Detection and avoiding ventricular suction of ventricular assist devices

Continuous flow blood pumps, such as axial flow and centrifugal pumps, have been gaining interest as circulatory devices for total artificial hearts (TAHs) and a biventricular assist device (BVAD) because of their smaller size and simpler structure compared to pulsatile pumps. However, continuous flow pumps are more prone to suction of the left ventricle than pulsatile pumps are. Sudden increases in flow rate to meet changes in physiological demand, especially in the left pump, often cause ventricle suction. In this study, a control algorithm to prevent suction from occurring in the left ventricle by controlling the rotational speed of the right pump, instead of reducing the cardiac output of the left pump, was developed and investigated. The method was tested in acute animal experiments with calves. The results indicate that this proposed method is capable of preventing suction and could simultaneously maintain circulatory control. A key advantage of this control system is that flow rates can be maximized while avoiding ventricle suction conditions particularly when the circulatory system is unstable such as in a the first few days after operation.

Validation of a 3D computational fluid-structure interaction model simulating flow through an elastic aperture

This work presents a validation of a fluid-structure interaction computational model simulating the flow conditions in an in vitro mock heart chamber modeling mitral valve regurgitation during the ejection phase during which the trans-valvular pressure drop and valve displacement are not as large. The mock heart chamber was developed to study the use of 2D and 3D color Doppler techniques in imaging the clinically relevant complex intra-cardiac flow events associated with mitral regurgitation. Computational models are expected to play an important role in supporting, refining, and reinforcing the emerging 3D echocardiographic applications. We have developed a 3D computational fluid-structure interaction algorithm based on a semi-implicit, monolithic method, combined with an arbitrary Lagrangian-Eulerian approach to capture the fluid domain motion. The mock regurgitant mitral valve corresponding to an elastic plate with a geometric orifice, was modeled using 3D elasticity, while the blood flow was modeled using the 3D Navier-Stokes equations for an incompressible, viscous fluid. The two are coupled via the kinematic and dynamic conditions describing the two-way coupling. The pressure, the flow rate, and orifice plate displacement were measured and compared with numerical simulation results. In-line flow meter was used to measure the flow, pressure transducers were used to measure the pressure, and a Doppler method developed by one of the authors was used to measure the axial displacement of the orifice plate. The maximum recorded difference between experiment and numerical simulation for the flow rate was 4%, the pressure 3.6%, and for the orifice displacement 15%, showing excellent agreement between the two.

Replacement of the left ventricle with a single-chambered artificial pump

Early clinical experience with total artificial hearts has stimulated further research and interest in this field. The concept of total heart replacement with a permanent mechanical device has been reevaluated, and its application as a bridge to heart transplantation is becoming more widely accepted. The size of total artificial hearts, however, limits the number of cases in which they can be used. In an effort to solve this problem, we evaluated a single-ventricle artificial pump in six Hereford calves. During surgery, the left ventricle was excised and replaced with a pneumatically actuated polyurethane pump connected to the mitral and aortic valve anulus. The right ventricle provided flow through the pulmonary vasculature, which eliminated the necessity of maintaining elevated right-sided filling pressures. The single-ventricle pump required less space than a biventricular device and was capable of maintaining adequate hemodynamic parameters in experimental animals. In comparison with the biventricular pump, this device offered the advantages of less extensive dissection requirements, ease of anastomosis, and a better anatomic fit. Patients whose pericardial cavities are too small for a biventricular artificial heart may benefit from the single-ventricle pump if they require hemodynamic support while awaiting heart transplantation.