The Cardiac Cycle

Question 1

What happens if cardiac muscle is stretched with a preload?

How about if an afterload is added and length is stabilized

Answer 1

It will contract stronger.

Contraction will not be as effective with afterload attached.

Question 2

Physiological preload correlate:

Answer 2

Ventricular filling from veins/atria. Stretches the cardiomyocytes in the ventricles.

Question 3

Physiological afterload correlate:

Answer 3

Existing arterial pressure. TPR = MAP/CO

Question 4

Explain the phases of the Wiggers Diagram:

Answer 4

A: LV pressure increases dramatically after QRS complex. This occurs because AP leads to contraction. Aortic pressure decreasing.

B: Volume decreases as LV pressure increases over aortic pressure. Aortic pressure then increases due to compliance. Ejection is occuring. LA pressure increases as blood fills it.

C: LV pressure decreases as relaxation occurs.

D: LA pressure higher than LV pressure, so volume increases as blood fills entricle.

Question 5

What does the beginning of the first LV volume plateau signify?

Why does the plateau exist?

What is this called?

Answer 5

Mitral Valve Closure. Here LVP>LAP.

Plateau exists because aortic valve is still closed. Aortic pressure > LVP.

This is called isovolumic contraction because the volume is constant, but the LV is contracting.

Question 6

What happens at the beginning of the second LV volume plateau?

What does this plateau signify?

What is happening to end the second plateau?

Answer 6

Aortic Valve closes because Aortic Pressure >LV pressure.

This plateau is isovolumic contraction. The volume stays the same because the aortic value is closed. The cells in the LV are relaxing so pressure decreases.

The mitral valve is opening because LAP > LVP

Question 7

Explain the rise in volume after the second plateau.

What is the bump?

Answer 7

This is where the LV is filling. Its pressure doesn’t change much because there’s no contraction, but the volume is increasing rapidly.

The bump is the atrial kick, where the LA contracts and shunts more blood into the ventricle.

Question 8

Location and explanation of heart sounds.

Answer 8

S1 : closing of AV values. Occurs to start off isovolumic contraction.

S2: Closing of aortic and pulmonary valves. Occurs to start off isovolumic relaxation.

Question 9

Purpose of valves?

Answer 9

To ensure unidirectional flow.

Question 10

Valvular insufficiency vs Valvular Stenosis

Answer 10

Insufficiency –> Valves do not close properly

Stenosis–> Partial blockage.

Question 11

Draw a pressure volume loop

Answer 11

Question 12

Where on the PV loop diagram do the aortic valve and mitral valve open and close?

Answer 12

Question 13

What is end systolic volume?

What part of PV loop corresponds to end systolic volume?

Answer 13

ESV is the volume in the ventricle after contraction.

Question 14

What is end diastolic volume?

What part of PV loop corresponds to end diastolic volume?

Answer 14

EDV is the volume in the heart before contraction.

Question 15

Stroke Volume

Answer 15

EDV-ESV

Width of the PV loop

Question 16

Ejection Fraction

Answer 16

SV/EDV

Question 17

Where are Pressure at end systole, end diastolic pressure, and left atrial pressure found on the PV loop?

Answer 17

Question 18

Systolic and diastolic blood pressure

Answer 18

Systolic BP: Highest aortic pressure

Diastolic BP: Pressure where ejection occurs

Systole is when ventricles contract. Diastole is when ventricles relax.

Question 19

Between what two boundaries does the PV loop sit?

Answer 19

ESPVR

EDPVR

End Systolic/Diastolic Pressure-Volume Relations

Question 20

Graph of EDPVR

Answer 20

Nonlinear, defines the lower boundary for the end-diastolic pressure volume point of the PV loop

Question 21

What does the slope of the ES/DPVR mean?

Answer 21

Flat=compliant, steep, less compliant

So, for EDPVR, at low volume, the ventricle is compliant. As it fills, it becomes less compliant and more difficult to fill.

Question 22

Increased preload effect on PV loop

Answer 22

Curve shifts to right along EDPVR. Stronger contraction occurs and higher pressures are generated, so shifts right along ESPVR too.

Increased preload equal increased stroke volume.

Question 23

Explain the Starling Curve

Answer 23

As preload increases (LVEDP), SV increases.

Question 24

What factors increase preload?

Answer 24

Fluid retention (in advanced heart failure)

Venoconstriction

Question 25

What factors decrease preload?

Answer 25

Dilation of veins, blood loss

Question 26

Increased afterload effect on PV loop

Answer 26

Shift to right along ESPVR, which will increase pressure and decrease SV. Isovolumic contraction increases because of higher resistance in arteries. Ejection cannot occur at lower pressures. No change in EDPVR.

Question 27

What increases afterload?

Answer 27

Temporary constriction of arterioles, chronic hypertension, aortic stenosis

Question 28

What decreases afterload?

Answer 28

Dilation of arterioles.

Question 29

How does contractility change PV loop?

Answer 29

Shifts the ESPVR. This occurs when inotropic drugs are given. Also, doesn’t affect point on EDPVR and does not affect ejection point.

Question 30

Factors that increase contractility

Answer 30

B adrenergic stimulation, increased plasma Ca, increased muscle mass

Question 31

Factors that decrease contractility

Answer 31

Beta blockers, ca blockers, ischemia/hypoxia, decreased muscle mass secondary to MI