Lecture 11- Cardiac output

Question 1

What is the formula for cardiac output?

Answer 1

Cardiac output = Heart rate x stroke volume

Question 2

Define all the parts of the Cardiac output formula

Answer 2

CO= HR x SV

Cardiac output= volume of blood ejected by each ventricle per minute. (L/min)

Heart rate= no. of contractions per minute.

Stroke volume= Volume of blood ejected by the heart per beat.

Question 3

What are the 3 ways in which the heart is innervated?

Answer 3

1. Blood volume reflexes- chemoreceptors and baroreceptors
2. Autonomic innervation. Parasympathetic nerves innervate SAN. Sympathetic innervate SAN and ventricles.
3. Sympathetic via adrenal gland.-
   Sympathetic to gland to release adrenaline

Question 4

How does a positive chronotropic effect change cardiac output?

Answer 4

Positive chronotropic means heart rate increases. So cardiac output increases

Question 5

How do adrenaline and noradrenaline affect heart rate?

Answer 5

They increase heart rate by increasing the slope of the pacemaker potential. Means it doesnt need to repolarize as much so there is more rapid depolarization. More action potentials generated.

Question 6

What effect does acetyl choline have on heart rate?

Answer 6

Slope of pacemaker potential decreases.

Negative chronotropic effect. The threshold for action potential shifts to more hyperpolarized potentials.

Question 7

WHat is the formula for stroke volume?

Answer 7

Stroke volume= End Diastolic Volume- End Systolic Volume

Question 8

How do you get a high stroke volume and so a high cardiac output?

Answer 8

High end diastolic volume and low end systolic volume.

High EDV, Low ESV

Question 9

What 3 things influence the dynamics of stroke volume?

Answer 9

1. Preload- degree of filling of the heart
2. Afterload- pressure opposing ejection influenced by blood vessel tone. (vasodilation/vasoconstriction?)
3. Energy of contraction- regulated by SNS and adrenaline