Cardiac Circulation And Physiology Flashcards
Draw the diagram for the coronary artery structures in the heart
Right, left coronary artery
LCx
LAD
(Typically associated to disease)
Branches of the coronary artery usually come back round to the back of the heart where they supply O2 + nutrients to the myocardium
Function of these Arteries in the Heart?
RCA - supplies blood to the RA, RV, bottom portion of the LV + back of the septum
Left Coronary Artery - divides into 2 branches
LCx - supplies blood to the LA + the side & back of the LV
LAD - supplies blood to the front & bottom of the LV + front of the septum
(Coronary veins - deoxygenated blood already been ‘used’ by muscles of heart returned to RA)
Septum = A muscular wall that divides Heart into the left and right side.
For a vascular bed, what’s so UNUSUAL about the coronary circulation?
Whereas flow in circulation in most part of the body is maintained at a constant rate, at certain stages during the cardiac cycle (systole) flow decreases right down to almost 0!
So when does most of the coronary perfusion occur?
In diastole.
Very important the Heart able to extract O2 it needs during this stage, bc it has a very high requirement for O2.
Why little/no flow in the Coronary Arteries during Systole?
Why is there flow in the Coronary Arteries during Diastole?
Bc when the ventricles are contracting, the smaller coronary arteries are compressed.
Pressure in Coronary Arteries (to get blood down them) «_space;pressure of ventricles.
When ventricles are relaxing, the opposite is true.
There’s a sanction effect - the small capillaries open up and blood is sucked into the coronary circulation
Where is the origin of the Coronary Arteries?
At the Coronary Ostium
> located just above the cusps of the semilunar valve in the Aortic route.
Oxygen Extraction formula?
O2ER = VO2 / DO2
(O2 consumption is very dependent on O2 delivery in the myocardium)
Max O2ER ~ 70% at point critical DO2
>beyond critical, any further increase in VO2/ decline in DO2 lead to tissue Hypoxia and anaerobic metabolism (lactate production)
-High O2ER suggests inadequate O2 delivery, or increased VO2.
Coronary BF against O2 consumption graph?
What does the graph show?
Graph.
Normal resting value: 60ml/min/100g at 8ml/min/100gm
Graphs shows that myocardium is very dependent on O2. If O2 supply is comprised - damage occurs bc low O2 conditions!
Myocardium extraction of O2 %?
At rest, the Myocardium extracts ~75% of the O2 delivered by the coronary BF. Thus there is little extraction reserve when Myocardium Oxygen consumption is augmented several fold during exercise.
The dominant control mechanism in the Coronary Arteries?
Metabolic vasodilatation
>’Active Hyperaemia’ - cause vasodilatation
Also, Endothelial Nitric Oxide generation is quite important to the coronary arteries (in order to maintain flow + dilatation)
Diminished NO2 bioactivity (endothelial dysfunction) may cause constriction of coronary arteries during exercise/mental stress and contribute to provocation of MI in patients with Coronary Artery Disease.
May also facilitate vascular inflammation that could lead to oxidation of lipoproteins and foam cell formation, the precursor of the atherosclerotic plaque.
Capillary density of the Coronary circulation
Very high ~ 3000mm-2.
The coronary circulation also has ‘functional end Arteries’. What does this mean?
The smaller arterioles down the vascular tree have smooth muscle which can vasodilate.
In other parts of body, only the proximal arterioles has smooth muscles
What are Collaterals in Coronary circulation?
Over time if you have chronic ischaemia (not treated), you can have ‘collateral growth’ of coronary arteries - development of arteries that grow out from proximal to blockage to supply myocardium with blood + O2
Distal to blockage - retrograde flow into artery from the other side. Bc there’s no forward pressure on artery.
