Integrated control of CO & HF stuff

Question 1

What can CO be defined as?

Answer 1

The volume of blood ejected by one ventricle in one minute

Question 2

What is a normal value for CO?

Answer 2

5 litres per minute at rest

this can rise to >25litres/min during strenuous exercise

Question 3

Go over Guyton model

Answer 3

OneNote - BP section

Question 4

Describes Starlings law

Answer 4

Starling’s law of the heart states that the force generated upon contraction is dependent upon muscle stretch. In stretched muscle there is less filament overlap so more cross-bridges can form, increasing contractile force. In addition, stretch increases Ca2+ sensitivity, so in stretched muscle, more Ca2+ binds to troponin C and more cross-bridges form.

Question 5

Describe what preload and afterload are?

Answer 5

filling pressure of the right ventricle is the preload (this is set by the central venous pressure)
resistantce to outflow from the left ventricle (i.e. the arterial resistance) is the afterload

Question 6

How may intracellular Na+ levels affect force of contraction?

Answer 6

Elevated intracellular concentrations of Na+ reduces Ca2+ extrusion via the Na-Ca exchanger (because the Na+ gradient is reduced), and so induces a rise in the baseline intracellular Ca2+ concentration. This Ca2+ rise stimulates SERCA pumps, which enhance Ca2+ loading into the SR, and thus enhance subsequent Ca2+ release from the SR during an action potential. This increases the amplitude of the cytoplasmic Ca2+ transient seen during the cardiac action potential, which means more Ca2+ is available to bind to troponin C which increases the force of contraction.

Question 7

What does SV increase in response to?

Answer 7

Increase EDV (PRELOAD) which depends on:

• filling pressure (CVP)
• filling time (longer filling time means more EDV)
• ventricular compliance

Question 8

Draw Frank-Starling graph

Answer 8

OneNote

Question 9

Define mean circulatory filling pressure

Answer 9

The average integrated pressure throughout the circulatory system - can be measured by stopping blood flow and allowing the pressure throughout the circulatory system to reach equilibrium

Question 10

Define systemic vascular resistence

Answer 10

Refers to the resistance to blood flow offered by all of the systemic vasculature, excluding some of the pulmonary vasculature
Sometimes referred to as the TPR

Question 11

What is central venous pressure?

Answer 11

The blood pressure in the vena cava, near the right atrium of the heart
It reflects the amount of blood returning to the heart and the ability of the heart to pump the blood back into the arterial system
Often used as a surrogate for preload

Question 12

What is EDV?

Answer 12

• end diastolic volume

- ‘pre-pumping volumr’

Question 13

What can SV be broken down into?

Answer 13

Preload
Contractility
Afterload

Question 14

What is HF?

Answer 14

When CO is insufficient to meet the body’s needs

Question 15

What is the most common cause of HF?

Answer 15

Ischaemia - may or may not be associated with MI → causes destruction of a part of the myocardium → reduced contraction

Question 16

How is ischaemic HF a vicious cycle?

Answer 16

a reduction in CO
- Lowered BP activates the SNS and RAAS (due to reduced renal perfusion) in attempt to
boost BP back to normal  retention of Na+ and water to increase blood volume, diluting
plasma proteins, thus leading to oedema where excess fluid enters tissues
- As shown in the figure, this increased work eventually results in a reduced CO as a result of
ventricular remodelling
- Vicious cycle  gradual deterioration of the condition

Question 17

How does HF result in oedema? Discuss oedema

Answer 17

one of the most characteristic symptoms; pulmonary oedema in left-sided
failure and peripheral oedema in right-sided failure.
 This is due to the reduction in CO, which leads to blood backing up into veins and
increasing the hydrostatic pressure at the venous end of capillaries 
extravasation of fluid, which is exacerbated by fluid retention that often also
occurs
 Pulmonary oedema  impaired gas exchange – can cause respiratory failure. Signs
of pulmonary oedema include breathlessness + cyanosis.

Question 18

Aside from oedema, what is another characteristic of HF?

Answer 18

Acidaemia from reduced CO leading to poor tissue perfusion and increased anaerobic respiration

Question 19

What do a combination of oedema and acidaemia lead to?

Answer 19

Marked exercise intolerane

Question 20

What do drugs used to treat HF aim for?

Answer 20

1 - reduce symptoms

2 - prevent further ischaemic damage to the heart

Question 21

List main drug classes used in the treatment of HF

Answer 21

Diuretics:
Including thiazide, loop and potassium-sparing diuretics.

Vasodilators:
Angiotensin converting enzyme (ACE) inhibitors.
Angiotensin receptor blockers (ARBs).
Nitric oxide donors.
Natriuretic peptides.
Phosphodiesterase inhibitors.

Cardio-stimulatory (inotropic) drugs:
Digitalis.
Sympathomimetic drugs (beta-agonists.
Phosphodiesterase inhibitors.

Cardio-inhibitory drugs:
Beta-blockers.
Ca2+-channel blockers

Question 22

What is first line for HF treatment. Discuss

Answer 22

Diuretic

Question 23

Descibe using ACE inhibitor for HF? Why are they good? Downsides?

Answer 23

Antagonist the RAAS by inhibiting ACE (AI🡪AII)
This increases Na+ elimination from the body as AII and aldosterone synthesis = inhibited, causing a diuresis to treat the oedema
Also has a vasodilatory effect as AII is a vasoconstrictor 🡪 reduces peripheral resistance and hence reduces the contractile force needed to pump a sufficient CO
But this treatment has downsides e.g. can promote postural hypotension + reduce venous return, potentially causing the heart to work harder
These treatments are successful at alleviating the problems in 25% of patients

Question 24

Describe using a beta blocker for HF? Why are they good?

Answer 24

This also relieves oedema by inhibiting sympathetically-mediated renin release, and protects the myocardium from further ischaemia by reducing sympathetic tone and so O2

Question 25

Symptoms of left-sided HF

Answer 25

• oxygen rich blood
• causes:
  1. blood to back up into the lungs - respiratory symptoms (increased wor of breathing)
  2. laterally displaced apex beat

Question 26

Symptoms of right-sided HF

Answer 26

1. pulmonary hypertension or stenosis

2. oedema etc

Question 27

What is circulatory shock?

Answer 27

A state of insufficient blood flow to the tissue of the body as a result of problems with the circulatory system

• weakness
• fast HR
• fast breathing
• sweating

Question 28

Types of shock

Answer 28

• low volume
• cardiogenic (heart attack)
• obstructuve
• distributive

Question 29

Treatment of shock

Answer 29

treatment of underlying cause