Biomedical subjects

G Rakhorst

Publications and source records attributed to G Rakhorst.

46 records · Page 3Linked to original sources

PubMed1994

Design improvements of the HIA-VAD based on animal experiments.

Since 1990, development of the Helmholtz-Institute at Aachen ventricular assist device (HIA-VAD) was mainly based on animal tests performed at the University of Groningen. Although various in vitro tests had been performed previously, animal testing resulted in significant improvements of the HIA-VAD with regard to hemodynamics and pump handling. The most important design improvement was a new trileaflet polyurethane valve, which was designed as a blood-pump valve with an emphasis on opening behavior and flow resistance. Excellent hydrodynamic performance and sufficient durability of this new valve were confirmed by various in vitro tests. Further design and manufacturing improvements resulted in a completely transparent pump, which can be easily deaired and optically controlled. Final pump design was evaluated during subsequent animal tests, and the results are very promising in view of an efficient cardiac support system.

Animals↗

PubMed1994

In vitro evaluation of the influence of pulsatile intraventricular pumping on ventricular pressure patterns.

The Pulsatile catheter (PUCA) pump consists of a single port membrane pump connected to an indwelling valved catheter. This so-called transarterial blood pump was originally designed to be introduced through a superficial artery into the left ventricular cavity to pump blood from the left ventricle into the ascending aorta. By introducing the catheter directly into the thoracic aorta or the pulmonary artery, the possibility is created of applying large-diameter catheter PUCA pumps as left, right, or biventricular assist devices (LVAD, RVAD, or BIVAD) without damaging any of the structures of the heart. The pump performance of an 8 mm PUCA pump prototype (internal diameter catheter, 8 mm; catheter length, 40 cm; stroke volume, 80 ml) was studied in a mock circulation to investigate the influence of pulsatile intraventricular pumping on ventricular pressure patterns. The pumping mode of the PUCA pump was changed from approximately 1:1 ([n + 1]:n) to 1:2 ([1/2n + 1]:n) and 1:3 ([1/3n + 1]:n) in relation to the frequency of a ventricle-simulating membrane pump. Apart from the pumping mode, timing of the PUCA pump driving system (ejection phase) seems to be crucial in obtaining optimal unloading of the ventricle.

Aorta↗

PubMed1994

Myocardial protection during coronary angioplasty with autoperfusion and forced perfusion: an in vitro comparison.

During coronary angioplasty, perfusion distal to the inflated angioplasty balloon can be maintained with autoperfusion balloon catheters and coronary perfusion pumps. The blood flow rates through the autoperfusion balloon catheters and the flow rates achieved with a perfusion pump were compared in vitro with fresh human blood at 37 degrees C. In a specially designed system, blood flow rates through Stack autoperfusion balloon catheters were measured at 40, 60 and 80 mmHg continuous pressure. In another system, driving pressures were measured during perfusion with the pump, through a specially designed forced perfusion catheter at 20, 40 and 60 ml/min flow. The pressure applied in the autoperfusion experiments was converted into atmospheres (atm) to facilitate comparison with the driving pressures measured during pumping (1 mmHg = 1.316 x 10(-3) atm). Mean flow rates through the autoperfusion balloon catheters were: 46 ml/min at 0.05 atm, 66 ml/min at 0.09 atm and 75 ml/min at 0.1 atm. Mean pressures during pumping were: 1.8 atm at 20 ml/min, 3.5 atm at 40 ml/min, 5 atm at 60 ml/min. Due to the phasic nature of coronary blood flow, the flow through autoperfusion balloons is generally lower than the minimum required for adequate myocardial protection (= 60 ml/min). Thus, autoperfusion balloon catheters are simpler and cheaper devices than perfusion pumps, but generally they are not able to provide adequate myocardial protection.

Angioplasty, Balloon, Coronary↗

PubMed1994

Design and test of a hands-free tracheostoma valve to improve the rehabilitation process after laryngectomy.

The surgical treatment of throat cancer often requires total laryngectomy. The necessary tracheostoma attracts attention, especially during speech, when one must close it manually to force air into the esophagus. To avoid this manual control, several devices have been developed. These must be placed in or around the tracheostoma and possess a valve which closes with a large air flow value. Most devices have a major drawback; coughing calls for manual adaptation, which again attracts attention. A new hands-free tracheostoma valve has been developed. The device consists of two magnetic valves, one which closes the outflow to allow speech, and one which opens to cough. Prototypes were tested in a physical model. Air flow resistance and closing pressures of the speech valve proved to be comparable to those of existing devices. Patients were enthusiastic about the new approach, even though air leakage sometimes occurred.

Humans↗

PubMed1993

Transneuronal viral labelling of rat heart left ventricle controlling pathways.

Retrograde transneuronal viral labelling and immunocytochemical methods were used for revealing neuronal networks controlling the left ventricle myocardium of the rat heart. After injections of 1 microliter pseudorabies virus solution (3 x 10(6) PFU ml-1) into the left ventricle, infected orthosympathetic preganglionic cells were found in the intermediolateral cell groups of the first 6 thoracic spinal segments. Preganglionic parasympathetic neurones were seen both in the nucleus ambiguus/retro-ambiguus area and the dorsal motor vagus nucleus. Large numbers of infected projecting interneurones were found in the rostral, caudal and medial parts of the ventral medulla oblongata, the Kölliker-Fuse nucleus and catecholaminergic cell group A5 and in the paraventricular hypothalamic nucleus.

