Shintaro Fukunaga

Evaluation of two new liquid-liquid oxygenators.

The authors devised two liquid oxygenator units in which blood is directly oxygenated with oxygenated perfluorocarbon (PFC), a substance harmless to the blood that has a high specific gravity. 1) The droplet-type oxygenator unit is composed of a blood oxygenating chamber and a PFC oxygenating chamber. Blood is oxygenated by the infusion of PFC droplets into the blood oxygenating chamber; PFC is then spontaneously separated from the blood because of a difference in specific gravity, and reoxygenated in the PFC oxygenating chamber. Experimental results obtained using mongrel dogs indicated this oxygenator to have a high efficacy of oxygenation (&OV0422;p/&OV0422;t=0.63-0.78 with blood flow of 450-300 ml, O2 Transfer Rate=64 ml/min with blood flow of 300 ml), and high carbon dioxide discharge ( ΔCO2/ PaCO2=0.07-0.13, CO2 Transfer Rate=11 ml/min with blood flow of 300 ml). Pathology examination showed microthrombi containing PFC in the lung and liver. 2) The disk type oxygenator unit is composed of a cylinder and 18 rotors connected to an axle. Oxygenated PFC enters into the lower part of the oxygenator and mixes with venous blood flowing above the PFC layer. The rotation of the disk in the oxygenator causes the blood and PFC to mix. Experimental results obtained using mongrel dogs showed excellent O2 exchange (&OV0422;p/&OV0422;t=0.48-0.83, O2 Transfer Rate=52 ml/ min with blood flow of 300 ml) and CO2 removal capacity ( Δ CO2/PaCO2=0.05-0.10, CO2 Transfer Rate=9 ml/min at blood flow rate of 300 ml/min) for 2 hours. Histologic examination showed no deposition of PFC in the capillaries of the lungs or liver. Liquid-liquid oxygenators present the advantages of efficient oxygenation, anti-thrombogenicity, and harmlessness to the blood.

Acute Animal Experiment Using a Linear Motor-Driven Total Artificial Heart

A linear pulse motor developed by the authors was selected as the actuator for a total artificial heart, because it had the highest thrust/volume ratio, at 0.76 N/ml, of the eight kinds of linear motor considered. This paper summarizes the results of an acute animal experiment using a linear pulse motor-driven total artificial heart (linear TAH). The linear TAH consisted of a linear pulse motor, two sac type blood pumps, and four artificial valves. The mass was 1.3 kg and the volume was 540 ml. The volume of the TAH was a little larger than the target size, equal to the volume of an adult humans fist. The linear TAH was attached to a sheep of body weight 42 kg to evaluate its hemodynamic performance. The descending aortic flow rate was 1.5 1/min, equal to 50% of the rate in the control data. The difference between the flow rates of the left and right blood pumps was 12 to 13%, when the left atrium pressure reading indicated normal pressure. The sheep was sacrificed two hours after the operation. The data obtained suggest that the linear TAH can be used as a circulation-supporting device that satisfies clinical circulatory requirements.

Implantable motor-driven artificial heart

An implantable artificial heart was made using a flat-type brushless dc motor, a cylindrical cam, and Harmonic Drive as a reduction gear. A specially designed cylindrical cam makes the one-directional slow revolution into the reciprocating motion, then two sacs inside the driver are pushed alternately by the pusher plates located at both ends of the cam. The percentage systole of the driver is fixed at 50%. The two sacs, blood chambers, are 87 ml (left) and 81 ml (right) in volume and are made of polyurethane rubber. Bjork-Shiley monostrut valves are placed at the inflow and outflow of the sacs.

Analysis of Flow Patterns in a Ventricular Assist Device: A Comparative Study of Particle Image Velocimetry and Computational Fluid Dynamics

In order to develop a diaphragm-type ventricular assist device (VAD), we studied the flow field change following structural modifications. We devised a center flow-type pump by putting a small projection on the center of the housing and/or diaphragm to provide a center in the flow field, and examined the following four types of VADs: N type without a projection, D type with a projection on the diaphragm, H type with a projection on the housing, and DH type with projections on both the diaphragm and housing. Computational fluid dynamics (CFD) was used for flow simulation. Particle image velocimetry (PIV) was also used to verify the reliability of the CFD method and to determine how the flow field changes in the presence of a projection. The results of the PIV and CFD analyses were comparable. The placement of a projection on the housing was most effective in rectifying the flow field.

Numerical Simulation of Nonpulsatile Left Ventricular Bypass

A computer simulation was carried out to investigate the influence of nonpulsatile left ventricular assistance on hemodynamics. A simulation circuit was constructed to represent the circulatory system. A source of current was added to denote the nonpulsatile blood pump. The left and right ventricles were replaced by variable compliances. Left heart failure was simulated by decreasing the amount of compliance change of the left ventricle. We introduced a pulsatility indicator (PI) to clarify the pulsatility characteristics in the hemodynamics; this PI was defined as the ratio of the pulse pressure (PP) to the mean aortic pressure (AoP). When nonpulsatile bypass flow increased, the mean AoP, tension time index (TTI), and diastolic pressure time index (DPTI) increased, and cardiac output, PP, and PI decreased. When assisted flow increased with the constant total flow rate, the mean AoP and DPTI changed little; the PP, TTI, and PI decreased, and the endocardial viability rate increased. The PI would be helpful in evaluating the effect of pulsatility.

