Special Circulations: Coronary & Skeletal Flashcards
What is the primary determinant of coronary blood flow?
aortic pressure (provides pressure gradient for flow into coronary arteries)
Is the epicardium or endocardium more at risk of ischemia in pathological conditions?
endocardium (may partially be due to decreased perfusion)
When does maximal left coronary blood flow occur? Why?
it occurs early in diastole because tissue pressure (in LV) falls to ~0 mmHg (high tissue pressures can prevent perfusion of coronary arteries)
Why may left coronary blood flow actually reverse in early systole?
this is because the left ventricular pressure is at its highest and the aortic pressure is at its lowest; thus, the pressure gradient drives coronary flow backwards
How can oxygen delivery be increased to the heart?
The only way is by increasing blood flow; a-vO2 for the heart will NOT change with increased metabolic demand because the heart is already basally operating at almost its maximum oxygen extraction.
The relationship between coronary blood flow and myocardial metabolic activity is ________.
linear (more blood flow=more oxygen consumption of heart)
What are examples of metabolic substrates for the heart?
fatty acids (60%), carboydrates (35-40%), and other things like ketones, lactate, and proteins
Why is oxygen supply to the heart flow limited?
This is because 80% of the oxygen supply to the heart is removed from blood during its passage through the heart; if oxygen consumption is to increase, then coronary blood flow must also increase.
What is cardiac work equal to?
Force (MAP) x distance (systolic stroke volume)
Does pressure or volume work consume more energy?
pressure work… this is why HTN causes a disproportionate increase in oxygen consumption (heart is working harder and utilizing more oxygen) –> need a subsequent increase in blood flow to prevent ischemia
What are things that influence myocardial oxygen demand?
- afterload
- heart rate
- contractility
What is coronary “steal”?
A local ischemic event in which an increase in blood flow in one region of the heart can cause a decrease in blood flow in another region.
What constitutes the largest vascular bed in the body?
skeletal muscle! (this is why it is so important in regulating blood pressure)
Skeletal muscle blood flow can increase by 20x during exercise…where does this increased flow come from?
it comes from the shunting of blood from other areas (areas in which blood flow is not needed during exercise)
What is active hyperemia?
an increase in blood flow due to metabolic activity (ex: if muscle contraction is happening during running, more than 80% of CO can be directed to contracting muscles)
