The Cardiac Cycle 1

Question 0

What’s a normal peak systolic pressure? What areas of the heart / vasculature experience this pressure?

Answer 0

Roughly 120 mmHg.

The left ventricle and aorta experience this pressure.

Question 1

Should you confuse flow rate with flow velocity?

Answer 1

Nope.
Flow rate: L / min
Flow velocity: cm / s

Question 2

What are the 4 phases of the cardiac cycle, from the perspective of the ventricles? How long does each last?

Answer 2

Isovolumetric relaxation (myocytes relax, but not enough to cause the tricuspid and mitral valves to open).
Diastolic filling.
Isovolumetric contraction (myocytes contract, but pressure doesn’t in ventricle doesn’t exceed that of PA or aorta).
Systolic ejection.

Question 3

How long does isovolumetric relaxation usually last?

Answer 3

12-16ms

Question 4

How long does diastolic filling of the ventricles usually last?

Answer 4

150-800ms depending on HR

Question 5

How long does isovolumetric contraction usually last?

Answer 5

10ms

Question 6

How long does systolic ejection usually last?

Answer 6

250-280ms

Question 7

When do the atria fill?

Answer 7

During ventricular systole.

Question 8

About how long before ventricular systole does atrial systole occur? During what phase of the ventricles’ cardiac cycle does it end?

Answer 8

120 - 160ms beforehand.

It should end during isovolumetric contraction (there’s some overlap of systoles).

Question 9

Should diastolic relaxation be taken for granted?

Answer 9

Nope. It’s an active process, and optimum filling doesn’t occur when there’s reduced ventricular compliance.

Question 10

4 components of the AV valves (mitral and tricuspid)?

Answer 10

Valve leaflets
Annuli fibrosa
Chordae tendineae
Papillary muscles

Question 11

4 things that happen for AV valves to properly close?

Answer 11

Passive movement of valve leaflets driven by pressure.
Contraction of the annulus fibrosis.
Contraction of papillary muscles.
Proper contraction of ventricles such that valve leaflets line up.

Question 12

What are 2 requirements for semilunar valve closure?

Answer 12

Passive movement of leaflets.
Contraction of annulus fibrosis.
(they’re simpler than AV valves)

Question 13

What are 2 broad types of problems that occur with heart valves?

Answer 13

Regurgitation (backflow)

Stenosis (failure to fully open)

Question 14

What is pulse pressure?

Answer 14

The difference between systolic and diastolic pressure.

Question 15

What are the 3 phases of the arterial pressure waveform?

Answer 15

Rapid upstroke with early systole.
Rounded peak in mid to late systole (featuring the dichrotic notch due to semilunar valve closure).
Gradual decay of pressure in diastole.

Question 16

4 parts of the atrial pressure waveform?

Answer 16

A wave: positive deflection due to atrial contraction
X descent: negative deflection due to atrial relaxation (diastole)
V wave: positive deflection due to atrial filling
Y descent: negative deflection due to atrial emptying
(I like to think of the Y descent as the ventricles’ relaxation “sucking” the blood out of the atria, then the A wave contraction gives a little extra kick)

Question 17

What’s end diastolic pressure (LVEDP)? Significance?

Answer 17

Pressure in the LV at the end of diastole.

It reflects the extend of ventricular filling, aka. “preload.”

Question 18

Do large arteries cushion the systemic circulation from the pressure changes of systole/diastole?

Answer 18

Yup.

Question 19

Why is blood pressure in large arteries greater further from the heart?

Answer 19

Reflections from blood hitting small arteries.

the aortic valve seems to close just in time to be closed when the reflections hit

Question 20

How does the effect of pressure wave reflections in arteries vary between young and old people?

Answer 20

In young people, compliant arteries cushion the reflections.
In older people, arteries stiffened by atherosclerosis can’t cushion the reflections, which can contribute to hypertension.

Question 21

Say the systolic pressure is 120 mmHg in the LV. What’s the systolic pressure in the RV likely to be? Why?

Answer 21

Around 25 mmHg.

It’s lower because the top of the lungs aren’t as high up as the head (???… does that make sense?)

Question 22

Why is diastolic pressure lower in the RV than in the LV?

Answer 22

Because the RV is more compliant.

Question 23

What information does the right atrial pressure provide?

Answer 23

Blood volume and hydration state.

Question 24

What region of circulation has the same pressure as the mean left atrial pressure?

Answer 24

The pulmonary capillaries.