Biomedical subjects
K C Butler
Publications and source records attributed to K C Butler.
Continuing development of the Cleveland Clinic-Nimbus total artificial heart.
A completely implanted total artificial heart (TAH) is under development by Nimbus, Inc., and the Cleveland Clinic Foundation (CCF). Key features of the system include an electrohydraulic energy converter, an automatic control system that produces a Frank-Starling response, and dual ventricles composed of graphite-epoxy and titanium with gelatin blood contacting surfaces. The system is controlled by a single substrate, hybridized microcircuit (the hybrid). Fabrication of the TAH control hybrid has recently been completed and testing begun. Its design emphasizes simplicity, reliability, and efficiency. Particular attention was given to optimizing thermal management. Externally controlled TAH systems have been used in eight in vivo experiments of up to 120 days' duration. In the last two of these experiments, a variable volume device was also implanted with excellent results. In vivo use of the system has demonstrated the Frank-Starling pump response, but the systems quickly reach maximum output with the bovine animal models. Human fitting studies, including adult patients undergoing heart transplantation, demonstrated satisfactory fit of the pump within the pericardium without compression of the vascular structures or chest wall. Measurements of chest circumference, plain chest films, and transesophageal echocardiograms should provide reliable predictions of pump fit in the majority of patients.
In vivo evaluation of the Nimbus axial flow ventricular assist system. Criteria and methods.
Continuing in vivo trials are being conducted at the University of Pittsburgh using the Nimbus axial flow blood pump (AxiPump). To date, 14 sheep experiments have been performed to address several issues related to short-term support. Six acute experiments (< 6 hr) have been performed to assess hemodynamics related to speed regulation and to determine anatomic placement of the pump and cannulae. Eight short-term survival studies lasting up to 6 days have been performed to evaluate biocompatibility and system reliability, and to establish clinical management protocols. The AxiPump has been used as a left ventricular assist device (LVAD), right ventricular assist device (RVAD), and biventricular assist device (BiVAD) with left ventricular and right atrial cannulation. The AxiPump has demonstrated the ability to assume complete support of either the pulmonary or systemic circulation, or both. We have determined that sufficient surgical access may be obtained through left lateral thoracotomy for both LVAD and RVAD insertion. In the absence of post operative anticoagulation therapy, we have detected subclinical renal cortical infarctions in 6 of 8 short-term animals. Thrombus deposition has been observed at the ventricular cannula tip in 4 of 8 cases--necessitating design changes. Two short-term experiments have been terminated because of bleeding--one due to inflow cannula obstruction and one due to cannula failure. Plasma free hemoglobin levels were all below 15 mg/dl, except for one case complicated by inflow obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)
Mechanisms of red blood cell trauma in assisted circulation. Rheologic similarities of red blood cell transformations due to natural aging and mechanical stress.
Clinical experience with circulatory support devices has typically shown alteration of patient blood rheology exhibited through increasing blood viscosity and decreasing erythrocyte deformability. Our hemorheologic studies have additionally shown a remarkable increase in red blood cell (RBC) aggregation in the blood of artificial heart patients as compared to healthy donors. These hemorheologic changes may be caused by mechanical trauma to RBCs. The authors hypothesize that the mechanical trauma process, from a rheologic point of view, could be analogous to an "accelerated" RBC aging process. The hypothesis was examined through in vivo and in vitro experiments on RBCs, age-separated on the basis of density, specifically to identify the rheologic similarities between aged and mechanically traumatized RBCs. Older RBCs demonstrated an increased mechanical fragility, a decreased deformability, and a increased ability to aggregate as compared to younger RBCs. RBCs exposed to mechanical stress demonstrated similar alterations in the same rheologic parameters. Our experiments have also shown that mechanical stress decreases the negative surface charge of RBCs as is known to occur in aged RBCs. Similarities found between the processes of RBC mechanical trauma and senescence enhance our understanding of mechanisms of subhemolytic trauma incurred in assisted circulation. This may improve the design and evaluation of future heart assist devices through minimizing shear induced blood trauma.
In vivo evaluation of an extracorporeal pediatric centrifugal blood pump.
This paper summarizes the authors' in vivo experience in evaluating a miniature centrifugal blood pump designed for pediatric/neonatal ventricular support. Left ventricular bypass was accomplished in two adult sheep and five juvenile lambs (5.5-80.0 kg) via either central (left ventricle to carotid artery) or peripheral (jugular vein to carotid artery) cannulation. Animals were weaned from mechanical ventilation and continuously monitored. Hemodynamic parameters remained within a normal range over the duration of the bypass. Two of five lambs were electively killed at 8, and 76 hours; the remaining three lambs died from respiratory complications at 33, 44, and 156 hours. There were no mechanical complications, and blood seal integrity was confirmed beyond 6 days. The pump speed was maintained at 3,000-4,500 rpm with pump flow rates between 0.4-1.5 L/min. Average plasma free hemoglobin was below 20 mg/dl in the five lamb experiments. Renal, hepatic, and hematologic indices also remained within physiologic ranges. Histopathologic analyses of major organs revealed renal cortical infarctions in two of five lambs. Examination of the pump surfaces after explant indicated small areas of thrombus in the housing adjacent to the outflow ports in two experiments. These encouraging results support further testing and refinement of this miniature centrifugal pump.
Survival for up to six months in calves supported with an implantable axial flow ventricular assist device.
This paper summarizes the authors' in vivo experience to date with an implantable axial flow blood pump designed for long-term ventricular support. This small, valveless pump with blood-lubricated bearings has been implanted in six calves (83 +/- 6 kg) as a left ventricular assist device (LVAS). The left ventricle and descending thoracic aorta were cannulated by left thoracotomy, and the pump was placed in a subcutaneous pocket below the costal margin. Animals remained hemodynamically stable throughout the course of support during partial left ventricular bypass. Five animals were killed after 15, 27, 52, 57, and 181 days. The longest survivor (181 days) demonstrated normal pump function at the time death. Pump speed was maintained at 10,100 +/- 100 rpm, with an average pump flow rate of 4.9 +/- 0.5 L/min under resting physiologic conditions. Average plasma free hemoglobin was 17.4 +/- 7.5 mg/dl. Renal, hepatic, and hematologic indices remained within physiologic range in all of these animals, except during the immediate postoperative period. Histopathologic analyses of major organs after death revealed small renal cortical infarcts in five of six animals; the remaining organs were normal. These animal studies support the feasibility of this small implanted axial flow pump for long-term ventricular assistance.
Continued development of the Nimbus/University of Pittsburgh (UOP) axial flow left ventricular assist system.
Nimbus and the University of Pittsburgh (UOP) have continued the development of a totally implanted axial flow blood pump under the National Institutes of Health (NIH) Innovative Ventricular Assist System (IVAS) program. This 62 cc device has an overall length of 84 mm and an outer diameter of 34.5 mm. The inner diameter of the blood pump is 12 mm. It is being designed to be a totally implanted permanent device. A key achievement during the past year was the completion of the Model 2 pump design. Ten of these pumps have been fabricated and are being used to conduct in vitro and in vivo experiments to evaluate the performance of different materials and hydraulic components. Efforts for optimizing the closed loop speed control have continued using mathematical modeling, computer simulations, and in vitro and in vivo testing. New hydraulic blade designs have been tested using computational fluid dynamics (CFD) and flow visualization. A second generation motor was designed with improved efficiency. To support the new motor, a new motor controller fabricated as a surface mount PC board has been completed. The program is now operating under a formal QA system.