cardiac output

Question 1

define cardiac output

Answer 1

the amount of blood pumped by the heart per minute

Question 2

what 2 major factors determine the magnitude of cardiac output

Answer 2

heart rate and stroke volume (cardiac output = stroke volume x heart rate)

Question 3

what is the relationship between end diastolic volume and the magnitude of stroke voluem

Answer 3

end diastolic volume = the total amount of blood in the ventircles after completely filling (preload)
stroke volume = difference between end diastolic volume and end-systolic volume (increased end diastolic volume = increased stroke volume

Question 4

what are the 2 main factors that determine end-diastolic volume

Answer 4

the pressure difference between the lumen of the ventricles and the thoracic cavity

Question 5

define the frank-starling mechanism

Answer 5

a physiological principle that explains how the heart responds to changes in venous return. increases in venous return cause the heart’s chambers to fill with blood which then causes the heart to stretch more and contract more forcefully to pump more blood out to the rest of the body

as venous return increases, cardiac output increases

Question 6

define the term contractility

Answer 6

describe the relative abaility of the heart to eject a stroke volume at a given prevailing afterload and preload (ability to contract)

Question 7

when considering cardiac function, which index is more important for perfusion of peripheral tissues - cardiac output or blood pressure

Answer 7

caridac output: allows more blood to diffuse into the tissues. blood pressure is not a good indicator alone

Question 8

how does contractility of the heart change during physical activity? how is this brought about?

Answer 8

• contractility increases due to the increased need to provide skeletal muscles with O2
• enables the heart to be able to handle a greater preload and empty more ompletely
• increase in SNS tone results in increase in HR. activation of beta 1 adrenoreceptors on cardiomyocytes - this is activated by noradrenaline being released from the SNS which increases intracellular calcium

CO increases, rate of contraction increases along with strength of contraction, stroke volume increases, systolic BP increases (no change in diastolic BP)

Question 9

what changes occur to HR, venous return, total peripheral tissue fluid volume and urine output after major haemorrhage

Answer 9

HR: decrease in BP due to blood volume loss leads to HR increasing to compensate and maintain cardiac output. regulated by the SNS which releases noradrenaline to stimulate beta-1 adrenergic receptors on the heart
venous return: reduced venous return due to decreased blood volume. and dilation of vessels
total peripheral resistance: decreases since BP = cardiac output x TPR)
tissue fluid volume: decreases as tissue perfusion decreases and tissue fluid will enter the circ. system to help with blood loss
urine output decreases as less blood perfusion to kidney to make urine ( also SNS restricts urinary function)
controlled by SNS

Question 10

what happens to cardiac output in heart failure

Answer 10

decreases - limits stroke volume by increasing end diastolic volume. heart unable to contract as well as has to work harder