Pulmonary Veins Function as Echo Chambers in Persistent Atrial Fibrillation: Circuitous Re-Entry Generates Outgoing Wavefronts.

BACKGROUND: Although the substrate in persistent atrial fibrillation (PeAF) is not limited to the pulmonary veins (PVs), PV isolation (PVI) remains the cornerstone ablation strategy. OBJECTIVES: The aim of this study was to describe the mechanism of outgoing wavefronts (WFs) originating in the PV sleeves during PeAF. METHODS: Eleven patients presenting for first-time PeAF ablation were recruited (mean age 63.1 ± 10.9 years, 91% men). A 64-electrode catheter (Constellation; 38 mm) was positioned within the PV under fluoroscopic guidance. An inverse mapping technique was used to reconstruct unipolar atrial electrograms on the PV surface, and the resulting phase maps were used to identify incoming and outgoing WFs at the PV junction and to classify focal and re-entrant activity within the PV sleeves. RESULTS: During PeAF, the PVs gave rise to outgoing WFs with a frequency of 3.7 s-1 (Q1-Q3: 3.4-5.4 s-1) compared with 3.6 s-1 (Q1-Q3: 2.8-4.2 s-1) for incoming WFs. Circuitous macroscopic re-entry was the dominant mechanism driving outgoing WFs (frequency of re-entry 2.7 s-1 [Q1-Q3: 2.0-3.3 s-1] compared with focal activity 1.4 s-1 [Q1-Q3: 1.1-1.5 s-1]; P < 0.006). This was initiated by incoming WFs in 80% of cases. Consecutive focal activation from the same location was infrequent (10.0% ± 6.6%, n = 10). Rotors ≥360° were never observed. The median ratio (R) of outgoing to incoming WF frequency was 1.14 (Q1-Q3: 0.84-1.75), with R > 1 in 6 of 11 PVs. CONCLUSIONS: Electric activity generated by PV sleeves during PeAF is due mainly to circuitous re-entry initiated by incoming waves, frequently with R > 1. That is, the PVs act less as drivers of atrial fibrillation than as "echo chambers" that sustain and amplify fibrillatory activity.

A pneumatic reconfigurable socket for transtibial amputees.

Many transtibial amputees rate the fit between their residual limb and prosthetic socket as the most critical factor in satisfaction with using their prosthesis. This study aims to address the issue of prosthetic socket fit by reconfiguring the socket shape at the interface of the residual limb and socket. The proposed reconfigurable socket shifts pressure from sensitive areas and compensates for residual limb volume fluctuations, the most important factors in determining a good socket fit. Computed tomography scan images are employed to create the phantom limb of an amputee and to manufacture the reconfigurable socket. The performance of the reconfigurable socket was evaluated both experimentally and numerically using finite element modelling. The study showed that the reconfigurable socket can reduce interface pressure at targeted areas by up to 61%.

A pilot study to evaluate changes in pelvic floor muscle tone following pelvic organ prolapse surgery using a novel intra-vaginal pressure sensor device.

INTRODUCTION AND HYPOTHESIS: Pelvic floor muscle weakness is a common cause of pelvic organ prolapse and urinary incontinence. Surgical repair of prolapse is commonly undertaken; however, the impact on pelvic floor muscle tone is unknown. The aim of this study was to compare the effect of anterior and posterior colporrhaphy on pelvic floor activation. METHODS: Patients aged under 70 undergoing primary anterior or posterior colporrhaphy were recruited. Intra-vaginal pressure was measured at rest and during pelvic floor contraction using the Femfit® device (an intra-vaginal pressure sensor device [IVPSD]). Peak pressure and mean pressure over 3 s were measured in millimetres of mercury. The pre- and post-operative measurements were compared. The difference between the means was assessed using Cohen's D test, with significance set at p<0.05 RESULTS: A total of 37 patients completed pre- and post-operative analysis, 25 in the anterior colporrhaphy group and 12 in the posterior colporrhaphy group. Anterior colporrhaphy showed no significant change in pelvic floor tone. Change in peak pressure was -1.71mmHg (-5.75 to 2.33; p=0.16) and change in mean pressure was -0.86 mmHg (-4.38 to 2.66; p=0.31). Posterior colporrhaphy showed a significant increase in peak pelvic floor muscle tone of 7.2 mmHg (0.82 to 13.58; p=0.005) and mean pressure of 4.19 mmHg (-0.09 to 8.47; p=0.016). CONCLUSIONS: Posterior colporrhaphy significantly improves pelvic floor muscle tone, whereas anterior colporrhaphy does not. Improved understanding of the impact of pelvic floor surgery may guide future management options for other pelvic floor disorders. Further work is needed to confirm the association of this improvement in pelvic floor disorders.

