chapter 20( Cardiac output, venous return and their regulation) Flashcards Preview

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cardiac output

quantity of blood pumped into arota each minute by the heart each minute


venus return

quantitiy of blood flowing from the veins into the right atrium each minute.


factors that affect cardiac output

metabolism, whether someone excersizes, age, size of body.


frank starling law of the heart

increased blood flow to heart stretches the walls of the heart chamber which causes them to contract harder


heart peripheral resistance

more resistance= less output. Less resistance= more output


cardiac output

arterial pressure/ total peripheral resistance


hypereffective heart

pumps better than normal


name 2 factors that help the heart pump better than normal

1. nervous stimulation which increases the strength of contraction
2. hypertrophy which allows the heart to have a huge output


hypoeffective heart and what causes it.

pumps less than normal. Hypertension, inhibition of nervous excitation of heart, abnormal heart rhythms, coronary artery blockage, valvular disease, congenital heart disease


name some cases where you have a high cardiac output caused by low peripheral resistance

beriberi, arteriovenous fistula, hyperthyroidism, anemia



caused by insufficient quantity of Thiamine ( B1) in diet. This diminishes the ability of tissues to use some cellular nutrients and the local tissue blood flow mechanisms in turn cause marked compensatory peripheral vasodilation


Arteriovenous fistula

when a major artery shunts with a vein. This decreases the peripheral resistance



oxygen usage increases and vasodilator products are released from tissue which lowers the peripheral resistance



blood is not as viscous due to less RBC's and resistance decreases


what are the two categories of low cardiac output?

abnormalities that cause pumping effectiveness, and those that lower the venous return


what causes abnormalities that cause pumping effectiveness?

anything that affects the heart. Cardiac shock- nutrientes are not getting to tissues


what causes abnormalities that lower venous return?

anything that interferes with venous return. Decreased blood volume, acute venous dilation, abstruction of large veins, decreased tissue mass, decreased metabolic rate of tissues


normal venous return

will decrease to zero when RA pressure rises to +mmHg


mean systemic filling pressure (psf)

systemic pressure when all flowing stops


mean circulatory filling pressure

when no flow is occurring the pressures everywhere in the circulation become equal


nervous systems role

strong sympathetic stimulation constricts all the systemic blood vessels, inhibition of these relax and dilate the systemic vessels


effect of mean systemic filling pressure

the greater it is , the more venous return curve shifts upward and to the right


resistance to venous return

most of it comes from veins and some arterioles and small arteries. Veins are distensible so when they are full, they don't really affect the pressure which would affect the resistance. But with slight accumulation of blood in the arteries the pressure can raise greatly as much as 30 times as much as the veins


effect of resistance to venous retunr on the venous return curve

a decrease in this resistance to ½ normal allows twice as much flow of blood and therefore rotates the curve upward to twice as great a slope. An increase in resistance to twice the normal rotates the curve rotates the curve downward to one half as great a slope.


blood volume increase on pressure

an increase in volume increases the pressure


compensatory effects returning blood to normal levels

increased cardiac output which increases the capillary pressure so the fluid flows out into the tissue, increased pressure in the veins causes them to distend gradually as well as the blood reservoirs like the spleen and liver which reduces venous volume, excess flow through the peripheral tissues causes autoregularoty increase in peripheral vascular resistance which increases the resistance to venous return.


what does sympathetic stimulation do on cardiac output

makes the heart a stronger pump, increases the mean systemic filling pressure in the systemic circulation due to contraction of peripheral vessels


oxygen fick method for measureing cardiac output



indicator dilution method for measuring cardiac output