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At least 883 records · Page 49Linked to original sources
PubMed1993

A straight path centrifugal blood pump concept in the Capiox centrifugal pump.

This article describes comparative studies of a newly developed "straight path" centrifugal pump (Capiox centrifugal pump) targeted for open-heart surgery and circulatory support. A unique straight path design of the rotor was very effective in reducing the pump's rotational speed and prime volume. This pump was evaluated for hydraulics, hemolysis, depriming characteristics, cavitation, and heat generation. Two commercially available centrifugal pumps, the Biomedicus cone-type pump and the Sarns 3M impeller-type pump, were used as controls. The new pump required the lowest pump speed to produce the same flow rates under the same pressure loads and demonstrated the lowest hemolysis and the lowest temperature rise with the outlet clamped. The air volume required to deprime the new pump was one-third to one-half that for the other pumps, and no sign of cavitation was observed even if a small amount of air was introduced to the pump inlet under a negative pressure of 200 mm Hg.

Animals↗
PubMed1993

Baylor Gyro Pump: a completely seal-less centrifugal pump aiming for long-term circulatory support.

A seal-less centrifugal pump aiming for long-term circulatory support has been developed. In this model, shaft seals that cause thrombus formation and blood leakage were eliminated. A brushless direct current motor was incorporated as a driving unit, and pivot bearings were used to support the impeller. With reference to its motor-driven system, this pump was named the M-Gyro Pump. The first model (M1) yielded an index of hemolysis of 0.005 g/100 L using bovine blood and demonstrated satisfactory performance as a right heart assist for 2 days (4 L/min, 60 mm Hg, 1,800 rpm). The second model (M2) has been developed for left heart assist by employing a stronger motor. The pump capacity was improved to 6 L/min against 240 mm Hg at 1,800 rpm, but significant heat generation was observed. By optimization of motor efficiency, the M2 model can be improved to meet the requirements of a pump for left heart assist.

Animals↗
PubMed1993

In vitro investigation of thrombogenesis in rotary blood pumps.

Thrombus formation at sealing and stagnation areas remains a major problem in the development of rotary blood pumps. Until now, the complex phenomena could only be studied in vivo. In this study, an in vitro mock circulation previously used for hemolysis studies was adapted for thrombosis evaluation. Blood was collected in the slaughterhouse with strict avoidance of air contact and was heparinized (1.5 U heparin/ml blood; activated coagulation time [ACT]: initially, 140-180 s; after collection, 400-600 s). During the test, the ACT decreased gradually. The tests were stopped after 90 to 180 min at an ACT of 1.5 times the initial value. Thrombus formation was observed at the same locations as observed in left-heart assist devices (sealing area, connecting bolts, and stagnant water areas at connectors). The thrombi were similar in shape, color, and histology to those found after 2 to 4 days in vivo. This test provides a valuable tool for evaluating thrombus formation in prototypes and screening tests of different rotary pump designs.

Animals↗
PubMed1993

In vitro performance of the Baylor/NASA axial flow pump.

A cooperative effort between Baylor College of Medicine and NASA/Johnson Space Center is under way to develop an implantable axial flow left ventricular assist device (LVAD). The pump is intended as an assist device for either pulmonary or systemic circulatory support for more than 3 months' duration. Currently, in vitro studies are under way to reduce the hemolysis generated by the axial flow pump. A system utilizing a testing matrix has been developed to analyze the effects of different pump parameters on hemolysis. The following parameters are being investigated: impeller blade tip geometry, impeller/flow tube clearance, impeller/stator clearance, number of impeller blades, number of stator blades, and length of the impeller. To date, an index of hemolysis of 0.038 g/100 L has been achieved. The test matrix is not complete, and further improvements are expected.

Animals↗
PubMed1993

Development of the Baylor-Nikkiso centrifugal pump with a purging system for circulatory support.