Non-Contact Intracardiac Potential Mapping Using Mesh-Based and Meshless Inverse Solvers.

Atrial fibrillation (AF) is the most common cardiac dysrhythmia and percutaneous catheter ablation is widely used to treat it. Panoramic mapping with multi-electrode catheters has been used to identify ablation targets in persistent AF but is limited by poor contact and inadequate coverage of the left atrial cavity. In this paper, we investigate the accuracy with which atrial endocardial surface potentials can be reconstructed from electrograms recorded with non-contact catheters. An in-silico approach was employed in which "ground-truth" surface potentials from experimental contact mapping studies and computer models were compared with inverse potential maps constructed by sampling the corresponding intracardiac field using virtual basket catheters. We demonstrate that it is possible to 1) specify the mixed boundary conditions required for mesh-based formulations of the potential inverse problem fully, and 2) reconstruct accurate inverse potential maps from recordings made with appropriately designed catheters. Accuracy improved when catheter dimensions were increased but was relatively stable when the catheter occupied >30% of atrial cavity volume. Independent of this, the capacity of non-contact catheters to resolve the complex atrial potential fields seen in reentrant atrial arrhythmia depended on the spatial distribution of electrodes on the surface bounding the catheter. Finally, we have shown that reliable inverse potential mapping is possible in near real-time with meshless methods that use the Method of Fundamental Solutions.

Intracardiac Inverse Potential Mapping Using the Method of Fundamental Solutions.

Introduction: Atrial fibrillation (AF) is the most prevalent cardiac dysrhythmia and percutaneous catheter ablation is widely used to treat it. Panoramic mapping with multi-electrode catheters can identify ablation targets in persistent AF, but is limited by poor contact and inadequate coverage. Objective: To investigate the accuracy of inverse mapping of endocardial surface potentials from electrograms sampled with noncontact basket catheters. Methods: Our group has developed a computationally efficient inverse 3D mapping technique using a meshless method that employs the Method of Fundamental Solutions (MFS). An in-silico test bed was used to compare ground-truth surface potentials with corresponding inverse maps reconstructed from noncontact potentials sampled with virtual catheters. Ground-truth surface potentials were derived from high-density clinical contact mapping data and computer models. Results: Solutions of the intracardiac potential inverse problem with the MFS are robust, fast and accurate. Endocardial surface potentials can be faithfully reconstructed from noncontact recordings in real-time if the geometry of cardiac surface and the location of electrodes relative to it are known. Larger catheters with appropriate electrode density are needed to resolve complex reentrant atrial rhythms. Conclusion: Real-time panoramic potential mapping is feasible with noncontact intracardiac catheters using the MFS. Significance: Accurate endocardial potential maps can be reconstructed in AF with appropriately designed noncontact multi-electrode catheters.

The Safety of Micro-Implants for the Brain.

