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Biomedical subjects

Y Taenaka

Publications and source records attributed to Y Taenaka.

At least 91 records · Page 5Linked to original sources
PubMed1984

[Left ventricular thrombus formation and cuspal fusion of the prosthetic valve during left heart bypass: their pathophysiological significance and echocardiographic observations].

The echocardiographic findings during left ventricular assist of a heart of a 36-year-old woman who underwent mitral valve replacement were described. Blood was bypassed from the left atrium to the aorta. Echocardiography demonstrated that the pulmonary and tricuspid valves functioned with each heart beat, but that the aortic and prosthetic mitral valves did not open, and the left ventricular wall did not contract. In the left ventricular cavity, there was a mobile and amorphous thrombus which correlated with dynamic intracavitary micro-echoes ("moya moya" echoes). With higher left atrial pressure, the left ventricular motion increased slightly, and the left ventricular dimension gradually decreased. These findings were interpreted as follows: (1) desired results were attained from the previous powerful assist, or (2) the most optimum pressure of the left atrium in relation to the left ventricle was relatively high. It has not yet been determined which is actually the case. The "moya moya" and thrombus echoes were decreased. The general condition of the heart appeared to be improved, but the prosthetic valve motion was not observed. Contrast study via an echocardiographically-guided catheter inserted retrogradely into the left ventricular cavity revealed prosthetic valve stenosis. Fusion of its cusps by fibrin was confirmed on repeat surgery. Although the patient's condition allowed removal of the left ventricular assist device after surgery, the patient died of progressive infection. Optimum powerful assist should be performed while the formation of thrombi and cuspal adhesions is being prevented by other methods, or a more mild assist may be desirable.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMedDate not supplied

Influences of ventricular assist device pumping on blood coagulation.

A left ventricular assist device (VAD) with a smooth surface of segmented polyurethane was implanted in five goats for 10-55 days, and plasma levels of fibrinogen (Fg), prekallikrein (PK), fibrinogen, fibrin degradation products (FDP), antithrombin III (AT III), prothrombin time (PT), partial thromboplastin time (PTT), platelet (Pl) count, and platelet aggregation (PlAg) induced by adenosine diphosphate were measured during the experiment. Heparin was administered during surgery and no systemic antithrombotic therapy was given thereafter. Before the third postoperative day (POD), plasma levels of Fg and PK were at their lowest, and increased afterward. Between the second and fifth POD PT and PTT increased to 130-160%, and returned to normal gradually. Plasma FDP appeared on the second POD and reached peak values of 10-40 micrograms/ml on the sixth POD. Platelet and AT III levels showed no uniform tendency, but the rate of PlAg decreased to levels of 6-77% before the fifth POD and remained low at approximately 80%, influenced by the pumping even after the 25th POD. In summary, VADs themselves activated coagulation and induced consumption coagulopathy to some degree. However, most of the parameters returned to normal within 2 weeks.

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PubMedDate not supplied

Regulation of coronary circulation during left ventricular assist.

Regulatory mechanisms of coronary circulation during left ventricular assist (LVA) were studied in chronic experiments using adult goats. In normal heart studies (n = 3), circumflex coronary artery flow (CxF) and endocardial blood flow (MBF) decreased in proportion to decrease of tension time index (TTI). Mean CxF/TTI was constant at 0.22, whether the LVA functioned or not. In the left anterior descending branch ligation model (AMI) study (n = 2), CxF decreased according to decrease of TTI throughout the experiment, if the bypass ratio was kept within a normal range of systemic pressure. Mean CxF/TTI was maintained at approximately 0.21 by LVA, fell to 0.16 when LVA was turned off during the early stages. Coronary circulation during LVA was regulated by oxygen demand if systemic circulation was maintained, and LVA improved oxygen demand-supply balance in failing hearts.

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PubMedDate not supplied

An electrohydraulic ventricular assist system with a linear actuator.

An electrohydraulic ventricular assist system with a linear actuator was developed, and in vitro and in vivo evaluations were performed. During in vitro evaluations this system could yield 5.6 L/min of pump flow against a mean afterload of 100 mmHg. Durability tests were performed for more than 4 months. The system was implanted in three goats and a maximum pump flow of 4.2 L/min was obtained against a mean afterload of 100 mmHg, and 3.2 L/min against 130 mmHg. These evaluations have proven that the system can maintain stable hemodynamics under various conditions.

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PubMedDate not supplied

Multi-institutional studies of the National Cardiovascular Center Ventricular Assist System: use in 92 patients.

A ventricular assist system (VAS) developed at the National Cardiovascular Center (NCVC) and produced by Toyobo Company has been clinically evaluated at 32 institutes. The system consists of a pneumatic and diaphragm-type pump, and a control-drive unit with an automatic bypass flow (BF) control system. The VAS was used in 85 adults and 7 children with acute, severe heart failure. Forty-eight patients were weaned from VAS, and 21 were long-term survivors. Heparin was not used when BF was above 2.0 L/min in an adult sized pump, and 0.8 in a pediatric one. Thrombus formation was noticed in the groove around the valve in eight cases, and in the pump in eight. Pump-originated serious complications were not seen. Hematologic and biochemical findings revealed that the VAS did not directly affect the major organs. The control-drive unit, including the automatic BF control system, functioned accurately, with less manpower, securing reliable control over the circulation. Two major causes of death were irreversible heart failure, and multiple organ failure, which resulted from delayed application. In conclusion, the NCVC-type VAS has been found effective and reliable, less thrombogenic, and requiring less manpower for its clinical use.