The Baylor-Nikkiso centrifugal pump is a magnetically coupled system with a V-ring seal separating the pump and the actuator chamber. To prevent thrombus formation behind the impeller and to extend the life of the pump to 2 weeks of continuous operation, we incorporated a purging chamber behind the V-ring seal. An external pump connected to this purging chamber infused fluid at a constant rate to wash the shaft-seal area. To evaluate the effectiveness of the purging system, we have carried out biventricular bypass experiments using calves. The purging system was successful in reducing the level of thrombus formation after 2 weeks of operation. The results of these studies confirmed that the Baylor-Nikkiso centrifugal pump with this purging system is suitable for at least 2 weeks of continuous operation as a circulatory support system.

Animals↗
PubMed1994

Pulsatile flow and simple flow control method during weaning period in centrifugal pump: toward more expanded usage in open heart surgery.

To expand the usage of the centrifugal pump (CP) in open heart surgery, we performed two studies. In the first, we evaluated pulsatile flow in the CP. In vitro pump performance of the Terumo Capiox pump (TCP) and the Sarns Delphin pump (SDP) and increase of free hemoglobin (mg/dl) after driving 6 h were investigated using bovine blood. A roller pump (RP) was used as a comparison. Equally effective pulsatile flow was obtained in both CPs. Hemolysis was less severe in TCP (120 mg/dl) than SDP (210 mg/dl) and RP (320 mg/dl). In the second study, we evaluated a simple flow control method. Flow rate was easily controlled with step-wise clamping of 3-pronged tubing (Triple-flow) without changing rotational speed, regardless of afterload. Fluctuation of flow was much less with this method than with the rotational speed change method. The use of pulsatile flow of TCP, with its minimum increase of hemolysis and the easier flow control method during the weaning process, may expand the usage of CP in open heart surgery.

Animals↗
PubMed1995

Computational prediction of hemolysis in a centrifugal ventricular assist device.

This paper describes the use of computational fluid dynamics (CFD) to predict numerically the hemolysis in centrifugal pumps. A numerical hydrodynamical model, based on the full Navier-Stokes equation, was used to obtain the flow in a vaneless centrifugal pump (of corotating disks type). After proper postprocessing, critical zones in the channel were identified by means of two-dimensional color-coded maps of %Hb release. Simulation of different conditions revealed that flow behavior at the entrance region of the channel is the main cause of blood trauma in such devices. A useful feature resulting from the CFD simulation is the visualization of critical flow zones that are impossible to determine experimentally with in vitro hemolysis tests.

Heart-Assist Devices↗
PubMed1996

Mock test characteristic of intraaortic balloon pump using linear motor.

This article describes the composition of the intraaortic balloon pump (IABP) system, which uses a linear pulse motor, that is, the linear type of IABP, and the results of the mock test that was performed. The expansion time is 100-110 ms, and the contraction time is 85-95 ms at the balloon of the linear type IABP. This level is similar to that of the IABP system used in the market. When the speed of the mover is 0.3 m/s, the necessary thrust of the linear pulse motor to drive the balloon of the IABP is 200 N. The conversion efficiency from the bellows to the balloon is 5.6%, and the efficiency of the entire linear type IABP system is 0.6%. The volume of the entire system is 45 L, and the mass is 40 kg excluding the chassis. Therefore, there is an expectation that the IABP system can be miniaturized to about half of the conventional model.

Electrocardiography↗
PubMed2004

Development of a suction detection system for axial blood pumps.