Technological advancements in electronics and micromachining now allow the development of discrete wireless brain implantable micro-devices. Applications of such devices include stimulation or sensing and could enable direct placement near regions of interest within the brain without the need for electrode leads or separate battery compartments that are at increased risk of breakage and infection. Clinical use of leadless brain implants is accompanied by novel risks, such as migration of the implant. Additionally, the encapsulation material of the implants plays an important role in mitigating unwanted tissue reactions. These risks have the potential to cause harm or reduce the service of life of the implant. In the present study, we have assessed post-implantation tissue reaction and migration of borosilicate glass-encapsulated micro-implants within the cortex of the brain. Twenty borosilicate glass-encapsulated devices (2 × 3.5 × 20 mm) were implanted into the parenchyma of 10 sheep for 6 months. Radiographs were taken directly post-surgery and at 3 and 6 months. Subsequently, sheep were euthanized, and GFAP and IBA-1 histological analysis was performed. The migration of the implants was tracked by reference to two stainless steel screws placed in the skull. We found no significant difference in fluoroscopy intensity of GFAP and a small difference in IBA-1 between implanted tissue and control. There was no glial scar formation found at the site of the implant's track wall. Furthermore, we observed movement of up to 4.6 mm in a subset of implants in the first 3 months of implantation and no movement in any implant during the 3-6-month period of implantation. Subsequent histological analysis revealed no evidence of a migration track or tissue damage. We conclude that the implantation of this discrete micro-implant within the brain does not present additional risk due to migration.

Using codesign to develop a mobile application for pelvic floor muscle training with an intravaginal device (femfit®).

AIMS: The aim of this project was to use codesign to develop a mobile application (app) for pelvic floor muscle training, with an intravaginal device (femfit®). The objective was to obtain user feedback to guide the design and development of a mobile app, consistent with the Mobile Application Rating Scale (MARS) framework. METHODS: Twenty-six women (22-62 years) provided mobile app feedback using a Design Thinking framework and grounded theory approach. Four focus groups (2 h each) and two sets of one-to-one interviews (1 h each) were held from May 2018 to October 2019. The researchers debriefed the focus groups and interviews, and undertook analysis based on project objectives and key questions. RESULTS: Recurring themes throughout the study aligned with sections of the MARS: (A) engagement (e.g., progress tracking), (B) functionality (e.g., intuitive interface), (C) aesthetics (e.g., smart graphics and colors), (D) information (e.g., clear, concise information). An internal preliminary assessment determined a MARS Quality Mean Score of 4.1 of 5 (engagement: 3.6 of 5; functionality: 4 of 5; aesthetics: 4.3 of 5: information: 4.4 of 5). CONCLUSIONS: The development of the mobile app is on track to meet MARS requirements, and to be a fun, motivating app for women. Future work is required to investigate its efficacy.

Assessing vaginal pressure profiles before and after prolapse surgery using an intravaginal pressure sensor (femfit®).

INTRODUCTION AND HYPOTHESIS: The impact of surgery on pelvic floor muscle (PFM) function remains uncertain. There is a pressure differential along the length of the vagina, influenced by surrounding active and passive tissue structures, giving rise to a pressure profile. The aim of this study is to determine if an intravaginal pressure sensor, femfit®, can measure differences in pressure profiles before and after surgery for pelvic organ prolapse (POP). METHODS: This pilot study includes 22 women undergoing POP surgery. Intravaginal pressure profiles were measured with femfit® pre- and post-surgery and differences tested using paired Student's t-tests. Patients completed validated questionnaires for vaginal, bowel, and urinary incontinence symptoms pre- and post-POP surgery and a femfit® usability questionnaire. RESULTS: Sixteen sets of vaginal pressure data were analysed. The highest pressure generated was identified as the peak PFM pressure, whilst all sensor measurements provided a pressure profile. Intra-abdominal pressure (IAP) was measured by the most distal sensor, 8. On average, the difference between peak PFM pressure and IAP was significantly greater post-surgery (p < 0.01). Urinary and vaginal symptom questionnaire scores were significantly improved after POP surgery. Femfit® usability questionnaires demonstrated high levels of patient acceptability. CONCLUSIONS: Women generate higher peak PFM pressures compared to IAP post-POP surgery, with pressure profiles that are comparable to women without POP. This metric might be useful to assess the outcome of POP surgery and encourage women to maintain this profile via PFM training, potentially reducing POP recurrence risk.

