Cardiac Output

Question 1

Cardiac output -

Answer 1

stroke V X HR

Question 2

Cardiac output vs cardiac index

Answer 2

similar but index accounts for body size (blood ejected per unit time per unit of body surface area)

Question 3

SV determinants:

Answer 3

• preload
• afterload
• ventricular contractility

Question 4

End Diastolic volume determinants:

Answer 4

• blood volume (hemorrhage, severe dehydration, excessive IV infusion)
• venous return-most common reason for changes in CO (changes in body position)
• intrathoracic pressure-can impede or facilitate venous return (straining or COPD = reduced return)
• effective atrial contraction-if you loose the atrial kick youre losing 20% of your EDV (a fib, AV block)
• AV valve function- mitral valve stenosis=narrow mitral orfice for filling of ventricle=dec EDV
• Ventricular compliance-compliance (stretch or dilation) of the ventricles. Could be dec due to restrictive cardiomyopathy or ischemia
• Conditions of the pericardium- pericardial effusion or chronic pericarditis= thickened pericardium = dec EDV
• changes in HR- shorten diastole = less time for filling and dec EDV

Question 5

What is Preload?

directly related to?

Answer 5

• Tension on the ventricular muscle before it contracts

- EDV (and also stroke volume)

Question 6

Frank Starling Law

Answer 6

• basically SV is directly related to EDV

- the more blood you put in it the more energy the heart will put into contraction up to a certain point (inotropy)

Question 7

Afterload what is it?

-factors?

Answer 7

• the force the ventricle must overcome to pump blood out into circulation
• force needed to overcome circulatory pressure to open aortic valve

Question 8

Factors affecting afterload?

Answer 8

• aortic valve stenosis - obstacle to flow

- peripheral arterial resistance- HTN, sympathetic activation, pulmonic valve stenosis or pulmonary arterial HTN

Question 9

End systolic function is?

• indicator of?
• factors?

Answer 9

• amount of blood in ventricle after A2 or P2 closes
• indicator of systolic function
• 3 factors: afterload, preload and contractility

Question 10

ANREP effect:

Answer 10

• cause abrupt increases in AFTERLOAD (hand grip exercise)
• afterload and contractility relationship

review this concept

Question 11

Bowditch phenomenon:

Answer 11

• faster stimulation rate inc force of contraction

- repetitive entry of Ca which each stimulation = accumulation of Ca in cardiac cells

Question 12

measuring CO

Answer 12

pulmonary artery catheterization thermodilution

• cardiac output is inversely related to the area undera thermodilution curve
• smaller area = higher CO