Biomedical subjects

G Rakhorst

Publications and source records attributed to G Rakhorst.

At least 37 records · Page 2Linked to original sources

PubMed2000

In vivo and in vitro experience with the PUCA-II, a single-valved pulsatile catheter-pump.

The Pulsatile Catheter (PUCA) pump is a trans-arterial pulsatile ventricular assist device that can be used for short-term left ventricular support. The separate inflow and outflow valves in the first version of the device (PUCA-I) were replaced by a single inflow/outflow valve in the latest PUCA pump version (PUCA-II). The new combined valve was tested during in vitro (mock circulation) and in vivo experiments for valve leakage, flow resistance, and thrombus formation. During the in vitro experiments a maximum valve leakage of 6% during ejection and 21% during aspiration was found. The maximum flow resistance coefficient (K) was 4. The animal experiments demonstrated that the PUCA-II could be positioned within a few minutes into the left ventricle without X-ray guidance and without using a vascular graft. Thrombi were not found in the combined valve after total pump time of 3 hours, which proved the good washout of the valve. Initial experiments to position the pump in the right ventricle through the pulmonary artery were successful and contributed to the development of a new application for the device.

Animals↗

PubMed2000

Numerical simulation of the influence of a left ventricular assist device on the cardiovascular system.

The PUCA (pulsatile catheter) pump is a left ventricular assist device (LVAD) capable of unloading the left ventricle (LV) and improving coronary flow by providing a counterpulsation effect. It consists of an extracorporeal located membrane pump, coupled to a transarterial catheter that enters the body via a superficial artery and ends in the LV. Blood is aspirated from the LV and pumped in the ascending aorta through the same catheter guided by a valve system. Timing and frequency of the PUCA pump influence its efficacy. To study the influence of several pump parameters a numerical model of the device and the circulatory system has been developed. Results of animal experiments were used to validate the model. Optimization studies resulted in a pump configuration with a stroke volume of 50 cc and pump:heart frequency mode of 1:2 that starts ejection at the beginning of diastole.

Animals↗

PubMed2000

Medical technology assessment: the use of the analytic hierarchy process as a tool for multidisciplinary evaluation of medical devices.

Most types of medical technology assessment are performed only after the technology has been developed. Consequently, they have only minor effects on changes in clinical practice. Our study introduces a new method of constructive medical technology assessment that can change the development and diffusion of a medical device to improve its later clinical effectiveness. The method, based on Saaty's Analytic Hierarchy Process, quantitatively supports discussions between various parties involved in technological development and diffusion. We applied this method in comparing a new blood pump with two competitors based on technical, medical and social requirements. These discussions changed the evaluators' perspectives, reduced diasagreements, and ended in a reliable evaluation of the pump's performance. On the basis of these results, adaptations were derived which improved the design and diffusion of the blood pump. This application shows the adequate potential of our method to steer technological development and diffusion of artificial organs.

Decision Making↗

PubMed2000

Mechanical circulatory support systems--a review.

Congestive Heart Failure (CHF) is a major health problem with a high mortality rate. Its ultimate therapy, heart transplantation, is limited by the shortage of donor hearts. Since decades researchers have been working to solve this problem by developing Mechanical Circulatory Support Systems (MCSS) that can replace or assist the failing heart. Short-term and intermediate-term ventricular assist devices are used nowadays frequently to bridge patients with severe heart failure to recovery. Long-term ventricular assist devices (VADs) and Total Artificial Hearts (TAHs) are used increasingly as a bridge to heart transplantations or as permanent circulatory support in patients with end-stage heart failure that are contraindicated for heart transplantation. The early TAHs and VADs were mainly driven from an external pneumatic drive unit. The latest generation TAHs and long-term assist devices are electrically powered, ultracompact, totally implantable, and have small wearable drive/control consoles, allowing patients to return to their daily activities. The article categorizes and reviews the development of MCSS, highlights the medical indications and contraindications of pump implantation, advantages and disadvantages of the various systems, and results of animal and clinical studies.

Adult↗

PubMed1999

Biocompatibility of a novel tissue connector for fixation of tracheostoma valves and shunt valves.

