Coronary Blood Flow

Question 1

Pouiselle’s Law (again)

Answer 1

Q = (DeltaP x pi x r^4)/(8n(viscosity)length)

Question 2

Pressure 1 and 2 When Talking About Coronary Flow

Answer 2

1: Aortic pressure, 2: RAP

Question 3

Notable Aspect of Heart Blood Flow Compared to Other Organs

Answer 3

Instead of following basic sinusoidal flow (high in sys, low in dia), actually opposite where it’s high in dias and drops sharply and even negatively in systole then increases again w/ dias

Question 4

Coronary A. Pressure

Answer 4

Pretty much follows aortic pressure exactly

Question 5

Throttle Effect

Answer 5

Systolic pressures in LV and coronary is equal (120), so perfusion forces are equal and opposite so no flow (however in diastole, pressure is 80 in coronary and 10 in LV so get flow). So LV is diastolically dependent (mainly endocardial surface)

Question 6

Reason RV Isn’t Diastolically Dependent

Answer 6

RV has much lower systolic pressure, so coronary P still above it

Question 7

2 Relevant Terms of Pouiselle’s Law

Answer 7

Pressure and radius. Those only 2 the body changes really

Question 8

Conductance and Resistance Vessels (and effect on flow-resistance graph)

Answer 8

Conductance are the big epicardial vessels before branching, resistance are once it starts branching and get smaller and smaller.

Question 9

Total Resistance

Answer 9

Linear. Rt = R1 + R2 + R0nak is gay + …

Question 10

Hemodynamically Significant Lesion

Answer 10

50% coronary stenosis. R1 in conductance vessels low but then shoots up and when R2 (constricted vessels/resistance vessels at rest) is too high, body dilates arterioles to reduce it

Question 11

Critical Stenosis

Answer 11

~70% coronary stenosis. Point where further vasodilation can’t keep up w/ increase in resistance

Question 12

Reactive Hyperemia Ratio

Answer 12

Hyperemic response equals almost exactly 2x the flow volume lost

Question 13

5 (6, kinda) Vasodilators Released on Cardiac Metabolism (that are washed out) (+ which most important)

Answer 13

H+
K+
Lactate
Adenosine - most important
CO2
Low O2

Question 14

Additional Adenosine Functions in Heart

Answer 14

Block AV Node conduction/slow (antiarrhythmic)

Question 15

Vasodilation on Exercise

Answer 15

Adenosine produced from energy use, so as production goes up so does vasodilation

Question 16

Coronary Artery Steal

Answer 16

In coronary w/ stenosis, R2 resistance vessels already fully dilated to maintain flow at rest. However w/ exercise, healthy neighboring coronary dilates, stealing flow from the coronary that can’t further decrease its resistance. So diagnoses hemodynamically significant non-critical stenoses w/ stress test or adenosine infusion

Question 17

3 Reasons Endocardium Vulnerability to Ischemia (& additional on exercise w/ stenosis)

Answer 17

1. Exposed to LV pressures/diastolically dependent
2. Terminal, so contraction anywhere above can block off
3. Sarcomeres inside can get shorter/need more energy
4. Already somewhat vasodilated at rest just to ensure enough flow gets down there, so can’t relax as much as earlier branches. Coronary steal effect of epicardials over endocardials

Question 18

ECG Hallmark of Subendocardial Ischemia

Answer 18

ST Depression