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Item The Effects of Spatial and Temporal Properties on a Viscoelastic Model of the Dyssynchronous Canine Heart(North Dakota State University, 2011) Satterlee, Cody MichaelIn this study, lumped parameter cardiovascular modeling has been used to understand the influence of muscle properties on mechanical dyssynchrony (MD) as well as general muscle dynamics. Incorporating viscous influence into the model allowed for an expanded view when analyzing muscle parameter response to MD. A unique method of ventricle segmentation was introduced that allowed fast analysis of regional and global ventricular properties. This segmentation process produced a ventricle with four identical sections each consisting of separately tunable muscle properties in the form of minimum and maximum elastance, elastance waveform delay, and myocardial viscous friction, yet these regional sections remained globally dependent. Elastance waveform delay proved to be the most influential property on MD as measured by internal flow fraction (IFF), followed by regional elastance magnitude, and finally regional viscosity influence. Due to the unique segmentation of this model, two metrics for IFF were derived: (1) the "true" IFF (IFF-4seg) and (2) the IFF as would be measured by an ideal conductance catheter (IFF-CC). The results of IFF-CC versus IFF-4seg show that conductance catheters are not capable of measuring IFF during a side-to-side volume transfer within the stacked cylinder under measurement. Finally, unique energetic situations were observed with this model that point to likely myocardium remodeling situations.Item Estimating Tau (τ) from Left Ventricular Pressure Waveforms During Vena Caval Occlusions(North Dakota State University, 2011) Gopinath, SushmaMany people are dependent on artificial pacemakers to have a normal cardiac function. Due to this it is important to study the effects of pacing on cardiac function, as well as, to determine the best site to pace with an artificial pacemaker that yields the best cardiac performance. Tau (τ), the time constant of left ventricular relaxation, has been studied as one measure of effective cardiac function, where high τ has been associated with myocardial ischemia and hence a low τ is desirable. The objective of the current study was to create a program in MATLAB™ that estimates τ from left ventricular pressure (LVP) data, verify this program using synthesized data and calculate τ for physiological data. LVP data was collected from five canines under four pacing modes: left ventricular (LV), bi-ventricular (BV), right atrial (RA) and right ventricular (RV) at rates of 90 or 100 and 160 bpm. Four models of τ were used: 1. A semi-logarithmic, zero asymptote model (τ L), 2. A semi-logarithmic model using data from the first 40ms of the isovolumic relation (τ 40), 3. Exponential model with non-zero asymptote of left ventricular pressure (τ E) and 4. A derivative model with non-zero asymptote of left ventricular pressure (τ D). The program successfully loaded all data files and computed τ for all dogs, all pacing sites and all heart rates.