A Capacitive Pressure Sensor Interface IC with Wireless Power and Data Transfer.

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The "1" of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a -20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C.

Thermal evaluation of a hermetic transcutaneous energy transfer system to power mechanical circulatory support devices in destination therapy.

Current generation left ventricular assist devices (LVADs) are powered by a percutaneous driveline. The high prevalence of driveline infections has motivated the development of transcutaneous energy transfer (TET) systems which eliminate driveline associated complications by wirelessly delivering power across the skin. Destination therapy (DT) requires long-term reliable operation of the TET electronics suggesting the use of hermetic packaging techniques as used in all other chronically implanted devices. TET coils dissipate heat during operation and in order for the technology to be suitable for patient use, sufficient power must be delivered while maintaining temperatures at levels deemed safe. The heating of a TET system designed for DT which uses hermetic packaging technology was evaluated in silico and in vivo. A numerical model was used to evaluate the temperature of the TET coils. The TET system was fabricated and assessed in vivo using an ovine model. The receiving coil was implanted subcutaneously in a sheep and the transmission coil placed in contact with the skin and concentric to the implanted coil. Temperatures of the system were measured using sensors fixed to the surface of the coils. Numerical modeling indicated that the maximum temperatures of the primary and secondary coil surfaces were 38.13°C and 38.41°C, respectively, when delivering 10 W continuously. Stable temperatures were observed in vivo after 70 minutes and the maximum skin and implant surface temperatures were 37.73°C and 38.31°C, respectively. This study showed that a hermetic, chronically implantable TET system is thermally safe when continuously delivering 10 W of power, sufficient to power modern LVADs.

Injection Molded Liquid Crystal Polymer Package for Chronic Active Implantable Devices With Application to an Optogenetic Stimulator.

Implanted electronics require protection from the body's fluids to avoid moisture induced failure. This study presents an injection molded liquid crystal polymer (LCP) package to protect active implantable devices for chronic applications, such as in optogenetic research. The technology is applied and assessed through a custom package for a fully implantable optogenetic stimulation system, built on a versatile telemetry system that can incorporate additional stimulating and recording channels. An adapted quasi-steady state model predicts the lifetime of an enclosure, where the definition of the lifetime is the time before the internal relative humidity (RH) reaches a time constant, or 63%RH, a conservative limit to minimize the risk of corrosion. The lifetime of the LCP optogenetic device is 94 days, and can be extended to 326 days with the inclusion of 5% w/v silica gel desiccant. Samples of the LCP optogenetic device containing humidity sensors testing in saline at 38 °C support the RH change predictions. Desiccants inside the implant enclosure can store permeating moisture and prolong the life expectancy of LCP-based implants to years or decades. The results of this study demonstrates the feasibility of providing reliable protection for chronic optogenetic implants, and the technology can be transferred to other applications as an easily-manufactured, cost-effective, radiofrequency compatible alternative to hermetic packaging for chronic studies.

Reliability and validity of intravaginal pressure measurements with a new intravaginal pressure device: The FemFit®.

