Ventricular Flow Field Visualization During Mechanical Circulatory Support in the Assisted Isolated Beating Heart.

Investigations of ventricular flow patterns during mechanical circulatory support are limited to in vitro flow models or in silico simulations, which cannot fully replicate the complex anatomy and contraction of the heart. Therefore, the feasibility of using echocardiographic particle image velocimetry (Echo-PIV) was evaluated in an isolated working heart setup. Porcine hearts were connected to an isolated, working heart setup and a left ventricular assist device (LVAD) was implanted. During different levels of LVAD support (unsupported, partial support, full support), microbubbles were injected and echocardiographic images were acquired. Iterative PIV algorithms were applied to calculate flow fields. The isolated heart setup allowed different hemodynamic situations. In the unsupported heart, diastolic intra-ventricular blood flow was redirected at the heart's apex towards the left ventricular outflow tract (LVOT). With increasing pump speed, large vortex formation was suppressed, and blood flow from the mitral valve directly entered the pump cannula. The maximum velocities in the LVOT were significantly reduced with increasing support. For the first time, cardiac blood flow patterns during LVAD support were visualized and quantified in an ex vivo model using Echo-PIV. The results reveal potential regions of stagnation in the LVOT and, in future the methods might be also used in clinical routine to evaluate intraventricular flow fields during LVAD support.

Experimental validation of numerical simulations: a comparison of computational fluid dynamics and the oil film method.

BACKGROUND: Today Computational Fluid Dynamics (CFD) is used for simulating flow in many applications. The quality of the results, however, depends on various factors, like grid quality, boundary conditions and the computational model of the fluid. For this reason, it is important to validate the performed computation with experimental results. In this work, a comparison of numerical simulation with the oil film method was performed for two cardiovascular applications. METHODS: The investigations were conducted at various geometries, such as a bended cannula tubing, an impeller of a magnetically levitated rotary blood pump and tips of inflow cannulas. The oil film for the experimental validation was composed of black oil color and varnish. In the numerical simulation, color abrasion was displayed with a special post-processing tool by means of wall-attached pathlines. RESULTS: With the proper choice of numerical parameters, the computer simulations and the oil film method demonstrated good correlation. Improper generation of the simulation grid did lead to divergent results between the numerical simulation and the experiment. For the pump impeller as well as for the inflow cannulas, the calculation and the experiment showed similar flow patterns with backflow and stall zones. CONCLUSION: The oil film method represents a fast and simple approach to help validate numerical simulations of fluid flow. The experimentally generated near wall flow patterns can be easily compared with the solution of the CFD analysis.

Experimental comparison of four methods of end-to-side anastomosis with expanded polytetrafluoroethylene.

BACKGROUND: Four established techniques of distal end-to-side anastomosis (direct anastomosis, Linton patch, Taylor patch and Miller cuff) were compared to investigate the local distribution of anastomotic intimal hyperplasia. The study aimed to elucidate whether mechanical factors or flow alterations are mainly responsible for the improved patency rates reported for vein cuff interposition techniques in infrainguinal arterial reconstructions using prosthetic graft material. METHODS: Thirty-two expanded polytetrafluoroethylene (ePTFE) femoropopliteal bypass grafts were implanted in 16 sheep using the four anastomotic techniques. After 6 months the grafts were explanted and examined histologically. The local distribution of intimal hyperplasia was determined, particularly for areas of material transition and of high and low shear stress. RESULTS: The mean amount and distribution of intimal hyperplasia were similar for all anastomotic types. Intimal hyperplasia was greatest along all transitions between ePTFE and venous patches, and between ePTFE and recipient artery. It was lower along the transitions between venous patches and artery, and was lowest at the host artery floor. CONCLUSION: Vein interposition did not reduce anastomotic intimal hyperplasia and did not change the distribution patterns of hyperplasia, which were influenced mainly by mechanical factors. The effect of vein interposition is to move areas of maximum intimal hyperplasia away from the small recipient artery up to the more capacious graft-patch anastomosis.

Numerical simulation of carotid hemodynamics in patients with rotary blood pump cardiac assist.

