Cardiovascular physiology part 3

Question 1

What is cardiac output?

Answer 1

volume of blood pumped out by each ventricle per minute.

Question 2

What are the two determinants of cardiac output?

Answer 2

stroke volume and heart rate
cardiac output = stroke volume x heart rate
at rest, cardiac output is close to total blood volume

Question 3

What is cardiac reserve?

Answer 3

the maximum percentage of increase that can happen to cardiac output.

Question 4

What is stroke volume?

Answer 4

the volume of blood pumped by each ventricle per beat. there is a difference between end diastole volume (EDV) and end systolic volume (ESV).
SV = EDV - ESV

Question 5

What is ejection fraction?

Answer 5

fraction of end diastolic volume that’s ejected during one systole. normal EF is from 50-80%.
SV/EDV = EF

Question 6

What does it mean if EF is less than 50%?

Answer 6

depressed myocardial contractiblity (heart attack, heart valve problems).

Question 7

What does stroke volume depend on?

Answer 7

preload - degree that myocardium is stretched before it contracts. increase in preload increases the force of contraction (Frank starling law)
after load - resistance against which blood is expelled
cardiac muscle contractility.

Question 8

When is there a decrease in ventricular cardiac muscle?

Answer 8

pathologically when there is increased pericardial pressure and decreased ventricular compliance (aged heart or myocardial infarction).

Question 9

What is afterload?

Answer 9

the tension in the ventricular wall after ejection. it is determined by atrial pressure.
it is higher than pre load and rise in after load reduces stroke volume.

Question 10

What is contractility?

Answer 10

contractile strength of cardiac muscle at length.

Question 11

What factors affect contractility?

Answer 11

parasympathetic inhibition, sympathetic activation and circulating catecholmines.

Question 12

What are enhancing factors of contractility?

Answer 12

• increased Ca in the cell
• hormones
• caffeine

Question 13

When is contractility decreased?

Answer 13

hyperkalemia, hypercapnia acidosis and hypoxia.

Question 14

What are the factors affecting stroke volume?

Answer 14

raised due to:
preload (increases end diastolic volume)
contractility (decreases end systolic volume)
afterload (increases end systolic volume)
lowered due to:
preload (decreases end diastolic volume)
contractility (increased end systolic volume)
afterload (decreases end systolic volume)

Question 15

Why does heart failure reduce contractility?

Answer 15

due to malfunctioning of the valves. this happens in both cats and dogs,