L11 Heart- Cardiac Muscle Mechanics

Question 1

Define the four determinants of cardiac output.

Answer 1

Heart rate
Preload
After load
Contractility

Question 2

How does heart rate affect cardiac output?

Answer 2

Increased HR= increased cardiac output

Question 3

How does preload affect cardiac output?

Answer 3

Increase in preload= increase stretch= increase cardiac output/stroke V

Question 4

How does afterload affect cardiac output?

Answer 4

Increase afterload (BP)= decrease cardiac output/ stroke V

Question 5

How does contractility affect cardiac output?

Answer 5

Increase contractility= Increase cardiac output/ stroke V

Question 6

Define isometric contraction.

Answer 6

Contraction WITHOUT shortening (no change in length)

-Muscle unable to generate enough force to meet the afterload

Question 7

Define isotonic contraction.

Answer 7

Contraction WITH shortening and constant force (no change in force)
-Muscle is able to generate enough force to meet afterload

Question 8

Define resting (diastolic) tension.

Answer 8

Amount of tension that develops passively by stretching the muscle (increasing preload)

• Preload is ventricular filling volume (end-diastolic V)
• Slope of resting tension curve is primarily determined by muscle compliance

Question 9

Define active (systolic) tension.

Answer 9

Amount of isometric tension that is developed by muscle contraction at a particular muscle length (preload)

• Systolic tension curve represents stroke V
• Slope of active tension curve is primarily determined by contractility

Question 10

Define the length-tension relationship of cardiac muscle.

Answer 10

1

Question 11

Define compliance.

Answer 11

Change in volume (length) in relation to change in pressure (tension)
change in V = Change in length
__________ _____________
Change in P Change in tension

-How much does something move when you push on it? How much does something stretch when you apply tension?

Question 12

How does compliance affect the slope of the resting tension curve?

Answer 12

1

Question 13

Define contractility.

Answer 13

I

Question 14

How does contractility affect the slope of the active tension curve?

Answer 14

1

Question 15

Define how contractility affects peak isometric tension development and relaxation.

Answer 15

1

Question 16

Define how contractility affects the amount of isotonic muscle shortening.

Answer 16

1

Question 17

Define the force-velocity relationship.

Answer 17

1

Question 18

How is the force-velocity relationship affected by changes in preload?

Answer 18

1

Question 19

How is the force-velocity relationship affected by changes in afterload?

Answer 19

1

Question 20

How is the force-velocity relationship affected by changes in contractility?

Answer 20

1

Question 21

How is stroke volume affected by changes in preload?

Answer 21

1

Question 22

How is stroke volume affected by changes in afterload?

Answer 22

1

Question 23

How is stroke volume affected by changes in contractility?

Answer 23

1

Question 24

Define preload

Answer 24

Load on the muscle BEFORE contraction is initiated, how much blood is in the heart before contraction
-Dependent on ventricular filling (end-diastolic V)

Question 25

Define afterload

Answer 25

Load on the muscle AFTER contraction is initiated, any force that resists muscle shortening, BP
-Arterial pressure is the force that resists L ventricle contraction

Question 26

Define contractility

Answer 26

Inherent ability of actin and myosin to form cross-bridges and generate contractile force

• Primarily determined by intracellular Ca
• More intracellular Ca= more cross bridge formation= stronger contraction
• Increased contractility (postive inotropic effect) shifts slope of active tension curve up and left
• Decreased contractility (negative inotropic effect) shifts slope of active tension curve down and right

Question 27

During a normal cardiac cycle, cardiac muscle initially generates _______ tension and then ______ contractions.

Answer 27

Isometric, isotonic

Question 28

What is the equation for cardiac output?

Answer 28

HR x stroke V