Biomedical subjects

H Sekii

Publications and source records attributed to H Sekii.

27 records · Page 2Linked to original sources

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.

Animals↗

PubMedDate not supplied

A VAD and novel high performance compact oxygenator for long-term ECMO with local anticoagulation.

A novel method of long-term ECMO was designed and evaluated experimentally. Special features of this ECMO method include: 1. using a pneumatic diaphragm type VAD with excellent blood compatibility as a pump system; 2. using a newly developed, high performance, compact oxygenator, with a novel gas exchange membrane in which micropores are blind at the blood contacting surface; 3. regional anticoagulation within the ECMO circuit with short-acting protease inhibitor FUT-175; and 4. right heart bypass with direct cannulation through a thoracotomy. Four goats implanted with a VAD between the right atrium and the pulmonary artery underwent ECMO by interposing a compact oxygenator in the return cannula for as long as 14 days. Blood clotting was regulated with continuous infusion of FUT-175 from the inflow cannula of the ECMO circuit. In this system, 2 to 4 L/min of bypass flow, 80 to 120 ml/min of O2, and 40 to 80 ml/min of CO2 gas exchange were obtained. Serum leakage in the oxygenator did not occur, and various blood chemical and hematologic parameters were maintained within the normal range. Regional anticoagulant therapy was successfully achieved with a significant difference of activated clotting time between the blood samples from the systemic circulation and those from the ECMO circuit. These results indicate that this method overcomes several problems with ECMO, and has the capacity for long-term respiratory assistance.

Animals↗

PubMedDate not supplied

An electrohydraulic total artificial heart with a separately placed actuator.

An electrohydraulic total artificial heart (EHTAH) system, consisting of a separately placed actuator and blood pumps with good anatomic fit, was designed. In the actuator is a brushless DC motor sandwiched between two metal bellows or two pusher-plate pumps connected with the blood pumps by polyvinylchloride tubes. A roller-screw system coupled with the bellows is used for alternative pumping, and silicone oil transmits the action. The pumps are elliptical, and the right pump has a flatter and longer shape than the left to fit the extremely short distance between the right atrium and the sternum. To evaluate in vivo performance, the pumps were implanted as a pneumatic system in a calf weighing 53 kg and three goats weighing 54-55 kg. The pump fit well in the animals, and the calf survived for 111 days, and one goat was alive for 8 days. The EHTAH system could provide an output of 6 L/min with pusher-plate pumps as oil chambers on in vitro evaluation. This system could become one of the most suitable approaches for a totally implantable system.

Animals↗

PubMedDate not supplied

Chronic in vivo evaluation of a portable electrohydraulic ventricular assist system with a linear actuator.

Chronic experiments of the electrohydraulic ventricular assist system with a linear motor actuator were performed in two goats weighing 54 kg and 56 kg, and the system was used for more than 30 days. The actuator was designed to be fixed on the goat's back with a saddle. The pump was connected between the left atrium and descending aorta and placed paracorporeally on the chest wall. Linear action of an actuator bellows was delivered by silicone oil in a U-shaped polyvinylchloride tube to activate the pump. The maximum output in the 56 kg goat was 5.0 L/min. Goats could stand and sit freely. The first goat with a pusher-plate type pump died on the fifth day because of thromboembolism, but the second goat with a diaphragm type pump survived for 42 days. Blood chemistries remained within normal limits. Pump control was easy in both the duty-control mode and the stroke-control mode. With the automatic negative pressure control (ANPC) to prevent atrial wall sucking, the left atrial pressure was kept within +/- 10 mmHg, although left atrial pressure sometimes went below -80 mmHg without ANPC. Considering reliability, automaticity, and portability, the electrohydraulic ventricular assist system has become another choice for a practical, electrically driven ventricular assist system.

Animals↗

PubMedDate not supplied

A composite driving system for LVAS and IABP: practical and effective driving and weaning.

We have devised a new method, termed alternate synchronous driving (ASD), to wean patients from a left ventricular assist system (LVAS) to a pressure assist intraaortic balloon pump (IABP). We have built a new drive unit, VCT200, to apply ASD easily and automatically. After IABP insertion in the final weaning stage, this method drives the LVAS and IABP alternately, with electrocardiogram (ECG) synchronization. The pumping ratio of IABP increases while that of LVAS decreases according to recovery of natural heart function. In in vitro studies, ASD was effective when bypass flow (BF) was less than 50% of total flow (TF) (TF:BF + cardiac output [CO]), and its advantages increased under lower BF conditions. Mean aortic pressure (mAP) and CO increased 10 mmHg and 15%, respectively, with this method (IABP:LVAS = 1:1) when BF was 30% of TF. During in vivo studies, mAP increased 75.7 +/- 6.7 mmHg to 80.1 +/- 3.6 mmHg (p less than 0.001), and the CO increased from 3.1 +/- 0.5 L/min to 3.3 +/- 0.5 L/min (p less than 0.001), while the endocardial viability ratio (DPTI/TTI) increased 20-30%. This method was used in a 62-year-old man in which LVAS was applied after ventricular aneurysmectomy, BF was reduced from 2.2 L/min to 1.1 L/min by using ASD without any change in systemic perfusion. This reduction of BF could not be achieved with LVAS alone. From these data, this system could wean patients from LVAS and then switch to IABP smoothly, easily, and automatically, without hemodynamic instability.