In recipients of rotary blood pumps for cardiac assist, the pulsatility of arterial flow is considerably diminished. This influences the shear stress patterns and streamlines in the arterial bed, with potential influence on washout and subsequent plaque growth. To study these effects, a three-dimensional computer simulation of the carotid bifurcation at various levels of flow pulsatility was performed. The results showed that as expected pulsatile shear stress varied considerably, whereas local mean shear stress levels were nearly identical for all degrees of pulsatility. Particle residence time in the carotid bulb did only increase for less than 15%, with secondary washout patterns contributing to good washout also in nonpulsatile conditions. It is concluded that also under continuous pump support the local flow patterns in the carotids provide sufficient washout and fluid exchange to prevent excessive plaque growth.

Development of the Baylor Gyro permanently implantable centrifugal blood pump as a biventricular assist device.

The Baylor Gyro permanently implantable centrifugal blood pump (Gyro PI pump) has been under development since 1995 at Baylor College of Medicine. Excellent results were achieved as a left ventricular assist device (LVAD) with survival up to 284 days. Based on these results, we are now focusing on the development of a biventricular assist device (BVAD) system, which requires 2 pumps to be implanted simultaneously in the preperitoneal space. Our hypothesis was that the Gyro PI pump would be an appropriate device for an implantable BVAD system. The Gyro PI 700 pump is fabricated from titanium alloy and has a 25 ml priming volume, pump weight of 204 g, height of 45 mm, and pump diameter of 65 mm. This pump can provide 5 L/min against 100 mm Hg at 2,000 rpm. In this study, 6 half-Dexter healthy calves have been used as the experimental model. The right pump was applied between the infundibular of the right ventricle and the main pulmonary artery. The left pump was applied between the apex of the left ventricle and the thoracic descending aorta. As for anticoagulation, heparin was administered at the first postoperative week and then converted to warfarin sodium from the second week after surgery. Both pump flow rates were controlled maintaining a pulmonary arterial flow of less than 160 ml/kg/min for the sake of avoidance of pulmonary congestion. Blood sampling was done to assess visceral organ function, and the data regarding pump performance were collected. After encountering the endpoint, which the study could not keep for any reasons, necropsy and histopathological examinations were performed. The first 2 cases were terminated within 1 week. Deterioration of the pump flow due to suction phenomenon was recognized in both cases. To avoid the suction phenomenon, a flexible conduit attached on the inlet conduit was designed and implanted. After using the flexible inflow conduit, the required power and the rotational speed were reduced. Furthermore, the suction phenomenon was not observed except for 1 case. There was no deterioration regarding visceral organ function, and pulmonary function was maintained within normal range except for 1 case. Even though the experimental animal survived up to 45 days with the flexible inflow conduit, an increase in power consumption due to thrombus formation behind the impeller became a problem. Lower rotational speed, which was probably produced by the effectiveness of the flexible inflow conduit, was speculated to be one of the reasons. And the minimum range of rotational speed was 1,950 rpm in these 6 BVAD cases and the previous 3 cases of LVAD. In conclusion, 6 cases of BVAD implantation were performed as in vivo animal studies and were observed up to 45 days. The flexible inflow conduit was applied in 4 of 6 cases, and it was effective in avoiding a suction phenomenon. The proper rotational speed of the Gyro PI 700 pump was detected from the viewpoint of antithrombogenicity, which is more than 1,950 rpm.

Can hypocapnia reduce cerebral embolization during cardiopulmonary bypass?

