Legacy Theses and Dissertations (1940-2009)
Permanent URI for this collectionhttps://hdl.handle.net/10657/6771
This collection gathers digitized University of Houston theses and dissertations dating from 1940.
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Browsing Legacy Theses and Dissertations (1940-2009) by Department "Biomedical Engineering, Department of"
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Item Application of a homogeneous half-space model in the analysis of micropipette measurements of cultured bovine aortic endothelial cells which have been exposed to shear stress(1987) Theret, Didier P.; Wheeler, Lewis T.; Nerem, Robert M.; Goochee, Charles F.; Ktonas, Preiklis Y.Experimental studies have shown that endothelial cells which have been exposed to shear stress maintain a flattened and elongated shape after detachment. Their mechanical properties, which are studied using the micropipette technique, are influenced by the level as well as the duration of the shear stress. In this project, the micropipette technique has been modeled in order to characterize the mechanical properties of the elongated cells. Two mathematical models suggested by cytoskeletal studies and by the geometry peculiar to their post-exposure state have been used. The two models differ in their treatment of the contact zone between the cell and the micropipette. The main results are expressions of the effective Young's modulus for the cells. These are used in conjunction with the micropipette data to determine an effective Young's modulus for bovine endothelial cells, and to discuss the dependence of this modulus upon exposure to shear stress.Item Evaluation of prosthetic heart valve performance by a time integrated power loss analysis(1987) Gross, Jeffrey M.; Hwang, Neddy H. C.; Mailman, David S.; Kleis, Stanley J.; Ktonas, Preiklis Y.Traditional evaluation of heart valve prosthesis (HVP) by the method of transvalvular pressure drop and percentage of flow regurgitation has shown discrepancies among investigators. In order to alleviate the ambiguities associated with this type of approach, a phase-by-phase analysis based on the time integrated power loss through a HVP is proposed. The theoretical basis and physical significance for such an analysis are discussed by Stibdividing the cardiac cycle into three phase categories: the ejection phase, the dynamic regurgitation phase, and the leakage phase. The summation of HVP power losses during each of these three phases constitute the total power loss (TPL) for the HVP during the cardiac cycle. Utilizing a mock circulatory flow loop to produce physiologic pressure and flow waveforms, the performance of five current aortic HVPs and four current mitral HVPs is examined by the power loss analysis. The TPL illustrates an upward trend with increasing heart rate. At heart rates less than 90 bpm, results indicated the ejection phase power losses (EPL) dominated the TPL for the valves, and at heart rates greater than 90 bpm, the TPL was influenced to a greater extent by the regurgitation phase power losses (RPL) than the EPL.Item Fluid dynamic study of angioaccess venous anastomoses(1988) Shu, Mark Chong-Sheng; Hwang, Neddy H. C.; Fitzgibbon, William E., III; Gross, D. R.; Hartley, Craig J.; Williams, Anthony N.; Ktonas, Preiklis Y.Longer life expectancy of patients receiving chronic hemodialysis requires that patency is maintained in their arteriovenous angioaccess loop graft (AVLG) system. However, there still is a high incidence of complications leading to failure of the AVLG system. Earlier studies have indicated that hemodynamic behavior of blood may play an important role in the failure. Unfortunately, the characteristics of hemodynamic contributions to the failure have not been clearly identified. To characterize the role of hemodynamics in the etiology of the failure, an in vivo/in vitro AVLG system was created to study flow phenomena and blood reaction. The work reported here was the in vitro part of a comprehensive study undertaken to study hemodynamic activity in the AVLG system. Three elastic transparent flow models were fabricated from silicone rubber casts and represented the detailed luminal geometry of the in vivo AVLG loop system. The hemodynamic characteristics of the three models with different area reduction (AR), acute, minor and significant, were compared under identical in vitro flow conditions. Flow visualization indicated that a distinct boundary layer separation region was observed downstream from the venous anastomotic "toe". A stagnation region was created at the venous wall, opposite to the venous anastomosis, by the oscillatory impinging jet originating from the graft conduit Momentum calculations indicated that a strong hydrodynamic force, from the impinging jet acted at the stagnation region. Oscillating wall shear stresses, with opposite sign, were found at the region. Retrograde flow in the distal vein occurred in an "oscillating" manner following each cardiac cycle. Local velocity mapping, using Laser velocimetry, provided detailed characteristics of hemodynamic flow phenomena. A low wall shear stress region was observed in the boundary layer separation region near the venous anastomotic "toe", while relative high wall shear stress was observed at the proximal side opposite to the venous anastomosis. Low magnitudes of turbulence intensity and Reynolds shear stresses were presented in all the flow models studied. The analysis of power spectral density of velocity fluctuation indicated that pronounced spectral humps occurred at about 100 Hz in the flow model with the significant area reduction.Item Instantaneous screw axis identification using holographic interferometry(1988) Sanchez, Lilia Armida; Kleis, Stanley J.; Shoup, Terry E.; Anderson, Wallace L.; Mistree, Farrokh; Wood, Lowell T.; Ktonas, Preiklis Y.Exact description of human joint movement is difficult because it is likely to involve all six degrees of freedom allowable in three-dimensional