Portable pneumatic biventricular driver for the Thoratec ventricular assist device.

As patients with left ventricular (LVAD) and biventricular assist devices are supported for increasingly long durations while awaiting heart transplantation or cardiac recovery, there is a need to facilitate greater patient mobility and ambulation. To meet these needs, the authors have developed the Thoratec TLC-II Portable VAD Driver, which is a small brief-case sized (33 x 34 x 13 cm) pneumatic unit for Thoratec's paracorporeal and implantable VADs. The TLC-II consists of an electric motor driven air compressor for supplying both positive and negative air pressure, solenoid valves for switching between LVAD/RVAD filling and ejection, and microcontroller based electronics and firmware. Four power sources are provided: external power, two rechargeable lithium-ion battery packs, and an emergency battery that drives an independent electronic back-up system. The 8 kg TLC-II can be carried by hand, with a shoulder strap, or pushed on a wheeled mobility cart. Trend information stored in the TLC-II can be accessed by an external system computer with a color touchscreen mounted on a docking station, which also houses the battery charger. Control configurations (univentricular/biventricular operation, beat rates, etc.) are entered on the touchscreen and programmed into the TLC-II. In vitro testing demonstrates the ability to pump VAD outputs up to 7 L/min. By providing improved patient mobility, this small driver will enhance rehabilitation and improve the quality of life of VAD patients.

A volume sensor for a pneumatically driven LVAD.

The volume sensor has proven to be a valuable tool in the operation and characterization of our pneumatically driven LVAD. It compensates for the decoupling between driver and LVAD that occurs in pneumatically actuated LVADs due to gas compressibility. Uses to which we have put the volume sensor represent only a small fraction of the potential applications. Additional uses contemplated include: Use as an alternate or backup for the R-wave detection network currently used to achieve synchronization with the natural heart. This could be done by starting the LVAD ejection phase when the filling flow rate drops below a given threshold, indicating that the left ventricle has finished filling the LVAD. Use for feedback for closed loop control of plate motion. Such control could reduce actuation delays without overdriving the LVAD. Use as a diagnostic tool to aid in the study of the LVAD and its interaction with the cardiovascular system. When used in conjunction with information on left ventricular, aortic, and drive pressures, it is possible to determine the resistance, inertia and compliant characteristics of the major elements of the LVAD and the vascular system to which it is joined.