Ellyce Stehlin

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 sensors 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.

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 β-adrenergic-agonist isoproterenol, β1-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.

MRI interactions of a fully implantable pressure monitoring device

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.

874 Chronic measurement of left ventricular pressure and dP/dt in freely moving rats during the development of heart failure following myocardial infarction

Background: Understanding the mechanisms involved in the progression from cardiac injury to heart failure is essential in order to develop better treatment strategies. Using a rat model of heart failure following myocardial infarction (MI) we can study the development of heart failure. Recently we have developed a method to chronically measure left ventricular pressure (LVP) in conscious rats allowing the use of the maximum rate of change of LVP (dP/dt) as an index of contractility of the heart. Methods: High-fidelity dual-pressure telemetry units were surgically implanted, with pressure sensors continuously monitoring arterial pressure and LVP (through the apex of the heart). After a two-week baseline period the rats underwent either sham surgery, or MI (ligation of the left anterior descending coronary artery). Data were then continuously recorded for a further 6 weeks. Results: Results indicate that we can reliably record baseline arterial pressure and LVP data in conscious rats for at least 10 weeks. Ultrasound results have shown ventricular function to be maintained following LVP sensor implantation, with no change in fractional shortening before and 4 weeks post implantation. After MI, maximum dP/dt was shown to closely follow the changes in ventricular function as assessed by ultrasound. Conclusions: These results demonstrate that the use of the high-fidelity telemetry units can reliably assess dP/dt in the conscious animal without adverse affects on ventricular function. We propose that the chronic measurement of LVP in conscious rats can provide a valuable tool in following the progression of heart failure following MI.