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.

Animals↗

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

A miniature intraventricular axial flow blood pump that is introduced through the left ventricular apex.

A new intraventricular axial flow blood pump has been designed and developed as an implantable left ventricular assist device (LVAD). The pump consists of a tube housing (10 cm in length and 14 mm in diameter), a three-vane impeller combined with a guide vane, and a DC motor. This pump is introduced into the LV cavity through the LV apex, and the outlet cannula is passed antegrade across the aortic valve. Blood is withdrawn from the LV through the inlet ports at the pump base, and discharged into the ascending aorta. A pump flow of > 8 L/min was obtained against 90 mmHg differential pressure in the mock circulatory system. In an acute dog model, this pump could produce a sufficient output of 200 ml/kg/min. In addition, the pump flow profile demonstrated a pulsatile pattern, although the rotation speed was fixed. This is mainly due to the changes in flow rate during a cardiac cycle--that is, during systole, the flow rate increases to the maximum, while the differential pressure between the LV and the aorta decreases to the minimum. Thus, this simple and compact axial flow blood pump can be a potential LVAD, with prompt accessibility and need for less invasive surgical procedures.

Animals↗

PubMedDate not supplied

An intraventricular axial flow blood pump integrated with a bearing purge system.

The future development of implantable axial flow blood pumps must address two major issues: mechanically induced hemolysis and shaft seal reliability. The recent revisions to our miniature intraventricular axial flow left ventricular assist device (LVAD) were aimed particularly at addressing these concerns. To improve hemocompatibility, a new impeller has been designed according to the following criteria: 1) gradual pressure rise along the blade chord; 2) minimized local fluid acceleration to prevent cavitation; 3) minimum surface roughness; and 4) radius edges. Subsequent in vitro hemolysis tests conducted with bovine and ovine blood have demonstrated very low hemolysis (normalized index of hemolysis = 0.0051 +/- 0.0047 g/100 L) with this new impeller design. To address the need for a reliable seal, we have developed a purged seal system consisting of a miniature lip seal and ceramic pressure groove journal bearing that also acts as a purge pump. Several spiral grooves formed on the bearing surface provide viscous pumping of the purge fluid, generating more than 3,000 mmHg at 10,000 rpm. This purge flow flushes the lip seal and prevents blood backflow into the bearing. We have found this purge pump to offer several advantages because it is simple, compact, durable, does not require separate actuation, and offers a wide range of flow, depending upon the groove design. In vivo animal tests demonstrated the potential of the purged seal system.

Animals↗

PubMedDate not supplied

Relationship of blood pressure and pump flow in an implantable centrifugal blood pump during hypertension.

The purpose of this study was to evaluate the real time relationship between pump flow and pump differential pressure (D-P) during experimentally induced hypertension (HT). Two calves (80 and 68 kg) were implanted with the EVA-HEART centrifugal blood pump (SunMedical Technology Research Corp., Nagano, Japan) under general anesthesia. Blood pressure (BP) in diastole was increased to 100 mm Hg by norepinephrine to simulate HT. Pump flow, D-P, ECG, and BP were measured at pump speeds of 1,800, 2,100, and 2,300 rpm. All data were separated into systole and diastole, and pump flow during HT was compared with normotensive (NT) conditions at respective pump speeds. Diastolic BP was increased to 99.3+/-4.1 mm Hg from 66.5+/-4.4 mm Hg (p<0.01). D-P in systole was under 40 mm Hg (range of change was 10 to 40 mm Hg) even during HT. During NT, the average systolic pump flow volume was 60% of the total pump flow. However, during HT, the average systolic pump flow was 100% of total pump flow volume, although the pump flow volume in systole during HT decreased (33.1+/-5.7 vs. 25.9+/-4.0 ml/systole, p<0.01). In diastole, the average flow volume through the pump was 19.6+/-6.9 ml/diastole during NT and -2.2+/-11.1 ml/diastole during HT (p<0.01). The change in pump flow volume due to HT, in diastole, was greater than the change in pump flow in systole at each pump speed (p<0.001). This study suggests that the decrease of mean pump flow during HT is mainly due to the decrease of the diastolic pump flow and, to a much lesser degree, systolic pump flow.

Animals↗

PubMedDate not supplied

Experimental and clinical evaluations of the optimum combination in size and type of prostheses on double valve replacement.

Explore the source record for details and available documents.

Adolescent↗

PubMedDate not supplied

Development of a miniature intraventricular axial flow blood pump.

A new intraventricular axial flow blood pump has been designed and developed as a totally implantable left ventricular assist device (LVAD). This pump consists of an impeller combined with a guide-vane, a tube housing, and a DC motor. The pump is introduced into the LV cavity through the LV apex, and the outlet cannula is passed antegrade across the aortic valve. Blood is withdrawn from the LV through the inlet ports at the pump base, and discharged to the ascending aorta. Our newly developed axial flow pump system has the following advantages: 1) it is a simple and compact system, 2) minimal blood stasis both in the device and the LV cavity, 3) minimal blood contacting surface of the pump, 4) easy accessibility with a less invasive surgical procedure, and 5) low cost. A pump flow > 5 L/min was obtained against 100 mmHg differential pressure in the mock circulatory system. The pump could produce a passive pulsatile flow effect with a beating heart more efficiently than other non-pulsatile pumps because of minimal pressure drop and inertia along the bypass tract. Anatomic fit studies using dissected hearts of dilated cardiomyopathy (DCM) cadavers showed that this pump could smoothly pass through the aortic valve without any interference with mitral valve function. Recently, a dynamic pressure groove bearing and a miniature lip seal have been developed. The dynamic pressure groove bearing has a simple structure and acts as a pressure resistant sealing mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiomyopathy, Dilated↗

PubMedDate not supplied

Comparison of the closing dynamics of mechanical prosthetic heart valves.