BACKGROUND: Cerebral embolization is a major cause of central nervous dysfunction after cardiopulmonary bypass. Experimental studies demonstrate that reductions in arterial carbon dioxide tension (PaCO2) can reduce cerebral embolization during cardiopulmonary bypass. This study examined the effects of brief PaCO2 manipulations on cerebral embolization in patients undergoing cardiac valve procedures. METHODS: Patients were prospectively randomized to either hypocapnia (PaCO2 = 30 to 32 mm Hg, n = 30) or normocapnia (PaCO2 = 40 to 42 mm Hg, n = 31) before aortic cross-clamp removal. With removal of the aortic cross-clamp embolic signals were recorded by transcranial Doppler ultrasonography for the next 15 minutes. RESULTS: Despite significant differences in PaCO2, groups did not differ statistically in total cerebral emboli counts. The mean number of embolic events was 107 +/- 100 (median, 80) in the hypocapnic group and 135 +/- 115 (median, 96) in the normocapnic group, respectively (p = 0.315). CONCLUSIONS: Due to the high between-patient variability in embolization, reductions in PaCO2 did not result in a statistically significant decrease in cerebral emboli. In contrast to experimental studies, the beneficial effect of hypocapnia on cerebral embolization could not be demonstrated in humans.

First experiences with outpatient care of patients with implanted axial flow pumps.

As known from patients with pulsatile ventricular assist devices (VADs), early mobilization, physical exercise, and return to normal life are essential for optimal recovery. Recently, implantable rotary pumps became available for extended left ventricular support as bridges to transplantation. Modified procedures are essential for patient training and hospital discharge. The MicroMed-DeBakey VAD was implanted in 10 patients with end-stage heart disease. After recovery, regular ergometer training was performed with loads adapted to the patient's condition. Procedures for patient observation under outdoor conditions and a blood pressure measuring device for low pulse pressure conditions were developed. Improvement of physical condition was achieved in 8 patients. In the first 2 patients, exercise capacity was limited due to flow obstruction. In the following patients, an increase of workload on the ergometer up to 120 W was observed. Correlated with training, lactate/load relationship and heart rate decreased. Three patients were discharged from the hospital during support. The DeBakey-VAD system can support patients for extended time periods and is suitable for recovery and exercise. Under optimal patient and environmental conditions, discharge from the hospital can be obtained.

Lessons learned from the first clinical implants of the DeBakey ventricular assist device axial pump: a single center report.

BACKGROUND: The bridge to transplantation with pulsatile mechanical assist devices became a standard procedure for patients deteriorating on the waiting list. Recently, continuous flow axial impeller pumps were introduced to clinical application offering new advantages. METHODS: From November 1998 till September 2000, 6 male patients (mean age 53 plus or minus 11 years) with end-stage left heart failure were implanted with a DeBakey ventricular assist device (VAD) axial-flow pump for bridge to transplantation. RESULTS: Three patients were successfully transplanted after 74, 115, and 117 days, respectively. Two other patients died after 25 and 133 days. One patient is still on the device after 108 days. Because of modification of the implantation technique after the first 2 patients, mean pump-flow within the first 3 weeks was increased from 4.3 +/- 0.6 L/min to 6.7 +/- 0.3 L/min. Patients were put on regular bicycle-ergometer training and improved their exercise capacities up to a mean maximum oxygen consumption of 20.2 mL/kg/min. CONCLUSIONS: Initial implants of the DeBakey VAD demonstrated support properties comparable to pulsatile pumps but without significant restrictions for extended use.

Hemodynamic exercise response in calves with an implantable biventricular centrifugal blood pump.

An implantable biventricular assist device (BVAD) has been developed at Baylor College of Medicine using 2 centrifugal blood pumps. The aim of this study was to investigate the exercise-reflex response during nonpulsatile biventricular assistance and to evaluate to which degree the autoregulation of the system would accommodate the changed hemodynamic situation during physical exercise. The Baylor Gyro PI 710 BVAD has been implanted into 2 calves (strain half-Dexter) in a biventricular bypass fashion with native heart remaining. Allowing a 10 day convalescence, 2 animals were subjected to incremental exercise tests. The speed of the treadmill was increased at zero slope from 0.7 mph to 1.5 mph with increments of 0.2 mph every 3 min. During the exercise the pump flows were maintained at a fixed rate (6.93 +/- 0.01 L/min for the left ventricular assist device and 5.36 +/- 1.44 L/min for the right ventricular assist device). Hemodynamic parameters and pump performance were recorded continuously. The cardiac output (CO) and heart rate (HR) increased significantly during the exercise. CO increased from 11.1 +/- 0.3 to 13.1 +/- 0.4 L/min, and HR increased from 99 +/- 7.1 to 114 +/- 2.8 bpm, respectively. Mean aortic pressure, central venous pressure, and left arterial pressure did not change significantly. Also, no change was observed for the left and right pump flows. This totally implantable BVAD showed excellent long-term performance without any mechanical problems. It is feasible to operate without impairment under physical activity. However, the natural heart dominated the hemodynamic response during exercise under BVAD support. The left and the right pump flows did not increase spontaneously with exercise. We therefore conclude that a servo CO control system is necessary to regulate pump flows even during moderate exercise.

