Abstract
dc:descriptionCavitation at mechanical heart valves with it's character of impairment still represents a major task. In this dissertation -in continuation of the studies of Graf et al. -several investigations of cavitation, in particular of "severe" vapor cavitation, were conducted in order to describe the phenomenon of cavitation itself and to classify various mechanical heart valves with respect to their tendency of cavitation. For classification of mechanical heart valves, numerous tests with qualified measuring methods were carried out according to the regulations and procedures of the U.S. Food and Drug administration (FDA). Furthermore, following the results of the measurements, a model was developed for determination of time-dependent physical properties and dynamics of cavitation bubbles, such as size, pressure and temperature. In order to classify the tendency of cavitation of mechanical valves, a pulsatile hydraulic-driven circularly mock loop was used here. Beside the measurement of the relevant hemodynamic values and the acquisition of cavitation bubbles by means of a CCD-camera in combination with a flashlight-unit, the leaflet velocity of the valves were determined with a light-barrier-technique and with a laser-beam-method. In addition, numerous high resolution pressure measurements, in particular the pressure drops necessary for the initiation of cavitation (local atrium pressure drop), were performed. These pressure measurements (orbicular pressure measurements) were extended at various loading conditions over the periphery of the valves in order to get information about critical locations, where cavitation occurs more likely. For the investigation of bubble dynamics, a second pulsatile electro-magnetic-driven tester was designed and built-up. This tester allows miscellaneous parameter investigation. Here, a series of parameters and their influence on cavitation was analyzed. The parameters were split up in three groups: fluid parameters, loading parameters and valve specific parameters. For the fluid parameters, the influence of density, viscosity and temperature of the fluid (water) on the onset of cavitation was investigated in vitro. With respect to the loading parameters, a critical valve independent threshold (cavitation-threshold) of the local atrium pressure drop was found for all measured valves. Further on, a valve dependent correlation between left ventricular pressure gradient and the local atrium pressure drop was also provided. Finally, valve specific parameters were found to predict the tendency of cavitation for a specific heart valve. The combination of these parameters facilitate the validation of the tendency of cavitation. Additionally, several cavitation events were recorded with a digital high-speed video camera (up to 40.500 Frames Per Second) for all investigated heart valves and at different conditions. The images were stored and analyzed. Therefore, cavitation bubble dynamics could be examined more accurate in order to measure the time dependent bubble sizes. The implementation of a suitable model and ideal thermodynamic processes allows conclusions of the physical values of the bubbles. In particular, the high pressures and temperatures at bubble collapse, which reflect the destructive character of cavitation, could be determined. In view of the detection of cavitation bubbles in vivo, further acquisition methods (thermal image technique, light amplification) were checked. However, the acquisition technique with a digital high-speed video camera still represents the most suitable detection method of cavitation bubbles.
Degree
thesis:*- Grantor dc:publisher
- Logos-Verl
- Year dc:date
- 2003
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Eichler, Michael Johannes
- Contributors dc:contributor
-
- Rau, Günter
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger
Identifiers
dc:identifier.*- OAI identifier oai:identifier
- oai:publications.rwth-aachen.de:61969