Browsing by Author "Burrowes, Lindsay"

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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.