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.

[Testing the hydrodynamic properties of heart valve prostheses with a new test apparatus]. / Testung hydrodynamischer Eigenschaften von Herzklappenprothesen mit einem neuen Prüfstand.

A new test apparatus for the testing of artificial heart valves makes it possible to realize both physiological flow through the valve during the flow period, and physiological pressure differences across the artificial valve during the closing phase, both for aortic and mitral valve positions, with freely selectable stroke volume and heart frequency. The major hydraulic parameters of the valve are measured directly (pressure drop, closing volume and closing time, leakage volume) or are calculated (e. g. energy loss). In association with the demonstration of the suitability of the HKP+ test apparatus for the measurement of hydraulic parameters in accordance with ISO 5840, the hydraulic properties of various types and sizes of valve with respect to pressure drop (resistance), together with their closing behaviour and leakage flow, are described for different fluids, and the correlations shown.

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.

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.

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.