Controlling the flow balance: In vitro characterization of a pulsatile total artificial heart in preload and afterload sensitivity.

The objective of this study is to identify the preload and afterload sensitivity of the ReinHeart TAH 2.0. For adequate left-right flow balance, the concept of a reduced right stroke volume (by about 10%) and active adaption of the right diastole duration are evaluated concerning the controllability of the flow balance. This study used an active mock circulation loop to test a wide range of preload and afterload conditions. Preload sensitivity was tested at atrial pressures (APs) between 4 and 20 mm Hg. Left afterload was varied in a range of 60-140 mm Hg mean aortic pressure (MAP), right afterload was simulated between 15 and 40 mm Hg. Four scenarios were developed to verify that the flow difference fully covers the defined target range of 0-1.5 L/min. Although a positive correlation between inlet pressure and flow is identified for the right pump chamber, the left pump chamber already fills completely at an inlet pressure of 8-10 mm Hg. With increasing afterload, both the left and right flow decrease. A positive flow balance (left flow exceeds right flow) is achieved over the full range of tested afterloads. At high APs, the flow difference is limited to a maximum of 0.7 L/min. The controllability of flow balance was successfully evaluated in four scenarios, revealing that a positive flow difference can be achieved over the full range of MAPs. Under physiological test conditions, the linear relationship between flow and heart rate was confirmed, ensuring good controllability of the TAH.

Downsizing of a Pulsatile Total Artificial Heart-The Effect on Hemolysis.

A downsized version of the ReinHeart total artificial heart (TAH) was developed. Hemocompatibility needs to be revised since the operating point of the downsized TAH has changed to a higher pump frequency to accomplish the same cardiac output. A mock circulation loop was designed, containing a left side for hemocompatibility testing and a right side to mimic realistic work conditions. A protocol for hemolysis testing was established using pooled porcine blood with an operation point of 5 L/min, a mean outlet pressure of 100 mm Hg and a mean inlet pressure of 12 mm Hg. Six trials were performed testing two downsized TAH (one with a compliance chamber [CC] connected, necessary for a pneumatic decoupling of both membranes and one open to atmosphere) and a BPX-80 as reference pump. The average modified index of hemolysis and normalized index of hemolysis (NIH in mg/100L) from six individual trials of the reference pump were 0.34 (0.07) and 3.21 (0.61) and of the TAH open to atmosphere 4.18 (1.19) and 38.85 (10.59), respectively. In between TAH with and without CC, there was no significant difference. A NIH ratio of TAH and reference pump was calculated to minimize variation of the different blood batches used in individual trials. Due to the downsizing, the ReinHeart's hemolysis level increased by around 22% compared with the original size version. Comparing the results to clinically approved left ventricular assist devices, the level of hemolysis can still be considered acceptable.

In vitro thrombogenicity testing of pulsatile mechanical circulatory support systems: Design and proof-of-concept.

Thrombogenic complications are a main issue in mechanical circulatory support (MCS). There is no validated in vitro method available to quantitatively assess the thrombogenic performance of pulsatile MCS devices under realistic hemodynamic conditions. The aim of this study is to propose a method to evaluate the thrombogenic potential of new designs without the use of complex in-vivo trials. This study presents a novel in vitro method for reproducible thrombogenicity testing of pulsatile MCS systems using low molecular weight heparinized porcine blood. Blood parameters are continuously measured with full blood thromboelastometry (ROTEM; EXTEM, FIBTEM and a custom-made analysis HEPNATEM). Thrombus formation is optically observed after four hours of testing. The results of three experiments are presented each with two parallel loops. The area of thrombus formation inside the MCS device was reproducible. The implantation of a filter inside the loop catches embolizing thrombi without a measurable increase of platelet activation, allowing conclusions of the place of origin of thrombi inside the device. EXTEM and FIBTEM parameters such as clotting velocity (α) and maximum clot firmness (MCF) show a total decrease by around 6% with a characteristic kink after 180 minutes. HEPNATEM α and MCF rise within the first 180 minutes indicate a continuously increasing activation level of coagulation. After 180 minutes, the consumption of clotting factors prevails, resulting in a decrease of α and MCF. With the designed mock loop and the presented protocol we are able to identify thrombogenic hot spots inside a pulsatile pump and characterize their thrombogenic potential.