Combined Modality Therapy↗

PubMedDate not supplied

Physiologic reactions of awake animals to an immediate switch from a pulsatile to nonpulsatile systemic circulation.

The purpose of this study is to clarify physiologic reactions to an immediate switch of flow pattern from pulsatile to nonpulsatile. A pulsatile ventricular assist device (VAD) was implanted in four 40-64 kg goats. Blood was drawn from the left atrium and ventricle and expelled into the aorta. After 2 weeks the VAD was quickly replaced by a centrifugal pump, MD-10 (Iwaki Pump, Tokyo, Japan), 760 g in weight and phi 70 mm x 84 mm in size, set on the back, without anesthesia. A 100% nonpulsatile bypass flow was immediately obtained, and the pump was set to maintain the same mean aortic pressure as before the switch; central venous pressure, cardiac output, systemic vascular resistance, oxygen consumption, blood lactate, plasma adrenalin, noradrenalin, renin activity, angiotensin II, and aldosterone were measured. Behavior of the goats did not change, and fluid infusion and higher cardiac outputs were not required. Most of the parameters did not deviate from control levels after the switch. In conclusion, a mammal immediately accommodates well to nonpulsatile flow.

Aldosterone↗

PubMedDate not supplied

A blood-liquid interface for prolonged extracorporeal oxygenation with excellent antithrombogenicity.

The authors verified the excellent antithrombogenicity of a blood-liquid interface (BLI) and introduced an oxygenator based on the principle of gas exchange across direct BLI. In a newly developed oxygenator, three layers of liquid flowed horizontally, contacting one another: O2 saturated silicone oil on the top, O2 saturated fluorcarbon at the bottom, and blood in the middle. Gas exchange was carried out across both direct BLIs. This system provided excellent antithrombogenicity as well as good gas exchange. The results indicate that this method will become a promising modality for prolonged extracorporeal oxygenation.

Blood Coagulation↗

PubMedDate not supplied

Cardiac disuse atrophy during LVAD pumping.

The authors investigated morphologic changes of myocardial tissue of goats supported with a long-duration left ventricular assist device (LVAD). The bypass flow rates of the LVAD were kept at maximum levels (about 80% of total cardiac output) in four goats for 30 days, and at a limited flow rate (around 60%) in one goat each for 30 and 90 days. Morphometric studies using light and electron microscopy were performed on the left ventricles, comparing them to those in the four control studies. The results disclosed: 1) relative volume densities of the myocytes and interstitial tissue in the myocardium were unchanged; 2) cross-sectional areas of the myocytes in the maximum bypass cases were significantly reduced in comparison with pre-experimental data; 3) relative myocyte volumes, calculated by myocytes and nuclear volume densities, were reduced in three goats in the maximum bypass group; and 4) relative volume density of myofibrils was reduced in the maximum and 90 day bypass groups, whereas that of mitochondria was reduced only in the 90 day bypass case. These results indicate that LVADs cause cardiac atrophy which correlates with bypass flow rate and duration of assistance.

Animals↗

PubMedDate not supplied

A synthetic tetrapeptide as a novel platelet-preserving agent during cardiopulmonary bypass.

The possibility of using the synthetic tetrapeptide arginine-glycine-aspartic acid-serine (Arg-Gly-Asp-Ser, RGDS), which was recently identified as the common cell attachment site of adhesive plasma proteins, for platelet preservation during cardiopulmonary bypass (CPB) was investigated. The synthetic RGDS inhibited platelet aggregation and adhesion and secretion of thromboxane A2 in a dose-dependent manner, due to antagonistic inhibition via ligand-receptor interaction. Platelet consumption during CPB was drastically reduced by the administration of RGDS with no remarkable change in hemodynamics and a fairly rapid recovery of platelet functions. Electron microscopic observation revealed that this platelet-preserving effect of RGDS resulted from the inhibition of adhesion and aggregation on the artificial surface. These strongly indicate that the cell attachment site of adhesive plasma proteins plays an important role in platelet consumption during CPB. The synthetic RGDS acting as an antagonist of the platelet membrane receptor, is a novel platelet-preserving agent, especially useful when using an extracorporeal circuit with a large blood-material contact area, such as CPB.

Animals↗