AIMS: To test the reliability and validity of intravaginal pressure measurements acquired during pelvic floor muscle (PFM) tasks in different body positions using the FemFit®, a new intravaginal pressure device. METHODS: Twenty healthy adult women participated in this study. Two assessment sessions were conducted. Intravaginal pressure measurements using the FemFit® were repeated during PFM contraction and straining maneuvers while lying and standing. Maximal intravaginal pressures were collated and compared within and between sessions. They were also correlated to maximal force measurements obtained by dynamometry and vaginal digital palpation. Test-retest reliability was assessed using intraclass correlation coefficient, standard error of measurement and Bland-Altman plots. The validity of the pressure measurements was assessed using Pearson's correlation (dynamometry) and Spearman's rho (palpation). RESULTS: This test-retest study indicate excellent reliability for PFM contraction and straining maneuver both in lying and standing, within and between sessions. For the straining maneuver while standing, increased variability was suggested by a wider limit of agreement on Bland-Altman plots (spanning 31.3 to 43.3mm Hg). A significant moderate to strong correlation was found when comparing measurements of PFM contraction using the FemFit® and the dynamometer or the palpation (Pearson's coefficient = 0.72, P = .006; Spearman's rho = 0.68, P = .005, respectively). CONCLUSION: Our research findings suggest that intravaginal pressures can be reliably measured during PFM contraction and straining manoeuver while lying and standing, using the FemFit® device, both within and between sessions. A moderate to strong correlation between the FemFit® pressure and the force measurements obtained by dynamometry or palpation reinforce the validity of measurements.

Can you train the pelvic floor muscles by contracting other related muscles?

AIMS: The aim of this study is to assess whether contraction of muscles other than the pelvic floor muscles (PFM) would be of sufficient magnitude to provide a "training" effect for the pelvic floor. METHODS: Women were recruited via advertisement from a convenience sample of pelvic floor physiotherapists. A thin flexible array of pressure sensors (FemFit) was self-inserted into the vagina. Participants performed three maximum pelvic floor contractions and completed a randomized exercise protocol. Maximum pressures were determined for each sensor, for each exercise. Wilcoxon paired tests were used to ascertain the difference in pelvic floor muscle pressure between exercises, and between the pressures from the pelvic floor muscles sensors and those measuring abdominal pressure. Bonferroni correction α 0.005. RESULTS: Data was obtained from nineteen participants. Mean age 43 ± 11 years, BMI 22.4 ± 3.2 kg m-2 . Mean PFM pressure for pelvic floor muscle contractions was 16.3 ± 12.2 mmHg. Pressure in the region of the pelvic floor was significantly higher during a targeted contraction compared to that for all other exercises, except for cough and curl-ups (P = 0.009, P = 0.013 respectively). PFM pressure was significantly higher than abdominal for PFMC, internal rotators and gluteals (P < 0.001). CONCLUSION: Targeted PFM contractions develop higher pressures compared to abdominal pressure than any exercise tested in this study. The Femfit device was able to distinguish between abdominal and pelvic floor muscle pressures simultaneously. Exercising accessory muscles in an attempt to activate the pelvic floor sufficiently to illicit a training effect is not recommended.

Pulse-Width Modulation of Optogenetic Photo-Stimulation Intensity for Application to Full-Implantable Light Sources.

Optogenetics allows control of neuronal activity with unprecedented spatiotemporal precision, and has enabled both significant advances in neuroscience and promising clinical prospects for some neurological, cardiac, and sensory disorders. The ability to chronically stimulate light-sensitive excitable cells is crucial for developing useful research tools and viable long-term treatment strategies. Popular optogenetic stimulation devices often rely on bench-top light-sources tethered via an optical fibre to the research animal, or significant componentry protruding externally from animal. These approaches are prone to infection, vulnerable to damage and restrict the experimental approaches that can be conducted. An ideal optogenetic stimulator would be contained entirely within the animal and provide precisely controlled optical output. However, existing prototypes of fully implantable devices rely on amplitude tuning of wireless power, which can vary strongly with environmental conditions. Here we show that pulse-width modulation (PWM) of the intensity of a light-emitting diode (LED) can enable control of photo-stimulation intensity equivalent to direct amplitude modulation. This result has significant implications for fully implantable light delivery tools, as PWM can be implemented with simple and miniaturized circuit architectures. We have modified a telemeter device previously developed by our group to include a small form-factor LED capable of generating sufficient optical power with manageable electrical power requirements and minimal heat generation. We have tested key device components in an in vitro mouse brain slice preparation and shown that pulse-width-modulation is an alternative method to modulate photo-stimulation intensity using a miniature circuit and providing easy control.