Adult↗
PubMedDate not supplied

Experimental evaluation and clinical application of a pediatric ventricular assist device.

A pneumatic pediatric ventricular assist device (VAD) with a stroke volume of 20 ml has been developed to treat post-operative heart failure (HF), and maintain transplant candidates. The polyurethane VAD has two #21 Bjork-Shiley valves and the internal diameter of the cannula is either 6 or 8 mm. Hemodynamic effects of a left ventricular assist device (LVAD) on a HF after Fontan's procedure model, and those of a right ventricular assist device (RVAD) on right HF with pulmonary hypertension model, were investigated in acute experiments with four and five dogs, respectively. In the former, the pressure gradient across the lung and cardiac output (CO) increased with an LVAD; right atrial pressure decreased and CO increased with an RVAD in the latter. The pump was implanted as an LVAD in 8 young goats, 9-22 kg in weight, for 4-10 weeks and favorable in vivo performance was demonstrated. The VAD system was applied as an LVAD to two postcardiotomy patients, a 12 kg boy with a ventricular septal defect, and a 13 kg boy with an endocardial cushion defect. In these cases, CO was well maintained at the level of 2.5-4.1 L/min/m2 for three and seven days, respectively, and the pump was removed. In conclusion, this VAD will become a promising circulatory support system for pediatric uses.

Animals↗
PubMedDate not supplied

Left ventricular assist system with a simplified cannulation technique.

A simplified cannulation system was developed without thoracotomy for a ventricular assist system (VAS) that will be applicable even in an emergency. This system consists of an air driven and diaphragm type pump, cannulae, and devices for insertion. The inlet cannula was inserted into the left atrium through the femoral vein using a modified brockenbrough transseptal method. This system was installed without thoracotomy in a chronic experiment in two goats and was removed without any trouble after 14 days of pumping. In a 40 day experiment with this system implanted between the left atrium and the aorta, bypass flow was maintained at 2.7 to 3.3 L/min, and plasma free hemoglobin levels were below 7 mg/dl. When this system was implanted between the left atrium and the aorta, and activated in an induced heart failure goat, output through the pump was 3.0 +/- 0.4 L/min, and mean aortic pressure was increased to 91.7 +/- 15.9 mmHg from 55.8 +/- 15.4 mmHg. This system takes a middle position between an IABP and VAS with thoracotomy in capability of circulatory support and convenience.

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PubMedDate not supplied

A novel method for long-term respiratory support.

The authors designed a new extracorporeal membrane oxygenation (ECMO) method using a right ventricular assist device (RVAD) system and a membrane oxygenator (MO). An air-driven diaphragm type RVAD was implanted between the right atrium and the pulmonary artery in five goats, and an MO was set on the outlet conduit of the RVAD 2 weeks postoperatively. The MOs used in this study are silicon sheet MOs and prototype MOs using a novel multilayered composite membrane. Respiratory support with this system, under systemic heparinization, could be conducted for 4-8 days without major problems. This method solved several difficulties with ECMO, such as surgical bleeding, serum leakage, destruction of the blood components from the pump system, inadequate bypass flow, and fatal systemic thrombosis. This method is suitable for long-term respiratory support, especially as a bridge before lung or heart-lung transplantation.

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PubMedDate not supplied

A bioartificial ventricle used as a totally implantable circulatory assist device.

The authors designed a totally implantable circulatory assist device consisting of a bioartificial ventricle composed of a skeletal muscle ventricle lined with a bioartificial endocardium. The bioartificial endocardium consists of a structural matrix made of a polyurethane porous membrane, fragmented blood vessels, and collagen gel. The authors prepared the polyurethane porous membrane by solvent cocasting with salt powder. They used collagen gel with fragmented goat carotid vein to perform in vitro construction of the bioartificial endocardium. For in vivo construction of the bioartificial endocardium, the authors used a modified version of the tissue fragment method for vascular prostheses. The authors prepared suspensions of tissue fragments using collagen gel with fragmented goat carotid artery. They used a highly porous fabric vascular prosthesis as a structural matrix; tissue fragments were entrapped on the outer surface of the prosthesis, and the prosthesis then was implanted into the carotid artery of four adult goats. In specimens 1 and 3 months postimplantation, cells from the fragmented tissue regenerated an endothelium-like monolayer sheet on the inner surface of the prostheses. Output of a prototype bioartificial ventricle reached 660 ml/min at an afterload of 60 mmHg and a preload of 20 mmHg. Based on these data, the authors conclude that the bioartificial ventricle is promising as an implantable device with excellent antithrombogenicity.

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PubMedDate not supplied

A motor integrated regenerative pump as the actuator of an electrohydraulic totally implantable artificial heart.

The authors have developed a new actuator to drive an electrohydraulic totally implantable artificial heart. The basic concept of this artificial heart is that the blood pumps are implanted in the thorax and an actuator is placed separately in the abdominal region. The actuator is a regenerative pump that pumps fluids against high pressures and is thin enough for easy implantation. The rotor-magnet of the brushless DC motor is mounted on the impeller of the pump to miniaturize the actuator and reduce the number of moving parts. The height, diameter, and weight of the actuator are 32.5 mm, 73 mm, and 360 g, respectively. A pair of oil ports is connected to the left and right blood pumps with mesh reinforced tubes filled with silicone oil. The blood pumps are alternately driven by bidirectional rotation of the motor. Performance of the system was evaluated in in vitro and in vivo experiments. Maximum output of the right heart was 6.7 L/min in both experiments. Systemic circulation was well maintained in acute animal experiments using 49 and 50 kg goats. The feasibility of the actuator was confirmed.

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