Graft Resistance Difference after HVAD to HeartMate 3 Left Ventricular Assist Device Exchange.

BACKGROUND: A likely consequence of the discontinued distribution and sale of the HVAD System (Medtronic, Minneapolis, MN) will be an increase in replacement with the HeartMate 3 (Abbott, Chicago, IL) left ventricular assist device when device exchange is necessary. If part or all of the HVAD 10-mm-diameter outflow graft is retained during replacement, the HeartMate 3 will have to run at a higher speed than it would with its 14-mm-diameter graft. METHODS: A steady-state, in vitro study was run with 250-mm-long samples of HVAD, HeartMate 3, and half-HVAD/half-HeartMate 3 grafts and additionally 125- and 375-mm-long samples of the HVAD graft. Flows of 3.0, 3.9, 4.3, 4.7, and 6.0 L/min were applied to encompass expected clinical conditions. RESULTS: At typical and high flow rates of 4.3 and 6.0 L/min, HeartMate 3 rotor speeds with the full HVAD graft had to be increased relative to those with the HeartMate 3 graft from 5350 to 5700 and 6350 to 6900 rpm, respectively, with power consumption increases from 3.7 to 4.3 W (16%) and 5.5 to 6.8 W (24%), respectively. CONCLUSIONS: The study did not elucidate a severe consequence of using a remnant HVAD graft during pump exchange, but the incremental risks of a higher rotor speed, disadvantage to the patient in battery runtime, and the general benefit of complete conversion to the HeartMate 3 graft should be balanced against other procedural considerations. Complete graft replacement during HVAD-to-HeartMate 3 conversion remains the preferred approach from an engineering point of view.

Design and construction of three-dimensional physiologically-based vascular branching networks for respiratory assist devices.

Microfluidic lab-on-a-chip devices are changing the way that in vitro diagnostics and drug development are conducted, based on the increased precision, miniaturization and efficiency of these systems relative to prior methods. However, the full potential of microfluidics as a platform for therapeutic medical devices such as extracorporeal organ support has not been realized, in part due to limitations in the ability to scale current designs and fabrication techniques toward clinically relevant rates of blood flow. Here we report on a method for designing and fabricating microfluidic devices supporting blood flow rates per layer greater than 10 mL min-1 for respiratory support applications, leveraging advances in precision machining to generate fully three-dimensional physiologically-based branching microchannel networks. The ability of precision machining to create molds with rounded features and smoothly varying channel widths and depths distinguishes the geometry of the microchannel networks described here from all previous reports of microfluidic respiratory assist devices, regarding the ability to mimic vascular blood flow patterns. These devices have been assembled and tested in the laboratory using whole bovine or porcine blood, and in a porcine model to demonstrate efficient gas transfer, blood flow and pressure stability over periods of several hours. This new approach to fabricating and scaling microfluidic devices has the potential to address wide applications in critical care for end-stage organ failure and acute illnesses stemming from respiratory viral infections, traumatic injuries and sepsis.

Ion-selective optodes measure extracellular potassium flux in excitable cells.

Optodes have been used for detection of ionic concentrations and fluxes for several years. However, their uses in biomedical applications have not yet been fully explored. This study investigates optodes as a potential sensor platform for monitoring cellular ion flux with attendant implications in the field of drug screening and toxicology. A prototype system was developed to quantitatively measure extracellular potassium flux from a monolayer of cardiomyocytes. Optodes were created and immobilized on a glass coverslip for fluorescent imaging. The system detected potassium (K(+) ) ion flux during the repolarization phase of the cardiac action potential and further detected a decrease in the magnitude of the flux in the presence of a known K(+) channel inhibitor by optically monitoring local K(+) ion concentrations during field stimulation of the cardiomyocyte monolayer.

Fluorescent ion-selective nanosensors for intracellular analysis with improved lifetime and size.

We describe the synthesis and characterization of sodium-selective polymeric nanosensors that improves upon the lifetime and size of previous fiberless nanosensors. Sonication is used to form the polymer nanospheres that contain all the components needed for ion sensing. Even though the size is small (approximately 120 nm), the lifetime of these sensors in solution is on the order of a week. The surface coating has also been optimized for stability, biocompatibility, and ease of chemical modification.