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Biomedical subjects

K Affeld

Publications and source records attributed to K Affeld.

78 records · Page 5Linked to original sources
PubMedDate not supplied

The use of image processing in the investigation of artificial heart valve flow.

A circulation model enlarged ten times with a likewise enlarged model of the artificial heartvalve leads to a very slow motion of the fluid. Many methods of flow visualization can therefore be applied. The particle method has been chosen as the most appropriate for further processing. The flow is videotaped, two consecutive frames are selected and with the help of image processing the vector field, the streamlines and the velocity profiles are computed and drawn.

Blood Flow Velocity↗
PubMedDate not supplied

Novel cardiac assist valve with a purge flow in the valve sinus.

Clinical applications of cardiac assist systems continue to have a severe problem, that of thromboembolic complications. The problem originates mainly at the valves, which are usually made of a antithrombogenic material, such as bovine pericardium. However, the valve housing is made of a less suitable material, and wherever the blood flow is stagnant, a thrombus is likely to form. Such stagnant blood flow is found in the space between the housing of the valve and the leaflets, in the sinuses. Consequently, thrombi often are generated in the sinuses. The novel valve design presented in this article avoids the formation of the stagnation zone in the sinuses by a purge flow. This flow is taken from the main flow through the valve and is directed into each sinus of the res purges the sinuses. The purge flow effect is investigated with an experimental method in which the sinus is filled with dye, and washout during the valve action is observed and recorded on videotape, which is compared with washout in a valve without a purge flow. In addition, the purge flow effect is investigated by computational fluid dynamics. Both methods show that the purge flow effectively increases fluid exchange in the sinuses.

Computer Simulation↗
PubMedDate not supplied

A new valve for the treatment of hydrocephalus.

Presently available hydrocephalus valves still are not perfect. There are two major drawbacks: They have a tendency to clog and do not take into account the posture of the patient. The latter results in an intracranial pressure which is either too high or too low. To avoid these problems a new valve was designed which is described in this article. It introduces a pressure control: The force on the actual valve seat is augmented and balanced by a powerful spring. The large forces generated this way are able to overcome sticking forces due to fibrin or cellular debris. The valve functions well even with viscous and sticky cerebrospinal fluid (CSF). This mechanism maintains the pressure almost independent of the composition of the CSF. A valve insensitive to the posture of the patient can create an overdrainage, causing related problems such as subdural hygromas, slit ventricle syndrome, and consecutive proximal catheter obstruction. This is avoided by the valve presented here. It has two different pressure controllers: one designed for the supine position and another designed for the upright position of the patient. When the patient stands up or sits up, the pressure controller for the horizontal position is shut off by a gravity-activated sphere, and the drainage of CSF is directed into the appropriate controller for the upright position. In this way, the change of the hydrostatic differential pressure between the ventricles and the peritoneal cavity is taken into account and the intracranial pressure remains within physiological values. Laboratory investigations have shown that the new valve performs as designed.

Cerebrospinal Fluid↗