Browsing by Author "Tyberg, John V."
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Item Open Access A new teaching model of the systemic circulation that incorporates reservoir characteristics(2015-02-24) Tyberg, John V.; Bouwmeester, J. C.; Burrowes, Lindsay M.; Parker, Kim H.; Shrive, Nigel G.; Wang, Jiun-Jr.Abstract A hydraulic teaching model of the human systemic circulation is proposed, based on the principles of the reservoir-wave approach. Reservoir characteristics are portrayed by the arterial tall-and-narrow and venous short-and-wide columns, the relative compliances of which are signified by their diameters. Wave characteristics are represented by proximal arterial and venous resistances; rapid left ventricular ejection and rapid right atrial filling cause flow-dependent pressure drops across the respective resistances. (The value of the proximal arterial resistance is numerically equal to the characteristic impedance.) The pressure drop across the proximal arterial resistance, excess pressure, is understood to be fundamentally wave-related and has been shown to be a measure of the efficiency of cardiac-vascular coupling. Excess pressure also predicts an incremental risk of cardiovascular morbidity and largely accounts for the hysteresis evidenced by an open aortic pressure-volume loop.Item Open Access A novel approach to mitral flow(1995) MacRae, Jennifer Marie; Tyberg, John V.Item Open Access A Novel method for the measurement of pericardial pressure(1991) deVries-Owens, Gwyneth; Tyberg, John V.Item Open Access A study of the effects of left ventricular contractility and coronary tone on coronary flow dynamics using wave intensity analysis(2001) Sun, Yi-Hui; Tyberg, John V.Item Open Access Application of the reservoir-wave approach to the renal circulation(2012) Handkamer, Kristen Claire; Tyberg, John V.The reservoir-wave approach provided the idea that systemic vascular resistance could be modeled as several component resistors arranged in series. The purpose of this investigation was to apply the reservoir-wave approach to the renal circulation and examine how a renal venous constriction (RVC) or a renal arterial infusion of vasoactive agents into one kidney altered conductance, P oo, and series resistances. Endothelin-1 and Angiotensin 11 reduced conductance to 39.6 ± 5.1 and 64.4 ± 4.3%; total renal resistance increased but arterial reservoir resistance decreased to 64.8 ± 6.3 and 80.0 ± 6.1 % of the control respectively. Endothelin-1 and Angiotensin II also increased Poo by 14.5 ± 2.7 and l 0.2 ± 3.6 mmHg, and the microcirculatory plus venous resistance to 187.2 ± 21.0 and 180.0 ± 35.8% ofthe control respectively. RVC increased conductance to I 12.3 ± 4.4% of the control, in apparent compensation. The reservoir-wave approach is applicable to the renal circulation and its use in subsequent investigations is warranted.Item Open Access Assessment of left atrial mechanics and energetics in dogs using wave intensity analysis(2006) Hobson, Tracy Nicole; Tyberg, John V.Item Open Access Assessment of left ventricular diastolic suction using wave-intensity analysis(2003) Jalali, Fereshteh; Tyberg, John V.Left ventricular diastolic suction (LV DS) is defined as the property of the LV to refill itself during early diastole, independent of any force from the left atrium (LA). Two different mechanisms have been developed to explain this phenomenon. The first mechanism relates DS to the decrease in L V elastance. The second theory, relates DS to negative L V pressure, suggesting that the smaller the end-systolic volume, the greater the DS. In an attempt to reconcile these two mechanisms, wave-intensity analysis was used. The purpose of this study was to illustrate that Iw-BE (L V generated backward expansion wave) depends on both decreasing elastance and the L Vend-systolic volume. It was found that the energy ofLV DS is inversely proportional to -c and LV end-systolic volume. From these data a 3-D plot was formed demonstrating the non-linear dependence of L V DS on both of these variables.Item Open Access Cardiac function during mechanical ventilation in a canine model of oleic acid-induced acute lung injury(2008) Mitchell, Jamie R.; Tyberg, John V.Item Open Access Cervical spine manipulation and cervical artery dissections: a systematic review of the literature and experimental studies of a potential mechanism(2007) Wynd, Shari Elizabeth; Kawchuk, Greg; Tyberg, John V.Item Embargo External constraint to the left ventricle(1984) Kingma, Iris; Tyberg, John V.Item Open Access Finite element analysis of the interventricular septum(1999) Nelson, Gregory Scott; Tyberg, John V.Item Open Access Left ventricular filling dynamics(2006) Flewitt, Jacqueline Allison; Tyberg, John V.The Windkessel theory was effectively incorporated into wave intensity analysis (WIA) by correcting left ventricular (L V) wave intensity results for the effects of compliance. The corrected WIA revealed a sixty percent greater role of diastolic suction in early filling than previously calculated. 