Animals↗

PubMed1993

In vitro evaluation of blood flow through autoperfusion balloon catheters.

The effective flow rates with human blood through an autoperfusion catheter cannot be monitored in vivo and have not been experimentally determined in vitro. The manufacturers (Advanced Cardiovascular Systems [ACS], Temecula, CA) have suggested that "the flow rate" through the Stack over the wire and the RX-60 monorail catheter is 60 ml/min with a pressure gradient of 80 mmHg. We measured human blood flow rates in vitro through these catheters under different continuous pressure regimens (between 40 and 120 mmHg), with varying hematocrit levels (between 25% and 62%). Measured blood flows at a gradient of 80 mmHg were found to vary from 32 to 65 cc/min, with hematocrit levels of 62-25%. Minor variations in the circuitry, besides the viscosity of the medium, cause significant changes in observed flow rates (such as kinking of the catheter and blood sedimentation). In vitro determinations of blood flows cannot automatically be transferred to the in vivo condition, primarily because in vitro determinations do not account for the systolic intramural pressure increase (which may overcome the aortic pressure). If such a phenomenon is also considered, then the in vitro flow rates reported here should be multiplied by a factor of 0.40-0.60 to determine effective in vivo flow rates. Such information is relevant for the clinical operator of angioplasty, especially in the treatment of patients at high risk for undergoing percutaneous transluminal coronary angioplasty.

Angioplasty, Balloon, Coronary↗

PubMed1993

The PUCA pump: a left ventricular assist device.

Left ventricular assist devices (LVADs) that are being used clinically still have specific drawbacks. Therefore, a new concept for mechanical circulatory support was developed, the pulsatile catheter (PUCA) pump. It consists of an extracorporeally placed, pneumatically driven membrane pump that is connected 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 and ejected into the ascending aorta. Potential advantages of the catheter pump are its simple design and its fast application with minimal surgery. Preliminary in vitro tests with a first prototype showed that it is possible to create a pulsatile flow of 3 L/min and proved that further developing the PUCA pump will be worthwhile.

Heart-Assist Devices↗

PubMed1992

Electrocardiographic findings in calves with experimentally induced right ventricular hypertrophy.

Surface electrocardiograms (ECG) from 20 clinically healthy calves and 3 calves with experimentally induced right ventricular hypertrophy (RVH) were studied to assess the influence of RVH on the configuration of the bovine ECG. In the calves with RVH decreased cardiac axes and increased voltages of QRS complexes in leads I and aVL (extremity leads) and in bv1 and bv5 (precordial leads) were found. Using generally accepted human electrocardiographic theories, these findings could be explained from geometrical differences between the hearts of normal calves and the hearts of calves with RVH.

Animals↗

PubMedDate not supplied

Hypothermic machine perfusion of the liver and the critical balance between perfusion pressures and endothelial injury.

Hypothermic machine perfusion (HMP) provides better protection against cold ischemic injury than cold storage in marginal donor kidneys. Also, in liver transplantation a switch from static cold storage to HMP could be beneficial as it would allow longer preservation times and the use of marginal donors. A critical question concerning application of HMP in liver preservation is the crucial balance between perfusion pressure and occurrence of endothelial injury. Rat livers were cold-perfused for 24 hours to study perfusion pressures for both hepatic artery and portal vein. Cold storage served as control and was compared to HMP-preserved livers using a mean arterial perfusion pressure of 25 mm Hg and a portal perfusion pressure of 4 mm Hg (25% of normothermic liver circulation) and to HMP at 50 mm Hg and 8 mm Hg perfusion, respectively (50% of normothermic liver circulation). UW solution was enriched with 14.9 micromol/L propidium iodide (PI) to stain for dead cells and with an additional 13.5 micromol/L acridine orange to stain for viable hepatocytes. A low PI-positive cell count was found using HMP at 25% of normal circulation compared to cold storage. The PI count was high for the HMP group perfused at just 50% of normal circulation compared to HMP at 25% and compared to cold storage. In summary, for liver HMP, perfusion at 25% showed complete perfusion with minimal cellular injury. HMP using perfusion pressures of 25 mm Hg for the hepatic artery and 4 mm Hg for the portal vein is feasible without induction of endothelial injury.

Animals↗

PubMedDate not supplied

A novel implantable electromechanical ventricular assist device. First acute animal testing.

A novel ventricular assist device (HIA-EMLVAD-AT1, Helmholtz Institute Aachen-Electromechanical Left Ventricular Assist Device-Animal Test Version 1), driven by a uniformly and unidirectionally rotating actuator and a patented hypocycloidic pusherplate displacement gear unit, was developed and tested in an acute animal experiment. The excellent free filling behavior of the pump chamber with a stroke volume of 65 ml is obtained by a 2:3 ejection-filling time relationship. The uniform motor rotation facilitates simple sensorless pre and afterload detection by motor current analysis. In contrast to common apical cannulation, the inlet cannula was placed via the left atrium through the mitral valve into the left ventricle. This connection mode is preferable for left ventricular recovery and preservation. Left atrial, left ventricular, and aortic pressure curves, as well as pulmonary artery flow data, were obtained. The data show very effective unloading of the natural ventricle and demonstrate the feasibility of this novel assist device. Directions for further improvement of technical features were also identified.

Animals↗