To compare the closing dynamics of mechanical tilting disk prosthetic heart valves (OmniScience 25 [OS25], Medtronic-Hall 25 [MH25], Bjork-Shiley Monostrut 29 [BS29]) and bileaflet valves (CarboMedics 29 [CM29]) in the mitral position, an x-ray high speed video camera (XHVC) and a mechanical mock circulator were used. From the continuous images taken with the XHVC, the starting point of closing and the period during closing (PDC) were measured. Pressures and flow rate were recorded at 500 Hz synchronously with the XHVC. A pressure difference across the valves at the onset of closing (dpc) was newly introduced to compare the closing response. Using 60 and 100 bpm, the following results were obtained: 1) the CM29 had less PDC and maximum backflow rate than the BS29; 2) the dpc and the PDC at 100 bpm were larger than those at 60 bpm; 3) the dpc of the MH25 was the lowest; and 4) the PDC of the CM29 was the shortest. With regard to the effect of valve design on closing dynamics, it was shown that: 1) less momentum of inertia of the occluder and disk traveling angle resulted in lower dpc and shorter PDC, and 2) the higher the dpc and the PDC became, the larger the maximum backflow rate that was generated, and 3) low final closing speed will be achieved for small disk travelling angle.

Biomechanical Phenomena↗

PubMedDate not supplied

An implantable centrifugal blood pump for long term circulatory support.

A compact centrifugal blood pump was developed as an implantable left ventricular assist system. The impeller diameter is 40 mm and the pump dimensions are 55 x 64 mm. This first prototype was fabricated from titanium alloy, resulting in a pump weight of 400 g including a brushless DC motor. Weight of the second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbon to improve blood compatibility. Flow rates of over 7 L/min against 100 mmHg pressure at 2,500 rpm with 9 W total power consumption have been measured. A newly designed mechanical seal with a recirculating purge system ("Cool-Seal") is used as a shaft seal. In this seal system, seal temperature is kept under 40 degrees C to prevent heat denaturation of blood proteins. Purge fluid also cools the pump motor coil and journal bearing. The purge fluid is continuously purified and sterilized by an ultrafiltration filter incorporated into the paracorporeal drive console. In vitro experiments with bovine blood demonstrated an acceptably low hemolysis rate (normalized index of hemolysis = 0.005 +/- 0.002 g/100 L). In vivo experiments are currently ongoing using calves. Via left thoracotomy, left ventricular apex-descending aorta bypass was performed utilizing a PTFE (Polytetrafluoroethylene) vascular graft, with the pump placed in the left thoracic cavity. In two in vivo experiments, pump flow rate was maintained at 5-8 L/min, and pump power consumption remained stable at 9-10 W. All plasma free hemoglobin levels were measured at < 15 mg/dl. The seal system has demonstrated good seal capability with negligible purge fluid consumption (< 0.5 ml/ day). Both animals remain under observation after 162 and 91 days of continuous pump function.

Animals↗

PubMedDate not supplied

Long-term animal experiments with an intraventricular axial flow blood pump.

A miniature intraventricular axial flow blood pump (IVAP) is undergoing in vivo evaluation in calves. The IVAP system consists of a miniature (phi 13.9 mm) axial flow pump that resides within the left ventricular (LV) chamber and a brushless DC motor. The pump is fabricated from titanium alloy, and the pump weight is 170 g. It produces a flow rate of over 5 L/min against 100 mmHg pressure at 9,000 rpm with an 8 W total power consumption. The maximum total efficiency exceeds 17%. A purged lip seal system is used in prototype no. 8, and a newly developed "Cool-Seal" (a low temperature mechanical seal) is used in prototype no. 9. In the Cool-Seal system, a large amount of purge flow is introduced behind the seal faces to augment convective heat transfer, keeping the seal face temperature at a low level for prevention of heat denaturation of blood proteins. The Cool-Seal system consumes < 10 cc purge fluid per day and has greatly extended seal life. The pumps were implanted in three calves (26, 30, and 168 days of support). The pump was inserted through a left thoracotomy at the fifth intercostal space. Two pursestring sutures were placed on the LV apex, and the apex was cored with a myocardial punch. The pump was inserted into the LV with the outlet cannula smoothly passing through the aortic valve without any difficulty. Only 5 min elapsed between the time of chest opening and initiation of pumping. Pump function remained stable throughout in all experiments. No cardiac arrhythmias were detected, even at treadmill exercise tests. The plasma free hemoglobin level remained in the acceptable range. Post mortem examination did not reveal any interference between the pump and the mitral apparatus. No major thromboembolism was detected in the vital organs in Cases 1 or 2, but a few small renal infarcts were detected in Case 3.

Animals↗