Hierarchical algorithms have been developed for enhanced physiologic control and monitoring of blood pumps using pressure inputs. Pressures were measured at pump inlet and outlet using APEX pressure sensors (APSs). The APS is a patented, long-term implantable, flow-through blood pressure sensor and designed to control implantable heart pumps. The algorithms have been tested using a Donavan circulatory mock-loop setup, a generic rotary pump, and LabVIEW software. The hierarchical algorithms control pump speed using pump inlet pressure as a primary independent variable and pump outlet pressure as a secondary dependent variable. Hierarchical control algorithms based on feedback from pressure sensors can control the speed of the pump to stably maintain ventricular filling pressures and arterial pressures. Monitoring algorithms based on pressure inputs are able to approximate flow rate and hydraulic power for the pump and the left ventricle.
An implantable flow-through blood pressure sensor prototype has been developed for use with an implantable left ventricular assist device (LVAD). This sensor incorporates a flat pressure-sensing diaphragm that is designed to be integral with the wall of a titanium tube that may be placed in the inlet or the outlet flow path of any LVAD. The interior tube flow geometry is transitioned from a round to a D-shape such that flow separation is eliminated. Bench testing of 3 sensors was performed to characterize the sensor. The worst-case results showed a maximum nonlinearity of 0.64 mm Hg, a maximum hysteresis of 0.87 mm Hg, and a maximum nonrepeatability of 0.87 mm Hg. Long-term drift studies of 2 sensors at 193 days and 112 days resulted in a projected annual drift rate of 1.4 and 2.0 mm Hg, respectively. The APEX pressure sensors were evaluated in 5 ventricular assist acute calf experiments in which the sensor outputs were compared with Millar pressure catheter sensors. Pressure output comparisons showed similar pressure tracings. No visible evidence of thrombus formation was found on the APEX sensor compared with thrombus formation found on the Millar catheter at the entrance to the flow path. Tests demonstrated that the blood pressure sensor can accurately measure blood pressure and indicate that it has long-term stability.
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