space. A three-dimensional motion can be described by the movement of the instantaneous screw axis (ISA) so that the whole motion of a body at each instant can be given as a combination of a simple rotation about and translation along that axis. Double-exposure holographic interferometry is proposed as a noncontacting, noninvasive photo-optical technique for measuring small displacements of a body in space and approximating the ISA. Displacement measurements from double-exposure holograms generally involve a single hologram analysis which makes use of the static fringe-order method or a dynamic fringe-counting method. The static method requires identification of a zero-order fringe, which is often difficult or impossible. The dynamic method is severely restricted by the limited change in viewing direction bounded by the angle which the object subtends at the hologram. This restriction results in an ill-conditioned matrix of sensitivity vectors characteristic of the geometry of the experimental set-up. An improved measurement technique using a single double-exposure hologram is proposed which combines the dynamic and static methods to measure finite displacements resulting from rigid body motion. The dynamic fringe-counting method with a least-squares error analysis is used to extract the in-plane translations and rotations of the motion. A static fringe-order difference between two points on the surface of the object and the translations are used in the fringe-locus function to determine the out-of-plane rotations of the body. The existing dynamic method is also used for comparison of results. Both sets of experimental results for rigid body translations and rotations are compared to the actual micrometer readings. The results computed from the proposed dynamic fringe-counting/static fringe-order difference technique show considerable improvement over the dynamic method. The experimental ISA parameters compare very favorably with the the actual ISA parameters computed.Item Methods for time delay estimation between EEG signals : a critical evaluation(1988) Mallart, Raoul; Ktonas, Preiklis Y.; Anderson, Wallace L.; Frost, James D., Jr.; LaMotte, Lynn R.Three estimators of the time delay between signals, based on the methods of crosscorrelation, phase spectrum and an information theory-based method (AAMI), respectively, are critically evaluated. In some cases these methods can yield accurate measurements of the time delay between EEG channels, and can help to determine the location of an epileptic focus. The AAMI-based technique is efficient when a small number of data points is available, however, it requires large amounts of computer time, and its error analysis is not theoretically tractable. The other two methods provide theoretically tractable error analysis, and are comparatively faster. However, they require larger amounts of data. A good agreement with theory, as far as error is concerned, is achieved with the correlation and the phase spectrum-based method, provided that the number of equivalent degrees of freedom is large, the segment length is relatively large, and the normalized bandwidth of the signals is wide.Item Modeling regional differences in myocardial thickening using a geometrical model of the left ventricle(1986) Litowitz, Harvey; Nerem, Robert M.; Hartley, Craig J.; Hwang, Neddy H. C.; Ktonas, Preiklis Y.Reported values for thickening fractions(TF) and inner wall:outer wall thickening(IW:OW), two indices of left ventricular function, vary widely. First, we demonstrated that a single epicardial transducer can measure large deformations of material with multiple reflectors. Then, we measured changes in thickening using the transducer and calculated TFs and IW:OW at multiple sites around the left ventricle of three open chested anaesthetized dogs to determine if the variations are due to regional differences. Our results indicate that IW:OW thickening does vary from region to region being higher in the apical and basal regions than in the central region, but TFs are not significantly different. An ellipsoidal model of the left ventricle was developed to explain these regional differences in IW:OW thickening by simple geometrical changes in the ventricle assuming conservation of wall volume. Initial results indicate that the model is consistent with trends of IW:OW thickening seen in the animal experiments. We conclude that regional variations in IW:OW thickening do exist and that these differences can be explained by geometry.Item Multivariate statistical methods for the automated detection of epileptogenic EEG transients(1987) Webster, Laurie; Ktonas, Preiklis Y.; Glover, John R., Jr.; Jansen, Ben H.; Donaghey, Charles E.Automated detection of epileptogenic electroencephalograms (EEG) such as spikes and sharp waves (SSW)1 in general, relies on time-domain or frequency-domain analysis. Time-domain techniques, usually drawing on electrographic properties (e.g duration, amplitude, slope, sharpness, etc.) with emphasis on single-wave analysis, may result in a large number of features to be used in a classification scheme. The major thrust of this thesis is to investigate the utility of multivariate statistical methods (regression analysis, multivariate discriminant analysis) for selecting an optimum subset of this possibly numerous set of electrographic features and for using this subset for the classification of epileptogenic EEG activity. We studied the effects, on parameter selection and usage, of splitting SSWs into two classes (Spikes and Sharp Waves) and EEG Background into two classes (Fast Background and Slow Background). We also analyzed the sensitivity of various parameter selection methods and of classification based on these parameters to class variations in terms of class sizes and prior settings. Additionaly, we studied the comparative performance of parameter subsets in linear discriminant functions (LDFs). It was shown that splitting SSWs into two classes and Background into two classes