Right ventricular assist system feedback flow control parameter for a rotary blood pump.

At least 25-30% of patients with a permanent implantable left ventricular assist device (LVAD) experience right ventricular failure; therefore, an implantable biventricular assist system (BiVAS) with small centrifugal pumps is being developed. Many institutions are focusing and developing a control system for a left ventricular assist system (LVAS) with rotary blood pumps. These authors feel that the right ventricular assist system (RVAS) with rotary blood pumps should be developed simultaneously. A literature search indicated no recent reports on the effect of hemodynamics and exercise with this type of nonpulsatile implantable RVAS. In this study, a calf with an implantable right ventricular assist system (RVAS) was subjected to 30 min of exercise on a treadmill at 1.5 mph, resulting in excellent hemodynamics. The input voltage remained unchanged. Hemodynamic recordings were taken every 5 min throughout the testing period, and blood gas analysis was done every 10 min. Oxygen uptake (VO2), oxygen delivery (DO2), and oxygen extraction (O2ER) were calculated and analyzed. Two different pump flows were investigated: Group 1 low assist (<3.5 L/min) and Group 2 high assist (>3.5 L/min). In both groups, the RVAS flow rates were unchanged while the pulmonary artery (PA) flow increased during exercise; also, the heart rate and right atrial pressure (RAP) increased during exercise. There were no significant differences in the 2 groups. The PA flow correlates to the heart rate during exercise. In all of the tests, the VO2 and DO2 increased during exercise. Regarding VO2, no changes were observed during the different flow conditions; however, the DO2 of Group 2 was higher than that of Group 1. Because the implantable RVAS did not have pump flow changes during the test conditions, it was necessary to incorporate a flow control system for the implantable RVAS. During exercise with an implantable RVAS rotary blood pump, incorporating the heart rate and VO2 as feedback parameters is feasible for controlling the flow rate.

Development of the NEDO implantable ventricular assist device with Gyro centrifugal pump.

The Gyro centrifugal pump, PI (permanently implantable) series, is being developed as a totally implantable artificial heart. Our final goal is to establish a "functional TAH," a totally implantable biventricular assist system (BiVAS) with centrifugal pumps. A plastic prototype pump, Gyro PI 601, was evaluated through in vitro and in vivo studies as a single ventricular assist device (VAD). Based upon these results, the pump head material was converted to a titanium alloy, and the actuator was modified. These titanium Gyro pumps, PI 700 series, also were subjected to in vitro and in vivo studies. The Gyro PI 601 and PI 700 series have the same inner dimensions and characteristics, such as the eccentric inlet port, double pivot bearing system, secondary vane, and magnet coupling system; however, the material of the PI 700 is different from the PI 601. The Gyro PI series is driven by the Vienna DC brushless motor actuator. The inlet cannula of the right ventricular assist system (RVAS) specially made for this system consists of 2 parts: a hat-shaped silicone tip biolized with gelatin and an angled wire reinforced tube made of polyvinylchloride. The pump-actuator package was implanted into 8 calves in the preperitoneal space, bypassing from the left ventricle apex to the descending aorta for the left ventricular assist system (LVAS) and bypassing the right ventricle to the main pulmonary artery for the RVAS. According to the PI 601 feasibility protocol, 2 LVAS cases were terminated after 2 weeks, and 1 LVAS case and 1 RVAS were terminated after 1 month. The PI 700 series was implanted into 4 cases: 3 LVAS cases survived for a long term, 2 of them over 200 days (72-283 days), and 1 RVAS case survived for 1 month and was terminated according to the protocol for a short-term antithrombogenic screening and system feasibility study. Regarding power consumption, the plastic pump cases demonstrated from 6.2 to 12.1 W as LVAS and 7.3 W as RVAS, the titanium pump cases showed from 10.4 to 14.2 W as LVAS and 15.8 W as RVAS. All cases exhibited low hemolysis. The renal function and the liver function were maintained normally in all cases throughout these experimental periods. In the 2 RVAS cases, pulmonary function was normally maintained. No calves demonstrated thromboembolic signs or symptoms throughout the experiments except Case 1 with the plastic pump. However, in the plastic pump cases, bilateral renal infarction was suspected in 2 cases during necropsy whereas no abnormal findings were revealed in the titanium pump cases. There were also no blood clots inside the PI 700 series. As for the 601, the explanted pumps demonstrated slight thrombus formations at the top and bottom pivots except in 1 case. The Gyro PI series, especially the PI 700 series, demonstrated superior performance, biocompatibility, antithrombogenicity and low hemolysis. Also, the durability of the actuator was demonstrated. Based on these results, this titanium centrifugal pump is suitable as an implantable LVAS and RVAS. It is likely that the Gyro PI series is a feasible component of the BiVAS functional TAH.

