It is obvious therefore that when the compliance is

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It is obvious, therefore, that when the compliance is constant the pressure falls if the volume is reduced. Venous return is analyzed by constructing a vascular function curve, also known as the venous return curve. Increasing the pump output in (figure 1) in a stepwise fashion results in a change in venous pressure. The characteristics of the artificial systemic circulation can be set at values found in the normal circulatory system. In the model illustrated in figure 1, the systemic vascular resistance is set at 20 mm Hg/L/min, the compliance of the veins is set to be nineteen Q h = 0 L/min Mean circulatory pressure or static pressure = 7 mm Hg P v = 7 mm Hg P a = 7 mm Hg Q r = 0 L/min Pump (heart) Resistance Vessels
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Cardiac Output & Venus Return Vincent times greater than the arterial compliance, and enough blood is added to the system to give a mean circulatory pressure of 7 mm Hg at zero cardiac output. When the cardiac output is increased, there is a fall in central venous pressure and an increase in arterial pressure as blood redistributes from the venous circulation and accumulates in the arterial circulation. This occurs due to an imbalance between the output from the heart and the flow through the resistance vessels; in this case, the flow from the heart exceeds the flow through the resistance vessels. As the arterial pressure increases and the venous pressure decreases the pressure difference across the resistance vessels increases. Eventually the pressure difference across the resistance vessels will provide the driving force required to match flow through the resistance vessels with flow from the heart (cardiac output). One should note that the pressure difference required to match blood flow with cardiac output is dependent on the magnitude of the vascular resistance.
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  • Spring '19
  • Ham Sawyer
  • cardiovascular system

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