Lecture 28 - Cardiovascular System: The Cardiac Cycle and Cardiac Output

Question 1

What does the cardiac cycle generate?

Answer 1

It generates pressure to produce cardiac output, causing blood flow into and through the blood vessels. This pressure drives blood out of the heart and into the systemic and pulmonary circuits

Question 2

What is cardiac output and what is the formula to calculate it?

Answer 2

The volume of blood pumped into the aorta by the left ventricle each minute

CO = stroke volume (SV) x heart rate (HR) = mL/min

This describes the volume of blood (mL) moved through the heart into the systemic circuit given a time (min)

Question 3

What is heart rate (HR)?

Answer 3

The number of cardiac cycles (beats) per minute (bpm)

Question 4

What is stroke volume (SV)?

Answer 4

The volume of blood (mL) ejected into the artery during each cardiac cycle (mL/beat)

Question 5

Describe Wiggers Diagram

Answer 5

It shows the relationship between time, pressures, and volumes across cardiac cycle

Question 6

How does the cardiac cycle begin (and end)?

Answer 6

It begins and ends in ventricular (and atrial) diastole when passive filling of the ventricles occurs. During this time blood returning from the veins can flow through the atria and into the ventricles

State of the heart: all chambers are relaxed and the AV valves are open

Question 7

What happens when the atrial systole completes the filling of the ventricles?

Answer 7

The heart reaches its End Diastolic Volume (EDV). During this time, blood is squeezed from atria to ventricles, and the ventricles achieve their maximum volume (EDV)

State of the heart: atria contracting, ventricles relaxed and the AV valves are open

Question 8

Describe ventricular systole. What 2 components are associated with it?

Answer 8

It involves a brief period of isovolumetric contraction (occurs when pressure is rising, but both valves are still closed) and then a period of ventricular ejection (occurs as long as the semilunar valves are open), allowing the stroke volume to be squeezed into the artery

State of the heart: atria relaxes, ventricles contract. AV valves close and SL valves open

Question 9

Describe ventricular diastole. What component is associated with it?

Answer 9

The semilunar valves close. The remaining blood in the ventricle is the End Systolic Volume (ESV). Isovolumetric relaxation occurs when pressure is decreasing with no change in volume (both valves closed)

State of the heart: ventricles relax, SL valves close, AV valves open

Question 10

Describe venous return

Answer 10

When venous return increases, SV inc. When venous return decreases, SV dec.

It is the volume of blood that is delivered to the right atrium during the cardiac cycle. VR is affected by CO and by constriction of arteries or compression of veins

Question 11

Describe preload

Answer 11

Preload is the amount of stretching of the heart wall due to blood volume within the ventricle (inc. EDV = inc. stretch). This affects the EDV by stretching the myocardium

Question 12

Describe afterload

Answer 12

It is the amount of force the ventricle has to generate to open its semilunar valve (inc. aorta pressure = inc. afterload)

The greater the afterload, the lower the pumping efficiency of the heart, and the larger the ESV

Question 13

What is EDV affected by?

Answer 13

Venous return and ventricular filling time

Question 14

Describe filling time

Answer 14

The duration of ventricular diastole, which determines the time the AV valves are open. Filling time is a function of heart rate (inc. HR = dec. filling time)

Question 15

How does the Frank-Starling Law affect EDV and how does this occur?

Answer 15

It describes how increasing EDV increases the stroke volume ejected during that cycle. This occurs through preload - stretching the cardiac myocytes of the myocardium increases the force (pressure) they produce when they contract

Therefore, incd. ventricular pressure increases the duration of SL valve opening, ventricular ejection, and thus the SV

Question 16

What is the purpose of stretching sarcomeres?

Answer 16

Filling the ventricles stretches cardiac myocytes, optimizing their sarcomere length for maximum force generation. Stretching the myocardium stretches the sacromeres toward optimum performance

Question 17

What is ejection fraction (and thus ESV) affected by?

Answer 17

They are affected by afterload and contractility in the ventricle

Question 18

Describe contractility. What does it depend on?

Answer 18

The amount of force produced during a contraction. It depends on the given amount of preload

Question 19

What is afterload affected by?

Answer 19

It is affected by resistance (pressure) in the blood vessels

A semilunar valve will only open when the ventricular pressure exceed the pressure in its artery (pulmonary or aorta)

If arterial pressure rises, afterload for that side of the heart increases

Question 20

What happens if the SL valve opening is delayed?

Answer 20

The time for ventricular ejection is reduced. Therefore, less blood is released as SV and more remain as ESV

Question 21

What is contractility?

Answer 21

Contractility refers to the amount of force produced by contraction at a given EDV and is altered by sympathetic and hormone activity

Question 22

How can you increase cardiac output at rest?

Answer 22

Through exercise. During exercise:

• skeletal muscles use more oxygen and nutrients from systemic blood circulation
• skeletal muscles produce more waste products (and heat)
• thermal homeostasis needs to be maintained by radiating heat away at the dermis

Question 23

T/F? Increase in cardiac output is proportional to the intensity of the exercise

Answer 23

True

Question 24

What is heart rate primarily affected by?

Answer 24

ANS activity and by certain hormones. Primarily due to synaptic or hormonal signaling at the cells of the SA node through B-adrenergic receptors

Question 25

Why does heart rate primarily increase?

Answer 25

It is due to a reduction of diastole, but this has only a minor effect filling time

Question 26

What is stroke volume affected by?

Answer 26

It is affected by muscle activity, vessel blood flow patterns, sympathetic activity, and hormones

Question 27

T/F? Aerobic training does not increase stroke volume

Answer 27

False - it can lead to increases in stroke volume due to physiological and structural changes. It induces hypertrophy of cardiac myocytes, adding sacromeres in a way that increases the volume of the ventricle

Question 28

T/F? Maximum heart rate (HR_max) is variable, but generally declines with age

Answer 28

True

HR_max = 220 - your age