Development of an implantable small right ventricular assist device.

Currently, at least two permanent implantable left ventricular assist devices (LVADs) are used clinically. Unfortunately, there is no small implantable right ventricular assist device (RVAD) available, even though at least 25-30% of this patient population has right ventricular failure. If a small implantable RVAD were available, biventricular assist could support patients with right ventricular failure. A small atraumatic and antithrombogenic RVAD is being developed to meet this clinical need. This small centrifugal blood pump, the Gyro PI pump, is 6.5 cm in diameter and 4.6 cm in height and has three unique characteristics to prevent thrombus formation: (1) the double pivot bearing and magnetic coupling system enable this pump to be completely sealless; (2) the secondary vanes at the bottom of the impeller accelerate the blood flow and prevent blood stagnation; and (3) the eccentric inlet port enables the top female bearing to be embedded into the top housing and decrease blood cell trauma. The inflow conduit consists of a wire reinforced tube and a hat-shaped tip that is biolized with gelatin to create a thrombus resistant material. This conduit is directly implanted into the right ventricle, and the outflow conduit is anastomosed to the PA. The pump can be implanted inside the abdominal wall or in the thoracic cavity. Biocompatibility of this pump was proved in two calves by thrombus free implantation as an LVAD for 284 days and 200 days. Two RVAD implantations were conducted, aiming for 1-month system feasibility studies. During the month, the RVADs operated satisfactorily without any thromboembolic incident. No blood clots or abnormal findings were seen inside the pump, nor were there abnormal findings in the explanted lungs except for small areas of atelectasis. The pump flow was 3.02 +/- 0.38 L/min in calf 1 and 3.75 +/- 1.18 L/min in calf 2. The power requirement was 7.28 +/- 0.43W for calf 1 and 14.52 +/- 3.93W for calf 2. The PaO2 was 72.0 +/- 3.60 mm Hg (calf 1) and 72.0 +/- 7.63 mm Hg (calf 2); PaCO2 was 38.3 +/- 2.17 mm Hg (calf 1) and 34.1 +/- 1.95 mm Hg (calf 2); and SaO2 was 94.1 +/- 1.37% (calf1) and 95.0 +/- 1.95% (calf 2). Gas exchange via the lungs was maintained. These studies indicate that the Gyro PI pump is suitable as a single implantable RVAD, and is a feasible RVAD as a part of a BiVAD system in terms of pump performance and thrombus resistance.

First clinical experience with the DeBakey VAD continuous-axial-flow pump for bridge to transplantation.

