Feasibility of a TinyPump system for pediatric CPB, ECMO, and circulatory assistance: hydrodynamic performances of the modified pump housing for implantable TinyPump.

The TinyPump is a miniature centrifugal blood pump with an extremely small priming volume of 5 ml, allowing blood transfusion free cardiopulmonary bypass as well as extracorporeal membrane oxygenation in pediatric patients. In this study, a new pump housing with the angled inlet port (25 degrees toward impeller center with respect to the flow axis) was designed to optimize the pump displaced volume and to extend the application of the TinyPump to implantable support The fluid dynamic performance analysis revealed that the head pressure losses increased from 3 to 17 mm Hg in comparison with straight port design as the pump rotational speed increased from 2,000 to 4,000 rpm. This was probably caused by perturbed flow patterns at the site of the inlet bent port area and streamline hitting the off-center of the impeller. No significant effect on pumping efficiency was observed because of modification in inlet port design. Modification in the inflow and outflow port designs together with the drive mechanism reduces the height of the pump system, including the motor, to 27 mm yielding the displaced volume of 68 ml in comparison with 40 mm of the paracorporeal system with the displaced volume of 105 ml. Further analysis in terms of hemolytic as well as antithrombogenic performance will be carried out to finalize the housing design for the implantable version of the TinyPump.

Deformability of human red blood cells exposed to a uniform shear stress as measured by a cyclically reversing shear flow generator.

Red blood cells (RBCs) suspended in a dextran solution were at first loaded with a uniform shear stress of 21, 43 and 64 Pa for the duration of 0, 10, 20, 30, 45 and 60 min, respectively, followed with measurement of the dynamic deformation in terms of stretching and recovery, using a cyclically reversing sinusoidal shear flow with the peak stress of 128 Pa at 2 Hz. The L/W value, where L and W were the major and minor axis length of the RBC images, was derived to compare the effects of the uniform shear stress level and the exposure time. The exposure to the uniform shear stress of 21 Pa for the duration of as long as 60 min caused statistically insignificant L/W change in comparison to the control RBCs with L/W of 4.6 +/- 0.1. The exposure to 43 and 64 Pa for longer than 45 and 20 min, respectively, induced statistically significant change in the maximal L/W when compared to that of 21 Pa (p < 0.05). The composition of the maximal L/W values varied depending on the stress level and exposure time; with 21 Pa, the majority of cells exhibited the maximal L/W larger than 4.0 and few cells less than 2.0, whereas with the increase in the stress level to 43 and 64 Pa, cells having less than 2.0 exceeded 50%. Cyclic reversing shear flow is a useful means to measure dynamic deformation capability of RBCs which may be sub-hemolytically sheared without lysis.

Creation of myocardial tubes using cardiomyocyte sheets and an in vitro cell sheet-wrapping device.

Regenerative medicine involving injection of isolated cells and transplantation of tissue-engineered myocardial patches, has received significant attention as an alternative method to repair damaged heart muscle. In the present study, as the next generation of myocardial tissue engineering we demonstrate the in vitro fabrication of pulsatile myocardial tubes using cell sheet engineering technologies. Three neonatal rat cardiomyocyte sheets, which were harvested from temperature-responsive culture dishes, were wrapped around fibrin tubes using a novel cell sheet-wrapping device. The tubular constructs demonstrated spontaneous, synchronized pulsation within 3h after cell sheet wrapping. Contractile force measurements showed that the contractile force increased in accordance with both increasing rest length (Starling mechanism) and increasing extracellular Ca(2+) concentration. Furthermore, the tissue-engineered myocardial tubes presented measurable inner pressure changes evoked by tube contraction (0.11+/-0.01mmHg, max 0.15mmHg, n=5). Histological analyses revealed both well-differentiated sarcomeres and diffuse gap junctions within the myocardial tissues that resembled native cardiac muscle. These data indicate that tissue-engineered myocardial tubes have native heart-like structure and function. These new myocardial tissue constructs should be useful for future applications in physiological studies and pharmacological screening, and present a possible core technology for the creation of engineered tissues capable of independent cardiac assistance.

Quantification of the secondary flow in a radial coupled centrifugal blood pump based on particle tracking velocimetry.

Secondary flow in the centrifugal blood pump helps to enhance the washout effect and to minimize thrombus formation. On the other hand, it has an adverse effect on pump efficiency. Excessive secondary flow may induce hemolytic effects. Understanding the secondary flow is thus important to the design of a compact, efficient, biocompatible blood pump. This study examined the secondary flow in a radial coupled centrifugal blood pump based on a simple particle tracking velocimetry (PTV) technique. A radial magnetically coupled centrifugal blood pump has a bell-shaped narrow clearance between the impeller inner radius and the pump casing. In order to vary the flow levels through the clearance area, clearance widths of 0.25 mm and 0.50 mm and impeller washout holes with diameters of 0 mm, 2.5 mm, and 4 mm were prepared. A high-speed video camera (2000 frames per second) was used to capture the particle images from which radial flow components were derived. The flow in the space behind the impeller was assumed to be laminar and Couette type. The larger the inner clearance or diameter of washout hole, the greater was the secondary flow rate. Without washout holes, the flow behind the impeller resulted in convection. The radial flow through the washout holes of the impeller was conserved in the radial as well as in the axial direction behind the impeller. The increase in the secondary flow reduced the net pump efficiency. Simple PTV was successful in quantifying the flow in the space behind the impeller. The results verified the hypothesis that the flow behind the impeller was theoretically Couette along the circumferential direction. The convection flow observed behind the impeller agreed with the reports of other researchers. Simple PTV was effective in understanding the fluid dynamics to help improve the compact, efficient, and biocompatible centrifugal blood pump for safe clinical applications.

