Control of Cardiac Output and System responses

Question 1

what determines…
The arterial pressure
The venous pressure

Answer 1

Arterial: CO X TPR
Venous: rate blood enters veins and leaves, blood volume

Question 2

If Cardiac Output doesn’t change, and
a) TPR falls
b TPR rises
what happens to arterial and venous pressure?

Answer 2

a) arterial pressure falls, venous pressure rises

b) arterial pressure rises, venous pressure falls

Question 3

If TPR doesn’t change, and
a) CO falls
b CO rises
what happens to arterial and venous pressure?

Answer 3

TPR and arterial pressure are proportional:

a) Arterial pressure falls, venous pressure
b) arterial pressure rises, venous pressure falls

Question 4

When does Cardiac output increase?

Answer 4

1. A rise in venous pressure: increases SV through starling’s law and HR
2. A fall in arterial pressure: Causes an increase in sympathetic activity: HR and FOC increase which also, in turn, increases the SV

Question 5

What defines the stroke volume

Answer 5

difference between the end of diastolic volume and end of the systolic volume (the upstroke)

Question 6

What is the ventricular compliance curve?

Why is it important to have a long diastole? How is this related to venous pressure?

Answer 6

Relationship between ventricle volume and venous pressure

A longer diastole means there’s more time for perfusion to reach tissues and more venous pressure means the heart fills better in diastole (more ventricular volume)

Question 7

Explain how starling’s law of the heart is related to venous pressure

Name one other factor that aids contractions

Answer 7

The more the heart fills (with venous blood) the harder it contracts, stronger contractions increase the stroke volume

Muscle fibre length is proportional to the energy in a contraction

Question 8

Name 2 things that assist starling’s law

Answer 8

1. Increasing central venous pressure: venoconstriction increases pressure and drives venous blood up to the heart
2. Lowering BP: activates the sympathetic system

Question 9

What two things determine the end-systolic volume

Answer 9

End-systolic volume: how much the ventricles emptied
1. The strength of the contraction: contractility (sympathetic activity) and end-diastolic volume (how much ventricles were filled)

2. How difficult it is to eject blood: aortic impedance
   Depends on the TPR, which is proportional to arterial pressure. A low TPR means low arterial pressure, therefore it is easier to eject blood and SV rises and end-systolic volume falls

Question 10

Where are rises in venous pressure sensed?

Explain the Bainbridge reflex

Answer 10

Sensed in the R atria,
BB reflex: senses an increase in central venous pressure and signals a reduction in parasympathetic activity and an increase in HR

Question 11

Explain how the CVS is restabilized after a meal

Answer 11

1. Post-meal: gut releases vasodilatory metabolites
2. This lowers the TPR and arterial pressure, venous pressure rises
3. Baroreceptors in the carotid sinus and aortic arch signal to the medullary oblongata to increase the HR and CO
4. a rise in venous pressure signals the Bainbridge reflect to increase HR
5. Once HR has increased, arterial pressure is re-raised and venous pressure falls
   Back to normal!

Question 12

What happens in this scenario: HR is the only thing that increases, all other factors stay the same.
What can you conclude from this?

Answer 12

If only the HR increases, it makes no difference to the system
1. Initially CO rises but TPR stays the same
2. CO rising reduces the venous pressure
3. SV falls (due to starling’s law: heart filling up less)
4. CO falls back to its initial value
Therefore, HR is driven by circulation (not the other way around)

Question 13

What does exercise do to arterial pressure?

Answer 13

Using muscles pushes extra blood back to the heart; decreasing arterial pressure. BUT TPR lowers to compensate, and keeps the arterial BP raised

Question 14

What is a pulmonary consequence of having venous pressure that is too high?

Answer 14

The amount of blood flow going through the R ventricle is so high that it can back up in the lungs and cause a pulmonary edema

Question 15

What does the brain do at the beginning of exercise to ensure that venous pressure doesn’t become too high?

Answer 15

Increases HR

Question 16

Explain the difference between static and dynamic exercise

How does this affect the gym life of certain patients?

Answer 16

Static: Weights raise BP
Dynamic: Cardio increases the HR (which also increases CO) but the mean BP doesn’t rise as much, muscular vasculature eventually vasodilates so diastolic BP decreases over time

You should discourage static exercise in patients with ischemic heart disease; such as angina and hypertension, as a higher BP will increase vascular resistance and put more strain on the L ventricle

Question 17

What happens to venous pressure in postural hypotension?