BACKGROUND: A shortage of donor organs and increased numbers of deaths of patients on the waiting list for cardiac transplantation make mechanical circulatory support for a bridge to transplantation a standard clinical procedure. Continuous-flow rotary blood pumps offer exciting new perspectives. METHODS AND RESULTS: Two male patients (ages 44 and 65 years) suffering from end-stage left heart failure were implanted with a DeBakey VAD axial-flow pump for use as a bridge to transplant. In the initial postoperative period, the mean pump flow was 3.9+/-0.5 L/min, which equals a mean cardiac index (CI) of 2.3+/-0.2 L. min(-1). m(-2). In both patients, the early postoperative phase was characterized by a completely nonpulsatile flow profile. However, with the recovery of heart function 8 to 12 days after implantation, increasing pulse pressures became evident, and net flow rose to 4.5+/-0.6 L/min, causing an increase of mean CI up to 2.7+/-0.2 L. min(-1). m(-2). Patients were mobilized and put through regular physical training. Hemolysis stayed in the physiological range and increased only slightly from 2. 1+/-0.8 mg/dL before surgery to 3.3+/-1.8 mg/dL 6 weeks after implantation. CONCLUSIONS: The first clinical implants of the DeBakey VAD axial-flow pump have demonstrated the device to be a promising measure of bridge-to-transplant mechanical support.

The erythrocyte-perfused "working heart" model: hemodynamic and metabolic performance in comparison to crystalloid perfused hearts.

A brief period of ischemia was used to evaluate an erythrocyte-enriched Krebs-Henseleit (KH) buffer (n=8) compared to KH only (n=8) in an isolated working rabbit heart. Experimental protocol was as follows: preischemic baseline, 5 min of global ischemia followed by 45 min of reperfusion. Preischemic heart rate was identical, coronary flow was significantly lower (2.7 versus 5.6 mL/min/g wet wt, p<0.01), the other hemodynamic and biochemical values were significantly higher in erythrocyte-perfused hearts: aortic flow 23.5 versus 12.0, p<0.01; cardiac output 26.2 versus 17.6, p<0.01; all in mL/min/g wet wt; dp/dt max 1286 versus 997 mmHg/s, p<0.01; myocardial oxygen consumption 3.5 versus 2.3 micromol/min/g wet wt, p<0.05. During early reperfusion, in the erythrocyte-perfused hearts, coronary flow further increased (p<0.003), the other hemodynamic parameters returned to baseline values in both groups. High-energy phosphates showed significantly higher values (ATP 2.0+/-0.1 versus 1.3+/-0.1, p<0.05; CrP 2.0+/-0.2 versus 1.6+/-0.1, p<0.05 all in micromol/g wct wt), water content was significantly lower (81% versus 74%, p<0.05) in erythrocyte-perfused hearts. It can be concluded that the erythrocyte-perfused working heart model provides excellent oxygenation, leading to superior hemodynamic and metabolic performance. Additionally, in the erythrocyte-perfused hearts preservation of coronary flow reserve underlines the physiological competency of this preparation.

[The DeBakey VAD axial flow pump: first clinical experience with a new generation of implantable, nonpulsatile blood pumps for long-term support prior to transplantation]. / Die DeBakey VAD-Axialpumpe: Erste klinische Erfahrungen mit einer neuen Generation von implantierbaren, nonpulsatilen Blutpumpen als Langzeit-Uberbrückung bis zur Transplantation.

Because of the high frequency of acute hemodynamic deterioration in patients awaiting cardiac transplantation, mechanical techniques of circulatory support to bridge the period until transplantation have become a standard clinical procedure. Continuous-flow rotary blood pumps offer exciting new perspectives in terms of ventricular assistance and/or as a total cardiac substitute. A DeBakey VAD axial flow pump was implanted in two male patients (aged 44 and 65 years, respectively) suffering from end-stage left heart failure. In the initial postoperative period the mean flow rate of the pump was 3.9 +/- 0.5 l/min. In both patients, the early postoperative phase was characterised by a completely non-pulsatile flow profile. Two weeks after implantation and partial recovery of the natural left ventricle, increasing pulse pressures became evident and net flow increased to 4.5 +/- 0.6 l/min. Patients were mobilised and made to under-go regular physical training. Hemolysis produced by the pump was low while free haemoglobin stayed in physiological ranges, increasing only slightly from 2.1 +/- 0.8 mg/dl preoperatively to 3.0 +/- 1.5 mg/dl ten weeks after implantation. One patient was successfully transplanted on day 74 after implantation of the DeBakey VAD while the second patient is, after 110 days of pumping, still waiting for transplantation. This first experience concerning clinical implantation of the DeBakey VAD axial flow pump showed that the device is promising as a means of providing mechanical support to bridge the period until cardiac transplantation.

