Browsing by Author "Howell, Sarah"

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    Novel Approaches to the Assessment of Systemic Circulation and Ventricular Performance
    (2019-02-27) Howell, Sarah; Tyberg, John V. T.; Shrive, Nigel; Phillips, Aaron A.; Sheldon, Robert Stanley; Fedak, Paul
    The purpose of evaluating the systemic circulation using systemic vascular conductance and head-capacity curve to quantify left ventricle performance is to validate these assessment approaches instead of more commonly used cardiovascular indexes (i.e., systemic vascular resistance and ejection fraction) used for physiologic responses. Systemic vascular conductance is reciprocal of systemic vascular resistance and is defined as the flow to the systemic circulation that determines arterial pressure. Systemic vascular conductance is calculated by dividing cardiac output by arteriovenous pressure difference. Left ventricle performance is assessed using head-capacity curve. It states that left ventricle as a pump, works under a head-capacity curve. The aim of this study is to increase our understanding of systemic circulation and ventricular performance by studying how changing loading conditions using drug interventions (phenylephrine, sodium nitroprusside, and isoproterenol), proximal aortic constriction, and volume loading will affect the systemic vascular conductance and left ventricle performance. The ultimate goal of this study is to combine circulatory and ventricular properties quantitatively and define the relationship between output produced by the heart and input of the circulation. Overall, results are consistent with the hypothesized physiological changes and allow the application of both proposed indices to determine the global cardiovascular performance in a simple manner. These results further enhance our understanding that conductance of each intervention in systemic circulation determines the mean arterial pressure. Systemic vascular conductance changes markedly with changing cardiac index and these changes are mediated by left ventricle. The potential benefits of these assessment parameters will help provide insights to optimize circulatory performance in patients with cardiovascular disease.