New multimodal data obtained in-vivo from a single ultra-miniature transducer.

Recent advances in multimodal sensing technology and sensor miniaturization technologies are paving the way for a new era in physiological measurement. Traditional approaches have integrated several transducers on a single silicon chip or packaged several sensing elements within a biocompatible catheter. Thermal and electrical cross-talk between sensors, time-lag between parallel measurements, lower yields associated with the increased complexity, and restrictions on the minimum size are challenges presented by these approaches. We present an alternative method which enables simultaneous measurement of temperature, pressure and heart rate to be obtained from a single ultra-miniature solid-state transducer. For the first time multimodal data were obtained from the sensor located within the abdominal aortas of five rats. The catheter-tip sensor interfaces with a fully implanted and inductively powered telemetry device capable of operating for the lifetime of the animal. Results of this study demonstrate good agreement between the core-temperature measurement from the catheter-tip sensor and the reference sensor with mean difference between the two sensors of 0.03 °C ± 0.02 °C (n = 5, 7 days). Real-time data obtained in the undisturbed rat, revealed fluctuations associated with the rest-activity cycle, in temperature, mean arterial pressure and heart rate. The stress response was shown to elicit an elevation in the core temperature of 1.5 °C. This was heralded by an elevation in mean arterial pressure of 35 mmHg and heart rate of 160 bpm. Obtaining multiple parameters from a single transducer goes a considerable way towards overcoming challenges of the prior art.

MRI interactions of a fully implantable pressure monitoring device.

PURPOSE: To investigate the potential patient risk and interactions between a prototype implantable pressure monitoring device and a 3T clinical magnetic resonance imaging (MRI) machine to guide device design towards MR Conditional safety approval. MATERIALS AND METHODS: The pressure monitor device contained a catheter-mounted piezo-resistive pressure sensor, rechargeable battery, wireless communication system, and inductive pickup coil. Standard testing methods were used to guide experiments to investigate static field induced force and torque, radiofrequency (RF)-induced heating, image artifacts, and the MR's effect on device function. The specific clinical application of intracranial pressure monitoring was considered. RF-induced heating experiments were supported by numerical modeling of the RF body coil, the device, and experimental phantom. RESULTS: Sensing catheter lead length and configuration was an important component of the device design. A short 150 mm length catheter produced a heating effect of less than 2°C and a long 420 mm length catheter caused heating of 7.2°C. Static magnetic field interactions were below standard safety risk levels and the MR did not interfere with device function; however, artifacts have the potential to interfere with image quality. CONCLUSION: Investigation of MR interactions at the prototype stage provides useful implantable device design guidance and confidence that an implantable pressure monitor may be able to achieve MR Conditional safety approval.

Clinical evaluation of a high-fidelity wireless intravaginal pressure sensor.

INTRODUCTION AND HYPOTHESIS: A wireless intravaginal pressure sensor (IVPS) has been developed to quantify abdominal pressure (P(abd)) changes during exercise and activities of daily living to guide post-operative advice given to women. In this pilot study, we aimed to compare IVPS performance, comfort, retention, and acceptability to a standard fluid-filled intrarectal pressure catheter currently used to measure P(abd) during routine urodynamics. METHODS: A Life-Tech 3-mm urodynamic intrarectal catheter and IVPS were inserted concurrently in volunteers attending a urodynamics clinic. The IVPS was positioned above the levator plate and the intrarectal catheter positioned in routine fashion well above the anal sphincter. Routine urodynamics was undertaken, with women asked to perform star jumps if coughing or Valsalva did not invoke leakage. Subjects rated device comfort using a visual analogue scale (0-10). Repeated measures Bland-Altman analysis determined level of agreement (LOA) between the two devices for peak pressures for each activity. RESULTS: Twenty-seven women were recruited, 67% of the participants preferred the IVPS, 18% the intrarectal catheter, while 15% had no preference. Mean comfort score was 0.9 ± 1.7 and 2.1 ± 2.6 (p = 0.049) for the IVPS and intrarectal catheter respectively. Bland-Altman analysis demonstrated minimal bias for cough and Valsalva, however LOA were wide. Differences were more prominent during star jumps where rapid dynamic pressure changes occurred. CONCLUSIONS: The IVPS had a higher comfort score and was well retained. The LOA between the two systems was moderate, but the high sampling rate and lower susceptibility to motion artefacts of the IVPS may provide more accurate information that will be important clinically.