Axial flow blood pumps for cardiac assistance have proven their clinical viability and benefit in recent years. However, the clinical systems to date have no direct mechanism to decrease pump speed when adequate supply is not available. This may lead to ventricular collapse or increase the probability of hemolysis and thrombotic risks. Based on various experiences with left ventricular assist device (LVAD) patients in various states of recovery, at implant, in the intensive care unit, in the standard ward, and during physical exercise, 11 different algorithms were developed for the automatic detection of ventricular suction. These detection algorithms analyze the flow pattern for the presence of distinct suction indicators. For selection and optimization of the algorithms, 1000 records from approximately 100 patients were collected. Each record contains 5 s of pump flow, current, and arterial pressure. Three experts classified these records in terms of suction probability and other abnormalities. The optimization was developed in Matlab, capable of solving a fifth-dimensional optimization problem with 256 different algorithm combinations. The optimization resulted in a set of 6 algorithms, each with specific thresholds. The system detects 100% of the known suction events with 0.28% of false-positive interpretations. If tuned to avoid any false-positive detection, 90.7% of the certain events would be detected. A strategy for the development of a robust suction detection system for axial blood pumps was found. This system will be integrated into an automatic pump speed control system to provide adequate perfusion for the LVAD recipient, without excessive unloading of the ventricle.

Algorithms↗
PubMed1991

Cardiac electrophysiological experiments in numero, Part II: Models of electrophysiological processes.

This article is the second part of a three article series reviewing computer simulation models of the heart, in particular of cardiac electrophysiology. The previous section of the review discussed the methodological principles of the construction and application of computer models. This article overviews the development of mathematical and computer modeling studies applied to cardiology. The models are classified according to the physiological processes that were simulated; this article distinguishes models oriented to cardiac mechanics, hemodynamics, and electrophysiology. The electrophysiology models are discussed in more detail and the review classifies them into four main categories: models of cellular processes, models of tissue behavior, models of the ventricular electric field, and models of macroconduction disturbances. In each category, the historical development of the models and their key achievements are described.

Animals↗
PubMed1991

A massively parallel computer model of propagation through a two-dimensional cardiac syncytium.

A computer model of electrical propagation through a two-dimensional (2D) sheet of cardiac tissue has been developed to run on the massively parallel processor Connection Machine (CM-2) computer. The transmembrane ionic currents in each of 16,384 (128 x 128) 100 x 100 microns 2 patches of cardiac tissue are described by modified Beeler-Reuter membrane equations. These equations, along with the parabolic differential equation derived from 2D cable theory, are solved in parallel to study normal and abnormal 2D propagation. The sheet is paced with planar waves at a basic cycle length of 500 msec (control). When a premature ectopic stimulus of sufficient strength and appropriate timing is then applied to a local region of the syncytium, one of two types of reentry is observed: (a) stable figure-of-eight reentry, or (b) unstable but self-sustaining "fibrillation-like" reentry. During this fibrillatory activity, action potential durations are 79.8 +/- 36.8 msec (control = 244.9 +/- 0.9 msec) and coupling intervals average 96.7 +/- 31.3 msec (control = 500 +/- 0 msec). We also observed that passive electrotonically-induced depolarization of already refractory tissue extended the refractory period of that tissue, and that the duration of this extension depended on the magnitude of the electrotonic effect.

Action Potentials↗
PubMed1991

Cardiac electrophysiological experiments in numero, Part I: Concepts and strategies of mathematical and computer models.

This article is the first of three articles that review mathematical and computer models of the heart and describe their construction, development, research potential, and clinical utility. This article explains the methodological principles of mathematical and computer simulation of biomedical systems. The strategies of model construction, testing, and application are presented; the advantages and limitations of computer simulation studies are explained, and the basic value of computer simulation for cardiological research and practice is discussed.

Cardiac Pacing, Artificial↗
PubMed1995

Effect of implantable nonthoracotomy defibrillation system on permanent pacemakers: an in vitro analysis with clinical implications.

