Heart as a Pump (it up)

Question 1

Cardiac Output (CO) Definition and Equation

Answer 1

Volume of blood pumped per minute by left ventricle. CO = Stroke Volume (SV) * Heart Rate (HR). or CO = arterial pressure ÷ total peripheral resistance

Question 2

CO is mainly affected by….?

Answer 2

Heart Rate. The HR can increase by a large percentage than SV can which causes larger increases in CO.

Question 3

Stroke Volume Determinants and their effects

Answer 3

Afterload- Negative
Preload- Positive
Contractility (Inotropy)- Positive

Question 4

Two factors that affect contraction strength

Answer 4

1) Length-Dependent intrinsic mechanism (Frank-Starling)

2) Length-Independent mechanism (Inotropy) - regulated via sympathetic nervous system stimulation

Question 5

Edema results from….?

Answer 5

Unequal cardiac output from both sides of the heart.

Question 6

Define Diastole

Answer 6

The atrium is full of oxygenated blood which is signaled to contract by the SA node. As the atrium contracts, the atrial pressure increases which opens the mitral valve and allows blood to fill the left ventricle.

Question 7

Define Isovolumetric Expansion

Answer 7

As the left ventricle begins to contract, the mitral valve immediately closes as the pressure begins to rise. The pressure continues to rise with both valves closed as the ventricle contracts until the pressure in the ventricle is greater than that in the Aorta. It is at this point that the aortic valve opens and ejection begins.

Question 8

Define Ejection Phase

Answer 8

Once the pressure in the left ventricle exceeds that of the aortic pressure, the aortic valve open and ejection occurs. Contraction continues to occur until the max systolic blood pressure at which point the ventricle begins to relax and pressure drops until it is below that of the aortic pressure and the aortic valve closes again.

Question 9

Define Isovolumetric Relaxation

Answer 9

Once the aortic valve is closed, the pressure continues to fall rapidly while both valves are closed. The pressure will fall below that of the atrium and the mitral valve will open once again and this marks the end of isovolumetric relaxation.

Question 10

Explain Pressure-Volume Graphs

Answer 10

The graph presents the end-diastolic and systolic pressures for a range of blood volumes. The systolic is the pressure at maximum ventricular contraction and the end-diastolic is the pressure of the ventricle full of that specific volume of blood. The difference between the two lines is the active tension.

Question 11

Define a Starling Curve

Answer 11

It is a plot of cardiac performance as a function of preload. It is also based on the difference of the systolic and diastolic PV curves. All healthy hearts function on the ascending limb of the curve and ONLY hearts that are failing function in the descending portion.

Question 12

End Diastolic Pressure-Volume Relationship (EDPVR) is determined by…?

Answer 12

The elastic properties of the ventricle. This is known as compliance which is defined as C = deltaV / deltaP, however, EDPVR plot is the inverse of C. The EDPVR represents the PRELOAD on the heart.

Question 13

Define Preload

Answer 13

The length to which a muscle is stretched before shortening. For left ventricle, preload ~ end diastolic volume.

Question 14

Define Afterload

Answer 14

The load against which a muscle contracts.

For left ventricle, afterload ~ aortic pressure.

Question 15

Define Active Tension

Answer 15

Difference in force between peak systolic pressure and end diastolic pressure curves

Question 16

Three ways to state Starling’s Law

Answer 16

a) Heart responds to an increase in EDV by increasing the force of contraction.
b) Healthy heart always functions on the ascending limb of the ventricular function curve
c) What goes in, must come out. Cardiac output MUST equal venous return and cardiac output from left and right ventricles MUST match (on average).

Question 17

Molecular basis for Starling’s law

Answer 17

a) Cardiac titin isoform is very stiff, resists stretch.
b) Ca2+ sensitivity of myofilaments increases as sarcomeres are stretched. So the same intracellular Ca2+ produces a greater force of contraction.
c) Closer lattice spacing – stretched sarcomeres have altered spacing between actin & myosin which results in more force generated per crossbridge.

Question 18

Bainbridge Reflex

Answer 18

Stretch sinus node → increase in heart rate

Question 19

Filling Phase (PV Loop Diagram)

Answer 19

A to C

Question 20

Isovolumetric Contraction (PV Loop Diagram)

Answer 20

C to D

Question 21

Ejection Phase (PV Loop Diagram)

Answer 21

D to F

Question 22

Isovolumetric Relaxation (PV Loop Diagram)

Answer 22

F to A

Question 23

What point is the diastolic blood pressure?

Answer 23

D

Question 24

What point is the systolic blood pressure?

Answer 24

E

Question 25

What two sets of lines define the stroke volume?

Answer 25

C to D minus F to A (or C minus A)

Question 26

Point E minus Point D is what value?

Answer 26

Pulse Pressure!

Question 27

Stroke Volume equals?

Answer 27

EDV - ESV

Question 28

Ejection Fraction equals?

Answer 28

EF = SV/EDV or (EDV-ESV) / EDV

Question 29

Stroke work is?

Answer 29

Energy per beat (joules) that corresponds to the integral of the PV loop diagram. NOT the same for both sides of the heart.

Question 30

Factors that affect preload

Answer 30

o Blood volume (IV fluid, hemorrhage)
o filling pressure (venous blood pressure)
o filling time (reduced at high heart rates)
o resistance to filling (e.g. AV valve stenosis)
o resistance to emptying = afterload (e.g. hypertension)
o reduced inotropy (contractility)

Question 31

Compliance volume to pressure relationship? Slope?

Answer 31

Increased compliance causes a decreased pressure for any given volume. This causes a decreased slope. The reverse is also true for decreased compliance.

Question 32

Causes of increased and decreased compliance?

Answer 32

Decreased- Hypertrophy or diastolic heart failure

Increased- Dilated cardiomyopathy

Question 33

Increased EDV (preload) results in what?

Answer 33

Immediate effect is an increase in stroke volume via Starling’s Law. Ventricle matches increased EDV with increased stroke volume. Subsequent beats = SV returns to normal.

Question 34

Increased Afterload results in what?

Answer 34

Decrease in SV on the next beat. (EDV unchanged, EF decreased, ESV increased and SV decreased). SV recovers on next beat due to the increased ESV with constant venous return means increased EDV → increased SV

Question 35

Increased Inotropy results in what?

Answer 35

Results in a new Starling Curve. Increased systolic pressure at any given volume, increased stroke volume and ejection fraction and a decrease in end systolic volume. These effects last as long as the inotropy remains high.