro-Electromechanical Systems

Microsensors realized by micro-electromechanical systems (MEMS) technology play a key role as the input devices of systems. In this report, the following sensors are reviewed: piezoresistive and capacitive pressure sensors, surface acoustic wave (SAW) wireless pressure sensors, tactile sensor networks for robots, accelerometers, angular velocity sensors (gyroscopes), range image sensors using optical scanners, infrared imagers, chemical sensing systems as Fourier transform infrared (FTIR) spectroscopy and gas chromatography, flow sensors for fluids, and medical sensors such as ultrafine optical-fiber blood pressure sensors and implantable pressure sensors.

A Minimally Invasive Implantable Wireless Pressure Sensor for Continuous IOP Monitoring

This paper presents a minimally invasive implantable pressure sensing transponder for continuous wireless monitoring of intraocular pressure (IOP). The transponder is designed to make the implantation surgery simple while still measuring the true IOP through direct hydraulic contact with the intraocular space. Furthermore, when IOP monitoring is complete, the design allows physicians to easily retrieve the transponder. The device consists of three main components: 1) a hypodermic needle (30 gauge) that penetrates the sclera through pars plana and establishes direct access to the vitreous space of the eye; 2) a micromachined capacitive pressure sensor connected to the needle back-end; and 3) a flexible polyimide coil connected to the capacitor forming a parallel LC circuit whose resonant frequency is a function of IOP. Most parts of the sensor sit externally on the sclera and only the needle penetrates inside the vitreous space. In vitro tests show a sensitivity of 15 kHz/mmHg with approximately 1-mmHg resolution. One month in vivo implants in rabbits confirm biocompatibility and functionality of the device.

459 Monitoring of Respiratory Rate Derived from an Implantable Right Ventricular Pressure Sensor in Patients with Heart Failure

Monitoring of Respiratory Rate Derived from an Implantable Right Ventricular Pressure Sensor in Patients with Heart Failure E. Chung, M. Erickson, V. Torres, G. Haas, A. Magalski, P. Adamson, M.R. Costanzo, J. Murillo. The Christ Hospital, Cincinnati, OH; Medtronic, Inc., Mounds View, MN; Loma Linda University, Loma Linda, CA; The Ohio State University Medical Center, Columbus, OH; Mid America Heart Institute, Kansas City, MO; Oklahoma Heart Hospital, Oklahoma City, OK; Midwest Heart Specialists, Naperville, IL; Sentara Cardiovascular Research Institute, Norfolk, VA.

Maintained functionality of an implantable radiotelemetric blood pressure and heart rate sensor after magnetic resonance imaging in rats

Radiotelemetric sensors for in vivo assessment of blood pressure and heart rate are widely used in animal research. MRI with implanted sensors is regarded as contraindicated as transmitter malfunction and injury of the animal may be caused. Moreover, artefacts are expected to compromise image evaluation. In vitro, the function of a radiotelemetric sensor (TA11PA-C10, Data Sciences International) after exposure to MRI up to 9.4 T was assessed. The magnetic force of the electromagnetic field on the sensor as well as radiofrequency (RF)-induced sensor heating was analysed. Finally, MRI with an implanted sensor was performed in a rat. Imaging artefacts were analysed at 3.0 and 9.4 T ex vivo and in vivo. Transmitted 24 h blood pressure and heart rate were compared before and after MRI to verify the integrity of the telemetric sensor. The function of the sensor was not altered by MRI up to 9.4 T. The maximum force exerted on the sensor was 273 ± 50 mN. RF-induced heating was ruled out. Artefacts impeded the assessment of the abdomen and thorax in a dead rat, but not of the head and neck. MRI with implanted radiotelemetric sensors is feasible in principal. The tested sensor maintains functionality up to 9.4 T. Artefacts hampered abdominal and throacic imaging in rats, while assessment of the head and neck is possible.

Design, fabrication, and implementation of a wireless, passive implantable pressure sensor based on magnetic higher-order harmonic fields.

A passive and wireless sensor was developed for monitoring pressure in vivo. Structurally, the pressure sensor, referred to as the magneto-harmonic pressure sensor, is an airtight chamber sealed with an elastic pressure membrane. A strip of magnetically-soft material is attached to the bottom of the chamber and a permanent magnet strip is embedded inside the membrane. Under the excitation of an externally applied AC magnetic field, the magnetically-soft strip produces a higher-order magnetic signature that can be remotely detected with an external receiving coil. As ambient pressure varies, the pressure membrane deflects, altering the separation distance between the magnetically-soft strip and the permanent magnet. This shifts the higher-order harmonic signal, allowing for detection of pressure change as a function of harmonic shifting. The wireless, passive nature of this sensor technology allows for continuous long-term pressure monitoring, particularly useful for biomedical applications such as monitoring pressure in aneurysm sac and sphincter of Oddi. In addition to demonstrating its pressure sensing capability, an animal model was used to investigate the efficacy and feasibility of the pressure sensor in a biological environment.

An implantable Fabry-Pérot pressure sensor fabricated on left ventricular assist device for heart failure

Continuous flow left ventricular assist devices (LVADs) are commonly used as bridge-to-transplantation or destination therapy for heart failure patients. However, non-optimal pumping speeds can reduce the efficacy of circulatory support or cause dangerous ventricular arrhythmias. Optimal flow control for continuous flow LVADs has not been defined and calls for an implantable pressure sensor integrated with the LVAD for real-time feedback control of pump speed based on ventricular pressure. A MEMS pressure sensor prototype is designed, fabricated and seamlessly integrated with LVAD to enable real-time control, optimize its performance and reduce its risks. The pressure sensing mechanism is based on Fabry-Pérot interferometer principle. A biocompatible parylene diaphragm with a silicon mirror at the center is fabricated directly on the inlet shell of the LVAD to sense pressure changes. The sensitivity, range and response time of the pressure sensor are measured and validated to meet the requirements of LVAD pressure sensing.