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
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.
RESUMO
This study describes five programs that may be used on compact, low-cost programmable calculators with adequate memory and sufficient numbers of program steps to compute cardiorespiratory variables. These short programs are especially useful in the operating room and at the bedside.
RESUMO
Our laboratories are engaged in the design of a clinically-oriented electrically actuated long-term intracorporeal (abdominal) left ventricular assist device ("E-type" ALVAD) or partial artificial heart. This infradiaphragmatic blood pump is designed to be powered by implantable electrical to mechanical energy converter systems. THE FOLLOWING ANALYSES WERE UNDERTAKEN TO: [List: see text] The proposed "E-type" ALVAD should be capable of pumping 4-7 liters per minute at heart rates of 75-100 beats per minute during rest, and 10 liters per minute at rates of 120 beats per minute during moderate exercise. These performance levels should be exceeded with a maximum device stroke volume of 85-90 ml and a mean pump inflow (filling) impedance of
RESUMO
The feasibility of radioisotope-fueled circulatory support systems depends on the ability of the body to dissipate the reject heat from the power source driving the blood pump as well as to tolerate chronic intracorporeal radiation. Our studies have focused on the use of the circulating blood as a heat sink. Initial in vivo heat transfer studies utilized straight tube heat exchangers (electrically and radioisotope energized) to replace a segment of the descending aorta. More recent studies have used a left ventricular assist pump as a blood-cooled heat exchanger. This approach minimizes trauma, does not increase the area of prosthetic interface with the blood, and minimizes system volume. Heat rejected from the thermal engine (vapor or gas cycle) is transported from the nuclear power source in the abdomen to the pump in the thoracic cavity via hydraulic lines. Adjacent tissue is protected from the fuel capsule temperature (900 to 1200 degrees F) by vacuum foil insulation and polyurethane foam. The in vivo thermal management problems have been studied using a simulated thermal system (STS) which approximates the heat rejection and thermal transport mechanisms of the nuclear circulatory support systems under development by NHLI. Electric heaters simulate the reject heat from the thermal engines. These studies have been essential in establishing the location, suspension, surgical procedures, and postoperative care for implanting prototype nuclear heart assist systems in calves. The pump has a thermal impedance of 0.12 degrees C/watt. Analysis of the STS data in terms of an electrical analog model implies a heat transfer coefficient of 4.7 x 10(-3) watt/cm(2) degrees C in the abdomen compared to a value of 14.9 x 10(-3) watt/cm(2) degrees C from the heat exchanger plenum into the diaphragm.