Chronic measurement of left ventricular pressure in freely moving rats.

Measurements of left ventricular pressure (LVP) in conscious freely moving animals are uncommon, yet could offer considerable opportunity for understanding cardiovascular disease progression and treatment. The aim of this study was to develop surgical methods and validate the measurements of a new high-fidelity, solid-state pressure-sensor telemetry device for chronically measuring LVP and dP/dt in rats. The pressure-sensor catheter tip (2-Fr) was inserted into the left ventricular chamber through the apex of the heart, and the telemeter body was implanted in the abdomen. Data were measured up to 85 days after implant. The average daytime dP/dt max was 9,444 ± 363 mmHg/s, ranging from 7,870 to 10,558 mmHg/s (n = 7). A circadian variation in dP/dt max and heart rate (HR) was observed with an average increase during the night phase in dP/dt max of 918 ± 84 mmHg/s, and in HR of 38 ± 3 bpm. The ß-adrenergic-agonist isoproterenol, ß1-adrenergic agonist dobutamine, Ca(2+) channel blocker verapamil, and the calcium sensitizer levosimendan were administered throughout the implant period, inducing dose-dependent time course changes and absolute changes in dP/dt max of -6,000 to +13,000 mmHg/s. The surgical methods and new technologies demonstrated long-term stability, sensitivity to circadian variation, and the ability to measure large drug-induced changes, validating this new solution for chronic measurement of LVP in conscious rats.

Intracranial temperature and pressure measurement: in vitro temperature sensing characteristics of the dual sensing element.

A pressure sensor has been used to measure temperature concurrently. We have designed, and characterized the measurement of temperature from the same sensor to allow simultaneous monitoring of intracranial temperature and pressure. The temperature measurement has a sensitivity of 85.08 mV/°C across the measurement range 20-45 °C. The time constant of the temperature sensor is 150 ms. We have evaluated the accuracy of the temperature measurement and the long term drift of 13 sensors over 28 days. The mean difference of the temperature measurements from the reference measurements was less than 0.2 °C.

Implantable ICP monitor for improved hydrocephalus management.

BACKGROUND: Hydrocephalus patients are commonly treated by insertion of ventriculoperitoneal shunts, but these have high complication rates. Monitoring of shunt and patient condition can be achieved through measuring intracranial pressure (ICP). Significant zero drift has limited previous developments towards a long-term implantable ICP monitor. We present a new implantable solid-state pressure sensor system appropriate for chronic (lifetime) monitoring of ICP. MATERIALS AND METHODS: Initial designs of the proposed ICP system were realised and the pressure sensor catheter underwent bench-top tests to analyse its characteristics. A drift rig was constructed for the long-term analysis of the sensor's zero drift. The pressure sensor catheter was used to continuously monitor blood pressure in rats. RESULTS: Three potential design solutions were realised: a standalone sensor, the sensor unit in line with a shunt system, and the sensor unit fully integrated into the shunt valve housing. Initial stability results across 46 days show a maximum drift of less than 2 mmHg and a minimum drift of less than 0.2 mmHg. CONCLUSION: Initial experience with the new implantable solid-state pressure sensor system confirms its suitability for chronic pressure monitoring. The device is promising for providing vital information on shunt and patient condition.