Regulation of stroke volume and heart rate

Question 1

regarding stroke volume, what does starlings law state?

Answer 1

the energy of contraction Is proportional to the initial length of the cardiac muscle fibre

Question 2

what is the afterload?

Answer 2

the load against which the muscle tries to contract

Question 3

if the afterload increases, what will happen to the stroke volume?

Answer 3

increase in afterload = increase in aortic pressure = increase in TPR
therefore the ventricle will have to work harder to push the blood which will be less effective as it is using up more energy.
this results in a decrease in SV

Question 4

afterload is set by the aortic pressure which depends on what?

Answer 4

TRP

Question 5

what is the parasympathetic affect on stroke volume?

Answer 5

it has little effect because the vagus nerve doesn’t innervate the ventricular muscle

Question 6

does hypercalcaemia cause an increase or decrease in stroke volume?

Answer 6

increase

Question 7

does ischaemia cause an increase or decrease in stroke vol?

Answer 7

decrease

Question 8

does hypocalcaemia cause an increase or decrease in stroke vol?

Answer 8

decrease

Question 9

how does the heart compensate for a reduction in pumping ability?

Answer 9

the heart will compensate by working around a greater EDV.

this however results in a lower ejection fraction and reduced exercise capacitance

Question 10

name a type of drug which causes a decrease in stroke volume?

Answer 10

barbiturates

Question 11

heart rate X stroke volume = ?

Answer 11

heart rate

Question 12

why does increasing the heart rate with an electronic pacemaker cause a small increase in CO but then SV decrease?

Answer 12

the shortened cardiac interval cuts into the rapid filling phase
this reduces EDV which reduces pre load and therefore stroke volume