Browsing by Author "Tyberg, John"

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    Contractile Properties of Cardiac Muscle Following Increasing Doses of Chronic Exercise Training and Overtraining in Rats
    (2016) Boldt, Kevin; Herzog, Walter; MacIntosh, Brian; Syme, Doug; Tyberg, John
    The positive effects of chronic endurance exercise training on health and performance have been well documented. However, these positive effects have been evaluated primarily at the structural level, and it remains poorly understood how the heart muscle adapts mechanically to exercise training. In order to gain some understanding, we subjected three-month-old Sprague-Dawley rats to treadmill running for eleven weeks at one of three exercise volumes (moderate, high, and overtraining). Following training, hearts were excised and mechanical testing was completed on skinned trabecular bundles. Animals in the overtraining group experienced a significant loss in body mass, a withdrawal from food and drink, and became less active. The control, moderate, and high duration groups responded with a dose-dependent increase in heart mass and passive stresses, with no difference in active stress production. These trends were all reversed in the overtrained animals, despite presenting the greatest fitness on a graded treadmill test.
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    Effects of Acute and Chronic Hypoxia Exposure on the Contractile Properties of Isolated Compact and Spongy Ventricular Myocardium From Rainbow Trout (Oncorhynchus mykiss)
    (2016) Roberts, Jordan Cyril; Syme, Douglas; Vijayan, Matt; Rogers, Sean; Tyberg, John
    The ventricle of salmonids is composed of an outer compact layer, routinely supplied with well-oxygenated arterial blood, and inner spongy myocardium receiving low oxygen venous blood. During hypoxia oxygen exposures for both these tissue layers declines. As well, hypoxia results in an increase to circulating epinephrine for trout, which may affect the contractile response during hypoxia. This thesis presents an investigation into effects of high epinephrine, as well, acute and chronic hypoxia exposure on the contractile performance of these ventricular tissues from rainbow trout (Oncorhynchus mykiss). Acute hypoxia resulted in a similar decline to work output in compact and spongy myocardium. High epinephrine however, improved contractile performance of spongy myocardium during hypoxia. Hypoxia acclimation resulted in a decline to work output from spongy myocardium across all oxygen exposures. It appears hypoxia causes a decline in ventricular performance; however, elevated epinephrine exposure may be important to maintain higher performance during hypoxia.
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    Importance of blood volume on female cardiac, hemodynamic, and pulmonary responses to endurance exercise
    (2021-03-16) Pentz, Brandon; Montero Barril, David; Jalal Aboodarda, Saied; Raj, Satish; Fine, Nowell; Tyberg, John
    Purpose: The fundamental role of BV on cardiorespiratory responses to exercise have been well studied in young males. However, it is unknown whether these responses can be extrapolated in female populations. Therefore, the purpose of this thesis was to investigate the effect of a 10 % blood withdrawal on cardiac, hemodynamic, and pulmonary responses to exercise in females. Methods: Cardiac function was assessed during exercise using transthoracic echocardiography. Hemodynamic variables were measured using a non-invasive blood pressure monitoring system. Pulmonary variables were assessed in supine, left-lateral tilt position within a LBNP chamber to assess VO2max. BV was determined via the CO rebreathing technique. Submaximal workloads were performed at a constant workload of 100 W. Primary outcomes included LVEDV, SV, Q, HR, and VO2. Results: During submaximal exercise, following blood withdrawal, both LVEDV (P ≤ 0.030) and SV (P < 0.019) were reduced while Q was unchanged (P = 0.139) due to an augmented HR (P < 0.026). MAP (P < 0.015), SBP (P < 0.005), and DBP (P < 0.038) were reduced while VO2 was unaltered (P = 0.250). During maximal exercise, following blood withdrawal, there was a reduction in LVEDV and SV (≥ 10 % decrements, P ≤ 0.009). Peak Q was proportionally reduced (P < 0.001). Blood withdrawal induced a 10 % decrement in VO2peak (P < 0.001). Conclusion: Moderate blood withdrawal in females results in impairment of cardiac filling and SV with compensatory increases in HR to preserve Q at acute, constant load submaximal exercise. Thus, BV determines the relative exercise intensity at submaximal workloads. At maximal exercise, blood withdrawal impairs cardiac filling, output, and aerobic capacity in precise proportion to the magnitude of hypovolemia.
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    Mechanisms of Early Filling in the Left Ventricle
    (2017) Burrowes, Lindsay; Shrive, Nigel; Tyberg, John; Sudak, Les; Thompson, Richard; Mehta, Sudarshan (Raj)
    Filling of the left ventricle (LV) occurs in two phases; early filling and late filling. Late filling, the mitral flow “A-wave”, is a result of the left atrial contraction. Early filling, manifest as the “E-wave”, is thought to be substantially due to diastolic suction (DS), a phenomenon whereby the LV aspirates blood and fills itself independent of atrial activity. The presence and importance of DS has been the source of much debate within the scientific literature, dating back to the early 20th century. It has been said that DS is important in order for the LV to fill efficiently as the heart adjusts to varying demands, for example, an increased heart rate due to exercise. The presence of a favourable pressure gradient (PG) that drives blood flow from the LA towards the LV has been well established. Additional studies have shown that, under abnormally small end-systolic volumes (ESV), or, with impeding LV inflow, a negative transmural pressure is recorded, which was considered evidence of suction. The purpose of this study was to vary the working conditions of the heart in a porcine model, and measure DS in two different ways and compare these measures of DS to ESV as well as ejection fraction (EF). By varying the working conditions of the heart using drug interventions (isoproterenol, phenylephrine & metoprolol), as well as volume loading, the amount of DS at different states was determined. The volume of filling due to suction, VDS, as well as the amount of energy resulting from suction (via a backwards decompression wave, BDW), are both indicative that ESV decreases as the amount of DS increases. As EF increased, both measures of DS also increased. Additionally, results for VDS display that DS is still present at ESV larger than baseline ESV. Finally, comparing the two measures of DS to each other showed good agreement. DS is often suggested to be a result of elastic recoil of the LV after contracting below an unstressed state. However, our findings that VDS exists at large ESV would contradict that DS is only a result of elastic recoil, suggesting that further studies must be conducted focusing on DS at large ESV.