Rehabilitation after laryngectomy often includes the use of a shunt valve and a tracheostoma valve to restore voice. To improve the fixation method of these valves, a new tissue connector has been developed, basically consisting of a ring that will be integrated into surrounding tracheal soft tissue. The valves can be placed in the ring. To test the principle of the tissue connector, a prototype consisting of a subcutaneous polypropylene mesh and a percutaneous titanium stylus was implanted into the backskin of 10 rats by a two-stage surgical procedure. We reasoned that if a firm connection can be realized with the skin, a firm connection with the trachea will also be possible. The subcutaneous part was implanted first, followed by the percutaneous part after 6 weeks. The complete tissue connector with surrounding tissue was removed 8 weeks later and examined histologically. The principle of the new tissue connector proved to be effective: hardly any epithelial downgrowth appeared, and adhesion of soft tissue was demonstrated. No infection or severe inflammation reaction was detected. The tissue connector seems appropriate for its intended use.

Administration, Cutaneous↗

PubMed1999

Numerical simulation of the pulsating catheter pump: A left ventricular assist device.

The pulsating catheter (PUCA) pump, a left ventricular assist device, consists of a hydraulically or pneumatically driven membrane pump, extracorporeally placed and mounted to a valved catheter. The catheter is introduced into an easily accessible artery and positioned with its distal tip in the left ventricle. Blood is aspirated from the left ventricle during systole and ejected into the ascending aorta during diastole. A numerical model of the PUCA pump has been developed to determine the internal diameter of the PUCA pump catheter that allows a certain blood flow. The model considers a limitation of mechanical blood damage and determines the accompanying pressure and flow profile for driving the pump. For a flow of 5 L/min, a catheter with an internal diameter of at least 6. 95 mm is required. For 3 L/min, the minimal diameter is 5.50 mm. The latter catheter can be introduced in the axillary artery, the former via the aorta during an open thorax surgical procedure. To validate the numerical model, 2 different PUCA pump configurations were tested in vitro. Results showed a good resemblance between model and in vitro behavior of the PUCA pump.

Aorta↗

PubMed1999

Evaluation of the optimal driving mode during left ventricular assist with pulsatile catheter pump in calves.

The pulsatile catheter (PUCA) pump, a left ventricular assist device, was tested during acute experiments in calves using asynchronous and ECG-synchronous assist modes. The aim of the study is to compare ECG-synchronous and asynchronous assist and to find the optimal driving mode for the PUCA pump with respect to left ventricular myocardial oxygen consumption (LV MVO2), pump flow, and coronary flow. LV MVO2 decreased significantly during the asynchronous (from 7.77 to 6.46 ml/min/100 g) as well as during the ECG-synchronous mode (from 8.88 to 7.84 ml/min/100 g). The pump flow was highest during the ECG-synchronous assist (2.94 L/min), followed by the asynchronous assist (2.79 L/min). The peak coronary flow depended strongly on pump ejection timing and showed the best flow patterns during the ECG-synchronous assist. We concluded that for PUCA pump support both asynchronous and ECG-synchronous assists significantly reduce LV MVO2 and that the pump flow generated is enough to maintain the systemic circulation. However, we find the ECG-synchronous mode preferable because this mode optimizes coronary flow patterns at the same time.

Animals↗

PubMed1999

Time-related contact angle measurements with human plasma on biomaterial surfaces.

Axisymmetric drop shape analysis by profile (ADSA-P) was used to assess in time contact angle changes of human plasma drops placed on four different biomaterials. Results were related with conventional blood compatibility measurements: albumin adsorption, fibrinogen adsorption and platelet adhesion. While contact angle measurements with water are material-related but constant in time, contact angle measurements with plasma changed over time owing to protein adsorption on the solid-liquid interface. The contact medium plasma did not influence the initial contact angle. Contact angles on PDMS decreased most in time (41 degrees) and demonstrated highest levels of conventionally measured albumin and fibrinogen adsorption and platelet adhesion. PTFE, with the lowest contact angle decrease over a 500 minutes period (19 degrees), showed low fibrinogen and albumin adsorption as well as low platelet adhesion. PU and HDPE demonstrated almost similar initial contact angles with plasma and contact angle decreases (26 and 27 degrees), intermediate protein adsorption, and platelet adhesion. We conclude that biocompatibility properties of the tested materials may be more related to the behaviour of their contact angles in time, than to the initial hydrophobic or hydrophilic state.

Adsorption↗

PubMed1998

Measuring changes in step parameters during an exhausting running exercise.

A treadmill with four force transducers was used to analyze gait during running. 39 volunteers ran on a treadmill until they were exhausted. The step parameter variances showed a very distinct change in time. 17 subjects showed a sudden increase in variance. The other 22 subjects did not show such an effect, probably because they stopped too soon. This was confirmed by lactate measurements. In conclusion, the described treadmill is able to register continuously the running pattern of healthy volunteers. During an exhausting exercise, the running pattern becomes irregular in the last phase of the exercise. Copyright 1998 Elsevier Science B.V.

