All about the Wiggers Diagram

Question 1

Define: Cardiac Output

Answer 1

CO is the flow of blood into the aorta from the heart

Question 2

What transmitter do sympathetic nerves use on the heart? On what type of receptor does it act? What happens to the second messenger? What results from stimulation?

Answer 2

Norepinephrine acts on B1 adrenergic receptors. This increases cAMP and increases the HR and contractility of the muscle

Question 3

What transmitter do parsympathetic nerves use on the heart? On what type of receptor does it act? What happens to the second messenger? What results from stimulation?

Answer 3

Acetylcholine which acts on M2 receptors to decrease cAMP, decreasing HR and contractility

Question 4

What are some intrinsic mechanisms that can regulate CO?

Answer 4

EDV (increased preload) and a change in the membrane potential

Question 5

How is cardiac output related to oxygen consumption?

Answer 5

Directly. Increased O2 consumption increases CO

Question 6

What are some factors that increase CO?

Answer 6

Exercise, fever, anxiety, greater body weight, pregnancy, hyperthyroidism, anemias

Question 7

What are some factors that decrease CO?

Answer 7

Sleep, aging, severe anoxia, hemorrhage, heart disease

Question 8

How does exercise affect cardiovascular function? Give specific mechanisms

Answer 8

Mechanically, muscle contractions enhance venous return which increases EDV and thus CO. Chemically, lower blood O2 levels with higher blood CO2 levels stimulate local vasodilation which decreases MAP. Baroreceptors respond to this by stimulating an increase in CO

Question 9

In a normal ECG, what does the P wave represent? What about the PR interval? The QRS complex? The ST segment? The T wave?

Answer 9

P wave- atrial depolarization
PR interval- atrial contraction
QRS complex- ventricular depolarization (and atrial repolarization)
ST interval- ventricular contraction
T wave- ventricular repolarization

Question 10

How do the different waves and intervals of the EKG correspond to the phases of the cardiac cycle?

Answer 10

QRS complex- Phase 0 (inward Na current)
ST interval- Phase 2 (plateau, inward Ca and outward K currents)
T wave- Phase 3 (outward K current)
TP segment and P wave- Phase 4 (iK1 channel and outward K current)

Question 11

When does most ventricular filling occur? What is the significance of atrial contraction?

Answer 11

Early in diastole (before atrial contraction). Atrial contraction is at the end of diastole and contributes to a small change in ventricular pressure

Question 12

Why does LV volume increase but pressure decreases at the beginning of diastole?

Answer 12

The forward momentum of the blood expands the ventricles upon filling, causing an increase in volume and a decrease in the ventricular pressure

Question 13

Why does blood get ejected from the LV? Is this always true?

Answer 13

P (LV) > P (aorta) during rapid ejection of blood
During slow ejection of blood, P (aorta) is greater and blood moves into the aorta because it has enough forward momentum to keep moving forward while the ventricle relaxes

Question 14

What do the waves in jugular pulse represent? (A, C and V)

Answer 14

A- atrial contraction
C- closure of tricuspid valve
V- atrial filling and emptying

Question 15

What does the S1 heart sound correspond to? What about the S2 sound? S3? S4?

Answer 15

S1- “lub”, mitral valve closure (end of diastole)
S2- “dub”, aortic valve closure (end of systole)
S3- diastolic filling “gallop.” recoil of ventricles that have limited compliance
S4- Atrial contraction “gallop.”

Question 16

Describe what occurs to form the dichotic notch

Answer 16

In the aortic pressure curve, pressure drops slightly at the end of systole then rises a bit. This is because when the aortic valve closes, some blood moves against it towards the ventricle. The valve catches it and drives it forward, increasing the pressure in the aorta slightly

Question 17

Which atrium contracts first? Which ventricle?

Answer 17

Right atrium is first. Left ventricle is first

Question 18

Which valve is open for a longer period of time: mitral or tricuspid? How about aortic or pulmonic?

Answer 18

Tricuspid and pulmonic are open longer

Question 19

Why does the left ventricle undergo isovolumic contraction and relaxation?

Answer 19

It needs to exceed P (aorta) to pump the blood into it. But it also needs to be less than P (LA) so it can receive blood in diastole. The isovolumic contraction and relaxation allow it to change in pressure to do these things

Question 20

On a pressure-volume loop, how would you define ventricular stroke work?

Answer 20

The area inside the loop

Question 21

What are some factors that influence stroke volume?

Answer 21

Increase SV: increased contractility, increased EDV, increased ventricular compliance, increased filling time
Decreased SV: Increased afterload, increased HR, increased atrial filling pressure

Question 22

Define: ejection fraction. How would you calculate it?

Answer 22

EF= SV/EDV. The proportion of blood ejected by the ventricle in 1 contraction. In a normal person, is about 55%