Lee continued that from the pneumatic drive, air travels to the patient through about 5 ft of 14-in. flexible tubing. The air then flows into or out of the blood pump. Lee explained, “There is only a single pneumatic lead (tube) connecting the blood pump to the driver, where the air is shuttled between positive and negative pressure (vacuum) to help assist the blood sac (pump) during filling and ejection.”

The main component of the pump is a blood sac. Blood flows into this sac and is pushed out by the pump. Biomedical quality check valves ensure that blood only flows into the sac during filling, and only flows out during ejection.

Lee continued, “The air from the pneumatic driver does not contact the blood sac directly. Instead, a diaphragm separates the air chamber in the pump from the blood sac. So in the unlikely event that the diaphragm is compromised, there still is a safety barrier to prevent air from getting into the blood sac. The diaphragm and blood sac are both made from our proprietary, polyurethane-based polymer that can endure several million cycles of deflection needed to support patients for several years.”

Versatile control
Lee explained, “The Implantable VAD has two operating modes that affect the pump rate. The first is fixed mode, which would be set by a clinician through a touchscreen that communicates with the TLC-II driver. The internal controller board then commands the solenoids to open or close valves for positive and negative pressures for every beat to fill or eject the blood in the pump. This rate is in the 70-80 bpm range for most patients.

“The second operating mode is Auto mode, which is preferred. A sensor in each pump detects when the blood sac has become filled completely. The sensor signal passes to the TLC-II Driver (via a cable from the pump to the driver), at which point the controller board knows that the pump is full and instructs the solenoids to stop passage of vacuum to the pump, and allow positive pressure to initiate sac ejection.

“As the patient exerts himself or herself, the cascade of events in turn produces greater filling pressures to the heart, which causes more blood to flow to the blood sacs, so they fill faster.

The sensor detects more rapid complete filling and initiates the next pump ejection cycle. This causes the driver to increase the pump rate automatically to accommodate the physiologic needs of the patient automatically. If the patient rests, less pressure is generated to the pump, so the driver rate will automatically slow down.

For more information on Thoratec, including videos and patient testimonials, visit www.thoratec.com.

For more information on Humphrey’s line of products, services, and engineering capabilities, visit www.humphrey-products.com.