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Biomedical subjects

K Affeld

Publications and source records attributed to K Affeld.

At least 37 records · Page 2Linked to original sources
PubMed1998

Test procedure for artificial mitral valves.

The flow curve of a valve-tester has a great influence on the performance of a valve. Usually the flow curve of the aorta is used. However, the mitral valve flow curve differs greatly from the flow curve of the aortic valve. It varies with the pulse rate and is further changed in patients with certain heart diseases. To investigate the different mitral flow conditions, ultrasonic flow curves from patients with a mechanical artificial mitral valve were analyzed. The curves show that a mitral valve prosthesis has not only to work under physiological flow conditions, but also in pathologically deviant flows. According to these results three different characteristic flow curves were selected and used to test several valves with a computer controlled valve-tester. The mean diastolic pressure difference and the whole closing behavior were influenced by the flow curve; and the differences in energy losses were particularly great. This indicates, that the flow curve must be adjusted appropriately.

Aorta↗
PubMed1998

Atherosclerotic lesions, myocardial damage and lipidograms: a multiarterial study applying an atherometric system and canonical correlation.

472 autopsy subjects were examined with the following aims: to study the association pattern of atherosclerotic lesions between different arterial sectors, the impact of serum lipid disorders (total cholesterol, HDL-c, LDL-c, VLDL-c, and triglycerides were analyzed) and the association pattern between the atherosclerotic lesions in different arterial sectors and the degree of heart damage. For morphometric analysis of the vessels (aorta, circle of Willis, coronary, renal, iliac, and femoral arteris) the atherometric system was used. The most relevant results were as follows: the lipid disorders show their greatest impact in the heart, coronary and femoral arteries and abdominal aorta, whereas the strongest correlations between the atherosclerotic lesions in different arterial sectors were found in those with anatomical continuity.

Arteries↗
PubMed1997

[A new method of ex vivo whole blood perfusion of isolated mammalian organs, exemplified by the kidney of swine].

A new method for the ex vivo perfusion of organs from large mammals is described. Gas exchange and dialysis are carried out simultaneously with a low-flux polysulfon dialysis module. The dialysate (e.g. Tyrode solution) is aerated with a mixture of oxygen and carbon dioxide to ensure gas exchange with the blood. Dialysis is carried out in a closed thermostatically controlled system. Monitoring of ultrafiltration is maintained by continuously weighing the blood reservoir and adjusting an afferent and efferent blood pump. Initial results obtained with isolated pig kidneys demonstrate the suitability of the new method for use as a model for the replacement of animal experiments. Theoretically, clinical application in the area of in vivo regional organ perfusion may also be possible.

Animals↗
PubMed1997

Technical obstacles on the road towards a permanent left ventricular assist device.

After many years of research, various left ventricular assist systems (LVADs) are now entering clinical practice and are exposed to wider application. Currently, we are seeing a change in concept: after the successful application of LVADs as a bridge to transplant, today the permanent use of these devices is attracting the attention of the scientific community. LVADs based on pulsatile blood pumps necessarily contain many discrete elements. However, by integration of parts they can be made fairly simple and safe. Thrombo-embolic complications can be reduced by better design of the valves, avoiding stagnant flow altogether.

Equipment Design↗
PubMed1995

Fluid mechanics of the stagnation point flow chamber and its platelet deposition.

The interaction of flow and thrombus generation often is a crucial question for the engineer working in the field of artificial organs. However, this interaction is only incompletely known, and quantitative data under well-defined experimental conditions are especially rare. These can be attained with the stagnation point flow chamber. This flow model applies platelet-rich plasma (PRP) as fluid. Its flow conditions are assessed with the help of computational fluid mechanics. In addition, the concept of the boundary layer is introduced, which permits assessment of the platelet flow along the wall. The results of the experiment indicate that platelets are deposited at a defined shear rate.

Animals↗
PubMed1994

A new electrohydraulic energy converter for a left ventricular assist device.