Effect of the elastic conditions around a stentless valvular bioprosthesis on opening behavior.

Stentless valvular bioprostheses have been used clinically for over 8 years and the excellent properties of the bioprostheses have been demonstrated in clinical studies. The present study examined how differing elastic conditions around the bioprosthesis at the aortic position affect the hydrodynamic characteristics of the bioprosthesis. Bioprosthesis implantation is typically performed using either the subcoronary or the full-root technique. These procedures for implanting a stentless prosthetic heart valve at the aortic root were hydrodynamically evaluated in a mock circulatory system. Forward flow rate was 11% greater with the subcoronary technique than with the full-root technique. In a high-speed video camera study, the orifice area at full opening was 12% larger for the subcoronary technique than for the full-root technique. Evaluation of bioprosthetic characteristics in terms of mechanical conditions is important when considering surgical options.

In vitro investigation of opening behavior and hydrodynamics of bileaflet valves in the mitral position.

The performance of four 25 mm bileaflet valves of different designs was evaluated in the mitral position of our own pulse simulator. With the aid of a high-speed video camera, it was demonstrated that both the St. Jude Medical (SJM) valve (Hemodynamic Plus [HP] Series, St. Jude Medical, Inc., St. Paul, MN, U.S.A.) and the CM valve (CarboMedics, Inc., Austin, TX, U.S.A.) were able to open fully and that the CM valve fluttered much more vigorously at the fully open position than did the SJM HP valve. Conversely, neither the ATS valve (ATS Medical, Inc., Minneapolis, MN, U.S.A.) nor the On-X valve (Medical Carbon Research Institute, Austin, TX, U.S.A.) exhibited movement to a fully open configuration. The overall average opening angles of the ATS and the On-X, on 3, 4, and 5 L/min flow rate for a heart rate of 70 bpm and 5, 6, and 7 L/min for 100 bpm, were 74.8 degrees and 81.6 degrees, respectively, whereas their design opening angles were 85 degrees and 90 degrees. Pressure drops across the CM and the ATS were consistently higher than those of the On-X and the SJM HP. Closing volumes for all the valves were below 8% for a heart rate of 70 bpm. This in vitro investigation yielded the following conclusions: The ATS and On-X valves are not able to open fully in the mitral position, but this does not impair their normal function; both a larger orifice diameter and a large opening angle can decrease the pressure drop; in general, the On-X valve achieves its design goals in this experiment (i.e., it produces a lower pressure drop and lower closing volume by virtue of its large orifice and high-profile design); however, the hinge flow in the non-fully open state should be investigated further.

Effects of Surface Roughness on Mechanical Hemolysis.

Previous in vitro hemolysis test results showed that an inlet taper or a round corner in the leading edge of a stenotic connector played an important role in the reduction of hemolysis. However, computational fluid dynamics (CFD) analysis of these results indicated that the shear rate and hemolysis level were not always related to each other. Then, further research was performed, focusing on the effects of surface roughness on hemolysis. The results thus far can be summarized as threefold. First, the rate of hemolysis occurring at an abrupt change in the stenotic section was different if the longitudinal length of the stenosis was changed. The level of plasma-free hemoglobin after 6 h of circulation was decreased from 280 mg/dl to 70 mg/dl when the longitudinal length was shortened from 15 mm to 1 mm. Second, a comparison of hemolysis rates in identical stenotic connectors with differing surface roughness (Ra = 0.45 and 1.35 u.m) revealed that a smooth surface achieved as much as an 80% reduction in the rate of hemolysis. Third, the in vitro hemolysis results obtained were further defined through CFD analysis.

Basic Performance of a Miniature Intraventricular Axial Pump.

A miniature intraventricular axial pump for left ventricular (LV) support is under development. This pump was designed for placement in the LV cavity by insertion through the LV apex with the outlet located at the ascending aorta via the aortic valve. The basic hydro-dynamic characteristics represented as a relationship between pump head (H) and flow (Q) showed a negative linear relationship under a constant head. This characteristic was generally the same as that obtained by other axial rotation pumps. However, the actual H-Q relationship was represented as anticlockwise "loops" caused by the contraction of the natural LV. The comparative in vitro data on these H-Q loops showed that the shape of the loops was changed drastically by the connecting condition between the pump and natural cardiovascular system.