Microspheres based detoxification system: in vitro study and mathematical estimation of filter performance.

Because of the closed plasma (secondary) circuit in the Microspheres based Detoxification System (MDS), a convective blood purification system, the same amount of filtrated plasma is backfiltrated into the blood circuit. Therefore, there is no direct way to determine the ultrafiltrate production rate, which is an important factor of efficiency. The only possible way to estimate the filtration properties of the filter is to consider pressure values. In this study the pressure distribution in the filter was investigated in vitro. To explain the results and to calculate inaccessible parameters, a mathematical model was established which also considered the asymmetric behaviour of the filter membrane. The result was a linear pressure gradient, agreement with the measurements was reasonably good (calculated primary pressure loss differs <13% from measured value when using mean measured filter resistance as model parameter). Linear pressure distribution offers the possibility of easily calculating the filtration length, a parameter which can be used to estimate the filter condition. The comparison between calculated filtration and backfiltration rates offers an instrument of control for these values.

Development of a totally implantable biventricular bypass centrifugal blood pump system.

BACKGROUND: During the past 2 years, the development of a totally implantable biventricular bypass rotary blood pump system has been made. METHODS: An extracorporeal gyro centrifugal pump, the CIE3, was miniaturized and developed into the PI601, a totally implantable plastic pump. Two-day anatomic and hemodynamic feasibility studies demonstrated that these two pump systems were easily implantable inside a calf's abdominal wall, directly under the diaphragm. The priming volume of the pump was 20 mL, with sufficient cardiac outputs at approximately 2,000 rpm and requiring less than 10 W of power. Two-week antithrombogenic screening tests also revealed these pump systems to be quite antithrombogenic. In addition, 1-month system reliability studies demonstrated fail-safe reliable performances. RESULTS AND CONCLUSIONS: Encouraged by these preliminary studies, the PI601 model was converted to the permanently implantable titanium gyro pump PI702 model. The long-term implantations were initiated approximately 3 months ago, and two such long-term LVAD studies are currently underway with no sign of difficulty (October 10, 1997). They were followed 283 days and 72 days, respectively. Both terminated due to functional inflow obstruction. There were no blood clots or emboli at autopsy.

Blood flow in distal end-to-side anastomoses with PTFE and a venous patch: results of an in vitro flow visualisation study.

OBJECTIVES: non-physiological flow behaviour plays a significant role in the development of distal anastomotic intimal hyperplasia. To investigate flow patterns in four anastomotic types of femoral end-to-side distal bypass graft anastomoses, a flow visualisation study was performed. METHODS: transparent 1:1 casted replicas of distal vascular graft anastomoses created by conventional technique, Miller-cuff, Taylor- and Linton-patch were fabricated. A pulsatile mock circulation with a high-speed video system was constructed. Flow pattern was determined at mean Reynolds numbers 100-500. Migrations of the stagnation points on the bottom of the anastomoses at mean Reynolds numbers 100, 230, and 350 were measured. RESULTS: a vortex forms during early systole and increases to maximum systole in all anastomoses. During the diastolic phase the vortex moves in the Miller-cuff distally to the toe of the anastomosis and remains standing, while in the other anastomotic types the vortex moves proximally to the heal of the junction and breaks down. The shift of the stagnation point in the Miller-cuff was considerably smaller than in the other anastomoses. CONCLUSION: conventional, Linton and Taylor anastomoses show similar flow patterns. The Miller-cuff with its wider cavity shows lower shift of the bottom stagnation point, but a persistent washout of the anastomotic cavity, which may contribute to its reported good clinical performance.