A pulsatile cardiopulmonary bypass system that prevents negative pressure at the membrane oxygenator

Negative pressure is a problem in pulsatile cardiopulmonary bypass (CPB). To avoid this, the authors designed a pulsatile CPB system containing a Sarns centrifugal pump (CP) and a Univox membrane oxygenator, in which the inertial flow is not obstructed by the CP. In both an in vitro study and a clinical study, negative pressure was not observed in the arterial line of the CPB circuit when this system was used. When a roller pump (RP) was used, however, instead of a CP, negative pressure did occur. In a clinical study using this system, mean pulse pressure was 36 mmHg and hemolysis, expressed as the rate of rise in plasma free hemoglobin from 10 to 70 min of CPB, was 26.2 mg/dl/hr, which did not exceed that seen with a pulsatile CPB using an RP instead of a CP. The hemolysis seen in the study caused no clinical problems. Thus, pulsatile CPB using a CP and Univox membrane oxygenator should be considered for clinical use to prevent the occurrence of negative pressure.

Use of an Improved Linear Motor-Driven Total Artificial Heart in an Acute Animal Experiment

Linear motor-driven total artificial hearts (linear TAH) have been developed and evaluated by our group. A linear motor is capable of directly driving the reciprocating motion of pusher plates in a pulsatile artificial heart. A linear TAH has the advantages of a simpler transmission mechanism and fewer components in comparison with a rotary motor-driven TAH. The improved linear TAH was developed with a view to high thrust generation and low flow resistance. The total volume of the linear TAH is 580 mL. The linear TAH provided a maximum left pump flow rate of 5.9 L/min at a pumping rate of 113 bpm in a mock circulatory system. An acute animal experiment using a sheep was conducted to evaluate the hemodynamic performance. The maximum flow rate of the left pump was 4.2 L/min at 85 bpm in this animal experiment.

Second Type of Linear Motor-Driven Total Artificial Heart

We evaluated the performance of the first type of linear motor-driven total artificial heart (TAH) in an acute animal experiment reported previously. Artificial circulation in an adult sheep was maintained for only 2 h, indicating that the linear motor needed more powerful thrust. A second type of linear motor-driven TAH was constructed, on the basis of the information obtained from the acute animal experiment. The second TAH has a maximum static thrust of 146 N, achieved by enlarging the thrust action area in the linear motor. The mass of the TAH is 1.9 kg, and the volume TAH is 560mL; this size is suitable for implantation in a human subject weighing 80 kg. The second TAH provides a left pump flow rate of 7.2 L/min at a pumping rate of 120 bpm in a mock circulatory system.

Efficiency of a centrifugal pump for distal circulatory support during cross-clamping of the descending thoracic aorta

To demonstrate efficiency and to determine the ideal circulatory support using the centrifugal pump, the authors designed an experimental study in 6 mongrel dogs 13.3 to 18.5 kg in weight. The descending thoracic aorta was cross-clamped for two hours without the use of vasoactive drugs or blood products. They developed methods of optimizing use of the centrifugal pump to achieve satisfactory hemodynamic and metabolic efficiency Aortic pressure proximal to the clamp was essentially maintained unchanged by regulating flow with the pump during cross-clamping. Bypass flow tended to decrease (from 83 ±13 to 53 ±22 mL/kg/min) during prolonged clamping; distal nonpulsatile pressure was still maintained between 114 ±34 to 127 ±30 mmHg (mean ±SD). Animals were observed for more than twenty-four hours postexperiment; 3 of six dogs were able to stand and walk normally, while the other 3 dogs were only able to move their hind legs but unable to walk normally or stand for more than twenty-four hours. The cause of the paraparesis was unclear. It may be related to spinal cord ischemia secondary to hepatic steal. It also suggests that this method of circulatory support is not able to prevent paraplegia following two-hour cross-clamping of the descending thoracic aorta.

Development of an air lift pump oxygenator

The authors devised an air lift pump oxygenator, comprised of double cylinders connected together and filled with perfluorocarbon (FC-75, 3M) as an oxygen carrier. While the oxygen enters the FC-75 through the lower inlet of one cylinder, the oxygenated FC-75 is lifted by an air lift pump and circulates in the two cylinders. FC-75 adds oxygen to the blood that infuses from the lower inlet of the other cylinder. The oxygenated blood is separated from the FC-75 by gravity and infused into the subject. The size of the cylinder is 2.2 cm in internal diameter and 17 cm in effective oxygenation height. The capacity of the oxygenator is 160 ml. PO2 went from 62 mmHg to 96 mmHg and PCO2 decreased from 31 mmHg to 25 mmHg at a blood flow of 50 ml/min and an oxygen flow of 2 L/min. Maximum blood flow was 60 ml/min and the blood reserve capacity was 20 ml/min. The air lift pump oxygenator has advantages, such as simple structure, no motor, and a small priming volume.