Flashcards in chapter 20( Cardiac output, venous return and their regulation) Deck (29)
quantity of blood pumped into arota each minute by the heart each minute
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
arterial pressure/ total peripheral resistance
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
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