Session 2 Flashcards
What is the cardiac cycle?
The events that occur during the beating of the heart
Arterial vessels drive blood supply to specific areas of the body, these can be described as ____________ vessels
Resistance vessels
The vessels in the venous system can ‘store’ blood depending on the demands of the body, they are also known as _____________ vessels
Capacitance
During exercise blood supply to the ______ will be heavily reduced and blood supply to the _____________ _________ will be increased
Gut
Skeletal muscle
The systemic circulation acts under what sorts of pressure?
High pressure
The pulmonary circulation acts under what sorts of pressure?
Low pressure
The output of the left and right side of the heart over time must be…
Equal
What is systole?
The contraction and ejection of blood from ventricles
What is diastole?
The relaxation and filling of ventricles
What is the typical pressure (mmHg) found in the left atrium?
8-10 mmHg
What are the typical systolic and diastolic pressures found in the left ventricle?
120 mmHg
10 mmHg
What are the typical systolic and diastolic pressures found in the aorta?
120 mmHg
80 mmHg
What is the typical pressure found in the right atrium?
0-4 mmHg
What are the the typical systolic and diastolic pressures found in the right ventricle?
25 mmHg
4 mmHg
What are the typical systolic and diastolic pressures found in the pulmonary artery?
25 mmHg
10 mmHg
How much blood does each ventricle typically pump out per beat at rest? What is the name given to this amount?
~70 ml
Stroke volume
So at a normal rate of 70bpm how much blood is pumper per minute by the heart? What is the name given to this term? What does this amount of blood equate to?
4.9 litres
Cardiac output
Approximately the volume of blood in the whole body
Heart muscle cells are discrete cells but interconnected _____________
Electrically
What causes the contraction of myocardial cells?
Action potentials resulting in a rise in intracellular calcium
How long does a cardiac action potential typically last? How does this compare to other action potentials?
~280 ms
Relatively long
What are the four valves of the heart?
Tricuspid
Pulmonary
Mitral
Aortic
The valves of the heart open or close depending on what?
The differential blood pressure on each side of the valve
How do valve cusps affect blood flow in the heart?
They are pushed open to allow blood flow
They close together to seal and prevent backflow
The cusps of the mitral and tricuspid valves are attached to what? This prevents what?
Papillary muscles via chordae tendineae
The inversion of the valves on systole
How do the AV valves work compared to the output valves?
AV valves will close when the output valves are open and vice versa - they work in synchrony
What cells of the heart generate the first action potential?
Pacemaker cells in the SA node
What happens to the action potential generated in the pacemakers cells in the SA node?
The activity spreads over the atria resulting in atrial systole
What happens to the conduction of action potentials in the heart after atrial systole? (4)
The action potential reaches the AV node where it is delayed for ~120 ms
Excitation spreads from AV node down the septum
Spreads through ventricular myocardium from inner to outer surface
Ventricle contracts from the apex up forcing blood through the output valves
How long is the electrical activity delayed at the AV node during contraction?
~120 ms
How does the electrical activity in the heart spread through the ventricular myocardium?
From the inner (endocardial) to outer (epicardial) surface
The cardiac cycle can be split into which 7 phases?
Atrial contraction Isovolumetric contraction Rapid ejection Reduced ejection Isovolumetric relaxation Rapid filling Reduced filling
What is typically longer, systole or diastole?
Diastole
What does a Wiggers diagram show?
Pressure changes in different parts of the heart against time
The changes in pressure are related to changes in volume that are occurring simultaneously
As well as measuring changes in pressure and corresponding changes in the volume of the heart against time? What else can a Wiggers diagram be compared against?
Different phases of the ECG
Different sounds of the heart (phonocardiogram)
Wiggers diagrams are usually plotted for…
The left side of the heart
If a Wiggers diagram were to be plotted for the right side of the heart, how would it look?
Very similar to the left side of the heart but at lower pressures
What valves are open during atrial contraction?
Mitral/Tricuspid are open
Aortic/Pulmonary are closed
At the end of phase 1 (atrial contraction) the ventricular volumes are their maximum, what name is given to this volume? What value does it typically take?
End-diastolic volume
~120 ml
What happens to atrial pressure during atrial contraction? What does this causes on the Wiggers diagram?
It rises
Results in the A wave - a small increase in pressure on the Wiggers diagram
Atrial contraction only accounts for ~_____% of ventricular filling? What can affect this percentage? How are the ventricles mostly filled?
10%
Age and exercise
Passively filled through open valves
What wave in the ECG signifies the onset of atrial depolarisation?
The P wave
What valves are open during isovolumetric contraction?
All valves are closed
What causes the mitral valve to close during isovolumetric contraction?