did not improve the performance of the LDFs in detecting SSWs. The LDF performance was higher (i.e., more SSWs were detected with a lower error rate) when we kept SSWs as one class and Background as one class. Included in this investigation is the comparison of distribution-free thresholding methods for the automatic detection of SSWs to thresholding methods that depend on thresholds computed based on normal distribution assumptions and on multivariate linear discriminant functions (LDFs). Also, two LDFs in cascade (one for separation of SSWs + Background from Artifact and one for separation of SSWs from Background) were investigated, and the performance results suggest that this strategy is promising and should be pursued.Item Power losses through mechanical heart valve prostheses(1986) Torche, Dominique; Hwang, Neddy H. C.; Nerem, Robert M.; Hazelwood, Robert L.; Ktonas, Preiklis Y.A new parameter for the evaluation of the performance of heart valve prosthesis (HVP) is developed. The mean power loss is computed from the pressure drop and the flow through HVPs obtained in a pulsatile mock loop system. Eight mechanical HVPs are studied (five in the mitral position and three in the aortic position). The power loss is categorized into three periods within a heart cycle: the first two periods together constitute the ejection power loss (EPL). The last period is the power loss due to regurgitation (RPL). The discussion is more concerned about the mitral HPVs because, in the aortic position, the conditions of measurements combined with the potential energy storage in the elastic aorta make the results less interpretable. The results indicate that EPL closely reflects the closure behavior of the valve occluder and the mean transvalvular pressure drop. RPL is much higher (almost IO times more) than EPL. The overall power loss (OPL) shows that RPL is more important compared to EPL. OPL evaluates the relative Influence of energy losses resulting from the pressure drop and regurgitation volume, and defines a unique performance parameter.Item Search : an expert system for peripheral neurology(1985) Adams, Thomas Leander; Henley, Ernest J.; Donaghey, Charles E.; Winter, Dean C.This thesis describes an expert system, nailed Search, that was produced for the microcomputer. Using the KnowledgeManager database system, a program was produced to aid in medical diagnosis in the field of peripheral neurology. One hundred and three 'If-Then' rules are used to diagnosis ten diseases or conditions. Diagnoses require eleven or less program-asked questions. The KnowledgeManager system allows the If-Then rules used in the Search program, the knowledge base, to be stored on a diskette and accessed as needed by the program. With this disk storage, the program can function on a microcomputer with a minimum capacity of 256K. The disk access is rapid enough so that there is only a three to four second lag between a user response and the next program-asked question. The Search program does forward and backward chaining. It also contains a number of additional features, such as in-program editing, key-word searching, listing of questions used to reach a diagnosis, a search for additional information on the current question and several help commands. Diagnoses and help commands are high lighted by special colored displays. Calculations indicate that the size of the program's knowledge base could be expanded to three thousand If-then rules with no modifications in the current program's structure. With some minor modifications, the knowledge base could contain ten thousand If-Then rules.Item The application of polynomial spatial warping to effect global image rectification for the direct comparison of 165 rRNA oligonucleotide signatures(1986) Schomer, Donald Floyd; Fox, George E.; Nerem, Robert M.; Goochee, Charles F.; Ktonas, Preiklis Y.Comparative partial sequencing of the ribosomal RNA provides a powerful experimental tool for the investigation of procaryotic molecular systematics. This thesis presents a novel technique that expedites comparison of the 16S rRNA signatures used to establish procaryotic phylogenetic relationships. A global transformation is defined that maps the two-dimensional electrophoretogram of the ribonuclease T1 16S rRNA fragments of one organism onto that of another. This mapping provides a method of directly comparing the similarities between the organisms without resorting to the tedious biochemical analysis that is currently employed. Six organisms of varying degrees of similarity that had been catalogued by the conventional method were compared "S’nq this technique. The results demonstrate the feasibility of employing this technique as part of an automated analysis package for the interpretation of 16S fingerprints.Item The measurement of blood flow using the radioactive microsphere technique(1986) Thai, BichLan Ngo; Levesque, Murina J.; Nerem, Robert M.; Hartley, Craig J.; Goochee, Charles F.The purpose of this investigation was (i) to develop a technique for measuring organ blood flow in anesthetized animals and (ii) to apply the technique to the measurement of heart, kidney and femur blood flow in both dogs and pigs. Hypertension in the dog experiments was achieved by aortic constriction, which produces an elevation in aortic pressure and a decrease in femoral pressure, and by drug injection (i.e. Arterenol) which produces elevation of arterial blood pressure in both the aorta and femoral arteries. Radioactive microspheres were injected under control, aortic constriction and arterenol infusion in four dogs and under control conditions in two dogs and two pigs. It was found that coronary blood flow rose by 80% during aortic constriction and by 158% during arterenol infusion. This increase in blood flow was not uniform throughout the heart, and higher increases were observed in the middle and apex regions of the left ventricle. It also was found that acute hypertension has little effect on kidney and femur blood flows.