Implantable cardioverter defibrillation systems are capable of delivering over 700 volts, and upwards of 40 joules (J) directly to the heart. Nonthoracotomy lead (NTL) systems allow the delivery of this energy to the inside of the heart, and potentially in close proximity to the leads of an endocardial pacing system. The effect of repeated maximal energy discharges (stored energy 40 J, delivered energy 38 J), utilizing both monophasic as well as biphasic shock pulses delivered via two different configuration NTL systems on a series of Pacesetter polarity programmable present generation single, and dual chamber pacemakers was evaluated in vitro using a saline test tank. All pulse generators studied demonstrated normal function and were not reprogrammed nor adversely affected by repeated defibrillation shocks. The current induced in the leads was assessed, and shown to be as high as 1.5 amps in the proximal conductor and 1.2 amps in the distal conductor of the ventricular lead, which may cause damage at the electrode-myocardial interface, and explain some of the postshock rise in capture and sensing thresholds that have been reported with implanted pacing systems postdefibrillation.

Defibrillators, Implantable↗
PubMed2006

Na"Fuzzy space": does it exist, and is it important in ischemic injury?

Work is reviewed which provides evidence for the presence of a subsarcolemmal microdomain, in which the [Na(+)] is influenced by Na(+) influx via the Na(+) channel and the activity of the Na pump. The sarcolemma adjacent to this microdomain, which has been referred to as "Na(+) fuzzy space," appears to include Na-Ca exchangers, and thus alterations of [Na(+)] in this space may influence Ca(2+) influx and efflux, and thus Ca(2+) loading, more directly than do alterations of bulk cytoplasmic [Na(+)]. The degree of Ca(2+) loading is an important determinant of contractility in heart muscle, and therefore alterations in fuzzy space [Na(+)] may be important in mediating the positive inotropic effects of Na pump inhibitors, such as digitalis, and the negative inotropic effects of Na(+) channel blockers such as disopyramide. During ischemia, myocyte Ca(2+) overload can contribute to ATP depletion by activation of Ca(2+)-dependent ATPases and by induction of the mitochondrial permeability transition, and thus is an important contributor to myocyte dysfunction and injury. Hypoxia associated with ischemia can induce Na(+) influx via a persistent opening of the Na(+) channel. It is likely that this Na(+) influx elevates [Na(+)] in the fuzzy space, and thus increases Ca(2+) influx via Na-Ca exchange, and increases Ca(2+) loading. Inhibition of the persistent Na(+) current with a resulting decrease in Ca(2+) loading by drugs such as tetrodotoxin (TTX) and ranolazine may be a mechanism by which these agents produce a cardio-protective effect during ischemia.

Animals↗
PubMed2006

Sodium channel inactivation in heart: a novel role of the carboxy-terminal domain.

Electrical activity in the heart depends critically on the interactions of multiple ion channels to coordinate the timing of excitation and contraction of the ventricles. Voltage-gated sodium channels underlie the rapid spread of impulses through the atria and ventricles, but the importance of sodium (Na(+)) channels to the control of the ventricular action potential has only most recently become apparent through the investigation of the relationship between mutation-induced clinical phenotypes and the altered function of mutant Na(+) channels linked to inherited arrhythmias. Investigation into the structural basis of disease-associated mutations of the cardiac Na(+) channel has led to the discovery of novel role of the Na(+) channel carboxy-terminal (CT) domain in controlling channel inactivation. Intramolecular interactions between the carboxy-terminal domain and an intracellular peptide loop that forms the inactivation gate are required to minimize channel reopening during prolonged depolarization. Disruption of this interaction leads to persistent sodium channel current, action potential prolongation, and elevated risk of cardiac arrhythmia.

Animals↗
PubMed2006

Modulation of cardiac Na(+) and Ca(2+) currents by CaM and CaMKII.

Sarcolemmal sodium (Na) and calcium (Ca) currents are fundamentally involved in shaping the cardiac action potential. Alterations in Na or Ca currents can change action potential characteristics and therefore might result in cardiac arrhythmias. Also, these ions contribute to excitation-contraction coupling and therefore are important in myocyte shortening and contractility of the heart. This review article summarizes how sarcolemmal Na and Ca channels are regulated with an emphasis on the novel role of Ca-dependent proteins Calmodulin (CaM) and especially Ca/CaM-dependent protein kinase II (CaMKII) to modulate sarcolemmal Na and Ca channels in the heart.

