Physiologic control of cardiac assist devices

Total artificial hearts (TAHs) and biventricular assist devices (BVADs) have varying levels of acceptance and reliability, and the research on both focuses on their control mechanisms. Efforts generally aim to achieve a response to physiologic demand and left/right output balance, and beneficial cardiac output (CO) and effective control mechanisms have been achieved by eliciting a Starting-like response to preload and afterload. Such control mechanisms, however, generally base device output on a single parameter, such as the preload on the heart. Current TAHs and BVADs provide relatively fixed oxygen delivery to patients with large physiologically induced variations in oxygen consumption. This paper aims to document fluctuations in oxygen consumption that are normal in BVAD and TAH patients, identify a number of patient-generated signals that reflect these fluctuations, and describe a multitiered control algorithm based upon these signals. Such a control system may offer better response times and more physiologic cardiac outputs. There currently exists a microprocessor-based control mechanism that can be adapted to control TAHs and BVADs using input from a variety of sensors, and it can be found in modern implantable pulse generators (IPGs). Today's pacemakers are capable of rate control and can run diagnostic programs and store data that could be valuable in the evaluation of the patient's condition.