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    P1.14 Analysis of Left Ventricular Filling Dynamics
    (2015-11-23) Burrowes, Lindsay; Satriano, Alessandro; Thompson, Richard; Shrive, Nigel; Tyberg, John
    Abstract Diastolic filling of the left ventricle (LV) occurs in two phases, early and late filling. Early filling, manifest as the “E-wave”, is thought to be substantially due to diastolic suction (DS), a phenomenon where the LV aspirates blood and fills itself, independent of atrial activity. Late filling, resulting in the mitral flow “A-wave” is a result of left atrial contraction. Adequate filling of the LV is necessary to maintain normal heart function at rest and under stress. DS is thought to be an important mechanism in the efficiency of filling. To study DS, we have invasively measured pressure and used cardiac MRI to evaluate cavitary volume and flow in an animal model to quantify different measures of DS under varied experimental conditions. The amount of filling due to DS (VDS), determined by the change in volume between mitralvalve opening and LV pressure minimum of the pressure-volume loop (Katz 1930), is related to the measured end systolic volume (ESV). As ESV decreases the VDS increases. The smaller the ESV, the larger the recoil energy of the LV as it relaxes towards resting volume. This contributes increased energy for the suction of blood into the ventricle in early filling. Wave intensity analysis (the separation of forward and backwards waves and wave type) and intraventricular pressure gradients will also be considered in order to determine which best describes DS and whether they can be used together to better understand changes in filling dynamics under varied loading conditions.
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    P1.4 Hemodynamics of Pulmonary Hypertension: Application of the Reservoir-Wave Approach
    (2015-11-23) Ghimire, Anukul; Andersen, Mads; Burrowes, Lindsay; Bouwmeester, J. C.; Grant, Andrew; Belenkie, Israel; Fine, Nowell; Borlaug, Barry; Tyberg, John
    Abstract Using the reservoir-wave approach, previously we characterized pulmonary vasculature mechanics with multiple interventions in a canine model. In the present study, we measured high-fidelity pulmonary arterial (PA) pressure, Doppler flow velocity, and pulmonary capillary wedge pressure in 11 patients referred for evaluation of exertional dyspnea. The analysis was performed using the reservoir-wave approach; wave intensity analysis was subsequently utilized to characterize the PA wave pattern. Our objective was to identify specific abnormalities associated with pulmonary hypertension. Seven patients with varying PA pressures had reduced pulmonary vascular conductance (i.e., the amount of flow that the lungs can accept per pressure gradient), suggesting that these patients might benefit from pulmonary vasodilator therapy, some even in the absence of markedly elevated PA pressures. Right ventricular (RV) performance was assessed by examining the work done by the wave component of systolic PA pressure. Wave work, the non-recoverable energy expended by the RV to eject blood, varied directly with mean PA pressure. Wave pressure was partitioned into two components: forward-travelling and reflected backward-travelling waves. Among patients with lower PA pressures, we found pressure-decreasing backward waves that aided the RV during ejection, as previously reported in normal experimental animals. Among patients with higher PA pressures, we detected pressure-increasing backward waves that impede RV ejection. We conclude that it is important to measure pulmonary vascular conductance to properly assess the pulmonary vasculature. The reservoir-wave approach and wave intensity analysis may prove to be valuable tools to evaluate RV performance and may facilitate development of therapeutic strategies.
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    Pulmonary Hypertension: Insights From the Reservoir-Wave Approach
    (2016) Ghimire, Anukul; Tyberg, John; Fine, Nowell; Belenkie, Israel; Grant, Andrew
    We employed the reservoir-wave approach to analyze high-fidelity pulmonary arterial (PA) pressure and Doppler flow velocity in 11 patients with varying cardiac diseases. Our specific objectives were to (1) to characterize PA wave pattern and (2) evaluate right ventricular (RV) performance. Wave pressure was partitioned into its forward and backward components. Among patients with lower PA pressures, pressure-decreasing and flow-increasing reflected waves that assist RV ejection were detected. Among the more pulmonary hypertensive patients, pressure-increasing and flow-decreasing reflected waves that impede RV ejection were detected. The four patients with the highest PA pressures showed an early systolic deceleration in flow, which was found to coincide with reflected pressure-increasing, flow-decreasing waves. Wave work done by the RV increased with PA pressure, but expressed as a fraction of total RV work, did not change. The reservoir-wave approach may prove to be a valuable tool to characterize PA-RV interaction and evaluate RV performance.