1 The backward expansion wave of diastolic suction consistently prevailed over the forward compression wave of LA passive decompression in determining the acceleration portion of the E wave. Little evidence of wave action was found to explain the deceleration portion of the E wave and an equilibrating reservoir model was proposed. A number of inconsistencies were found between the early filling velocity and flow waveforms which are believed to be a function of the changing mitral valve area. It is proposed that the morphodynamic advantage is to maintain and conserve momentum through the mitral valve in preparation for ventricular ejection.Item Open Access Limitations to left ventricular diastolic filling in the prenatal period(1989) Grant, Daniel Allen; Tyberg, John V.Item Open Access Mechanics of the ventricular septum(1991) Dong, Sheng-Jing; Tyberg, John V.Item Open Access Oxygenation-sensitive CMR for assessing vasodilator-induced changes of myocardial oxygenation(BioMed Central, 2010-03-31) Vöhringer, Matthias; Flewitt, Jacqueline A.; Green, Jordin D.; Dharmakumar, Rohan; Wang Jr, Jiun; Tyberg, John V.; Friedrich, Matthias G.Item Open Access Predicting Thrombus Formation in Patients with Internal Carotid Artery Webs(2017) Ali, Syedah Salwa; Mitha, Alim P.; Di Martino, Elena; Tyberg, John V.; Egberts, Philip; Wood, David; Natale, GiovanniantonioCarotid webs are fibro-intimal growths affecting the internal carotid artery but are pathologically different from common atherosclerotic plaques. They cause moderate stenosis and are difficult to diagnose. However, if treated, patients present themselves again with recurrent ischemic strokes due to thrombus formation distal to the stenosis. Lack of knowledge urged the need to conduct hemodynamic analysis. This is the first study to quantify hemodynamic changes in the carotid web region. We conducted transient analysis on 3 symptomatic stroke patients with carotid webs. Carotid web region in each of the 3 carotid arteries with web was calculated with high OSI levels (0.3 approx.), low TAWSS values (less than 0.4Pa) and high RRT values. We also visualized recirculating flow behind the web during deceleration phases of cardiac cycle. All these factors reveal that carotid webs disturb blood flow patterns to cause blood stagnation, recirculation and thrombus formation to cause stroke.Item Open Access Splanchnic vascular capitance, heart failure and the cardiac vagal reflex(1991) Wang, Yudi; Tyberg, John V.Item Open Access Subcellular Distribution and Function of Cardiac Ryanodine Receptor in Ventricular Myocytes and Hippocampal Neurons(2018-01-23) Hiess, Florian; Chen, S. R. Wayne; Turner, Ray W.; ter Keurs, Henk E D J; Rho, Jong M; Tibbits, Glen F; Nguyen, Minh Dang; Tyberg, John V.Cardiac ryanodine receptors (RyR2s) are intracellular calcium (Ca2+) release channels most abundantly expressed in the heart and brain. They are clustered in the endo/sarcoplasmic reticulum (ER/SR) membrane to form elementary units for Ca2+ release. The distribution of these units determines the spatiotemporal profile and stability of ER/SR Ca2+ release. Thus, RyR2 distribution is believed to be essential in cellular processes, such as excitation-contraction coupling and learning and memory. The distribution of RyR2s has been extensively studied in cells/tissues using anti-RyR2 antibody immunostaining. However, sample preparation required for immunostaining may affect cellular structures, besides rendering the cells/tissues non-functional. Hence, the functional relevance of the distribution of RyR2 clusters in live cells/tissue is unclear. We have generated a knock-in mouse model that expresses green fluorescence protein (GFP)-tagged RyR2s. These mice allow us to monitor cellular/subcellular distribution of RyR2 in live cells/tissues by virtue of GFP fluorescence. To improve the detection of GFP-RyR2, we developed a novel GFP-specific probe based on anti-GFP single domain antibodies (nanobodies). Fluorescence imaging was employed to study Ca2+ release and the distribution of GFP-RyR2 in the interior and periphery of live ventricular myocytes and in intact hearts isolated from GFP-RyR2 expressing mice. We found highly-ordered arrays of stationary GFP-RyR2 clusters in the interior of cardiomyocytes in the z-line zone. In contrast, irregular and dynamic distribution of GFP-RyR2 clusters was observed in the periphery of cardiomyocytes. Imaging of intact GFP-RyR2 brain sections revealed a widespread distribution of RyR2 in various brain regions, most prominently in regions involved in spatial learning and memory, such as the hippocampus. To investigate the functional role of RyR2 in this region, we performed electrophysiological studies using hippocampal slices prepared from knock-in mice harboring a cardiac arrhythmia-associated human RyR2 mutation (R4496C) with enhanced channel activity. We found that enhanced RyR2 function reduces long-term potentiation (LTP) in Schaffer collateral inputs to CA1 pyramidal cells. Thus, RyR2 plays a critical role in LTP at these synapses. Behavioral studies on RyR2 mutant mice further supported the role of RyR2 in learning and memory. Overall, these results reveal, the distribution of RyR2 clusters and its functional significance in living ventricular myocytes and hippocampal neurons.Item Open Access Item Open Access The dynamics of left ventricular torsion throughout the cardiac cycle(1994) Gibbons Kroeker, Carol A.; Tyberg, John V.