RESUMO
The pumping diaphragm of the Texas Heart Institute (THI) E-Type ALVAD must perform the dual functions of providing a flexible blood interface and isolating the electrical actuator from adjacent fluids. Thus, protection is required against fluid leakage and moisture diffusion to prevent corrosion and damage to electrical actuator components. Average diffusion rates up to 1 ml per day through currently used elastomeric diaphragm materials have been measured during static in-vitro and in-vivo tests. To circumvent this problem, an improved pumping diaphragm has been recently developed for use with the electrically-actuated THI E-Type ALVAD. This trilaminar diaphragm consists of a composite Biomer and butyl rubber design. A.010 inch layer of butyl rubber (characterized by an extremely low diffusion rate for water, approximately 0 ml per day) is positioned between two Biomer layers (.020 and.010 inches in thickness). Initial invitro and in-vivo studies, in calves, indicate that this composite diaphragm provides an excellent barrier to water permeation, without sacrificing biocompatibility or structural integrity under conditions of chronic flexure.
RESUMO
Intraaortic balloon pumping (IABP) is an established therapeutic adjunct in the treatment of postcardiotomy/infarction low cardiac output states. Although the common femoral or iliac arteries are the preferred sites for balloon insertion, severe arterial occlusive disease may preclude entry by these methods. To circumvent this problem, alternative methods of insertion utilizing transthoracic approaches have evolved. In our institution, direct (transaortic) IABP insertion, combined with delayed sternal closure to avoid cardiac compression and possible tamponade, was performed in 28 adult postcardiotomy patients (mean age 60.4 +/- 3 years). The severity of generalized atherosclerosis was reflected in an overall survival rate of 28.6%. Retrospective analyses of the clinical courses of these patients revealed that the transaortic approach allowed utilization of larger and more effective balloons. Successful insertion of 30 and 40 ml balloons was accomplished in 27 of 28 (96%) of these patients, and one patient with a hypoplastic aorta required a 20 ml balloon. There were no complications directly attributable to this alternative site of balloon insertion, and tamponade was avoided. Delayed sternal closure was accomplished within 48 to 96 hours. We concluded that when severe peripheral vascular occlusive disease prevents insertion of intraaortic balloons via the femoral or iliac arteries in patients with low cardiac output, the alternative transaortic approach is indicated. Combined with delayed sternal closure in patients with postcardiotomy dilatation, additional benefits accrue.
RESUMO
The conceptual design and development of a long-term, low-profile intracorporeal left ventricular assist device is a multifaceted project involving a series of technical, anatomic and physiologic considerations. Patients with severe left ventricular failure refractory to all other forms of therapy could benefit from such a device. Prior to fabrication of such a blood pump, consideration must be given to physiologic parameters of the projected patient population. The pump must be designed to meet physiologic demands and yet conform to the anatomic constraints posed by the patient population. We measured the body surface area (BSA) of a group of patients (n=50) and found the mean BSA for this group to be 1.804 +/- 0.161 m(2). Using 25 ml/m(2) as a stroke volume index indicative of left ventricular failure and a stroke volume index of 45 ml/m(2) as normal, distributions of stroke volumes (normal and in left ventricular failure) were plotted for a potential population and demonstrated that 63% of the projected population can be returned to normal by a pump with a stroke volume >/= 83 ml. Cadaver fitting studies established that 73% of the potential population can accommodate an ALVAD 10.8 cm in diameter. In-vitro tests demonstrated that a pump stroke volume >/= 83 ml could be achieved by the proposed pump with a 15 mmHg filling pressure at rates up to 125 B/min. A pusher-plate stroke of 0.56 inches would be necessary to provide a stroke volume >/= 83 ml. The percent of the patient population that could be served was determined by excluding those in whom the pump would not fit or in whom it would provide less than a normal resting stroke volume. Approximately 73% of the projected patient population would accommodate this pump and be returned to normal circulatory dynamics.
