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20 Cards in this Set
- Front
- Back
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O2 need during exercise |
VO2 may increase 12 fold VO2 = deltaAVO2 * CO deltaAVO2 can only increase 3 fold. Thus, CO must increase 4 fold |
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Resistance and cardiac output during exercise |
TPR falls to 1/3 basal level during exercise due to vasodilation. CO must increase 3-fold to maintain MAP. |
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Cardiac Function Curve and why it does not fully predict CO |
Quantifies effect of preload on SV or CO. But CO also influences preload because CO becomes preload (EDP) after flowing through systemic vasculature. |
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Factors that determine cardiac factors |
Cardiac factors - heart rate, myocardial contractility Coupling factors - preload, afterload |
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Measuring preload |
R.V.E.D.P = MRAP = CVP Because little resistance over tricuspid valve and right heart. Thus, CVP = Preload |
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SIMULDOG Model |
Heart and lungs - Pump oxygenator Arteries - tall tube (low compliance) Capillaries - pinch valve (resistance) between arteries and veins Veins - short tube (high compliance) |
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Experimental setup for VFC |
Right heart bypass = can control flow/CO. Change CO and assess effect on preload (CVP) |
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SIMULDOG - Stop the pump |
Without driving force, pressure gradient between arteries and veins dissipates. Arterial pressure falls and venous pressure rises. |
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Dead Pressure |
Equilibrated pressure, in absence of any flow. Also called mean circulatory filling pressure or mean systemic pressure. 7.5 mmHg |
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SIMULDOG - Restart pump |
Arterial pressure rises and venous pressure falls. Compliance and TPR accounts for this effect. |
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Effect of increasing blood volume on dead pressure |
Increases dead pressure |
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Experiment - Effect of increasing CO on Pa/Pv |
Arterial pressure rises and CVP falls. Arteries and veins undergo same change in volume but arteries are less compliant so same change in volume results in larger pressure change. |
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Effect of increasing blood volume on VFC |
Increasing blood volume increases dead pressure |
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Effect of increasing venous tone on VFC |
Increasing venous tone (constriction of veins) increase venous pressure. Thus, it increases dead pressure. |
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Effect of changing TPR on VFC |
Dead pressure does not change because no flow at dead pressure. Increased TPR dams more blood in arterial system and lowers CVP, thus decreasing slope of VFC. |
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Operating point - effect of increase in CVP |
1) CFC - increased CVP = increased preload = increased CO 2) VFC - increased CO = decrease in CVP 3) Repeated cycle restores stable operating point. |
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Mechanisms of Pressor Response |
Evoked when baroreceptors sense reduction in MAP. Increased sympathetic stimulation of heart = increased contractility and heart rate Increased sympathetic and decreased parasympathetic stimulation of VSM = increased TPR, venous tone |
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Example of Pressor Response - Hemorrhage |
Severe decrease in blood pressure Decrease in dead pressure = reduction in CO Pressor response - increase HR and contractility = increased slope of CFC Increase venous tone = dead pressure goes back up. Constriction of arterioles (increased resistance) causes reduction in slope of VFC. Result - normal CO and normal MAP. |
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Effect of Myocardial Damage |
Decrease in cardiac contractility = depressed CFC. Reduction in CO and increase in CVP Pressor response: Increased HR and contractility = increased slope of CFC. Less than ideal because damaged heart. Increased venous tone = increase in dead pressure; increased TPR = decrease in slope of VFC. Result - pressor response restores CO and MAP. |
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Effect of exercise |
Exercise -> sympathetic activation -> increased contractility and HR -> increased slope of CFC Vasodilation -> decreased TPR = increase in slope of VFC Sympathetic activation -> increased venous tone -> increase in dead pressure = increase in VFC Skeletal muscle pump -> increase in dead pressure -> Increase in VFC Result - much higher CO (4-5 fold) and increased CVP. |