The intraventricular pressure exceeding the atrial pressure
What changes are seen in left ventricular pressure in a Wiggers diagram during isovolumetric contraction?
A rapid rise in ventricular pressure
What is the C wave? What causes it?
A small increase in the left atrial pressure curve
Closing of the mitral valve
Why is phase 2 of the cardiac cycle termed isovolumetric?
There is no change in ventricular volume as all the valves are closed
What complex in the ECG signifies onset of ventricular depolarisation?
The QRS complex
What causes the first sound of the phonocardiogram (S1)? In what phase of the cardiac cycle does this take place?
Closure of the mitral and tricuspid valves
Isovolumetric contraction
Which valves are open/closed in phase 3 (rapid ejection) of the cardiac cycle?
Aortic/pulmonary - OPEN
Mitral/tricuspid - CLOSED
What causes ejection to begin in the rapid ejection phase of the cardiac cycle?
The intraventricular pressure exceeding the pressure within the aorta causing the aortic valve to open
What happens to the atrial pressure during the rapid ejection phase of the cardiac cycle? What name is given to the change in the pressure curve?
Initially decreases as the atrial base is pulled downwards as the ventricle contracts
X descent
What happens to the volume in the ventricle during rapid ejection phase of the cardiac cycle?
Rapidly decreases
Does blood still flow into the atria during rapid ejection?
Yes blood continues to flow into the atria from their respective venous inputs
What valves are open/closed during the reduced ejection phase of the cardiac cycle?
Mitral/Tricuspid - Closed
Aortic/Pulmonary - Open
What causes the reduced rate of ejection during phase 4 of the cardiac cycle?
Repolarisation of the ventricle leading to a decline in tension
What happens to the atrial pressure during the reduced ejection phase of the cardiac cycle? What is the name for this change in the Wiggers diagram?
It gradually rises due to continued venous return from the lungs
V wave
Ventricular repolarisation is depicted by what wave on an ECG?
T-wave
What valves are open/closed during isovolumetric relaxation (phase 5) of the cardiac cycle?
All valves are closed
Systole lasts from the isovolumetric contraction point where the mitral valve closes to the…
End of the reduced ejection phase where the aortic valve closes
What causes the aortic valve to close in the isovolumetric relaxation phase of the cardiac cycle?
Intraventricular pressure falls below aortic pressure and there is a brief backflow of blood
What happens to the aortic pressure during the isovolumetric relaxation phase of the cardiac cycle? What is the name given to this feature on a Wiggers diagram? What causes this?
Falls
Dicrotic notch
Valve closure
What happens to the ventricular pressure during the isovolumetric relaxation phase of the cardiac cycle? What happens to the volume?
Rapid decline
Remains constant as all valves are closed
The lowest volume found in the ventricles is found during which phase? What is the name given to this volume?
Isovolumetric relaxation
End-systolic volume
Stroke volume is equal to…
EDV - ESV
What sounds are heard in the isovolumetric relaxation phase of the cardiac cycle? Why?
S2 due to closure of the aortic and pulmonary valves
What valves are open/closed in the rapid filling phase (phase 7) of the cardiac cycle?
Mitral/Tricuspid - Open
Aortic/Pulmonary - Closed
What happens to atrial pressure during the rapid filling phase of the cardiac cycle? Why? What name is given to the change in pressure seen on a Wiggers diagram?
Falls
Due to mitral valve opening
Y descent
What causes the mitral valve to open in phase 6 of the cardiac cycle?
The intraventricular pressure falling below the atrial pressure
What is the normal sound of ventricular filling? When can abnormalities be heard?
Normally silent
S3 can sometimes be present in the rapid filling phase in children (normal) or in adults (pathological)
Which valves are open/closed in the reduced filling phase of the cardiac cycle?
Mitral/tricuspid - Open
Aortic/pulmonary - Closed
The rate of filling in the ventricles slows in the reduced filling phase of the cardiac cycle, why? What drives further filling at this point?
Ventricle reaches its inherent relaxed volume.
Venous pressure
By the end of phase 7 of the cardiac cycle at rest the ventricles are how full?
~90% full
What is stenosis in relation to valves? What consequences can it have?
Narrowing of a valve
Valve doesn’t open enough, obstruction to blood flow
What is regurgitation in relation to valves? What consequences can it have?
Valve doesn’t close all the way
Back leakage when valve should be closed
What sound is heard in aortic valve stenosis?
Crescendo-decrescendo murmur
What are the causes of aortic valve stenosis? (3)
Degenerative (senile calcification/fibrosis)
Congenital (bicuspid form of valve)
Chronic rheumatic fever —> Inflammation —> Comissural fusion
What affects can aortic valve stenosis have on the heart? (4)
LV hypertrophy
Syncope
Angina
Microangiopathic haemolytic anaemia
What causes the LV hypertrophy seen in aortic valve stenosis?
