Blood flow through the heart
- venous return via great veins (SVC and IVC) into the right atrium
- goes through the tricuspid valve
- enters the right ventricle
- goes through the pulmonary semilunar valve
- enters the pulmonary arteries
- lung circulation
- pulmonary veins bring blood to the left atrium
- goes through mitral (bicuspid) valve
- enters the left ventricle
- goes through the aortic semilunar valve
- enters the aorta
- systemic circulation
The cardiac cycle can split into 4 steps. What are these steps?
- ventricular filling/atria contraction
- isovolumetric contraction
- ejection
- isovolumetric relaxation
Describe phase 1, ventricular filling/atria contraction
- there is a higher pressure in the atria, as they have been filling up with blood.
- so, higher pressure in atria>ventricles
- pressure gradient means that the tricuspid and mitral valve open
- so, blood is going to move from atria into the ventricles
- at the end of ventricular filling, you get atrial contraction. this gives an extra oomph to filling the ventricles
Describe phase 2, isovolumetric contraction
- so, higher pressure in ventricles > atria
- so, tricuspid and mitral valve close to prevent the backflow of blood
- this means we have a period of time where we have a closed ventricular chamber. nothing is going in, nothing is coming out
- walls of the ventricles start to contract. pressure in the ventricular chambers increases (in order to increase the pressure relative to the arteries)
Describe phase 3, ejection
- higher pressure in ventricles > aorta and pulmonary artery
- ventricular chambers continue to contract, but as the pressure is greater than that of the aorta and pulmonary artery, the aortic valve and pulmonic valve open
- so, blood flows out of the heart via the arteries
- blood enters atria
Describe phase 4, isovolumetric relaxation
- higher pressure in aorta and pulmonary artery > ventricles
- aortic and pulmonic valves close - so now we have a closed ventricle with not much blood in it. this is known as isovolumetric relaxation
- ventricles relaxes, expands, ready to receive
- blood is still returning to atria
What is EDV?
End diastolic volume
When mitral valve closes
approx 120 ml
What is ESV?
End systolic volume
amount of blood left in the chamber after ejection has occurred which is approx 40ml
Describe left ventricular pressure changes
- during ventricular filling, pressure is very low
- as ventricle fills, pressure starts to increase
- arial systole causes more blood to enter ventricle.
- and so pressure in ventricles > atria
- so mitral valve closes - resulting in a closed ventricle - nothing going in or out
- then isovolumetric contraction occurs - causing pressure to greatly increase
- pressure in left ventricle > aorta
- aortic valve opens
- ventricular ejection
- pressure is increasing then gradually decreases in ventricles
- pressure in aorta > left ventricle and so aortic valve closes
- isovolumetric relaxation - closed chamber
- pressure drops
- pressure in left atrium > left ventricle so mitral valve opens
- left ventricle starts to fill - pressure increases
how is stroke volume calculated from EDV and ESV
SV = EDV - ESV approx = 80ml
How is ejection fraction calculated?
SV / EDV
What are normal heart sounds
S1 and S2
whats happening during S1 and S2
S1 - lubb
- closure of the tricuspid and mitral valves at the beginning ventricular systole
- aka the end of ventricular filling and atrial systole - beginning of isovolumetric contraction and ejection
S2 - dupp
- closure of the aortic and pulmonary valves at the beginning of ventricular diastole
- between lubb dupp is when you are getting ejection
What are abnormal heart sounds
S3 - occasional
- turbulent blood flow into ventricles detected near end of first 1/3 diastole
- common in young
- not necessarily pathological
S4 - pathological in adults
- forceful atrial contraction against a stiff ventricle -potentially abnormal
What does the area inside a left ventricle pressure-volume loop show
amount of stroke work done
relates to the amount of energy consumption used to produce stroke volume
important to consider in particular disease situations
What is valve stenosis?
narrowing of valve, doesn’t fully open, reduces blood flow through it
What does pressure-volume loop of aortic stenosis show?
- aortic valve not fully open
- build of high pressure in left ventricle
- poor ejection
- graph shows we’re only producing 50% SV, but using same energy
What does pressure-volume loop of mitral stenosis show?
- mitral valve not fully open
- poor filling of left ventricle
- low EDV → less pressure
- reduced ejection
- poor SV ⇒ affects exercise
Describe right atrium pressure changes
- blood returns to the right side of the heart pressure is going to increase.
- atrial contraction also increases pressure of RA
- this leads to ejection of blood from RA to RV ( A wave)
- whats left in the RA is very little blood, so pressure greatly decreases.
- at this point, ventricles are full and start ejecting blood to the pulmonary circulation (x descent)
- during this period of time, blood returns from systemic circulation back to the great veins and RA and so RA pressure starts to rise as it fills up (v wave)
- then, pressure rises in RA to the point where the tricuspid valve opens which causes the beginning of ventricular filling (y descent)
- rise in pressure in atria → decrease in pressure → increase in pressure
what is the clinical relevance of right atria and jugular venous pressure changes
if RA is not working properly (not ejecting blood so well) → RV pressure builds up which then causes pressure in RA and great veins to increase aswell (knock on effect) → greater back pressure → elevated JVP
right sided heart failure
