Lecture 27 10/23/23

Question 1

What factors determine cardiac output?

Answer 1

-heart rate
-preload
-afterload
-contractility

Question 2

What two factors determine the regulation/distribution of cardiac output?

Answer 2

-venous return
-vascular resistance

Question 3

What is heart rate, in terms of cardiac cycles?

Answer 3

the number of cardiac cycles per minute

Question 4

How does heart rate relate to cardiac output?

Answer 4

direct relation (one increases, the other increases)

Question 5

What is afterload related to?

Answer 5

-aortic pressure
-ventricular geometry

Question 6

Why is afterload considered to be complex?

Answer 6

the factors affecting it vary with each cardiac cycle

Question 7

How does afterload relate to ventricular emptying/stroke volume?

Answer 7

increased afterload = harder for ventricle to empty (inverse relationship between afterload and stroke vol.)

Question 8

What are the key points of afterload?

Answer 8

-forces that oppose myocardial shortening
-inversely related to stroke volume

Question 9

How do contractility and stroke volume relate?

Answer 9

increased contractility = increased stroke vol.

Question 10

What are the characteristics of the Frank-Starling mechanism?

Answer 10

-describes length-tension relationship of intact heart
-describes relationship between preload and cardiac output

Question 11

How does preload relate to stroke volume?

Answer 11

increased preload (increased ventricular filling) = increased stroke vol.

Question 12

How does ventricular filling relate to myocardial contraction?

Answer 12

increased end-diastolic volume/ventricular filling and stretch = increased force of contraction

Question 13

What are the microscopic characteristics of the Frank-Starling mechanism?

Answer 13

-stretch optimizes myosin-actin interaction
-stretch increases sensitivity of troponin-C to Ca2+

Question 14

What is the Fick principle?

Answer 14

cardiac output is inversely related to arteriovenous oxygen difference

Question 15

What is an example of the Fick principle?

Answer 15

-fast-moving blood = less O2 used = smaller arteriovenous difference = greater cardiac output

Question 16

Why does the Fick principle exist?

Answer 16

the slower blood moves, the more oxygen is extracted, causing a larger arteriovenous difference in oxygen conc.

Question 17

What are the characteristics of physiologic sinus arrythmia?

Answer 17

-normal p-wave preceding QRS by a consistent interval
-vagal input required, occurs at low heart rates
-gradual changes in RR
-rate increases with inspiration
-abolished by atropine

Question 18

What determines CO according to Frank-Starling?

Answer 18

venous return

Question 19

How does vascular resistance impact afterload?

Answer 19

vascular resistance changes in response to pressure and flow, and changes the associated afterload

Question 20

What is a cardiac output curve?

Answer 20

graph showing the relationship between preload and cardiac performance

Question 21

What are the determinants of venous return?

Answer 21

-intravascular volume
-muscular venous pump
-venous tone

Question 22

How does venous return impact preload and stroke volume?

Answer 22

increased venous return = increased preload and increased stroke volume

Question 23

What local factor impacts distribution of cardiac output?

Answer 23

increase in metabolism results in dilation of arterioles and local decrease in resistance/increase in flow

Question 24

What autonomic factor impacts distribution of cardiac output?

Answer 24

sympathetic tone causes vasoconstriction and local increase in resistance/decrease in flow

Question 25

What is the exception to SNS causing vasoconstriction?

Answer 25

beta-2 mediated vasodilation that increases flow to working muscle