Lecture 17 - Special Circulations I: Coronary and Cerebral Flashcards
Where do epicardial coronary arteries originate from?
From the base of the aorta:
- Right coronary artery from the right aortic semilunar cusp
- Left coronary artery from the left aortic semilunar cusp
What is the richest microcirculation of the CV system?
Coronary circulation
Describe the collateralization of the coronary circulation.
If there is a blockage in one of the coronary vessels, collateral vessels will take over
These are normally closed but can become well-developed overtime as cardiovascular disease progresses
What is myocardial infarction?
Death of tissue due to ischemia
What do epicardial coronary arteries give rise to?
Branches that penetrate both the myocardium and the endocardium
What are the 3 regions of the myocardium?
- Subepicardium (outermost)
- Middle myocardium
- Subendocardium
Describe the pressure generated in the branches of the epicardial arteries in the 3 regions of the myocardium.
Pressures generated within each layer are different which is important when considering the perfusion of the cardiac wall, especially for the LV
How do the pressures in the myocardium of the LV increase during systole? What are the implications of this?
Extravascular/tissue pressures increase from the subepicardium to the subendocardium => means that during systole the pressure in the subendocardium rises above 120 mmHg in order to generate the ventricular pressure => this exceeds arterial pressure and impedes perfusion of this region of the myocardium during a portion of systole => subendocardial region of LV myocardium is particularly susceptible to ischemia and infarction
Other name of epicardial coronary artery?
Extramyocardial coronary artery
What is the BP in the epicardial coronary arteries?
120/80 mmHg
Are there perfusion issues in the RV myocardium during systole?
NOPE because much smaller pressures generated
In which region of the myocardium intramyocardial pressure the highest during systole?
Subendocardium (inner third)
Describe the flow curve of the right coronary artery.
Follows the aortic pressure curve
Describe the flow curve of the left coronary artery.
- During isometric contraction, preceding the rise in aortic pressure, flow falls to 0 as tissue pressure rises to generate the LV systolic pressure
- For the rest of systole flow curve follows the aortic pressure curve
- During isometric relaxation flow greatly rises due to release of intramyocardial pressure and build up of metabolites (adenosine) during preceding systole which cause vasodilation (aka reactive hyperemia)
- For the rest of diastole flow curve follows the aortic pressure curve
During what cardiac cycle phase does the greatest flow occur in the RCA?
Mid-systole because that is when aortic pressure is highest and there is little intervening pressure
During what cardiac cycle phase does the greatest flow occur in the LCA?
Isometric relaxation
What metabolite is primarily responsible for reactive hyperemia in the LV during isometric relaxation and overall metabolic regulation of coronary arteries?
Adenosine
Describe myogenic regulation of coronary arteries.
Can be demonstrated in the coronary circulation but is less important than metabolic regulation or effects of extravascular pressure
Describe sympathetic regulation of coronary arteries.
Sympathetic constriction can be demonstrated, although in normal function increased work of the heart during SNS activation results in metabolic vasodilation of coronary arteries which overrides sympathetic constriction
When do myogenic regulation and sympathetic regulation of coronary arteries become important?
If the heart is diseased with flow limitations then the effects of those regulations will be much more pronounced since the heart is not working as well and not producing as many metabolites
What is the area under the LVP curve during systole a measure of?
LV work and O2 demand
What is the area under the aortic pressure curve during diastole a measure of?
O2 supply to the LV since the highest flow to the myocardium occurs during diastole
What balance is important to maintain in the heart? When is this balance difficult to maintain?
LV O2 demand and LV O2 supply
Difficult to maintain in ill cardiac patients
In what part of the body is the VO2 the lowest at rest? Why?
Heart because it is the most metabolically active organ in the body and because of the difficulty of perfusion its walls