Session 2 ILOs - The heart as a pump and control of cardiac output Flashcards
Describe the basic structure of the heart, naming the chambers, valves, and main vessels and the main differences between the right and left heart
Chambers:
- Left Ventricle
- Left atrium (behind LV)
- Right ventricle
- Right atrium (behind RV)
Valves:
Semilunar valves:
- Pulmonary (right)
- Aortic (left)
Atrioventricular valves:
- Tricuspid (right)
- Mitral (left)
Major blood vessels:
- Aorta
- Pulmonary artery (2)
- Inferior and superior vena cava (2)
- Pulmonary veins (4)
- Chordae tendineae connect atrioventricular valves to ventricle walls
- Papillary muscles are found in ventricles and attach to atrioventricular valves via chordae tendineae and contract to prevent the prolapse of valves
Left ventricle wall thicker than right
The right side of the heart collects de-oxygenated blood from the body and brings it to the lungs to be filled with fresh oxygen. The left side of the heart receives oxygenated blood from the lungs and sends it out to the rest of the body.
Define the terms Systole and Diastole and give the relative timings at rest and understand how this changes with exercise
Systole: contraction and ejection of blood from ventricles (0.35 seconds)
Diastole: relaxation and filling of ventricles (0.55 seconds)
Total duration of contraction (at 67bpm) is 0.9 seconds for 1 cycle
Diastole lasts for approx 2/3 of the cycle and systole for 1/3.
Systole is constant in duration at all heart rates whereas diastole duration decreases as heart rate increases (ie during exercise)
Explain the origin of the 1st and 2nd heart sounds in relation to the cardiac cycle
1st sound ‘lub’
- Isovolumetric contraction
- Closing of the mitral and tricuspid valves
2nd sound ‘dub’
- Isovolumetric relaxation
- Closing of the aortic and pulmonary valves
Define cardiac output and explain how it is controlled
Cardiac output is defined as the amount of blood the heart pumps in 1 minute (in L/min)
Cardiac output is defined as SV x HR
CO is controlled by:
- How hard the heart contracts (determined by EDV and contractility)
- How hard it is to eject blood (aortic impedance)
Explain preload, afterload and contractility
Preload – Amount the ventricles are stretched (filled) in diastole – related to the end diastolic volume or central venous pressure
Afterload – Pressure against which the heart works (roughly equivalent to aortic pressure)
Contractility - the force of contraction for a given fibre length
Define stroke volume and give typical values
Stroke volume: volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction/beat
Typical value: Resting is 70mL/beat
HR of 70bpm
= 4.9L/min
Explain the Frank-Starling Law of the heart
Frank-Starling Law of the heart =
- If you stretch the fibres of the heart before contracting, it will contract harder
- the more the heart fills, the harder it contracts (up to a limit)
(The harder the heart contracts, the bigger the stroke volume. An increase in venous pressure will fill the heart more)
Describe some common conditions associated with cardiac valves
and how these may be assessed
OR
Explain how mitral valve disease can affect the function of the heart and the heart sounds
Mitral valve disease:
Stenosis - valve doesn’t open enough
- Mitral valve Stenosis = snap as valve opens, diastolic rumble
- Caused by rheumatic fever (almost all cases)
- Less blood can get through the valve and flow from LA to LV so…. :
- Increases LA pressure:
1) Pulmonary hypertension/oedema and dyspnea = leads to RV hypertrophy
2) And LA dilation = atrial fibrillation and thrombus formation OR oesophagus compression and dysphagia - Mitral valve Regurgitation = holosystolic murmur
Causes:
- Papillary muscle and chordae tendineae usually prevent prolapse during systole
- Myxomatous degeneration (changes in collagen expression that weaken expression of chordae tendineae and make valve more likely to prolapse)
- Damage to papillary muscle after heart attack, left sided heart failure (leading to LV dilation and valve stretching) or rheumatic fever
These things can lead to prolapse of valve
- Blood leaks back into LA
- Increases preload as more blood enters LV in subsequent cycles = LV hypertrophy
Describe some common conditions associated with cardiac valves
and how these may be assessed
OR
Explain how aortic valve disease can affect the function of the heart and the heart sounds
Aortic valve disease - 2 disease states:
- Aortic valve stenosis = crescendo-decrescendo murmur
Causes:
- Degenerative changes - stenile calcification/fibrosis of valve leaflets
- Congenital (aortic valve has 2 leaflets instead of 3, so those 2 under more strain)
- Chronic rheumatic fever (leads to autoimmune attack of heart valves, so you get inflammation and commissural fusion)
- Less blood can get through the valve so…. :
- Increases LV pressure = LV hypertrophy
- And left sided heart failure = syncope (fainting) or angina
Another consequence of AVS is squeezing of RBC through narrow opening at high pressure = shear stress (and some of the burst open) = microangiopathic haemolytic anaemia
- Aortic valve regurgitation = early decrescendo diastolic murmur
Causes:
- Aortic root dilation (leaflets pulled apart)
- Valvular damage (endocarditis, rheumatic fever)
- Blood flows back into LV during diastole as it isn’t completely sealed
- Increases SV so systolic pressure increases and diastolic pressure decreases
- Bounding pulse (head bobbing) and LV hypertrophy
Given a diagram showing the pressure profile in the left atrium, left ventricle and aorta for a single cardiac cycle in a healthy adult, perform the following tasks:
o label the pressure axes and time base (assuming a heart rate of 60 bpm)
o indicate the points at which the mitral and aortic valves open and close
o indicate the position of the 1st and 2nd heart sounds
Interpret a Wiggers diagram of pressure and volume changes during the cardiac cycle.
NOTABILITY DIAGRAM
Describe the sequence of pressure and volume changes in the left atrium and ventricle over a complete cardiac cycle in the normal individual
Describe when in the cardiac cycle each valve in the heart opens and closes, and the pattern of flow through each valve
OR
List the 7 phases of the cardiac cycle stating the valve positions and blood flow for each phase (left side as example)
- Atrial contraction
- Depolarisation causes atria to contract.
- Atrial pressure increases (seen as the ‘a wave’ on the Wiggers diagram)
- At the end of the previous cycle the ventricle is 90% full, with atrial contraction accounting for the final 10% of ventricular filling (atrial kick). End diastolic volume is now reached. ~ 120ml
- AV valves open - mitral
- SL valves close - aortic - Isovolumetric contraction (because all valves closed so volume of blood in ventricle doesn’t change)
- Ventricle contracts
- Ventricle pressure exceeds atrial pressure
- This causes Mitral valve = close
- can be heard as 1st heart sound ‘lub’ - Rapid ejection
- Ventricular pressure exceeds the aortic pressure
- Aortic valve opens
- Mitral valve is closed - Reduced ejection
- Less of a gradient, ejection reduces
- Ventricle repolarises
- The ventricle begins to relax meaning the rate of ejection falls
- But as the pressure in the ventricle is still higher than the aorta, blood continues to leave - Isovolumetric relaxation (because all valves closed so the volume of blood in ventricles doesn’t change)
- Marks the start of diastole
- Ventricle pressure falls below aortic pressure
- Aortic valve closes
- 2nd heart sound ‘dub’
- End systolic volume is achieved. - Rapid filling
- Ventricle pressure falls below atrial pressure
- Mitral valve opens
- Passive flow of blood into ventricles from atria - Reduced filling
- Less of a gradient, ventricle filling reduces (90% full by the end of filling)
Draw the profile of pressure changes in the internal jugular vein,
labelling the 3 component areas
