Diaphragm Motion Affects Flow Patterns in an Artificial Heart

In the sac-driven artificial heart, the flow characteristics are coupled to the dynamics of the sac motion. The opening dynamics of the sac wall can, for example, strongly affect the chamber flow characteristics during diastole by directing or impeding the inflow. Poor sac motion can reduce the volume output of the pump and may increase the potential for thrombus formation within the ventricular chamber. It is particularly important for laboratory studies of the flow fields in artificial hearts that the diaphragm motion properly simulates the sac motion observed in vivo. In the present study, flow visualization was performed to investigate the relationship between the chamber flow characteristics of a Penn State artificial heart and the motion of the diaphragm during the filling phase during in vitro experimentation. The chamber flow pattern and diaphragm motion were recorded as a function of time, using high-speed videography. Experiments were conducted to determine the influence of diaphragm motion on the flow characteristics by altering the filling pressure, diaphragm thickness, and fluid density. Diaphragm motion was quantified by tracking the position of three surface points over the cardiac cycle. The alignment of these three surface trajectories can be used to quantify the uniformity of diaphragm motion. As a result, diaphragm motion was determined to be nonuniform under most operating conditions with the diaphragm opening in a wave-like pattern starting at the bottom of the chamber and propagating toward the inflow/outflow ports. This opening pattern simulates the opening pattern observed in an in vitro study of the clinical blood sac used in the Lionheart LVAD.