Journal Article↗

PubMed1998

Skeletal muscle perfusion measured by positron emission tomography during exercise.

The applicability of H215O-positron emission tomographic (PET) imaging for the assessment of skeletal muscle perfusion during exercise was investigated in five healthy subjects performing intermittent isometric contractions on a calf ergometer. The workload of the left calf muscles was kept constant in all exercises, while that of the right calf muscles was varied. During exercise H215O distribution in the calf muscles was measured by PET. Radioactivity measured in the left calf muscles was used as a reference for the radioactivity measured in the right calf muscles. In all studies, muscles were delineated by uptake of radioactivity. Four subjects demonstrated high radioactivity in the gastrocnemius medialis muscle, in one subject high radioactivity was distributed over the triceps surae muscles. The observed muscles demonstrated also local foci of radioactivity indicating regionally enhanced tissue perfusion. The right-left ratio of radioactivity in the active muscles increased as a function of the load. We conclude that inter- and intramuscle perfusion differences can be measured during exercise by H215O-PET imaging.

Adult↗

PubMed1998

Evaluation of a porcine internal mammary artery (No-React II) as a small-diameter conduit.

BACKGROUND: The patency of biologic small-diameter vascular grafts in the aortocoronary position is still unsatisfactory. Most of the studies suggest that xenografts are to be avoided as an aortocoronary bypass. METHODS: The porcine internal mammary artery treated by the No-React II procedure was developed for use as an alternative coronary artery bypass conduit. The attempt of this study was to evaluate the patency and histologic changes of the porcine internal mammary artery in animals. Five calves underwent coronary artery bypass grafting with a porcine internal mammary artery graft to the right coronary artery. After euthanasia of the animals 103 days later, the samples of these grafts were studied morphologically for patency, structural changes, calcifications, and inflammatory and immunologic response. RESULTS: One animal died during the procedure as result of acute thrombosis of the porcine internal mammary artery graft. In the other 4 animals all grafts became occluded. In the histologic sections of the grafts we noted multiple calcifications and a host-graft immunologic reaction (severe chronic rejection). CONCLUSIONS: The present study demonstrates a very poor experience with the porcine internal mammary artery (No-React II) conduit. We do not recommend this prosthesis for clinical use in humans.

Animals↗

PubMed1997

Analysis of the mechanical behavior of the Nijdam voice prosthesis.

The valveless Nijdam prosthesis is a new voice prosthesis for laryngectomized patients using tracheoesophageal speech. An "umbrella-like hat" covers the esophageal side of the tracheoesophageal fistula and is deformed during speech by air pressure. To decrease pressure loss during speech, a good understanding of the mechanical behavior is essential. In the present study, the Finite Element Method (FEM), used in engineering to analyze the mechanical behavior of complex structures, was applied to analyze eight possible improvements of the Nijdam prosthesis. This study found that, during speech, deformation of hat and soft tissue occur. Distinct differences in the hat's deformation of the eight models also were found. It is concluded that complex structures like the Nijdam prosthesis can be analyzed by FEM. An optimal model was found to decrease pressure loss while stresses in the device remain safe.

Equipment Design↗

PubMed1997

Development of a numerical simulation model of the cardiovascular system.

A numerical simulation model of the cardiovascular system has been developed. It consists of a model of the left atrium, the left ventricle, the coronary vascular system, the aorta, the arterial system, and the venous system. The input of the complete model is the elastance (pressure/volume ratio) developed by the left ventricle. The shape of this elastance is constant in different circumstances. Left ventricular (LV) myocardial oxygen consumption and the amount of oxygen offered to the left ventricle can be calculated with the model. The model has been validated using data from a patient suffering from coronary artery disease. The measured clinical hemodynamical waveforms could be fitted to those generated by the model. With the numerical simulation model, it is possible to predict the functioning of the left ventricle under different circumstances. This makes it possible to study in vitro various pathological clinical situations.

Aorta↗

PubMed1997

Blood interaction with a Bioline heparin coated HIA-VAD: a study on calves.

