Term
| How is cardiac output related to venous return? |
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Definition
The heart can only pump what it receives The heart generates pressure by ejecting the stroke volume against a resistance Venous return requires a pressure gradient between the venous blood and the right atrium Over time the venous system can only return the volume of blood that has been pumped into it |
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Term
| Explain the cardiac function curve |
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Definition
Increases right atrial pressure (end-diastolic volume) -> increases in cardiac output up to a certain point according to Frank-Starling relationship Increases venous return -> increases atrial pressure -> increases end-diastolic volume -> increases end-diastolic fiber length -> increases in cardiac output At steady state: Cardiac Output ejected by left ventricle = Venous Return receive by the right atrium |
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Term
| Explain the vascular function curve |
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Definition
Inverse relationship between venous return and right atrial pressure The flat portion of the curve (knee) occurs when atrial pressure is negative -> large veins collapse -> venous return levels off |
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Term
| Explain mean systemic pressure |
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Definition
Mean systemic pressure is the right atrial pressure when the venous return is zero (hypothetical situation) Two factors affect mean systemic pressure: 1- Blood volume in the venous pool 2- Compliance of the veins Increases blood volume and decreases compliance of the veins -> increases mean systemic pressure (shift vascular function curve to the right) Decreases blood volume and increases compliance of the veins -> decreases mean systemic pressure (shift vascular function curve to the left) - increased compliance means the veins can hold more volume and the amount of unstressed volume increases (stressed volume decreases) |
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Term
| How are the vascular function and cardiac function curves coupled? |
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Definition
The point where the curves intersect is where cardiac output is equal to venous return This intersection is normally where CO is 5 L/min and RA pressure is 2 mm Hg |
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Term
| How do inotropic agents affect the cardiac function and vascular function curves? |
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Definition
* positive inotropic effect - CO curve is shifted to the left, increased CO and reduced RA pressure. ONLY the CO curve is affected * negative inotropic effect - CO curve is shifted to the right, decreased CO and increased RA pressure. ONLY the CO curve is affected |
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Term
| How do changes in blood volume affect the cardiac and vascular function curves? |
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Definition
* increase in blood volume - increase in venous return, increase in RA pressure, increase in CO. ONLY vascular function curve is shifted * decrease in blood volume - decrease in venous return, decrease in RA pressure, decrease in CO. ONLY vascular function curve is shifted |
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Term
| How do changes in total peripheral resistance (TPR) affect the cardiac and vascular function curves? |
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Definition
* increase in TPR - decreases CO and decreases venous return. BOTH curves are shifted down * decrease in TPR - increases CO and increases venous return. BOTH curves are shifted up |
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Term
| How does muscle blood flow change during exercise? |
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Definition
Skeletal muscle blood flow At rest: 3-4 ml/min/100g muscle During extreme exercise: 50-80 ml/min/100g muscle Low flow during contraction= muscle "squeeze" effect on the vessels |
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Term
| How is blood flow to skeletal muscle increased during exercise? |
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Definition
*ANS -> increased sympathetic outflow and decreased parasympathetic outflow (HR only) increased HR, increased contractility, increased CO, constriction of arterioles (splanchnic and renal), constriction of veins, decrease in unstressed volume - increased systolic arterial pressure -> increased blood flow *local responses - increased vasodilator metabolites, dilation of skeletal muscle arterioles, decreased TPR leads to increased blood flow |
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Term
| How does cardiac output change during exercise? |
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Definition
Exercise -> significant increase in cardiac output due to sympathetic stimulation which leads to: a) increased contractility b) increased HR |
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Term
| How does venous return change during exercise? |
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Definition
Exercise -> significant increase in venous return due to: a) increased mean systemic pressure (sympathetic stimulation) b) decreased resistance in all blood vessels in the active muscle c) increased ventilation (thoracic suction pump) d) Pumping action of contracting muscle |
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Term
| How do cardiac and vascular function curves change during heart failure and the compensation that follows? |
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Definition
1) heart failure decreases CO and increases RA pressure - shifts CO curve to the right 2) sympathetic activity is significantly increased (shifts CO curve up), increased venous tone (vascular curve shifted up) - CO increased while RA pressure stays constant 3) sympathetic activity decreases to a slightly higher than normal level (shifts CO curve to the right), kidney kicks in to retain more fluid (increase blood volume) - CO slightly increased while RA pressure increased 4) sympathetic activity decreases to normal levels and kidney retains even more fluid - CO slightly increased while RA pressure increased |
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