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Prosthetic heart valves (PHVs) are routinely used to replace defective native heart valves in patients suffering from valvular heart diseases. While PHVs are life-saving, they have limitations in performance and durability. Therefore, it is crucial to rigorously test and evaluate their designs before their implantation. PHVs are commonly examined using cardiovascular testing equipment that measures the hemodynamic characteristics of the valves, while also providing the opportunity for their visual assessment by collecting high-quality videos. Such visual data, obtained during mechanical simulations, are typically assessed by human experts, which is a tedious and error-prone task. Automatic assessment of PHVs from video data is possible, however, there are some challenges that need to be addressed. The evolution of the valve orifice area during one cardiac cycle is one of the key quality metrics for PHV visual assessment. Very fast motion of the valve’s leaflets is one of the challenges while dealing with the visual data. Nevertheless, the more important issue lies in the orifice being partly occluded by the inner side of the leaflets or inaccurately depicted due to its transparency. This issue has not been addressed in the literature. In the first part of the thesis, a novel orifice area segmentation algorithm is proposed for automatic quantitative performance analysis of PHVs, based on the leaflet free edges to accurately extract the actual orifice area. The video frames, recorded by a high-speed digital camera during in vitro simulations, are used to obtain an initial estimate of the orifice area using active contouring methods. This initial estimate is then refined to detect leaflet free edges via a curve extension scheme and considering brightness and smoothness criteria. Both of the developed algorithms are later modified for addressing challenges related to the fast motion of leaflets, automatic detection of the beginning of a cycle, and overly bright spots and narrow areas. Evaluation on several cases including three different PHVs and with different video qualities demonstrated the effectiveness of the proposed approach and adjustments in detecting valve leaflet free edges and extraction of the actual orifice area. The proposed method significantly outperforms a baseline algorithm both in terms of valve design and computer vision evaluation metrics. It can also cope with lower quality videos and is better at processing frames with a very small opening, which is a very crucial quality for determining the malfunctions related to improper closing of the valves. In the second part of the thesis, the above-mentioned segmented orifice area is used for the durability estimation of the prosthetic heart valves. More than 50% of PHVs encounter a structural failure within 15 years post-implantation mostly because of the excessive localized forces on some areas. We perform a computer vision (CV)-based analysis of the visual symmetry of valve leaflet motion and investigate its correlation with the functional symmetry of the valve. We hypothesize that an asymmetry in the valve leaflet motion will generate an asymmetry in the flow patterns, resulting in added local stress and forces on some of the leaflets. Two pair-wise leaflet symmetry scores are proposed based on diagonals of orthogonal projection matrices (DOPM) and dynamic time warping (DTW) techniques. The proposed symmetry score profiles are compared with fluid dynamic parameters (vorticity and velocity values) at the leaflet borders, obtained from valve-specific numerical simulations. Experiments on four cases including different tricuspid PHV designs yielded promising results, with DTW scores showing good coherence with respect to the simulations, which confirms our hypothesis. The established link between visual and functional symmetry opens the door for durability estimation of prosthetic heart valves using computer vision techniques. / Graduate

Bileaflet mechanical heart valves (BMHVs), though a life-saving tool in treating heart valve disease, are often associated with serious complications, including a high risk of hemolysis, platelet activation, and thromboembolism. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation. Regions of flow stasis in the valve vicinity may also allow activated platelets to aggregate and form thrombus. This thesis addresses the hypothesis that passive flow control may have the potential to reduce flow-induced thrombogenicity by altering the fluid mechanics of bileaflet mechanical heart valves. To test this hypothesis, a steady model of the regurgitant b-datum line jet was developed and studied. This model served as a test bed for various vortex generator array designs. The fluid mechanics of the b-datum line jet model was investigated with flow visualization and particle image velocimetry. In vitro tests with whole human blood were performed with and without the vortex generators in order to determine how the presence of the passive flow control affected the propensity of the blood to form thrombus. An effort was then made to correlate the fluid mechanics of the jet model with the procoagulant potential results from the blood experiments. The effect of the vortex generators on the fluid mechanics of the valve under physiologic pulsatile conditions was also investigated via flow visualization in the Georgia Tech Left Heart Simulator. By studying a steady model of the regurgitant b-datum line jet, it was found, using an in vitro system with whole human blood, that the presence of vortex generators significantly decreased the blood's propensity for thrombus formation. The potential of applying passive flow control to cardiovascular hardware in order to mitigate the injurious effects of shear-induced platelet activation is thus demonstrated. The investigation into the effect of vortex generators on the fluid mechanics of the b-datum line jet showed that the jet oscillated aperiodically and that the effect of the applied flow control was played out at both the scale of the chamber (large-scale) and on the scale of the vortex generator fins (small-scale). On the large scale, the presence of vortex generators appeared to decrease the magnitude or frequency of jet oscillation, thereby stabilizing the jet. After removing the effect of the large-scale oscillations via phase averaging, the effect of the vortex generators on the small scale was examined. On the small scale, the jet without flow control was found to have higher levels of velocity RMS, particularly on the jet periphery, and higher levels of Reynolds shear stress. It is proposed that the vortex generators effect this change by generating vorticity in the plane of the jet. This vorticity is theorized to stabilize the jet, delaying roll-up of the jet shear layer which occurs via the Kelvin-Helmholtz instability. The method by which the vortex generators acted on the fluid mechanics of the steady jet system to decrease the blood's procoagulant potential was investigated via flow visualization and DPIV. The results from these studies implicate two possible mechanisms by which the vortex generators may act. First, the peak turbulent shear stresses in the jet were reduced by 10-20% with the application of vortex generators. Even if only a few platelets were activated in each passage through the valve, the cumulative effect of this difference in peak stresses after many passes would be greatly magnified. Thus, this reduction in turbulent shear stresses may be sufficient to explain the change seen in the blood's procoagulant potential with the application of passive flow control. It is suspected, though, that the second mechanism is dominant. The flow fields revealed that the presence of the vortex generators delayed or prevented the roll-up of the Kelvin-Helmholtz instability in the b-datum jet's shear layers into discrete vortices. By doing so, it is thought that opportunities for the interaction of activated and unactivated platelets entrained in these vortices were prevented, thereby inhibiting further propagation of the coagulation cascade. Even if the rate at which platelets were activated was similar for cases with and without flow control, it seems that the flow fields experienced by the platelets subsequent to activation can determine the level of procoagulant potential. Under the steady conditions observed in this experiment, the jet influenced by vortex generators was thus shown to induce significantly lower levels of procoagulant potential.

This thesis is focused on the nursing care for patient after valvular defects surgery. The aim of this final paper is to ascertain the principles of specialized nursing care for patient after valvular defects surgery, analyse the condition of written standards for providing aftercare to patients who underwent valvular defects surgery, or the state of the nursing protocols in specialized nursing care. The purpose of qualitative - observational research in providing specialized nursing care is to find an answer to the question of whether the specifics of nursing care in Prague cardiac centres are significantly different. The theoretical section contains chapters describing cardiac centres, the history of surgical treatment of heart valves, and the most common valvular heart defects in adulthood. In the theoretical section of this study, I focus in detail on the nursing care for patients following cardiac procedure, ensuring not to forget the monitoring of physiological functions, artificial pulmonary ventilation, and immediate position after elective cardiac surgery. The empirical section is divided into quantitative and qualitative research. The quantitative empirical investigation is focused on an anonymous questionary survey that has been applied in three Prague cardiac centres. Approximately 150...

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