The blood compatibility of ventricular assist devices developed by the Helmholtz Institute Aachen (HA-VAD's) was tested on calves. Seven calves received a non-coated HIA-VAD (control) and three a Bioline heparin coated device. The circulatory support of these HIA-VAD's lasted one week. Mechanical blood cell trauma estimated by hematocrit (Hct), hemoglobin (total Hb) and free plasma hemoglobin (free Hb) levels did not differ in either group. All HIA-VAD's in the control group remained thrombus free, except on one occasion when an inflow cannula was obstructed by a thrombus located in the tip. After circulatory support, the animals in this group seemed clinically healthy. However, thrombus formation was observed in the three heparin coated HIA-VAD's. One animal in this group died from complications after re-operation for pneumothorax on the fifth day of support, whereas the other two animals seemed clinically healthy. In these three animals, a strong decrease in platelet numbers was measured even after 24 hours of support which recovered after 72 hours. This decrease in platelet numbers was associated with a lower degree of platelet aggregation ability stimulated by ADP (p < 0.05). Fibrin(ogen) degradation products (FDP) increased significantly immediately after the implantation procedure (p < 0.05). Fibrinogen levels initially decreased during the implantation procedure, but increased thereafter in both groups. The FDP levels remained high in this group, although the FDP levels in both groups were decreased after the implantation procedure. The ex vivo measured circulating heparin levels were lower in the heparin coated HIV-VAD group despite the equally administrated heparin doses in both animal groups. No differences were measured in either group with regard to white blood cell (WBC) numbers and complement hemolytic activity (CH50). Despite these hemostatic changes, no mechanical trauma could be demonstrated after seven days of circulatory support.

Animals↗

PubMed1997

Development of a new introduction technique for the pulsatile catheter pump.

The pulsatile catheter (PUCA) pump is an intraventricular blood pump that can be introduced into the left ventricular cavity through a superficial artery (transarterially) or directly through the thoracic aorta during open chest conditions. When positioned, the pump aspirates blood from the left ventricle and transports it into the ascending aorta. A pneumatic driving system allows the blood to be ejected in early diastole of every second or third heart beat. The main goal of this study was to develop an easy, fast, safe surgical introduction technique. Four different means of catheter introduction were tested in 20 acute open chest experiments with calves: introduction without any guidance at all, introduction by x-ray guidance only, introduction using a guide wire plus x-ray guidance, and introduction using a guiding pressure catheter. Introducing the PUCA pump catheter into the left ventricular cavity using a pigtail guiding pressure catheter proved to be easy. The large bore pump catheter followed the guiding catheter and passed the aortic valve well. The position of the PUCA pump could be monitored from the pressure patterns derived from the guiding catheter.

Animals↗

PubMed1997

Numerical modelling of blood flow behaviour in the valved catheter of the PUCA-pump, a LVAD.

Mechanical heart assistance, performed by the PUlsatile CAtheter (PUCA) pump, chronologically takes place by sucking blood from the left ventricle and ejecting it into the ascending aorta. Within the pump activity the problem of hemolysis and clotting is encountered. In this study the influence of valve geometry on blood cell damage and stagnant zones has been investigated. A variable valve length coupled to a catheter ejection gap and a variable valve angle have been studied. In case of the studied valve, optimal parameter values have been determined. Compared to small catheter ejection gaps with a corresponding valve length, blood damage is found to be less for large ejection gaps with corresponding valve dimensions. In systole a valve positioned in a 0 degree angle proves to be best, whereas in diastole a +20 degree angle is preferable. Because the system is operating in both systole and diastole, a 0 degree angle valve is applied.

Blood Coagulation↗

PubMed1996

Biological evaluation of mechanical circulatory support systems in calves.

Data from animal experiments with mechanical circulatory support systems (MCSS) performed in Groningen and Marseille over the past years were used to obtain normal values of hematological, coagulation, rheological and blood chemistry parameters in calves. These parameters were divided between two groups: a limited number of parameters necessary to assess biocompatibility properties of MCSS quickly and a more extensive number of parameters suitable for more detailed biological evaluation of blood pumps. All applied tests can be examined in calf blood as well as in human blood. Parameters were selected on clinical relevance and usefulness for standardization procedures. The obtained data were compared with normal values in human beings derived from the literature.

Animals↗

PubMed1994

In-vivo evaluation of the "HIA-VAD": a new German ventricular assist device.

Helmholtz Ventricular Assist Devices (VAD) are pneumatically driven polyurethane membrane pumps with various volumes. The pumps are placed paracorporeally and connected with commercially available cannulas between the left atrium and aorta (left ventricular assist device) and/or right atrium and pulmonary artery (right ventricular assist device, bi-ventricular assist device). The pumps can be driven with a stand-alone driving system or with a Helmholtz IABP-console interface. Seventeen animal experiments (on calves) with Helmholtz VAD's were performed to evaluate experimental protocols, to optimize surgical techniques, and to improve design and manufacturing techniques. Blood chemistry and cell counts demonstrated that the tested HIA-70 produces low mechanical blood damage. In the course of the animal experiments the Helmholtz VAD's were made totally transparent, whereby they became easy to de-air, efficient, and affordable.

Animals↗