Increased LV pressure
What causes the syncope and angina seen in aortic valve stenosis?
Left sided heart failure
What causes the microangiopathic haemolytic anaemia seen in aortic valve stenosis?
Shear stress
What sound is seen in aortic valve regurgitation?
Early decrescendo diastolic murmur
What causes aortic valve regurgitation? (2)
Aortic root dilation (leaflets pulled apart) Valvular damage (due to endocarditis rheumatic fever)
What are the effects of aortic valve regurgitation? (5)
Increases stroke volume Increases systolic pressure Decreases diastolic pressure Bounding pulse (head bobbing, Quinke's Sign) Left ventricle hypertrophy
What sound is heard in mitral valve regurgitation?
Holosystolic murmur
What causes mitral valve regurgitation? (4)
Myxomatous degeneration weakening the chordae tendineae and papillary muscle leading to prolapse
Damage to the papillary muscle after MI
Left sided heart failure –> LV dilation –> Stretching of the valve
Rheumatic fever –> Leaflet fibrosis –> Disruption of seal formation
What effect can mitral valve regurgitation have?
LV hypertrophy
What causes the LV hypertrophy seen in mitral valve regurgitation?
Blood leaks back into the left atrium, increasing preload (more blood entering left ventricle in subsequent cycles)
What sound is heard in mitral valve stenosis?
Snap as valve opens - diastolic rumble
What is the main cause of mitral valve stenosis?
Rheumatic fever resulting in commissural fusion of valve leaflets
What effect can mitral valve stenosis have?
Increased left atrial pressure
What can the increased left atrial pressure seen in mitral valve stenosis result in? (3)
RV hypertrophy
Atrial fibrillation —> Thrombus formation
Oesophagus compression —> Dysphagia
What is afterload? It is roughly equivalent to…
The load that the heart must eject blood against
Aortic pressure
What is preload? What is it related to?
The amount the ventricles are stretched in diastole
End diastolic volume or central venous pressure
What is the total peripheral resistance?
Resistance to blood flow offered by all the systemic vasculature
Which blood vessels offer the greatest resistance? Why?
Arterioles due to their thick muscular walls
_____________ of the arterioles increases their resistance
Constriction
How does an increase in resistance in the arterioles affect the pressure seen in the capillaries, venous system and arterial side?
Pressure on the arterial side will rise
Pressure in the capillaries and on the venous side will fall
How will arterial/venous pressure be affected by…
I) TPR falling, CO remaining the same
II) TPR increasing, CO remaining the same
I) Arterial pressure will decrease, venous pressure will increase
II) Arterial pressure will increase, venous pressure will decrease
How will arterial/venous pressure be affected by…
I) CO increasing, TPR unchanged
II) CO decreasing, TPR unchanged
I) Arterial pressure will increase, venous pressure will decrease
II) Arterial pressure will decrease, venous pressure will increase
If for example cardiac output decreases, why is there an increase in venous pressure?
Less blood being pumped from the heart, so less blood being taken from the venous system
If a tissue needs more blood, the arterioles and pre-capillary sphincters will…
How will this affect peripheral resistance?
How does this result in more blood being pumped by the heart?
Dilate
Peripheral resistance will fall
Means the heart will have to pump more so that the arterial pressure doesn’t fall and the venous pressure doesn’t rise
The heart sees changes in demand as changes in… (2)
Arterial blood pressure
Central venous pressure
Cardiac output is equal to…
Stroke Volume x Heart Rate
Stroke volume is equal to…
End diastolic volume - End systolic volume
What is the typical stroke volume of an average 70kg man at rest? What percentage of the initial EDV does this make up?
70ml
~67%
The ventricles fill with blood until…
The walls stretch enough to produce and intraventricular pressure = venous pressure
How will venous pressure affect the filling of the heart?
The higher the venous pressure the more the heart fills
The more the heart fills the harder it contracts. Why?
Due to Starling’s law - if you stretch the fibres before contracting, it will contract harder
What is the relationship between sarcomere length and the force of contraction of the heart?
A longer, stretched sarcomere will allow a greater contractile force
What is contractility?
The force of contraction for a given fibre length
How does a change in contractility affect the Starling curve?
Results in a change in the slope of the Starling curve
Which extrinsic mechanisms can affect contractility?
Sympathetic stimulation (e.g. reduced will reduce contractility)
What is aortic impedance?
The pressure in the aorta (afterload)
What factors affect cardiac output? (2)
How hard it contracts (dependent on contractility and EDV)
How hard it is to eject blood (aortic impedance)
Contractility and heart rate are controlled by the…
Autonomic nervous system
Eating a meal causes what effect in the vessels in the gut?
Local vasodilation
