Write Up CO_VR 2018.pdf

# One should also note that the volume of blood added

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One should also note that the volume of blood added to the arteries would be the same as the volume removed from the veins. However, the pressure change in the arteries will be nineteen times greater than in the veins because of the nineteen-fold difference in compliance. Changes in venous pressure that result from changes in cardiac output are shown graphically in figure 2 below. When cardiac output is increased from 0 to 1 l/min there is a decrease in venous pressure from 7 to 6 mm Hg as shown in figure1. As cardiac output is increased further, the graph is linear with a negative slope until the cardiac output is about 7 L/min. At this cardiac output the right atrial pressure equals atmospheric pressure, conven- tionally taken to be 0 mm Hg. The pressure cannot fall below this point, because the veins collapse when the pressure becomes negative. The factors that affect the vascular function curve are the blood volume, the venous compliance, and the peripheral resistance. Changes in blood volume will change the mean circulatory pressure and move the curve up or down with the resultant curve being parallel to the normal curve. Changes in systemic vascular resistance will not change the mean circulatory pressure, because the volume of blood in the arterioles is very small. An increase in peripheral resistance causes the curve to rotate downward and to the left around the normal mean 1 2 3 4 5 6 7 8 9 10 0 -1 Central venous pressure (mm Hg) Cardiac output (l/min) 1 2 3 4 5 6 7 8 9 10 0 Q h = 1 L/min R= 20 mmHg min/L Steady State Q r = 1 L/min ΔP = Q • R = 1L/min • 20 mm Hg •min/L = 20 mm Hg P v = 7 mm Hg P a = 7 mm Hg Q=ΔP/R rewrite to solve for ΔP = Q • R 1 mm Hg 19 mm Hg New P v = 6 mm Hg New P a = 26 mm Hg

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Cardiac Output & Venus Return Vincent circulatory pressure, because at any given cardiac output the arterial pressure will be increased and therefore venous pressure will be reduced. A decrease in systemic vascular resistance does the opposite, rotating the curve upward and to the right around the same point.
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• Spring '19
• Ham Sawyer
• cardiovascular system

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