In vitro evaluation of an implantable left ventricular assist device

Abstract

The development of implantable left ventricular assist devices (LVADs) has almost reached the stage of providing permanent circulatory support in patients who are unsuitable for, or denied, the transplant option. As part of our ongoing haemodynamic evaluation of the Thermo Cardiosystems Inc. (Boston, USA) mark 14 pneumatic LVAD, pressure-volume loops have been produced from in vitro Studies using a modified National Heart Lung and Blood Institute (NHLBI, USA) mock circulatory loop. These studies have demonstrated that during certain phases of [he pump cycle non-physiologically high and low pressures are generated within the LVAD. Such abnormal pressures ma), damage either the bioprosthetic valves in the LVAD or the native heart, and may have adverse effects on cardiovascular control mechanisms.

The aim of this research is to investigate, and thus counter, the adverse effects of tissue and ingress on the performance of the electrical resistance strain gauge when used in ascertaining in vivo loading on a spinal implant. Moisture absorption has been minimized to adopting maximum metallic coverage in a package comprising stainless steel foil on vacuum-injected pacemaker grade epoxide. In a simulation of the implanted environment, cyclic strain wet endurance testing in saline suggests that, in the body, the fall in indicated quasi-dynamic strain would be less than 1.5% at 24 weeks post-operation (the longevity needed to span adequately the born fusion phase). This implies that stiffening of the fusion mass will be deducible to a similar accuracy from stepped-load exercises), in which creep is a secondary deft. However, crucial information from quasi-static (passive) studies) regarding remodelling and load-sharing processor would be subject to a total signal error (primarily due to grid corrosion in excess of 16% by 24 weeks, since long-term darts are not inherently cancelled. Signal Compensation is therefore additionally required, and an approximate empirical characterisation of total error versus time has been derived.