Answer 17

Gravity allows blood to ‘pool’ in the superficial veins so central venous pressure falls, this means the SV falls (starling’s) and CO falls. This decreases the arterial BP

Baroreceptors sense the fall in arterial BP and increase the HR

This lowers venous pressure further as:

1. More blood is being pumped through circulation (spending less time in veins)
2. And increasing HR will bring back the arterial BP and TPR which also lowers venous pressure

Question 18

Explain how a hemorrhage effects venous pressure

Answer 18

Blood escapes from a ruptured blood vessel, lowering blood volume and thus venous pressure

1. Starling’s: CO falls
2. Arterial pressure and TPR falls
3. Baroreceptors sense a low arterial pressure and increase HR: lowering venous pressure further

Question 19

Name 2 things you can do to increase the venous pressure

Answer 19

1. Veno constriction

2. Auto-transfusion: the person receives own blood for transfusion

Question 20

What is the most important long term regulator of blood pressure, and which organ is responsible for controlling it?

Answer 20

Blood volume, controlled by the kidney

Question 21

Name 4 roles of starling’s law

Answer 21

1. Increases SV during upright exercise
2. Lowers CO during: orthostasis (standing, and hemorrhage and shock
3. Balances outputs of RV and LV
4. restores CO in response to IV infusions

Question 22

Name 3 things you can do to help a fall in central venous pressure (one is a type of drug)

Answer 22

1. Bed rest (no gravity)
2. Warmth (vasodilation)
3. alpha-adrenoceptor blocker (inhibit vasoconstriction)

Question 23

What is the function of the coronary sinus?

Answer 23

Collection of veins that collect blood from the myocardium and deliver less-oxygenated blood to the R atria

Question 24

How does digoxin help with heart failure?

Answer 24

Slows the HR down to improve filling of the ventricles

Question 25

Name 2 symptoms of a fall in central venous pressure and why they occur

Answer 25

If CVP falls = CO falls
2. Arterial pressure falls
3. Cerebral under-perfusion
Resulting in dizziness and vision problems

Question 26

What is the ejection fracture?

Answer 26

SV/Total volume in the L ventricle

Question 27

If there’s a stenosis, when will the murmur be heard in general?

Answer 27

During the phase that the valve is open (diastolic/systolic depending on the valve)

Question 28

If there’s a valve incompetence, when will the murmur be heard in general?

Answer 28

Valve incompetence means there will be a regurgitation. Therefore the murmur will be heard in the phase after the valve should have been shut (systolic or diastolic, depending on the valve)

Question 29

Describe the kind of murmur that occurs in an aortic valve stenosis

Answer 29

A systolic murmur

Systolic murmurs are louder: there’s a crescendo and decrescendo

Question 30

Describe the kind of murmur that occurs in an aortic valve incompetence

Answer 30

Diastolic murmur, fading murmur (not as high pitch as an aortic stenosis)

Question 31

What kind of murmur is a mitral valve stenosis

Answer 31

A diastolic murmur

Question 32

What is an ‘opening snap’?

Answer 32

When the stenosed valve finally opens (before the murmur begins)

Question 33

What does it indicate if there’s a decrescendo murmur?

Answer 33

A very stenosed valve having difficulty opening

Question 34

What often occurs as a result of a mitral valve stenosis?

What can be heard as a result of this?

Answer 34

Patients will have an enlarged atria to compensate and push blood through the stenosed mitral valve into the L ventricle.

Since the atria contract harder, the turbulent blood flow is given a boost - making the murmur louder

Question 35

What kind of noise is generated by a systolic regurgitation

Answer 35

Pancystolic murmur (no crescendo, decrescendo)

Question 36

Where does a ___ radiate:

a. Aortic stenosis
b. mitral regurgitation

Answer 36

a) Carotid arteries

b) Axilla

Question 37

When is an ejection systole heard?

Answer 37

Aortic and pulmonary stenosis

Question 38

What produces an early and mid-diastolic murmur

Answer 38

Early-diastolic: aortic and pulmonary regurgitation

Mid-diastolic: mitral and tricuspid stenosis

Question 39

Explain the meaning of RILE

Answer 39

The R heart is heard louder on inspiration: as the expanding thoracic cavity crushes the vena cava, causing venoconstriction and increased venous pressure – more blood going into the right heart

The L heart is heard louder on expiration: as there is an increase in pulmonary venous return

Question 40

What happens to the arterial and venous pressure when the body’s metabolism changes?

Answer 40

Since TPR is inversely proportional to the body’s need for blood, the TPR will increase or decrease which will relay onto the arterial and venous pressure