Heart Failure

Question 1

What is the equation for CO?

Answer 1

CO=HR* SR

3 determinants of stroke volume=contractility, preload, afterload

Question 2

WHat is the significance of preload and what is it measured as? How does cardiac function relate to preload?

Answer 2

the more a normal ventricle is distended (fille with blood) during diastole, the greater the amount of blood ejected during the next contraction (Frank-starling)

Cardiac function increases as a function of preload

preload is measured as end-diastolic volume or pressure (indicates the degree of myocardial stretch at the end of diastole

Question 3

What is afterload? how is afterload influenced by higher pressure load? How does the heart compensate for wall stress?

Answer 3

resistance ventricle must overcome to empty its contents (ventricular wall stress that develops during systolic ejection, estimated by LaPlace)

rises in response to higher pressure load (HTN) or increased chamber size (dilated LV)

increases in wall thickness serves a compensatory role to reduce wallstress

Question 4

What is contractility?

Answer 4

accounts for the changes in myocardial force for a given set of preload and afterload conditions (dependent on chemical and hormonal influences)

on a frank starling curve a change in contractility shifts the curve in an upward or downward fashion (doesn’t change slop just shifts it up or down)

Question 5

WHat is the purpose of a pressure-volume loop?

Answer 5

relates changes in ventricular volume to corresponding changes in pressure thorugh a cardiac cycle