Drive optimisation of a pulsatile Total Artificial Heart

Abstract

Drive optimisation of a pulsatile Total Artificial HeartTotal Artificial Hearts (TAHs) are required for the therapy of terminal heart diseases as heart transplants are only a limited option due to the available number of donor hearts. For implantation TAHs have to meet constraints regarding its dimensions, weight, perfusions and electrical losses. An innovative linear driven TAH is presented, which meets all constraints except weight. Therefore the geometry of the linear drive is optimised to reduce its weights while simultaneously limiting the electrical losses as much as possible. In order to calculate the losses, this paper introduced a combined calculation chain consisting of FEM simulations and analytical equations. Based on this chain the linear drive is optmised by the method of parameter variations. The results yield a hierachic order of parameters which are most suitable for the weight reduction of the drive for low losses. By this the weight of the linear drive is reduced by 25%. As the allowable loss limit is not exceeded yet, room for further weight reduction achieved by an optimisation of the axial geomtry parameters is given.

Image based evaluation of mediastinal constraints for the development of a pulsatile total artificial heart

“…Additionally a new version of the drive unit with a reduced outer diameter of 82 mm (originally 90 mm) became available [13] and could immediately be integrated. Whereas the arrangement of the ducts within one chamber was fixed during the actual trial, there still was one degree of freedom between the two chambers, which is the rotation around the centerline.…”

Validation of the electromagnetic design of a total artificial heart under physical load conditions

“…The calculations were performed across the stroke separately for each coil, when supplied by 1 A. The copper losses were calculated as described in Pohlmann et al (2010). Realistic boundary conditions are crucial as differences and tolerances for example in temperature, dimensions, current and force measurement reduce overall correlation of results.…”

“…In this way the flux coupling in the coils can be determined in every position (x) of the coil assembly. The flux density at each coil (B n ) can be put into relation of the flux density of all coils according to equation (2) and is referred to as the axial position dependent current factor (k I,n (x)): Equation 2 According to Pohlmann et al (2010) electric losses are minimized when the relation of the current in each coil follows equation (3), where (I sum ) represents the sum of the current in all coils and (I n ) represents the sum of the current in coil n: Equation 3 In a second step the required force profile is determined. Therefore, a pump chamber was connected to a physiologic hydraulic load and actuated by a servo‐hydraulic testing machine (Zwick HC5), which replaced the linear drive system and measured force and position of the pusher plate.…”

“…For designing the drive the following anatomical and physiological constraints have been considered:Due to the limited space in the human thorax, the dimensions of the pump unit should not exceed 85 mm in diameter and 95 mm in length, allowing a motor height of 36 mm.The total weight of the entire pump unit should be less than 800 g requiring a maximum drive weight of 500 g.The average blood flow should amount up to 5 l/min against a medium aortic pressure of 95 mmHg and provide an additional overload capacity.Electrical losses have to be less than 20 W to avoid blood and tissue damage due to excessive heat.The drive has to generate a force of up to 60 N (Pohlmann et al , 2010). The key specifications of the current version of the linear drive are listed in Table I.…”

“…While the dimensions exactly meet the requirements, its weight exceeds requirement (2). This problem has been addressed by a redesign of the magnetic circuit and presented in Pohlmann et al (2010).…”