Action Potentials↗
PubMed2006

Molecular control of cardiac sodium homeostasis in health and disease.

INTRODUCTION: Cardiac myocytes utilize three high-capacity Na transport processes whose precise function can determine myocyte fate and the triggering of arrhythmias in pathological settings. We present recent results on the regulation of all three transporters that may be important for an understanding of cardiac function during ischemia/reperfusion episodes. METHODS AND RESULTS: Refined ion selective electrode (ISE) techniques and giant patch methods were used to analyze the function of cardiac Na/K pumps, Na/Ca exchange (NCX1), and Na/H exchange (NHE1) in excised cardiac patches and intact myocytes. To consider results cohesively, simulations were developed that account for electroneutrality of the cytoplasm, ion homeostasis, water homeostasis (i.e., cell volume), and cytoplasmic pH. The Na/K pump determines the average life-time of Na ions (3-10 minutes) as well as K ions (>30 minutes) in the cytoplasm. The long time course of K homeostasis can determine the time course of myocyte volume changes after ion homeostasis is perturbed. In excised patches, cardiac Na/K pumps turn on slowly (-30 seconds) with millimolar ATP dependence, when activated for the first time. In steady state, however, pumps are fully active with <0.2 mM ATP and are nearly unaffected by high ADP (2 mM) and Pi (10 mM) concentrations as may occur in ischemia. NCX1s appear to operate with slippage that contributes to background Na influx and inward current in heart. Thus, myocyte Na levels may be regulated by the inactivation reactions of the exchanger which are both Na- and proton-dependent. NHE1 also undergo strong Na-dependent inactivation, whereby a brief rise of cytoplasmic Na can cause inactivation that persists for many minutes after cytoplasmic Na is removed. This mechanism is blocked by pertussis toxin, suggesting involvement of a Na-dependent G-protein. Given that maximal NCX1- and NHE1-mediated ion fluxes are much greater than maximal Na/K pump-mediated Na extrusion in myocytes, the Na-dependent inactivation mechanisms of NCX1 and NHE1 may be important determinants of cardiac Na homeostasis. CONCLUSIONS: Na/K pumps appear to be optimized to continue operation when energy reserves are compromised. Both NCX1 and NHE1 activities are regulated by accumulation of cytoplasmic Na. These principles may importantly control cardiac cytoplasmic Na and promote myocyte survival during ischemia/reperfusion episodes by preventing Ca overload.

Animals↗
PubMed1992

Experimental studies to define the geometry of the flow convergence region. Laser Doppler particle tracking and color Doppler imaging.

The color flow convergence method for calculating volume flow through regurgitant or forward flow restrictive orifices has gained significant interest and a number of in vitro studies have suggested that this method is accurate, even in pulsatile models. Clinical application of the method over a wide range of conditions will require improved understanding of the effect of orifice size, flow geometry, and flow rate on the flow convergence geometry. In this study, we performed laser particle tracking investigations to allow visualization of streamlines into stenotic orifices. These streamlines are theoretically perpendicular to the isovelocity surfaces used for flow convergence calculations. We compared those observations to color flow map, flow convergence images obtained with a Toshiba 160A for orifices 5 to 15 mm 2 with flow rates of 1.5 to 9.7 L/min. Our results show that for large orifices, low flow rates, and/or low pressure gradients, more oblique streamlines in the velocity of the orifice correspond to nonhemispherical, but more elliptical, flow convergence geometries. This can be corrected for by using lower Nyquist limits and calculating flow convergence at greater distances from the orifice. Under high flow and high gradient conditions, increased Nyquist limits and shorter aliasing radii are more suitable. Our studies yield insights into flow convergence geometry and yield corrective procedures to improve volume flow calculation.

Blood Flow Velocity↗