Unlike in animal experiments, the pump orientation of a total artificial heart (TAH) can change remarkably in humans with the recipient's posture (upright, supine, or prone), thus affecting its filling characteristics. The left master alternate control mode of the Cleveland Clinic-Nimbus (CC-N) TAH adjusts beat rate by maintaining the left pump at 90% filling, producing a Frank-Starling like preload sensitivity. In order to verify that the CC-N TAH functions properly regardless of the gravity effects on pump filling, the preload sensitivity curves of the CC-N TAH were evaluated on a mock circulatory loop with the simulated supine (right pump up) and prone (left pump up) positions in humans. The right preload sensitivity was slightly higher when the right pump was up versus down, and likewise the left preload sensitivity was higher when the left pump was up versus down. Despite these gravity effects on pump filling, right and left preload sensitivity remained within physiologic range and the automatic control of the CC-N TAH functioned properly without significant postural effects.
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