Coronary Circulation
What are categories of factors that influence coronary blood flow?
1. Local metabolism - mainly mediated by adenosine release. 2. Vascular endothelium - mainly mediated by nitric oxide and endothelin. 3. Autonomic neural effects - not as strong as local metabolic control.
Between what ranges of blood pressure can the coronary circulation autoregulate?
40-160mmHg
What is the normal rate of myocardial oxygen consumption at rest? What is the normal percentage oxygen extraction?
8-10ml per 100g per minute. 60%.
What pressure gradient determines coronary blood flow? How does this explain differences in phasic blood flow in right and left coronary arteries?
Difference between aortic pressure and extravascular myocardial pressure. Left ventricle myocardial pressure is much higher than right ventricle during systole. Blood flow stops completely in left coronary artery during systole but not in right coronary.
How does the coronary circulation meet increased oxygen demand?
Increased oxygen demand is dependent on increased coronary blood flow because oxygen extraction is already near-maximal at rest.
What happens to coronary blood flow with increased sympathetic stimulation? Explain.
Increases flow. 1. increased cardiac work from positive inotropy and chronotropy leads to increased myocardial oxygen demand. 2. Causes increased production of local metabolites. 3. This has a stronger influence on coronary tone than sympathetic stimulation - therefore, vasodilation predominates.
What defines right or left heart dominance? What myocardial territories are involved? What is the split in dominance in the population?
The vessel that gives rise to the posterior descending artery which supplies the inferior one third of the intraventricular septum. 50% right dominant. 20% left dominant. 30% both.