An energy converting system that can function for years without maintenance is required for the drive of a left ventricular assist device (LVAD). To meet the requirements of safety, the energy converter should have a simple design with few moving elements. The design applied herein has only one moving part and thus has greater inherent safety than competing systems. The only moving part is the rotor unit, comprised of the impeller of a centrifugal pump, the rotor of an electric motor, and the rotor of an electric axial actuator. A reversal of flow of the transmitter fluid can be achieved with an axial shift of this rotor unit. This fluid acts on the outer surface of a blood chamber and enables it to draw in blood and to expel it. Valves direct the flow of blood. The energy converter performs a flow of 12 L/min at a motor speed of 6,000 rpm against a pressure head of 115 mm Hg according to an output of the pulsatile blood pump of 5 L/min.

Electric Power Supplies↗
PubMed1994

Biomechanical tissue properties as an indicator of organ vitality prior to transplantations.

An organ's vitality prior to transplantation can be evaluated by analysis of its mechanical properties. A new apparatus was designed to measure these properties. The organ to be tested is placed in a reservoir with saline and submitted to the load of a cylindrical element. The load is applied in a stepwise mode and results in a small local deformation of the organ. This deformation is identical to the displacement of the cylinder and is measured as a function of time. This is compared to a theoretical analysis of the deformation of a viscoelastic halfspace. This theory was used to interpret the results of experiments which were carried out on eight rabbit kidneys. The instantaneous modulus of elasticity reaches a maximum within 15 minutes, then decreases and reaches a steady state after 30 minutes of warm ischemia. The method is easy to apply and appears to be useful for the quantification of an organ's vitality and in particular recognizes the level of the organ's edema before transplantation.

Animals↗
PubMed1993

Assessment of rowing efficiency.

Between one-fourth and one-third of the energy in rowing is lost to the flow of water around the blade which decreases efficiency, i.e., the ratio of effective energy to expended energy. Hitherto the assessment of this hydrodynamic rowing efficiency was difficult and could not be achieved as a function of rowing angle and time. By recording the path of the blade and the forces acting on the blade a method was found, which is practical to use and renders the hydrodynamic efficiency at each instant of the rowing action. The assessment is based on the measurement of boat velocity, angular velocity of the oar or scull, and moment exerted by the rower. These parameters are measured, digitized, and stored in the boat for later computation on shore.

Adult↗
PubMed1993

A computer controlled versatile pulse duplicator for precision testing of artificial heart valves.

Numerous devices and mock circulations have been described for the measurement of pressure loss, closure time, closing and leakage volumes and energy loss in artificial heart valves. However, all the devices have been troubled with difficulties in generating and assessing the precise flow through the valve, and problems in defining the arterial load, i.e. the artificial aorta. The new test device follows a radically different approach: a computer controlled piston forces the fluid through the test valve only--with no afterload. During systole, outflow follows a physiological curve which is identical for all types of heart valves of a given size. During diastole a mathematically defined physiological pressure difference curve is followed. Consequently, the measurements are independent of the individual machine, the lab where testing takes place, the scientist who executes the test, the time when measurements are taken and all other external influences.

Equipment Design↗
PubMed1990

Computer aided time-lapse video analysis of hepatocyte morphology during adhesion to cellulose membranes.

An investigation was performed to demonstrate that time-lapse cinematography and computer aided video analysis of cell morphology is suitable to study and compare the characteristics of hepatocytes during the adhesion process to membranes. We chose to compare ordinary cellulose Cuprophan membranes and membranes coated with collagen or fibronectin. Striking differences between uncoated cellulose and fibronectin or collagen coating were seen in the cell count per square millimeter and adhesion behaviour. On the investigated uncoated Cuprophan the hepatocytes were found to attach but not to spread whilst on collagen coated Cuprophan most of the cells spread spherically, and on fibronectin coated membranes most of the cells flattened spherically or polygonally. Time-lapse video microscopy seems to be a valuable technique for assessing the morphologic behaviour of cells in a detailed and quantitative manner in order to improve the hepatocyte culture technique in bioreactors for hybrid systems.

Animals↗